A few months ago, in our article on recent disappointing findings about fish oil (omega-3) supplements, we pointed out that the health benefits of fish itself, especially for the cardiovascular system, are much clearer. Since then a study in the Annals of Internal Medicine has offered perhaps the strongest evidence yet.
The study involved 2,700 healthy Americans over 65 (most in their seventies), whose blood levels of marine omega-3 fatty acids were measured in 1992. People taking omega-3 supplements were excluded, so the blood levels were a marker for fish intake. In 2008 the researchers correlated these omega-3 levels with the number of deaths in the previous years, after adjusting for other dietary, lifestyle and cardiovascular factors. This was the first large study of healthy people that used an objective measure of omega-3 intake (as opposed to self-reports of fish intake, which are much less reliable) to evaluate the effect on mortality rates.
People with the highest initial omega-3 blood levels were 27 percent less likely to die during the 16 years of the study than those with the lowest blood levels, with the greatest reduction seen in deaths from cardiovascular disease (notably those caused by abnormal heart rhythms). As a result, they lived 2.2 years longer, on average.
This finding suggests that eating fish after age 65 can extend life (relatively few interventions can do this at that late age, the researchers pointed out), though it’s likely that the higher omega-3 blood levels reflect long-term dietary habits. A limitation of this study is that the blood levels were measured only at the start of the study, so there’s no way to know how much fish people ate in earlier or later years.
You don’t have to go overboard to get the benefits. The researchers estimated that the biggest increase in omega-3 blood levels would come from eating about two servings of fatty fish a week. Intakes higher than that have diminishing effects on blood levels.
This study didn’t address the question of fish oil supplements. These raise blood levels of omega-3s but may not have the same benefits as fish itself, which contains other nutrients and substances that also help protect the heart and overall health. Fish also often replaces less healthy protein sources, such as red meat. Adding supplements to an unhealthy diet won’t do the trick.
Note: This study did not find a statistically significant link between omega-3 levels and cancer mortality. More recently, a study of men over 50, published in the Journal of the National Cancer Institute, linked higher blood levels of omega-3s to an increased risk of prostate cancer. We’ll investigate these surprising findings in an upcoming article.