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EFFECTIVE

• Imerslund-Grasbeck disease. Intramuscular vitamin B12 is effective for patients with this condition. Details: Administering intramuscular vitamin B12 (hydroxocobalamin) 1 mg daily for 10 days, followed by monthly injections for the remainder of a patient's life, is effective for treating familial selective vitamin B12 malabsorption (Imerslund-Grasbeck disease) (15,82862).
• Vitamin B12 deficiency. Administering vitamin B12 orally, intramuscularly, or intranasally is effective for preventing and treating vitamin B12 deficiency. Details: Vitamin B12 deficiency has varying definitions but is often defined as vitamin B12 (cobalamin) levels less than 180-200 pmol/L (or 240 pg/mL). Some believe that only intramuscular vitamin B12 is effective for treating vitamin B12 deficiency. However, clinical research shows that oral therapy increases cobalamin levels similarly to intramuscular administration, even in patients with pernicious anemia or malabsorption, if a high enough dose is given (2909,2911,2915,9335,82832) (82836,82949,82860,103976,103972,107141,107144). Some evidence suggests that the most effective oral dose is between 647-1032 mcg daily (13106). However, in certain situations, intramuscular treatment might be more appropriate. Guidelines by the British Committee for Standards in Hematology recommend only intramuscular vitamin B12 for initial treatment of severe vitamin B12 deficiency in patients with pernicious anemia, malabsorption disorders, or neurological involvement (94722). Intramuscular vitamin B12 is also appropriate in patients with diarrhea or vomiting and those likely to be nonadherent (103972). Vitamin B12 deficiency is especially common in older adults, primarily due to lack of intrinsic factor and malabsorption (2915,2919,9335). Daily supplementation with vitamin B12 50-100 mcg might be needed to correct deficiency (10126), while daily doses of 25-37.5 mcg help to maintain normal levels over time (9335). In addition to supplements, foods such as milk and bread fortified with vitamin B12 can be used and are approximately 55% to 60% absorbed by people over 60 years of age (10124). Vitamin B12 deficiency is also common in patients that have had gastric surgery, including gastrectomy and bariatric surgery (107144,107145). Taking vitamin B12 in the doses found in multivitamins or generic vitamin B supplements does not seem to prevent vitamin B12 deficiency following bariatric surgery (107145). However, taking methylcobalamin 500 mcg daily is beneficial for treating vitamin B12 deficiency associated with a total gastrectomy and taking cyanocobalamin 5000 mcg daily is beneficial for preventing vitamin B12 deficiency following gastric bypass (107144). Other people at risk for vitamin B12 deficiency include strict vegetarians who eat no animal products (vegans) and people with increased vitamin B12 requirements associated with pregnancy, thyrotoxicosis, hemolytic anemia, hemorrhage, malignancy, and hepatic and kidney disease. Moderate consumption of animal products may not be sufficient to restore and maintain vitamin B12 levels, especially in adolescents who had consumed macrobiotic (vegan type) diets for the first 6 years of life. High dietary intake of vitamin B12 or supplements is usually needed in order to restore and maintain optimal vitamin B12 levels in these adolescents (10125).

LIKELY EFFECTIVE

• Cyanide poisoning. Intravenous hydroxocobalamin (Cyanokit) is likely effective as an antidote for patients with suspected or known cyanide toxicity due to inhalation, ingestion, or skin exposure. Details: Treatment of cyanide poisoning with hydroxocobalamin (Cyanokit) up to 10 grams has been approved by the US Food and Drug Administration (FDA) and recommended by the Australian Resuscitation Council (82870,82905,82906). Hydroxocobalamin is also FDA-approved for treating cyanide toxicity during pregnancy (82904).

