Fish Oil: 'No Net Benefit' for Depression Prevention?

Megan Brooks

December 21, 2021

Fish oil supplementation does not help prevent depression or boost mood, new research suggests.

The VITAL-DEP study included more than 18,000 participants. Among adults aged 50 years or older free of clinically relevant depressive symptoms at baseline, long-term use of marine omega-3 fatty acid (omega-3) supplements did not reduce risk for depression or clinically relevant depressive symptoms — or make a difference in the quality of mood.

In fact, there was a small increase found in risk for depression or depressive symptoms with omega-3 supplements.

"While a small increase in risk of depression was inside the statistical margin of significance, there was no harmful or beneficial effect of omega-3 on the overall course of mood during the roughly 5 to 7 years of follow-up," lead author Olivia I. Okereke, MD, Massachusetts General Hospital and Harvard Medical School, Boston, told Medscape Medical News.

"The takeaway from our study is that there is no net benefit of long-term use of daily omega-3 fish oil supplements for preventing depression or boosting mood," Okereke said.

The findings were published online today in the Journal of the American Medical Association.

Assessing General Population Risk

For many years, experts have recommended omega-3 supplements for reduction in depression recurrence in some high-risk patients, Okereke noted.

"However, there are no guidelines related to the use of omega-3 supplements for preventing depression in the general population. Therefore, we undertook this study to provide clarity in the issue," she said.

The VITAL-DEP study enrolled 18,353 older adults (mean age, 67.5 years; 49% women). Of these, 16,657 were at risk for incident depression, defined as having no previous history of depression; and 1696 were at risk for recurrent depression, defined as having a history of depression but not having undergone treatment for depression within the past 2 years.

Roughly half the participants were randomly assigned to receive marine omega-3 fatty acids (1 g/d of fish oil, including 465 mg of eicosapentaenoic acid [EPA] and 375 mg of docosahexaenoic acid [DHA]) and the other half to matching placebo for an average of 5.3 years.

"Because of the large sample size and long follow-up, we were able to test the effects of daily omega-3 fish oil supplements on universal prevention of depression in the adult population," Okereke said.

No Significant Benefit

Results showed risk for depression or clinically relevant depressive symptoms (total of incident and recurrent cases) was not significantly different between the omega-3 group and the placebo group.

The omega-3 group had 651 depression or clinically relevant depressive symptom events (13.9 per 1000 person-years), and the placebo group had 583 depression or clinically relevant depressive symptom events (12.3 per 1000 person-years). The hazard ratio was 1.13 (95% CI, 1.01 - 1.26; P = .03).

There were also no significant between-group differences in longitudinal mood scores. The mean difference in change in 8-item Patient Health Questionnaire (PHQ-8) score was 0.03 points (95% CI, −0.01 to 0.07; P = .19).

"Patients, physicians, and other clinicians should understand that there are still many reasons for some people, under the guidance of their healthcare providers, to take omega-3 fish oil supplements," Okereke noted.

"These supplements increasingly have been found to have benefits for cardiac disease prevention and treatment of inflammatory conditions, in addition to being used for management of existing depressive disorders in some high-risk patients," she said.

"However, the results of our study indicate there is no reason for adults in the general population to be taking daily omega-3 fish oil supplements solely for the purpose of preventing depression or for maintaining a positive mood," she added.

Okereke noted, however, that the VITAL-DEP study used 1 g/day of omega-3 fatty acids and there may be a greater benefit from taking higher doses, such as 4 g/day.

Cautionary Notes

Commenting on the study for Medscape Medical News, Kuan-Pin Su, MD, PhD, Head of Depression Center of An-Nan Hospital, China Medical University, Tainan, Taiwan, highlighted some of the limitations cited by the investigators.

First, depression or depressive symptoms were defined using self-rating scales, which are "convenient to screen for depressive disorders, but a high score obtained on a self-rating scale does not necessarily indicate the presence of depressive psychopathology," said Su, who was not involved with the research.

He also noted that use of 465 mg of EPA and 375 mg of DHA in VITAL-DEP "might be too low" to have an impact. According to the clinical guidelines from the International Society for Nutritional Psychiatry Research, the recommended dosages should be 1-2 g of net EPA daily, from either pure EPA or an EPA/DHA formula.

Finally, Su said it is "very important to also address the potential for type I error, which makes the secondary and subgroup analyses less reliable."

VITAL-DEP was supported by a grant from the National Institute of Mental Health. Pronova BioPharma donated the fish oil and matching placebo. Okereke reported receiving royalties from Springer Publishing. Su is a founding committee member of the International Society for Nutritional Psychiatry Research, the board director of the International Society for the Study of Fatty Acids, and an associate editor of the journal Brain, Behavior, and Immunity.

JAMA. Published online December 21, 2021. Full text

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