Written by Stephen Daniels, August 31, 2011

Source: American Journal of Clinical Nutrition

The prevalence of depressive symptoms was 21% lower in women with a daily vitamin D intake of more than 800 International Units (IU) per day than in others with a daily intake of less than 100 IU. These findings were recently published in the American Journal of Clinical Nutrition.

The results of this study are based on data from 81,189 participants in the Women's Health Initiative (WHI).

Led by Joan Manson of Harvard, the researchers added that the apparent benefit of vitamin D was initially linked to dietary vitamin intake. Additional vitamin D supplementation lead to even better results. 

Researchers are also planning future studies to determine whether elevated vitamin D levels can prevent or treat depression, or both.

The vitamin

Vitamin D binds to two biologically inactive precursors, D3, also known as cholecalciferol, and D2, known as ergocalciferol. The one produced by the skin when exposed to UVB radiation (290-320 nm) is thought to be more bioactive.

Both precursors D2 and D3 are processed in the liver and kidneys in 25 (OH) D and in 1,25-dihydroxyvitamin D (1,25 (OH) 2D) - biologically active forms that are strictly controlled by the body.

While our bodies produce vitamin D from exposure to sunlight (UV-B radiation with a wavelength between 290-315 nm), levels in some northern countries are so low during the winter months that the body does not produce vitamin D at all. This means that taking supplements as well as fortified foods is the best way to increase your vitamin D intake.

Research details 

Dr. Manson and her colleagues conducted a detailed study and examined the prospects of vitamin D intake and depression. Vitamin intake was measured at the beginning of the study using questionnaires on the frequency of meals and the use of dietary supplements. Symptoms of depression were tested on an established scale, taking into account the use of antidepressants.

The results showed that in addition to a 21% reduction in the prevalence of depressive symptoms when taken above 800 IU, a further 20% reduction in risk could be added. How?

When researchers limited their calculations to women without the risk of depression, the risk of developing it was reduced by another 20% when the daily intake of vitamin D through food was 400 IU.

"Generally, our study supports possible feedback between vitamin D taken through food and depressive symptoms in postmenopausal women," they conclude.