POSSIBLY EFFECTIVE

• Canker sores. Sublingual or topical vitamin B12 seems to reduce canker sore symptoms. Details: Clinical research in patients with canker sores shows that applying a topical ointment containing vitamin B12 500 mcg in four divided doses daily for 2 days reduces pain levels by 80% when compared with a control ointment not containing vitamin B12 (96176). Other preliminary clinical research shows that taking vitamin B12 1000 mcg sublingually daily for 6 months reduces the duration of canker sore outbreaks, the number of ulcers, and level of pain when compared with placebo in patients with normal vitamin B12 levels (17242).
• Hyperhomocysteinemia. Oral vitamin B12 in combination with folic acid, and sometimes with vitamin B6, reduces homocysteine levels. Details: While folic acid 0.5-5 mg daily lowers fasting homocysteine levels by an average of 25%, adding vitamin B12 0.5 mg daily produces an additional decrease of about 7% on average (6883,9400,9401,9405,9409,50145,107136). Vitamin B12 in combination with folic acid and other vitamins also reduces homocysteine levels in patients with kidney failure, sickle cell disease, and those receiving nitrous oxide general anesthesia (1489,6883,6884,7289,7881,9324,9414,9415,9416,9481,82941). Some researchers recommend routine use of vitamin B12 with homocysteine-lowering regimens to avoid the risk of neuropathy in people with undetected vitamin B12 deficiency (9405). Using vitamin B12 alone has a limited effect on homocysteine levels, and probably only in those people with vitamin B12 deficiency (2147,9410,9512). Hyperhomocysteinemia is considered by some to be an independent risk factor for atherosclerosis, recurrent thromboembolism, deep vein thrombosis, myocardial infarction, and ischemic stroke (1899,2147,3323,9402,9405,9408,9409). Clinical research suggests that supplementation with folic acid, pyridoxine, and vitamin B12 decreases homocysteine levels and reduces the atherosclerosis progression in patients at risk for atherosclerosis when compared with placebo (50133,50056,82806). However, other research suggests that elevated homocysteine levels may be a marker, as opposed to a cause, of vascular disease (11387,11388). A 5 µmol/L increase in plasma homocysteine increases the risk of cerebrovascular disease by 50%, and the odds of coronary heart disease by 60% and 80% in males and females, respectively (9407,9411). However, it is not clear if reducing homocysteine levels results in reduced cardiovascular morbidity and mortality (1489,6883,6884,9400,9405,9409,96417). Folic acid, vitamin B6, and vitamin B12 supplementation can reduce total homocysteine from 13.4 to 11 µmol/L. However, this reduction does not seem improve endothelial function or help with secondary prevention of death or myocardial infarction, and some research even suggests an increase in cardiovascular disease (CVD) risk (11387,13482,50373,50314,97619). There is also some debate about whether supplementation with homocysteine-lowering B vitamins can reduce the risk of stroke. A number of large clinical studies and meta-analyses show that supplementation with folic acid, vitamin B6, and vitamin B12, alone or in combination, does not reduce the risk of stroke in patients with CVD or impaired kidney function (11387,13482,50423,83050,96150). However, a more recent meta-analysis of 10 clinical trials including over 44,000 patients shows that B vitamin supplementation reduces the relative risk of stroke by 10% when compared with placebo in patients at risk or with a history of CVD (97619). Also, a meta-analysis in adults with a history of stroke shows that B vitamin supplementation modestly reduces the relative risk of stroke recurrence by 13% and vascular death by 11% when compared with placebo (107136).
• Postherpetic neuralgia. Subcutaneous injections of vitamin B12 seem to reduce postherpetic neuralgia symptoms. Details: Clinical research in patients with subacute herpetic neuralgia shows that subcutaneous injection of vitamin B12 (methylcobalamin) 1000 mcg six times weekly for 4 weeks reduces pain when compared with oral vitamin B12 or subcutaneous lidocaine (90394). Another clinical study shows that administering local subcutaneous injections of methylcobalamin 1000 mcg plus lidocaine up to 20 mg daily for 12 injections over 14 days, starting within 7 days of the onset of subacute ophthalmic herpetic neuralgia, decreases the mean pain score by 63% to 79% when compared with intravenous lidocaine and intramuscular methylcobalamin. Less than 2 patients need to be treated to achieve a pain reduction to ≤3 out of 10. Healing of rash, itching, numbness, and tingling were also improved (96175). Additional clinical research in patients with postherpetic pain and itching shows that this same dosing regimen of subcutaneous vitamin B12 reduces pain and analgesic requirements when compared to baseline (90396).

