News review by Deborah Brauser
This important large-scale study adds to - and supports - a large body of existing evidence that links depression and other mood disorders to relative deficiencies in the long-chain omega-3 fatty acids found in fish and seafood (EPA and DHA). (See Freeman et al 2006 for an early review and treatment recommendations from the American Psychiatric Association)
The finding reported here that low blood DHA levels predict suicide risk confirms the results of an earlier, much smaller pilot study (Sublette et al 2006).
This study also found remarkably low average levels of omega-3 in US military personnel. Hopefully it will provide a much-needed wake-up call for governments everywhere to pay serious attention to the links between diet and mental health.
Low levels of docosahexaenoic acid (DHA), the major omega-3 fatty acid concentrated in the brain, may increase suicide risk, new research suggests.
A retrospective case-control study of1600 United States military personnel, including 800 who had committed suicide and 800 healthy counterparts, showed that all participants had low omega-3 levels. However, the suicide risk was 62% greatest in those with the lowest levels of DHA.
"Our findings add to an extensive body of research that points to a fundamental role for DHA and other omega-3 fatty acids in protecting against mental health problems and suicide risks," co–principal investigator Capt. Joseph R. Hibbeln, MD, acting chief, Section on Nutritional Neurosciences at the National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, Maryland, said in a statement.
He told Medscape Medical News that the US military "goes to great steps" to ensure they provide the best nutrition to their soldiers, especially in combat and deployment situations. However, these findings on the potential usefulness of omega-3 fatty acids for the brain should be taken into account when designing military diets in the future.
"Omega-3 is already recommended by the American Psychiatric Association as adjunctive therapy for anybody with a psychiatric disorder, especially for those with major depression," said Dr. Hibbeln.
When asked whether he would recommend omega-3 even to those without a diagnosis, Dr. Hibbeln replied, "it certainly wouldn't hurt."
"It's best not to categorize this as 'a drug,' but instead as a fundamental nutrient."
The study was published online August 23 in the Journal of Clinical Psychiatry.
Largest Study of Its Kind
"The recent escalation of U.S. military suicide deaths to record numbers has been a sentinel for impaired force efficacy and has accelerated the search for reversible risk factors," write the investigators.
They note that suicide rates in military personnel have doubled since the start of Operation Enduring Freedom and Operation Iraqi Freedom, and now "rival the battlefield in toll."
Previous research has shown that omega-3 essential highly unsaturated fatty acids (n-3 HUFAs), especially DHA, are needed for optimal neural function.
"Nutritional deficiencies in n-3 HUFAs may increase vulnerability to combat deployment stress, manifesting as psychiatric symptoms including adjustment disorders, major depression, impulsive violence, and suicide," the investigators write.
In addition, observational studies conducted in civilian populations have suggested that low DHA levels are linked to increased risk for suicide attempt and may contribute to adverse psychiatric symptoms.
For this study, prospectively collected blood samples from the Armed Forces Health Surveillance Center were evaluated from 800 suicide deaths (95.6% men; mean age, 27.3 years) and 800 randomly selected age- and sex-matched healthy control participants. All were active-duty personnel from the Army, Navy, Air Force, and Marines who served from 2002 to 2008.
"To our knowledge, this is the largest study of biological factors among suicide deaths," the authors write.
The Armed Forces Health Surveillance Center also maintains matched health data, including postdeployment health assessment questionnaires and International Statistical Classification of Diseases, Ninth Revision, mental health and substance abuse diagnosis reports.
Higher Suicide Risks
Results showed that "each standard deviation (SD) of lower DHA was associated with a 14% greater risk for suicide (odds ratio (OR), 1.14; 95% confidence interval (CI) 1.02-1.27; P < .03)," report the investigators.
Men who had serum DHA levels below 1.75% had a significantly greater risk of completing suicide than men with higher levels (adjusted OR, 1.62; 95% CI, 1.12 - 2.34; P < .01.)
There was also a 52% higher suicide risk for all participants who reported having witnessed fellow soldiers wounded, killed, or dead (OR, 1.52; 95% CI, 1.11 - 2.09; P < .01).
In addition, there was an increased risk for suicide associated with more inpatient mental health visits (OR, 1.47; P < .001). However, it was not associated with any substance abuse diagnosis.
Although women had a significantly higher mean DHA percentage compared with men (1.48% vs 1.15%), there was no difference in fatty acids found between the women who did and those who did not complete suicide.
"Nearly all US military personnel had low n-3 HUFA status in comparison to North American, Australian, Mediterranean, and Asian populations," write the researchers.
"Although these data suggest that low serum DHA may be a risk factor for suicide, well-designed intervention trials are needed to evaluate causality," they add.
The treatment committee for the American Psychiatry Association, of which Dr. Hibbeln was a member, issued recommendations in 2006 for 1 g/day of n-3 HUFAs for anyone with a psychiatric disorder, and the US Food and Drug Administration has determined that up to 3 g/day is considered safe.
Omega-3 Intake Matters
"I thought this was an impressive study with a very large sample size," Janice Kiecolt-Glaser, PhD, professor of psychiatry and psychology and S. Robert David Chair of Medicine at the Institute for Behavioral Medicine Research at Ohio State University College of Medicine in Columbus, told Medscape Medical News.
"It suggests that the diet of our military, in terms of omega-3 intake, is poor, and that it could have implications for mental health. And that's an important and cautionary note for all of us," said Dr. Kiecolt-Glaser, who was not involved in the study.
As recently reported by Medscape Medical News, Dr. Kiecolt-Glaser led a trial showing that omega-3 supplements may lower both anxiety symptoms and proinflammatory cytokines in healthy young adults.
Dr. Kiecolt-Glaser said she was surprised at how low the omega-3 intake was overall in the current study. "Given this is a population that's already under a lot of strains and at risk for depression, it's something that really needs attention."
She noted that Dr. Hibbeln "has become Mr. Omega-3 for a lot of the psychiatric literature," in terms of depression and omega-3 use.
"He's done cross-national studies in a variety of different cohorts that showed repeatedly that depression is associated with lower levels of omega-3. Then, in randomized controlled trials, we see that omega-3 intake has beneficial effects," she reported.
On the basis of the results of this study, said Dr. Kiecolt-Glaser, it's a "no brainer" to investigate whether making dietary improvements in military personnel makes a difference to mental health outcomes.
"For clinicians who treat civilians, I'd say that omega-3 intake matters, and that it's helpful to keep in mind that there might be dietary issues related to depression as well."
The study was supported by a grant from the Defense Advanced Research Projects Agency and by the Division of Intramural Basic and Clinical Research at the National Institute on Alcohol Abuse and Alcoholism. The study authors and Dr. Kiecolt-Glaser have disclosed no relevant financial relationships.
J Clin Psychiatry. Published online August 23, 2011. Abstract