Researchers have always known that B-vitamins play a critical role in mood, but now a study has definitively connected folic acid levels with depression.

Researchers at Harvard Medical School in Boston have said that low folic acid (folate) levels are associated with slower improvements of the medical treatment of depression. In this study, 110 outpatients with depression, who were given an eight-week trial of fluoxetine (Prozac), provided folate, B12, and homocysteine measurements before the study. The researchers defined the onset of clinical improvement as a 30% decrease in symptom scores leading to a 50% decrease in symptom scores by week eight. From this definition, patients with low folate levels were found to be more likely to lag behind in seeing improvements in their condition than those with normal folate levels.

Similarly, researchers at the University of New South Wales, Australia, found that low folate levels were associated with depression — this time for middle-aged people. They wanted to know if folate, vitamin B12 and high homocysteine levels were possible predictors of depression. Using a random sample of 412 persons, aged 60-64 years, from a larger community sample, they evaluated the severity of depression symptoms, plus folate, vitamin B12 and homocysteine levels. They found that both low folate levels and high homocysteine, but not low vitamin B12 levels, were linked with increased depressive symptoms.

Sources: Int J Neuropsychopharmacol. 2005 Dec;8(4):523-8; Psychol Med. 2005 Apr;35(4):529-38