POSSIBLY INEFFECTIVE

• Age-related cognitive decline. Oral vitamin B12 does not seem to improve cognitive function in older adults when used alone or in combination with other B vitamins. Details: Taking vitamin B12 100-1000 mcg plus folic acid 400-2000 mcg, with or without vitamin B6 3-50 mg, daily for up to about 2 years does not seem to improve tests of cognitive function in adults aged 65 or older, most of whom do not report cognitive impairment at baseline (14392,50225,50510,90392,107140). Also, supplementation with vitamin B12 does not seem to improve cognitive function in elderly individuals with low vitamin B12 levels (12305).
• Alzheimer disease. Oral vitamin B12, when used in combination with other B vitamins, does not seem to improve cognitive function in patients with Alzheimer disease. Details: Clinical research in patients with probable Alzheimer disease using routine medication shows that taking vitamin B12 1 mg, folic acid 5 mg, and vitamin B6 25 mg daily for 18 months does not have a beneficial effect on cognitive function or the severity of disease when compared with placebo. In this study, all patients were consuming a folate-fortified diet (50319). Also, a meta-analysis of clinical research in elderly adults with mild cognitive impairment or dementia shows that taking vitamin B12, usually with other B vitamins, does not improve cognitive function (50510). Observational research has also found that higher vitamin B12 intake over 3 years in a population consuming a folate-fortified diet is not associated with a decreased risk of developing Alzheimer disease (15270). In contrast, preliminary clinical research in patients with probable Alzheimer disease who are not consuming a folate-fortified diet shows that taking vitamin B12 50 mcg daily plus folic acid 1.2 mg daily for 6 months modestly improves some measures of cognitive performance and decreases levels of homocysteine when compared with placebo (107150). More research is needed to determine if any changes in this latter study are clinically relevant.
• Cataracts. Oral vitamin B12 does not seem to reduce cataract development. Details: Clinical research in women with existing cardiovascular disease (CVD) or at increased risk of CVD shows that taking a combination of folic acid 2.5 mg daily, vitamin B6 50 mg daily, and vitamin B12 1 mg daily for an average of 7.3 years does not reduce the risk of cataracts and seems to increase the risk of cataract extraction by 28% when compared with placebo (96149).
• Circadian rhythm sleep disorders. Oral vitamin B12 does not seem to improve sleep disorders. Details: Oral vitamin B12 (methylcobalamin) does not seem to be effective for treating delayed sleep phase syndrome. Methylcobalamin 0.5-1 mg three times daily, with or without bright light therapy, also does not seem to help people with primary circadian rhythm sleep disorders (1344,1345,1346,1347,1348).
• Cognitive impairment. Oral vitamin B12 does not seem to be beneficial for older adults with cognitive impairment. Details: A meta-analysis of clinical research in elderly adults with mild cognitive impairment or dementia shows that taking vitamin B12, usually with other B vitamins, does not improve cognitive function (50510). One clinical trial in elderly people with memory complaints shows that taking a combination of B vitamins, including folic acid 0.8 mg, vitamin B12 0.5 mg, and vitamin B6 (form not specified) 20 mg daily for 24 months reduces cerebral atrophy in the gray matter regions associated with Alzheimer disease by up to seven-fold when compared with placebo. However, this protection does not occur in patients with the lowest average blood levels of homocysteine (90374).
• Fall prevention. Oral vitamin B12 does not seem to reduce the risk of falls. Details: Clinical research shows that taking B vitamins, including folic acid 400 mcg and vitamin B12 500 mcg, daily for 2 years does not prevent falls when compared with placebo in elderly individuals also taking vitamin D (96148).
• Osteoporosis. Oral vitamin B12 does not seem to reduce the risk of osteoporotic fractures. Details: Clinical research in elderly patients or patients with a history of cerebrovascular disease shows that taking vitamin B12 500 mcg and folic acid 0.4-2 mg, with or without vitamin B6 25 mg, daily for 2-3 years does not seem to reduce the risk for osteoporotic fractures when compared with placebo (90377,90393). A 5-7 year follow-up of this research has also found no benefit (103981).
• Physical performance. Oral vitamin B12 does not seem to improve physical performance in older adults. Details: Clinical research shows that taking B vitamins, including folic acid 400 mcg and vitamin B12 500 mcg, daily for 2 years does not increase hand strength or improve performance such as walking when compared with placebo in elderly individuals also taking vitamin D (96148).

