Researchers in Holland have found that older people with low blood levels of vitamin D and high blood levels of the parathyroid hormone are more likely to be depressed.
About 13 percent of older individuals have symptoms of depression, and other researchers have suspected that vitamin D may be linked to depression and other psychiatric illnesses.
The researchers from Vrije Universiteit in Amsterdam say however that it is unclear whether these abnormalities are a cause or a consequence of depression.
Dr. Witte J. G. Hoogendijk and colleagues looked at 1,282 men and women, aged 65 to 95 years, taking part in a long-term study of aging.
They say other research has previously linked altered levels of vitamin D and parathyroid hormone with depression, but the relationship has never been systematically studied.
Their research revealed that almost 40 percent of the men and 57 percent of the women had low levels of vitamin D in their blood and among the 169 people suffering from minor depression, as well as the 26 with major depressive disorder, vitamin D levels were 14 percent lower than for people who were free from depression.
The researchers found that blood levels of the parathyroid hormone, which increase with vitamin D deficiency, were 5 percent higher in people with minor depression and 33 percent higher in those with major depression, relative to levels seen in seniors without depression.
The Dutch team say there are a number of ways that low vitamin D levels could affect mood because the vitamin plays a role in a number of neurological and hormonal processes.
They suggest that if vitamin D deficiency is a cause rather than a result of depression, vitamin supplements and increased exposure to sunlight could help treat the mood disorder.
The researchers say 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.
They say long-term studies with repeated assessments are needed to explore the question of whether decreased vitamin D levels and increased parathyroid hormone levels precede depression or follow it.
The research is published in the Archives of General Psychiatry, May 2008.
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