Some vitamin B products may exceed tolerable upper intake levels (UL), according to the latest independent evaluation by ConsumerLab.com.
All but one of the 21 products analysed by ConsumerLab.com contained the claimed amounts of vitamins, but nine of the products exceeded the upper intake levels set by the Institute of Medicine of the National Academies in the USA.
The risk of adverse effects increases when consumption of vitamins exceeds the UL on a regular basis.
The most common ingredient found at high doses was niacin (B3), for which potential side-effects range from skin flushing to liver toxicity.
Use of B vitamins has increased dramatically in recent years as a result of research indicating the roles of vitamins B6, B12, and folic acid in reducing the risk of heart disease, and of niacin (B3) in lowering cholesterol.
However, neither the US government nor any other agency is responsible for routinely testing B vitamin products or other dietary supplements for their contents or quality and the Food & Drug Administration does not require labels to warn of potential side effects.
Tod Cooperman, MD, President of ConsumerLab.com, said: "While there is scientific evidence behind the excitement over B vitamins, consumers should be aware that more than 40% of the products that we evaluated exceeded levels at which they are known to be safely tolerated, with some having more than 10 times the upper limit.
"There may be good medical reasons for exceeding these levels, but there may also be significant side effects.People interested in using high doses of B vitamins should consult with a healthcare professional."
The general findings from the research, and examples of approved products, are available on the ConsumerLab.com website .