Clinical Vitamin D Deficiency Linked to Depression in Older Adults

Megan Brooks

September 23, 2010

September 23, 2010 — In a British national survey of older adults, clinical vitamin D deficiency, defined as a serum 25-hydroxyvitamin D (25[OH]D) level less than 10 ng/mL, was significantly associated with depressive symptoms, independent of age, sex, social class, physical health status, and season.

Milder states of vitamin D deficiency were not strongly associated with depression in older adults, Robert Stewart, MD, of King's College London, and Vasant Hirani, MSc, of University College London, United Kingdom, report in the September issue of Psychosomatic Medicine.

"Although vitamin D deficiency has been investigated in relationship to mental disorders in younger adults, relatively little research has investigated this association in older people, despite the higher potential impact," the study authors write.

They analyzed data on 2070 adults 65 years and older who participated in the 2005 Health Survey for England. As part of the survey, information on health and health behaviors and sociodemographic data were collected, 25(OH)D levels were measured, and depressive symptoms scored using the Geriatric Depression Scale.

The directly measured vitamin D levels, the use of a widely used scale for depression in older adults, and the large nationally representative sample are key advantages of the study, the study authors say.

Independent Risk Factor

Overall, about one-quarter of the cohort (25.2%) had depressive symptoms, they report. The prevalence of depressive symptoms was 22.6% in the 85.4% of adults with 25(OH)D levels less than 30 ng/mL and 25.8% in the 51.4% of adults with 25(OH)D levels less than 20 ng/mL.

The prevalence of depression was highest (35.0%) in the 9.8% of the cohort with 25(OH)D levels less than 10 ng/mL (clinical deficiency).

The prevalence ratio for depressive symptoms in those with clinical vitamin D deficiency, relative to the remainder of the sample, was 1.45, the team notes, and the population-attributable fraction calculated from this was 4.2%.

In logistic regression analyses, associations between the 3 deficiency states and depression were significant before adjustment for covariates. After adjustment for age, sex, social class, season, smoking status, body mass index, long-standing limiting illness, and subjective general health status, only the association with clinical vitamin D deficiency remained significant and independent (odds ratio, 1.46; 95% confidence interval, 1.02 – 2.08; P = .04).

Further adjustment for alcohol intake and stratification by season of examination did not markedly or consistently alter the results, the researchers note.

Clinical Trial Warranted

Commenting on the study for Medscape Medical News, geriatrician and epidemiologist Luigi Ferrucci, MD, PhD, of the Clinical Research Branch of the National Institute on Aging in Baltimore, Maryland, who was not involved in the study, said there has been "a long series of papers" showing vitamin D deficiency is not only associated with bone problems but with a series of other problems, including low muscle strength, cognitive and vision problems, and depression.

"The studies on depression have been cross-sectional and the data were not very convincing for a number of reasons. The most important one, probably, is that if you have low vitamin D you are likely to have all these pathological problems associated with low vitamin D and these, by themselves, can cause you to be depressed."

Echoing this, Dr. Stewart and Mr. Hirani point out in their paper that "it is possible that depressive states were a cause, rather than a consequence, of vitamin D deficiency." However, if this were the case, they say the association with depression would be expected to be to a similar extent with any relative 25(OH)D deficiency rather than restricted to the 10% lowest levels, as was the case in the current study.

"Ultimately, prospective research is required to clarify the direction of cause and effect," the study authors note. Seconding that view, Dr, Ferrucci said, "An observational study is far from truly establishing causality, but there may be enough evidence at this point to start a clinical trial."

He believes we are reaching a "critical threshold of evidence where it may be worthwhile in investing in a clinical trial to study the effect of vitamin D supplementation on depression risk."

In such a study, Dr. Ferrucci explained, "we'd take people with no depression at baseline, but maybe at risk for depression, treat them with vitamin D or placebo, and what we'd expect to see is that those treated with vitamin D will be less likely to develop a depressive episode in the future; if we could demonstrate that, then the causal pathway is more likely, but we are not at that stage yet."

If vitamin D deficiency is demonstrated to be a cause of depression, correcting the problem "could be an effective public health measure to reduce depression prevalence in later life," Dr. Stewart and Mr. Hirani conclude in their report.

The study authors and Dr. Ferrucci have disclosed no relevant financial relationships.

Psychosom Med. 2010;72:608-612.

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