Older men and women with lower levels of vitamin D in their blood are more prone to become depressed over time.

Vitamin D, produced by the body when skin is exposed to sunlight, is also found in certain foods such as oily fish. It helps cells absorb calcium and is important for bone health. Low vitamin D levels have been linked to heart disease, stroke, high blood pressure, and more severe asthma. In older people, insufficient vitamin D is quite common, and has been linked to fractures, worse physical function, greater frailty, and a wide variety of chronic illness. Many studies have been published on the potential health benefits of vitamin D and the potential risks of deficiency. To explore the relation between low vitamin D and depression in older people, researchers from America followed 531 women and 423 men, aged 65 years and older for over six years.

At the study's outset, 42 percent of the women and 18 percent of the men were depressed, while three-quarters of the women and half of the men had levels of vitamin D below 50 nanomoles per liter, which is generally considered insufficient.

It was found that 72 percent of the depressed people and 60 percent of the non-depressed people had vitamin D insufficiency - the level above deficiency. Women with vitamin D insufficiency showed a worse decline in mood at three and six years of follow-up; their scores on a standardised test measuring depressive symptoms increased more at three and six years compared to the scores for women who had adequate vitamin D.

Women with low vitamin D who weren't depressed at the beginning of the study were also twice as likely to become depressed over the following six years as the women who had sufficient levels of the nutrient. While similar patterns were seen for men, the association wasn't as strong, and in some cases could have been due to chance.

It was concluded that vitamin D deficiency is a risk factor for the development of depressive symptoms in older persons. The strength of the prospective association is higher in women than in men. Further research is required to understand the potential cause between vitamin D deficiency and depression.