Some products sold as sports or weight loss supplements may contain synephrine, which may enhance the effects of caffeine, according to the German Federal Institute for Risk Assessment (BfR).
Synephrine is a compound found in plants such as bitter oranges (Citrus aurantium). Bitter orange comes from a flowering, fruit-bearing evergreen tree native to tropical Asia, but is now widely cultivated in the Mediterranean region and elsewhere. In 2004, the U.S. Food and Drug Administration (FDA) issued a final rule prohibiting the sale of dietary supplements containing ephedra because such supplements present an unreasonable risk of illness or injury. Due to the ban on ephedra in the United States, some products previously containing ephedra have been reformulated to include Citrus aurantium, which may also aid in weight loss.
According to BfR, because caffeine and synephrine both affect the heart and blood pressure, they may increase the other's effects when taken together. Most notably, taking caffeine and synephrine together may increase heart rhythm and blood pressure. Other ingredients contained in bitter orange extracts may also add to the effects of synephrine on the heart.
The BfR recommends that quantities of these compounds ingested through such products should be limited to food intake levels from oranges and bitter oranges. The institute advised that no more than 6.7 milligrams of synephrine be taken daily in the form of a food supplement. This quantity of synephrine may help ensure that even frequent consumers do not exceed a total daily intake of more than 25.7 milligrams of synephrine.
Due to dosage levels, some products that are currently available on the market may be classified as unsafe. The effects of these products on the heart may be more intense in people who are already putting increased strain on the heart due to physical activity or being overweight.
For more information about bitter orange, please visit Natural Standard's Foods, Herbs & Supplements database.
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