INSUFFICIENT RELIABLE EVIDENCE to RATE

• Age-related macular degeneration (AMD). Oral vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A large-scale clinical study shows that taking vitamin B12 1000 mcg, folic acid 2.5 mg, and vitamin B6 50 mg daily, reduces the risk of developing AMD in females over 40 years of age with a history of cardiovascular disease (CVD) or at least three risk factors for CVD. Those who took this combination for an average of 7.3 years had a 34% reduced risk of developing AMD and a 41% reduced risk of visually significant AMD when compared with placebo (14620). It is unclear if this effect is due to vitamin B12, other ingredients, or the combination.
• Amyotrophic lateral sclerosis (ALS, Lou Gehrig's disease). It is unclear if high-dose intramuscular vitamin B12 improves the prognosis of ALS. Details: A clinical study in patients with ALS symptoms for 3 years or less shows that intramuscular vitamin B12 (methylcobalamin) 25-50 mg twice weekly for 3.5 years does not slow functional decline or increase the time until ventilation or death when compared with placebo. However, other clinical research in patients with early-stage ALS shows that intramuscular methylcobalamin 50 mg twice weekly for 16 weeks is associated with slower functional decline and a longer period of time until death or full ventilation when compared with placebo (104947,111556). These effects seem to be particularly notable in fine and gross motor skills, but not bulbar or respiratory functions. Furthermore, vitamin B12 and riluzole slowed clinical progression of ALS more than riluzole alone (111556).
• Angioplasty. Oral vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Some evidence suggests that vitamin B12 400 mcg, folic acid 1 mg, and vitamin B6 10 mg daily can decrease the rate of restenosis in patients treated with balloon angioplasty (8009,9412,34540). However, this combination does not seem to be as effective for reducing restenosis in patients after coronary stenting (8009). An intravenous loading dose of folic acid, pyridoxine, and vitamin B12 followed by oral administration of folic acid 1.2 mg, pyridoxine 48 mg, and vitamin B12 60 mcg daily after bare metal coronary stenting also does not seem to reduce restenosis and might actually increase restenosis (12150,12151,34540). Due to the lack of evidence of benefit and potential for harm, this combination of vitamins should not be recommended for patients receiving coronary stents (12151). It is unclear if any effects are due to vitamin B12, other ingredients, or the combination.
• Anxiety. Although there is interest in using oral vitamin B12 for anxiety and panic attacks, there is insufficient reliable information about the clinical effects of vitamin B12 for these uses.
• Asthma. Although there is interest in using oral vitamin B12 for asthma, there is insufficient reliable information about the clinical effects of vitamin B12 for this condition.
• Atherosclerosis. Oral vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: One small clinical study in patients with intermediate risk for coronary heart disease shows that taking vitamin B12 100 mcg, aged garlic extract 250 mg, folic acid 300 mcg, vitamin B6 12.5 mg, and L-arginine 100 mg daily for 12 months reduces coronary artery calcium progression when compared with placebo (88385). It is unclear if this effect is due to vitamin B12, other ingredients, or the combination.
• Atopic dermatitis (eczema). It is unclear if topical vitamin B12 reduces the severity of eczema. Details: Preliminary clinical research shows that applying a specific topical vitamin B12 0.07% cream (Regividerm) twice daily reduces the extent and severity of atopic dermatitis when compared with placebo (15765).
• Attention. Although there is interest in using oral vitamin B12 for improving attention and focus, there is insufficient reliable information about the clinical effects of vitamin B12 for this use.
• Cancer. It is unclear if oral vitamin B12 reduces overall cancer risk when used in combination with other B vitamins. Details: An ancillary clinical study in middle-aged and elderly adults with cardiovascular disease shows that taking a combination of vitamin B12 (cyanocobalamin) 0.02 mg, folic acid 0.56 mg, and vitamin B6 3 mg, with or without eicosapentaenoic acid (EPA) 400 mg plus docosahexaenoic acid (DHA) 200 mg, for a median of 4.7 years does not reduce the risk of cancer when compared with placebo (90666). An additional secondary analysis of clinical research in patients recovering from stroke or transient ischemic attack shows that taking vitamin B12 500 mcg, folic acid 2 mg, and vitamin B6 25 mg daily for around 3.4 years does not reduce the risk of cancer when compared with placebo (90378). The validity of these findings is limited because the studies were not designed nor adequately powered to test for cancer risk.
• Cardiovascular disease (CVD). Oral vitamin B12, taken along with other B vitamins, does not seem to improve secondary prevention of death or myocardial infarction in patients with CVD. However, it might slightly reduce the risk of stroke. Details: Overall evidence from clinical research and meta-analyses shows that taking vitamin B12 in combination with folic acid and/or vitamin B6 does not seem to reduce the risk for secondary death or myocardial infarction in patients with or at risk for CVD (11387,13482,34540,50423,83050,90379,97619). In fact, some research suggests that long-term supplementation with vitamin B6, folic acid, and vitamin B12 for secondary prevention increases the risk of CVD by 20% despite lowering homocysteine levels by 30% (13482). However, other research shows that taking vitamin B12 in combination with other B vitamins modestly reduces the risk of stroke, although results are conflicting (11387,13482,50423,83050,96150,96165,97619,107136). It is unclear which specific combination of B vitamins, if any, might be optimal for reducing stroke risk and which patients are most likely to benefit. In 2001, prior to the publication of the highest quality research on this topic, the US Food and Drug Administration (FDA) approved a qualified health claim stating that, as part of a well-balanced diet that is low in saturated fat and cholesterol, folic acid, vitamin B6, and vitamin B12 may reduce the risk of vascular disease (102368).
• Cervical cancer. It is unclear if oral vitamin B12 reduces cervical cancer risk. Details: Some epidemiological evidence has found that increasing vitamin B12 intake from dietary and supplement sources, along with folic acid, thiamine, and riboflavin, might decrease the risk of precancerous cervical lesions (11074). Also, an analysis of two case control studies has found that increased intake of vitamin B12 is associated with a 75% reduced odds of cervical cancer (34609).
