Using the National Health and Nutrition Examination Survey, researchers from Tufts University in Boston diagnosed 2,526 participants as having no depression and 301 with major depression. Blood folate levels in both groups were then measured.
In their analysis, the scientists took into account risk factors that might have caused both depression and low folate levels, including alcohol consumption, and the use of vitamin supplements, cigarettes and illegal drugs.
Reporting in the journal Psychotherapy and Psychosomatics, Dr Martha Morris and colleagues found that participants with a lifetime diagnosis of depression had lower folate levels than those who had never been depressed.
Low folate levels were most often linked to patients recently recovered from depression.
“Our findings suggest that low folate status is a consequence of depression,” the researchers said.
“Our results should provide greater impetus for supplementing depressed people with folate, in that we have shown that folate status after a depressive episode can be very low,” they conclude.
They add that further studies are needed to examine the link between folate status and depression.