The study, published in the Archives of General Psychiatry, also linked depression to high blood levels of a hormone secreted by the parathyroid glands.

The study suggested low blood vitamin D levels and high parathyroid hormone levels can both be treated with higher dietary intake of vitamin D and increased sunlight exposure.

Study leader Dr. Witte Hoogendijk of the Vrije Universiteit Amsterdam measured blood levels of vitamin D and parathyroid hormone and assessed symptoms of depression among 1,282 community residents age 65 to 95.

Of those individuals, 26 had a diagnosis of major depressive disorder, 169 had minor depression and 1,087 were not depressed. The average blood vitamin D level was 21 nanograms per milliliter and the average parathyroid hormone level was 3.6 picograms per milliliter.

Blood vitamin D levels were 14 percent lower in individuals with major and minor depression compared with non-depressed participants. In addition, parathyroid hormone thyroid levels were an average of 5 percent higher in those with minor depression and 33 percent higher in those with major depressive disorder than in those who were not depressed.