• Chemotherapy-induced peripheral neuropathy. Oral vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research in patients receiving chemotherapy shows that a combination of B vitamins that includes vitamin B12 (cyanocobalamin) 1000 mcg, taken daily starting one week prior to treatment and finishing 12 weeks after treatment is completed, does not prevent peripheral neuropathy when compared with placebo (96173).
• Child development. It is unclear if oral vitamin B12 is beneficial for child development. Details: Population research has found that daily dietary intake of less than 2.26 mcg vitamin B12 in the third trimester of pregnancy is associated with an increased risk of poorer outcomes in the offspring for some measures of speech and mathematics ability, including vocabulary at 24 months, combining words at 38 months, speech intelligibility at 6 years, and math comprehension between ages 8-11 years, when compared with dietary intakes of at least 2.26 mcg daily. There was no association between prenatal vitamin B12 intake and reading or spelling abilities, vocabulary at other ages, or full-scale Intelligence Quotient (IQ) at ages 8 or 15 (107143).
• Chronic obstructive pulmonary disease (COPD). It is unclear if oral vitamin B12 reduces the risk of COPD. Details: Clinical research in patients with COPD shows that taking vitamin B12 500 mg daily for 8 weeks modestly improves endurance on the cycle ergometer, but does not improve oxygen consumption, when compared with placebo (96172).
• Cognitive function. Oral vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A moderate-sized clinical study in healthy, middle-aged adults shows that taking a combination product containing vitamin B12, other B vitamins, bacopa, and gingko biloba twice daily for 12 weeks does not improve measures of memory, attention, cognition, mood, or stress reactivity when compared with placebo (111554).
• Colorectal cancer. It is unclear if oral vitamin B12 reduces colorectal cancer risk. Details: Some epidemiological evidence has found that increased dietary intake of vitamin B12 is associated with a reduced risk of developing colorectal cancer (90383). However, preliminary clinical research shows that taking vitamin B12 1 mg, folic acid 2.5 mg, and vitamin B6 50 mg daily for up to 7.3 years does not reduce the risk of colorectal adenoma in females at high risk for cardiovascular disease (90389). Furthermore, a secondary analysis of clinical research in elderly patients suggests that taking vitamin B12 500 mcg and folic acid 400 mcg daily for 2 years might increase the risk of colorectal cancer when compared with placebo (90393).
• Coronavirus disease 2019 (COVID-19). It is unclear if oral vitamin B12 is beneficial for patients with COVID-19. Details: A small observational study in hospitalized patients with COVID-19 pneumonia has found that higher plasma vitamin B12 levels may be associated with an increased risk of transfer to intensive care or death than lower plasma levels. However, when multivariate regression was conducted, only patient age was associated with worsened outcomes. Additionally, the total study population was small, with only nine of 49 patients experiencing the worsened outcomes (107138).
• Dementia. It is unclear if oral vitamin B12 reduces the risk of developing dementia. Details: A large cohort of Danish adults has found that vitamin B12 levels or intake does not seem to impact the risk of developing Alzheimer disease or other dementias (104922). However, vitamin B12 might be beneficial in specific patient populations. A small observational study in patients with Parkinson disease has found that higher vitamin B12 levels (648.5 ng/L) are associated with a lower risk of developing dementia when compared with lower vitamin B12 levels (452 ng/L) (103975). It is not yet known if supplementation with vitamin B12 reduces the risk for dementia in these patients.
• Depression. It is unclear if oral vitamin B12 is beneficial for reducing depression risk. Details: A meta-analysis of epidemiological research has found that the highest dietary intake of vitamin B12 is associated with a 14% reduced risk of depression. However, in a sub-analysis, this association was not significant in males (107133). In contrast, one epidemiological study in older males included in the analysis has found that daily dietary intake of at least 4.79 mcg vitamin B12 is linked with a 58% lower risk of depression when compared with daily intake of less than 3.16 mcg. In this study, this inverse association was not observed in females (96168). Other observational research has found that low-normal serum vitamin B12 levels are associated with a 3.8 times increased risk for depression during pregnancy when compared with normal vitamin B12 levels (102384). It is unclear if increased intake of vitamin B12 through the diet or supplements reduces the risk for depression or is beneficial for treating symptoms of depression in any population. However, a meta-analysis of clinical research in elderly populations shows that supplementation with vitamin B12 100-1000 mcg daily, usually in combination with folic acid 400-2000 mcg daily, does not reduce symptoms of depression. Most individuals in these studies were not specifically diagnosed with depression (107140).
• Diabetes. It is unclear if oral vitamin B12 improves glycemic indices or prevents loss of skeletal muscle in patients with diabetes. Details: A small clinical study in patients with diabetes in India who are stabilized on metformin and/or a sulfonylurea shows that taking vitamin B12 (methylcobalamin) 500 mcg with or without folic acid 5 mg daily for 8 weeks seems to reduce glycated hemoglobin (HbA1C) by 1.3% to 1.5%, compared with a 0.3% increase with placebo (104917). This study is limited due its small sample size and lack of blinding. In elderly adults with type 2 diabetes, population research has found a lower dietary intake of vitamin B12 (average of 11.2 mcg daily) in individuals with a loss of skeletal muscle mass of at least 1.2%, compared with an average intake of 13.4 mcg daily in those with a skeletal muscle mass loss of less than 1.2%. However, further analysis determined that any relationship between vitamin B12 intake and loss of skeletal muscle mass was only significant in individuals with insufficient energy intake overall (107151).
