Older adults with low blood levels of vitamin D and high levels of parathyroid hormone may have an increased risk for depression, according to an article in the May issue of Archives of General Psychiatry.

About 13 percent of older adults have symptoms of depression, and other researchers have speculated that vitamin D may be linked to depression and other psychiatric illnesses, according to background information in the article.

"Underlying causes of vitamin D deficiency such as less sun exposure as a result of 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 authors wrote. "Moreover, poor vitamin D status causes an increase in serum parathyroid hormone levels."

Overactive parathyroid glands are frequently accompanied by symptoms of depression that disappear after treatment.

Witte J. G. Hoogendijk, MD, PhD, and colleagues at VU University Medical Center, Vrije Universiteit Amsterdam, the Netherlands, measured blood levels of vitamin D and parathyroid hormone and assessed symptoms of depression among 1,282 community residents age 65 to 95 years.

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 (ng/mL) and the average parathyroid hormone level was 3.6 picograms per milliliter (pg/mL).

Blood vitamin D levels were 14 percent lower in individuals with major and minor depression (average, 19 ng/mL) compared with non-depressed participants (average, 22 ng/mL). In addition, parathyroid hormone thyroid levels were an average of 5 percent higher in adults with minor depression (average, 3.72 pg/mL) and 33 percent higher in those with major depressive disorder (average, 4.69 pg/mL) than in those who were not depressed (average, 3.53 pg/mL).

The findings may be important to patients because both low blood vitamin D levels and high parathyroid hormone levels can be treated with higher dietary intake of vitamin D or calcium and increased sunlight exposure.

"Moreover, the clinical relevance of the present study is underscored by our finding that 38.8 percent of men and 56.9 percent of women in our community-based cohort had an insufficient vitamin D status," they concluded.

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