The prospective, follow-up study concludes that vitamin B12 supplements may increase the probability of a patient's recovery from a major depressive disorder.
Researchers from the Kuopio University Hospital in Finland monitored 115 outpatients, suffering from depression, over a six-month period, and grouped them according to how well they responded to treatment.
The researchers measured blood levels of vitamin B12 at baseline and again at the patients' six-month check up to calculate whether the vitamin influenced patient outcome.
The patients who responded fully to treatment had higher concentrations of vitamin B12 in their blood at both the start and the end of the study than those for whom treatment was less effective, report the authors in today's issue of BMC Psychiatry (3:17).
Further, the association of the level of vitamin B12 and the responsiveness to treatment remained significant even when other factors such as smoking and drinking habits, type of treatment received, and whether other family members had suffered from depression were taken into account.
"As far as we know, there have been no previous studies that have suggested a positive relationship between vitamin B12 and the treatment outcome in patients with major depressive disorder who have normal or high vitamin B12 levels," said the scientists.
Previous research has identified low levels of both vitamin B12 and folate in patients with depressive disorders. However the current study found only a weak link between folate levels and treatment outcome, finding it 'probably not dependent'.
A Norwegian study earlier this year found neither plasma folate levels nor vitamin B12 to differ between people with and without depression but they concluded that the folate in the blood was not being efficiently transferred to the cells in some people.
The Finnish researchers noted that their study included only young and middle-aged patients (average age 44) with moderate depression, which may have influenced the results.
"The association between folate and depression may be more prominent in elderly subjects, among whom folate deficiency has been relatively common in some studies," they write.
A previous study showed that elderly patients with depression responded better to treatment if they took a supplement containing vitamins B1, B2 and B6. This supplement indirectly increased the level of vitamin B12 in these patients' blood.
The authors also suggested that further study into why some depressed people have lower levels of these vitamins could be investigated. Further studies are also needed to confirm the positive association between vitamin B12 and recovery from depression.