Vitamin D Deficiency Linked to Increased Mortality in Older Adults

Abstract & Commentary

By Mary Elina Ferris, MD, Clinical Associate Professor, University of Southern California. Dr. Ferris reports no financial relationship to this field of study.

Synopsis: Low levels of serum 25-hydroxyvitamin D [25(OH)D] in non-institutionalized older adults were associated with future increased mortality from all causes and from cardiovascular disease.

Source: Ginde AA, et al. Prospective study of serum 25-hydroxyvitamin D level, cardiovascular disease mortality, and all-cause mortality in older U.S. adults. J Am Geriatr Soc 2009;57:1595-1603.

Using data from the U.S. National Center for Health Statistics Third National Health and Nutrition Examination Survey (NHANES III) gathered from 1988 to 1994, mortality causes extending through December 2000 were matched to baseline serum 25(OH)D values for 3409 participants age 65 years and older (mean age, 73 ± 0.2 years). Mean values were 66.0 nmol/L, with lower levels in women, non-Hispanic blacks, and Mexican Americans. Other factors associated with lower levels were poor socioeconomic status, winter season, Midwest region residence, lower physical activity, hypertension, diabetes, and history of stroke. Optimal range for 25(OH)D is 75-100 nmol/L; fully two-thirds of the group had 25(OH)D levels below that, with the majority falling within the 50-75 nmol/L range.

Approximately 44% of study participants died over the median 7.3 years of follow-up, with 51% caused by cardiovascular disease. Even after controlling for potential confounders and variables, there was an independent inverse association of low 25(OH)D levels and all-cause mortality. The largest risk was in the lowest stratum (< 25 nmol/L), and there appeared to be an inverse linear association continuing as the levels increased. The association of low levels and increased mortality was even stronger for participants with diabetes and cardiovascular mortality.

Commentary

Our successful campaigns to avoid sun damage from ultraviolet rays are contributing to the unintended consequence of decreased serum vitamin D levels. Elderly adults have the added disadvantage of decreased precursors in the skin, combined with less sun exposure if they engage in less outdoor activity. Previous research has suggested these lower levels impact both bone health and many other conditions such as cardiovascular diseases, cancer, and infections.1 This large prospective study based on interviews, examinations, lab studies, and subsequent mortality data confirms that older adults show significant inverse associations between low 25(OH)D levels and increased mortality.

However, whether the low 25(OH)D levels actually contribute to the increased mortality, or are merely a reflection of underlying poor health status, is not established yet, although in specific situations such as hemodialysis and kidney disease, vitamin D supplementation has had beneficial effects. Many authorities feel that current recommendations for vitamin D supplementation of 200-600 IU/d are too low, since serum levels only rise by 2.5 nmol/L for every 100 IU/d of additional vitamin D.2 The dose needed to raise the serum levels 25-50 nmol/L would be 1000-2000 IU/d of cholecalciferol (vitamin D3). The safe upper limit for daily vitamin D3 intake is 10,000 IU/d, so it's likely we will all be recommending much more of this daily supplement if future studies support its benefit.

References

1. Melamed ML, et al. 25-hydroxyvitamin D levels and the risk of mortality in the general population. Arch Intern Med 2008;168:1629-1637.

2. Heaney RP. Vitamin D in health and disease. Clin J Am Soc Nephrol 2008;3:1535-1541.