• Diabetic neuropathy. Small clinical studies suggest that oral vitamin B12 may modestly improve pain in patients with diabetic neuropathy. Details: Two small clinical studies in patients with diabetic peripheral neuropathy show that taking vitamin B12 (methylcobalamin) 1-1.5 mg for 4-12 months modestly improves pain when compared with baseline or placebo (82841,104923). Some research also shows that vitamin B12 may be beneficial in combination with other ingredients. Studies have evaluated products containing vitamin B12 (methylcobalamin or cyanocobalamin), benfotiamine, and vitamin B6 daily for 9-12 weeks (82931,82939); and vitamin B12 (methylcobalamin) 2 mg, folic acid (L-methylfolate) 3 mg, and vitamin B6 (pyridoxal-5'-phosphate) 35 mg (Metanx; Pamlab) daily for 24 weeks (90375).
• Diarrhea. It is unclear if oral vitamin B12 is beneficial for reducing diarrhea in children. Details: Preliminary clinical research in children aged 6-30 months from low- and middle-income countries shows that taking vitamin B12 at twice the recommended dietary allowance, with or without folic acid, does not reduce the risk for diarrhea when compared with placebo (90391).
• Fatigue. It is unclear if intramuscular vitamin B12 is beneficial for improving well-being in those with fatigue or tiredness. Details: A small crossover trial in patients complaining of tiredness or fatigue shows that receiving intramuscular injections of vitamin B12 (hydroxocobalamin) 5 mg twice weekly for 2 weeks seems to improve general well-being and happiness, and has a trend toward improving fatigue, when compared with placebo (10127). The validity of this study is limited by a large drop-out rate and unstandardized outcome measures.
• Hearing loss. Oral vitamin B12 has only been evaluated in combination with adenosine triphosphate; its effect when used alone is unclear. Details: A small observational study in adults with idiopathic sudden sensorineural hearing loss has found that taking vitamin B12 1.5 mg with adenosine triphosphate 300 mg daily for 8-16 weeks is associated with modestly reduced hearing loss at 4-6 months after starting treatment when compared with taking the combination for less than 8 weeks (104924). This finding is limited due to its observational nature and lack of a control group.
• Hepatitis C. It is unclear if intramuscular vitamin B12 is beneficial for sustaining viral response in patients with chronic hepatitis C infection. Details: A small clinical study in patients with chronic hepatitis C infection shows that intramuscular vitamin B12 (cyanocobalamin) 5000 mcg every 4 weeks along with standard care improves sustained viral response when compared with standard of care alone (90386).
• Hypertriglyceridemia. It is unclear if oral vitamin B12 is beneficial for reducing triglyceride levels. Details: Some evidence shows that taking vitamin B12 7.5 mcg with fish oil 5 grams might be superior to fish oil alone when used daily to reduce total serum cholesterol and triglycerides. This suggests vitamin B12 might have an independent effect in lowering serum cholesterol and triglycerides, but further investigation is needed to confirm this effect (8694).
• Infant development. It is unclear if taking oral vitamin B12 during pregnancy is beneficial for improving infant development. Giving oral vitamin B12 to infants does not seem to be beneficial. Details: Clinical research shows that supplementation with vitamin B12 50 mcg daily from less than 14 weeks gestation until 6 weeks postpartum does not improve cognitive development in infants by 9 months of age when compared with placebo (96174). When these children were evaluated at 30 months of age, a very small benefit of vitamin B12 on expressive language was identified; however, there was no effect on cognition, receptive language, fine motor skills, or gross motor skills (100169). It is unknown whether a longer duration of postpartum supplementation or supplementation in specific populations might be beneficial. Vitamin B12 supplementation in infants has also been evaluated. A large clinical trial in marginally stunted Nepalese infants aged 6-11 months shows that giving vitamin B12 (cyanocobalamin) 2 mcg daily for 12 months reduces homocysteine levels, but does not improve motor or cognitive development, when compared with placebo (104926).
• Inflammatory bowel disease (IBD). Although there is interest in using oral vitamin B12 for IBD, there is insufficient reliable information about the clinical effects of vitamin B12 for this condition.
• Lung cancer. Oral vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: The association between vitamin B12 and lung cancer is unclear. Some population research found no relationship between blood levels of vitamin B12 and lung cancer (9454). However, other observational research involving over 5,000 case-control pairs found that higher vitamin B12 levels are linked with an increased risk for lung cancer (102383). It is unclear if increased intake of vitamin B12, either through the diet or supplementation, directly affects the risk of lung cancer.
• Male infertility. Oral vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A retrospective study in adult males with idiopathic and varicocele-related infertility suggests that taking a combination product containing vitamin B12 1.5 mcg, L-carnitine, acetyl L-carnitine, citric acid, selenium, coenzyme Q10, vitamin C, zinc, and folic acid (Proxeed Plus) twice daily for 6 months is associated with improvements in ejaculate volume, sperm count, sperm concentration, total motility, and progressive motility in patients with idiopathic infertility when compared to baseline. However, improvement in sperm morphology was lacking. Furthermore, patients with more severe varicocele seem to benefit most, especially with regard to progressive motility (111296). The validity of these findings is limited by a lack of comparator group. Further, it is unclear if these effects are due to vitamin B12, other ingredients, or the combination.
• Multiple sclerosis (MS). Although there is interest in using oral vitamin B12 for MS, there is insufficient reliable information about the clinical effects of vitamin B12 for this condition.
• Nonalcoholic fatty liver disease (NAFLD). It is unclear if oral vitamin B12 is beneficial for NAFLD. Details: A small clinical study in adults with NAFLD shows that taking vitamin B12 1000 mcg daily for 12 weeks reduces serum levels of homocysteine but has no effect on serum aminotransferases, measures of steatosis, fibrosis scores, fasting blood glucose, serum insulin, measures of insulin resistance, triglycerides, low-density lipoprotein (LDL) cholesterol, or high-density lipoprotein (HDL) cholesterol when compared with placebo (111555).
