Problem From Low Blood Levels?

For this study, published in the July issue of Nutrition Journal, the researchers first identified 130 patients whose blood levels of vitamin D in the summer were considered normal -- about 24 ng/mL. However, some researchers believe that many Americans are vitamin D-deficient and that their blood level may be too low.

"If a patient measures at 24 ng/mL or less in the summer, it will likely drop to 16 ng/mL in the winter because the value you have in the summer is greater than what you'll have in February," says lead researcher Reinhold Vieth, PhD, a vitamin D researcher at Mt. Sinai Hospital in Toronto.

He then gave those patients a questionnaire to gauge their likelihood of depression. Those whose answers suggested a strong possibility of depression were then given supplements containing a daily dose of either 600 or 4,000 international units (IUs) of Vitamin D. They started taking the supplements in summer and continued through the winter.

The patients were re-evaluated a year later. With both doses, patients suffering from depression improved as their vitamin D levels increased to at least 40 ng/mL, what some vitamin D researchers recommend as a normal blood level.