Results of a new study confirm an association between folate levels and depression.

The study, a pooled look at various studies on the topic, showed that people with lower levels of the B vitamin had an increased risk of depression. Whether their low folate status caused the depression, however, is unknown.

“Our study is unique in that for the first time all the relevant evidence in this controversial area has been brought together,” Dr. Simon Gilbody, of the University of York, in York, UK, said in a university statement. “Although the research does not prove that low folate causes depression, we can now be sure that the two are linked,” he added.

Depression is quickly becoming the world’s second most common cause of disability. Currently, up to 1 in 10 individuals suffers depression, which is one of the top reasons for visits to primary care providers.

Many depressed patients have also been found to have low folate levels - a finding that contributes to hypotheses linking folate and depression. Another factor suggesting an association between the two is the body of research showing the benefits of folate supplementation in depression treatment. Other studies, however, have had contradictory findings.

To further explore the topic, Gilbody and his team reviewed 11 studies on the association between folate levels and depression. The studies involved a total of 15,315 mostly adult participants, 1,769 of whom had depression.

Confirming the results of smaller studies, individuals with low folate levels had up to a 55 percent increased risk for depression, the investigators report in the Journal of Epidemiology and Community Health.

This increased depression risk remained even when the researchers took into account factors that could confound the results, such as the reduced appetite and excessive alcohol drinking that has been associated with depression.

What’s more, not only did study participants with low folate levels have an increased risk of depression, but the converse was also true. Depressed individuals had lower folate levels than their non-depressed peers, the report indicates.

“Folic acid is a cheap and commonly used food supplement, and the identification of low folate status as a plausible specific risk factor for depression raises the possibility of using folic acid supplementation or improved diet in the prevention and treatment of depression at the population level,” Gilbody and his co-authors conclude.

SOURCE: Journal of Epidemiology and Community Health, July 2007.