Does fish oil lower cortisol? What the research does and doesn't show

Cortisol is a specific hormone measurement, not the same question as feeling stressed. Two small randomized trials have measured it directly after omega-3 supplementation — one in midlife adults under a lab stress test, one in pregnant women — both using doses well above a typical fish oil serving, with results that haven't been repeated.

What the evidence doesn't support

It doesn't support fish oil as a reliable way to lower cortisol in a general population — only two small trials have measured cortisol directly, in narrow, specific groups. It doesn't support one dose, because the two trials used different forms (a mixed omega-3 supplement in one, DHA alone in the other) at different amounts, both above a typical fish oil serving. And it doesn't support fish oil as a treatment for a stress-related hormonal condition — both trials measured cortisol's response to a controlled lab stressor in healthy volunteers, not a diagnosed disorder.

What the trials found

A 2021 randomized trial gave 138 sedentary, overweight, middle-aged adults either 2.5 g/day of omega-3, 1.25 g/day, or a placebo for 4 months, then measured salivary cortisol and inflammation markers before and after a standardized lab speech stressor (the Trier Social Stress Test). Adjusting for baseline reactivity, age, body size and sex, the 2.5 g/day group had 19% lower overall cortisol and 33% lower interleukin-6 across the stress test than the placebo group. (Interleukin-6 is a cytokine commonly used as a lab marker alongside inflammation research.) That's a specific result in a specific population — sedentary, overweight midlife adults — at a dose several times a typical fish oil serving, not a general finding about everyday stress.

A separate 2014 randomized trial gave 64 pregnant women 450 mg/day of DHA alone or a placebo, starting between 16 and 21 weeks of pregnancy. At 30 weeks, the DHA group had a smaller, more modulated cortisol response to the same kind of lab stress test than the placebo group. The trial was small and unevenly split (43 women on DHA versus 21 on placebo), studied only pregnant women in one demographic group, and hasn't been repeated since.

Questions people ask

Does fish oil lower cortisol?

Two small trials found lower cortisol readings around a lab stress test after omega-3 supplementation — one in midlife adults, one in pregnant women — but both used doses above a typical fish oil serving, in narrow populations, and neither has been confirmed by a larger trial. That's not enough to call fish oil a reliable way to lower cortisol.

What dose of omega-3 was used to measure cortisol?

2.5 g/day of a mixed omega-3 supplement in one trial, and 450 mg/day of DHA alone in the other — both different forms and amounts from a typical fish oil label, and neither established as a "cortisol dose" beyond that single study.

Does fish oil help with stress and feeling calm, generally?

That's a related but separate question from the cortisol measurements above — see does fish oil help with stress? for the dedicated review of trials measuring stress and anxiety symptoms directly.

Is cortisol the same as feeling stressed?

No. Cortisol is a hormone that rises and falls for many reasons, including a healthy daily rhythm and a normal response to a challenge. A lower lab measurement after a stress test in a trial isn't the same as someone feeling calmer day to day, and neither trial measured that separately.

When to talk to a doctor

Symptoms that suggest a cortisol or adrenal problem — unusual weight changes, persistent fatigue, or other signs a doctor would want to evaluate — are worth raising with a doctor rather than addressing with a supplement. Fish oil is not a treatment for a hormonal or stress-related disorder.

Related reading: does fish oil help with stress?, does fish oil help with anxiety?, and fish oil dosage: what the labels and the trials say.