• Pancreatic cancer. It is unclear if oral vitamin B12 is beneficial for reducing the risk of pancreatic cancer. Details: Most population research has found that increased intake of vitamin B12, as a supplement or in the diet, is not associated with a reduced risk of pancreatic cancer (9327,104927). However, a small, retrospective population study in which smoking and non-smoking adults recalled past eating habits found that increased dietary intake of vitamin B12 is associated with a 33% reduction in pancreatic cancer risk (97976). These conflicting findings may be related to study methodology, as well as the age, gender, or smoking status of the included patients.
• Periodontitis. Although there is interest in using oral vitamin B12 for periodontitis, there is insufficient reliable information about the clinical effects of vitamin B12 for this condition.
• Peripheral neuropathy. Oral vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research shows that taking a specific product containing vitamin B12 3 mcg, folic acid 400 mcg, and uridine monophosphate 50 mg (Keltican) daily for 60 days reduces pain by 44% and decreases analgesic use by over 75% when compared to baseline in patients with peripheral neuropathy, including those with lumbar/lumbosacral radiculopathy, sciatic pain, and cervical radiculopathy (90384). The validity of this finding is limited by the lack of a control group. Furthermore, it is unclear if the benefits are due to vitamin B12, other ingredients, or the combination.
• Psoriasis. Topical vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research shows that a specific cream containing vitamin B12 and avocado oil (Regividerm, Regeneratio Pharma AG) reduces symptoms of psoriasis as effectively as calcipotriol ointment (Psorcutan) after 12 weeks of therapy. The vitamin B12 combination cream also causes less irritation than calcipotriol (14909). It is unclear if the benefits are due to vitamin B12, other ingredients, or the combination.
• Respiratory tract infections. A small study suggests that oral vitamin B12 does not reduce the rate of respiratory tract infections in children. Details: Preliminary clinical research in children aged 6-30 months from low-and middle-income countries suggests that taking vitamin B12 at twice the recommended dietary allowance with or without folic acid does not reduce the risk for lower respiratory tract infections when compared with placebo (90391).
• Schizophrenia. Oral vitamin B12 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Clinical research shows that taking a combination of vitamin B12 400 mcg and folic acid 2 mg daily for 16 weeks improves negative symptoms when compared with placebo in patients with schizophrenia who have persistent symptoms and a specific genetic variant of the folate transporter gene FOLHI. This variant normally results in reduced folate absorption. However, in patients without this genetic variant, folate is not beneficial with respect to negative symptom improvement (90387).
• Sickle cell disease. Oral vitamin B12 has only been evaluated in combination with other B vitamins; its effect when used alone is unclear. Details: Preliminary clinical research in adults with sickle cell disease shows that taking vitamin B12 4.2-6 mcg, folic acid 700 mcg, and vitamin B6 4.2-6 mg daily might lower homocysteine levels. However, it is unknown if this will reduce the risk of endothelial damage in these patients (9324).
• Stroke. It is unclear if oral vitamin B12, either alone or with other B vitamins, is beneficial for stroke prevention. Details: Epidemiological research has found that people with a higher intake of vitamin B12 from dietary sources do not have a reduced risk of ischemic or hemorrhagic stroke (14316). A number of clinical studies and meta-analyses show that supplementation with folic acid, vitamin B6, and vitamin B12, alone or in combination, does not reduce the risk of stroke in patients with cardiovascular disease (CVD) or impaired kidney function (11387,13482,50420,50423,83050,90379,90380,96150). However, a more recent meta-analysis of 10 clinical trials including over 44,000 patients shows that B vitamin supplementation modestly reduces the relative risk of stroke by 10% when compared with placebo in patients at risk or with a history of CVD (97619). This meta-analysis differed from some of the earlier analyses due to the inclusion of several additional clinical trials. Also, a meta-analysis in adults with a history of stroke shows that B vitamin supplementation modestly reduces the relative risk of stroke recurrence by 13% and vascular death by 11% when compared with placebo (107136). In 2001, prior to the publication of the highest quality research on this topic, the US Food and Drug Administration (FDA) allowed a qualified health claim stating that, as part of a well-balanced diet that is low in saturated fat and cholesterol, folic acid, vitamin B6, and vitamin B12 may reduce the risk of vascular disease (102368). Unfortunately, even after the publication of higher quality research, it is still unclear which specific combination of B vitamins is optimal and which patients are most likely to benefit. One network meta-analysis suggests that a combination of folic acid and vitamin B6 lowers the risk of stroke more effectively than B vitamin mixtures that include vitamin B12 (96165). However, this analysis is limited because it didn't account for dosing. Another meta-analysis suggests that exposure to low, but not high, amounts of vitamin B12 (cyanocobalamin) seems to reduce stroke risk (96150).
• Tinnitus. It is unclear if intramuscular vitamin B12 is beneficial in patients with tinnitus. Details: A small clinical study shows that intramuscular vitamin B12 2500 mcg weekly for 6 weeks reduces tinnitus severity by 22% when compared to baseline in patients with chronic tinnitus and vitamin B12 deficiency, but not in patients with normal levels of vitamin B12. Vitamin B12 does not improve pitch or volume in either group of patients (96170). The validity of this finding is limited by the lack of a control group.
• Venous thromboembolism (VTE). It is unclear if oral vitamin B12 is beneficial for preventing VTE. Details: Epidemiological research has found that low levels of vitamin B12 are associated with an increased risk for VTE. However, clinical trials evaluating the use of B vitamins for prevention of VTE have shown conflicting results (90398). More evidence is needed to rate vitamin B12 for these uses.

