Although there isn't a lot of research to date on phytochemicals, experts say that they are generally healthy and safe when eaten as part of a balanced diet containing a wide range of fruits and vegetables. What raises concern is when they are ingredients in nutritional supplements, which are not regulated by the Food and Drug Administration.
Supplements cannot begin to replicate the wide variety of phytochemicals that occur naturally in foods; and in high concentrations, they might actually be dangerous. Certain phytochemicals in supplements have in fact been found to contribute to cancer cell growth. Beta-carotene, although it can be beneficial when taken naturally, has been found to increase the risk of lung cancer in male smokers when taken in a high-dose supplement. Some flavonoids can cause serious gastrointestinal or allergic problems when taken in high doses.
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