May 16 (HealthDay News) -- Low levels of vitamin D and high levels of a hormone secreted by the parathyroid glands may increase the risk of depression in older adults, according to a new report.

The Dutch study, published in the May issue of Archives of General Psychiatry, supports previous speculation by researchers that vitamin D, depression and other psychiatric illnesses are linked, according to background information in the article.

Underlying causes of vitamin D deficiency -- such as less sun exposure due to decreased outdoor activity, different housing or clothing habits, and decreased vitamin intake -- may be secondary to depression, but depression may also be the consequence of poor vitamin D status, the article's authors wrote. Moreover, poor vitamin D status causes an increase in serum parathyroid hormone levels.

Symptoms of depression often appear when the parathyroid glands are overactive, then disappear after the gland condition is treated.

Since both low vitamin D levels and high parathyroid hormone levels can be treated by increasing vitamin D or calcium in the diet and boosting exposure to sunlight, the findings could bring hope to depressed seniors, the researchers say. About 13 percent of older individuals have symptoms of depression.

Researchers at VU University Medical Center, in Amsterdam, found the vitamin D levels were 14 percent lower in test subjects diagnosed with major and minor depression compared with those non-depressed participants.

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.

The researchers measured blood levels of vitamin D and parathyroid hormone among 1,282 community residents over the age of 65. They also assessed symptoms of depression, diagnosing 26 with a major depressive disorder, 169 with minor depression and 1,087 as not depressed.

Additional studies are needed to determine whether changes in levels of vitamin D and parathyroid hormone precede the onset of depression or follow it, the authors said.

SOURCE: JAMA, news release, May 5, 2008