What is in your fish oil supplement?

Many take fish oil supplements to promote heart and vascular health. But a new analysis suggests that some consumers may not always get what they are paying for.

The new research, carried out by a testing company called LabDoor, analyzed 30 top-selling fish oil supplements for levels of omega-3 fatty acids, a group of compounds with anti-inflammatory effects. It found that six of those products contained levels of omega-3s that were, on average, 30 percent less than stated on their labels.

The research found more problems when it looked specifically at levels of two particular omega-3s that are promoted for brain and heart health: docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Tests showed that at least a dozen products contained DHA levels that were, on average, 14 percent less than listed on their packaging.

Researchers and health officials say that mislabeling is a frequent problem in the supplement industry.

A number of studies suggest that regular fish consumption is protective against heart disease, and some research suggests it may lower the risk of Alzheimer’s disease and other chronic conditions as well. Omega-3s are also essential for brain and nervous system health.

But research on fish oil has not been conclusive. A large meta-analysis of high quality clinical trials found that purified fish oil supplements did not appear to help people with a history of heart disease, though some experts questioned whether the patients studied had been taking the pills long enough to see an effect. Other research has raised questions about whether high levels of omega-3s may raise the risk of prostate cancer.