“Helps support emotional health,” says Country Life Omega 3 Mood supplement. Don’t count on it.

Researchers randomly assigned 18,353 adults to take a daily dose of fish oil (465 mg of EPA and 375 mg of DHA) or a placebo. None had experienced depression in the previous two years.

After five years, the fish oil takers had a slightly higher risk of depression. There were roughly 14 cases of depression a year for every 1,000 people who took the fish oil versus 12 cases for every 1,000 who took the placebo. Mood scores didn’t differ between groups, however.

In the same trial, the risk of depression was no different in people who were randomly assigned to take vitamin D (2,000 IU a day) rather than a placebo.

What to do

Don’t expect fish oil (or vitamin D) to prevent depression or boost your mood. And there’s only shaky evidence (from other studies) that fish oil helps people who already have depression. Check with your doctor.