The review is just the latest major study to debunk a health claim for omega-3 supplements. Earlier this year, for example, a large review reported that omega-3 supplements have no effect on reducing the risk of developing type 2 diabetes. Other reviews have found the supplements offer no protection against heart disease or stroke. Nor do they help ward off macular degeneration.
Because previous research has found lower levels of omega-3 in people with depression and anxiety, it’s been suggested that omega 3 supplements might help with the prevention and treatment of those disorders.
But as the authors of the new review point out, those studies were observational, and their findings may have resulted from reverse causation. In other words, it’s quite possible that the low levels of omega-3 fatty acids detected in people with depression and anxiety is the result of those conditions (because they can lead to a poor diet), not a contributor to them.
Analyzing the best data
For the current study, researchers at the University of East Anglia in the United Kingdom, reviewed 31 randomized clinical trials (considered the gold standard of medical research) involving more than 41,000 people with or without depression and anxiety. In those trials, which ran for at least six months, participants were randomly assigned to take either an omega 3 supplement or some kind of placebo.
At the beginning and again at the end of the studies, participants filled out special questionnaires designed to identify symptoms of depression and anxiety. When the before and after questionnaires were compared, the data revealed that the supplements had no effect on preventing either condition. Nor was there good evidence that the supplements helped relieve existing symptoms.
In fact, taking omega-3 supplements was associated in the studies with an increased risk of developing depressive symptoms, although the risk was quite small. (The data suggested that the supplements would have to be taken by 1,000 people for one person to develop depressive symptoms.)
“This large systematic review included information from many thousands of people over long periods,” said Lee Hooper, the study’s lead author and an epidemiologist at Great Britain’s University of East Anglia, in a released statement. “Despite all this information, we don’t see protective effects.”
“The most trustworthy studies consistently showed little or no effect of long-chain omega-3 fats on depression or anxiety, and they should not be encouraged as a treatment,” she added.
Limitations and implications
The review comes with caveats. The studies used different ways of assessing symptoms of depression and anxiety, for example. And some of the studies lacked complete information about the participants’ baseline levels of omega-3. Baseline levels could influence the effectiveness of taking omega-3 supplements because, presumably, increasing omega-3 would have a greater effect in people who start out with low levels of the nutrient.
Still, this review offers one of the most comprehensive analyses to date on the topic.
“Physicians should not recommend omega-3 supplements for reducing depression or anxiety risk, and evidence of effectiveness in existing depression is of very low quality,” the study concludes.
That’s not to say that people shouldn’t make sure they get omega-3 fatty acids from fish or other foods.
“Oily fish can be a very nutritious food as part of a balanced diet. But we found that there is no demonstrable value in people taking omega-3 oil supplements for the prevention or treatment of depression and anxiety,” says Katherine Deane, the study’s lead author and a clinical researcher at the University of East Anglia, in a released statement.
“Considering the environmental concerns about industrial fishing and the impact it is having on fish stocks and plastic pollution in the oceans, it seems unhelpful to continue to swallow fish oil tablets that give no benefit,” she added.