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LIKELY SAFE ...when used orally, topically, intravenously, intramuscularly, or intranasally and appropriately. Vitamin B12 is generally considered safe, even in large doses (15,1344,1345,1346,1347,1348,2909,6243,7289,7881)(9414,9416,10126,14392,15765,82832,82949,82860,82864,90386)(111551,111554).

PREGNANCY: LIKELY SAFE
when used orally in amounts that do not exceed the recommended dietary allowance (RDA). The RDA for vitamin B12 during pregnancy is 2.6 mcg daily (6243). There is insufficient reliable information available about the safety of larger amounts of vitamin B12 during pregnancy.

LACTATION: LIKELY SAFE
when used orally in amounts that do not exceed the recommended dietary allowance (RDA). The RDA of vitamin B12 during lactation is 2.8 mcg daily (6243). There is insufficient reliable information available about the safety of larger amounts of vitamin B12 while breastfeeding.

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General ...Orally, intramuscularly, and topically, vitamin B12 is generally well-tolerated.
Most Common Adverse Effects:
Intramuscular: Injection site reactions.
Serious Adverse Effects (Rare):
Intramuscularly: Severe hypokalemia has been rarely linked with correction of megaloblastic anemia with vitamin B12.

Cardiovascular ...In human clinical research, an intravenous loading dose of folic acid, vitamin B6, and vitamin B12, followed by daily oral administration after coronary stenting, increased restenosis rates (12150). Hypertension following intravenous administration of hydroxocobalamin has been reported in human research (82870,82864).

Dermatologic ...Orally or intramuscularly, vitamin B12 can cause allergic reaction such as rash, pruritus, erythema, and urticaria. Theoretically, allergic reactions might be caused by the cobalt within the vitamin B12 molecule (82864,90373,90381,103974). In one case report, oral methylcobalamin resulted in contact dermatitis in a 59-year-old Japanese woman with a cobalt allergy (103974). Vitamin B12 (intramuscular or oral) has also been associated with at least 19 cases of acneiform eruptions which resolved upon discontinuation of vitamin B12 (90365,90369,90388). High-dose vitamin B12 (20 mcg daily) and vitamin B6 (80 mg daily) have been associated with cases of rosacea fulminans characterized by intense erythema with nodules, papules, and pustules. Symptoms may last up to four months after the supplement is stopped and can be treated with systemic corticosteroids and topical therapy (10998,82870,82871).

Gastrointestinal ...Intravenously, vitamin B12 (hydroxocobalamin) 2. 5-10 grams can cause nausea and dysphagia (82864).

Genitourinary ...Intravenously, vitamin B12 (hydroxocobalamin) 5-15 grams has been associated with chromaturia in clinical research (82870,82871).

Hematologic ...According to case report data, the correction of megaloblastic anemia with vitamin B12 may result in fatal hypokalemia (82914).

Musculoskeletal ...According to case report data, correction of megaloblastic anemia with vitamin B12 has precipitated gout in susceptible individuals (82879).

Neurologic/CNS ...Treatment with vitamin B12 has been rarely associated with involuntary movements in infants with vitamin B12 deficiency (90370,90385,90397). In some cases these adverse reactions were misdiagnosed as seizures or infantile tremor syndrome (90370,90385). These adverse reactions presented 2-5 days after treatment with vitamin B12 and resolved once vitamin B12 was discontinued (90370,90385,90397).

Oncologic ...Although some epidemiological research disagrees (9454), most research has found that elevated plasma levels of vitamin B12 are associated with an increased risk of various types of cancer, including lung and prostate cancers and solid tumors (50411,102383,107743). One study found, when compared with blood levels of vitamin B12 less than 1000 ng/mL, plasma vitamin B12 levels of at least 1000 ng/mL was strongly associated with the occurrence of solid cancer (107743). It is unclear if increased intake of vitamin B12, either through the diet or supplementation, directly affects the risk of cancer. It is possible that having cancer increases the risk of vitamin B12 elevation. However, one observational study has found that the highest quintile of dietary intake of vitamin B12 is associated with a 75% increased incidence of developing esophageal cancer when compared with the lowest quintile in never drinkers, but not drinkers (107147).

Renal ...There is a case report of oxalate nephropathy in a 54-year-old male which was determined to be related to the use of intravenous hydroxocobalamin as treatment for cyanide poisoning. Intermittent hemodialysis was started 5 days after admission, along with a low-oxalate diet, oral calcium acetate, and pyridoxine 5 mg/kg daily (107148). A review of the use of intravenous hydroxocobalamin for suspected cyanide poisoning in 21 intensive care units in France between 2011 and 2017 resulted in a 60% increased odds of acute kidney injury and a 77% increased odds of severe acute kidney injury in the first week. However, biopsies were not conducted and a direct link with use of hydroxocobalamin could not be made (107139).

Other ...Several studies have found that higher vitamin B12 levels may be associated with increased mortality or decreased survival rates in hospitalized elderly patients (82889,82812,82857,82895). Human research has also found a positive correlation between vitamin B12 status and all-cause mortality in Pima Indians with diabetes (82863).

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