UW Today

May 1, 2012

Researchers determine Vitamin D blood level for reducing major medical risks in older adults

UW Health Sciences/UW Medicine

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In testing older patients blood vitamin D levels, theres uncertainty about where the dividing line falls between enough and not enough. The threshold amount has become controversial as several scientific societies set different targets.

To help resolve this debate, University of Washington researchers conducted an observational study. They wanted to learn how much vitamin D must be circulating in the blood to lower the risk of a major medical event. This category included heart attack, hip fracture, diagnosis of cancer, or death.

Vitamin D levels often drop during the dark cloudy days of northern winters.

Vitamin D levels often drop during the dark cloudy days of northern winters.Alice Gray

Vitamin D is measured in the blood as 25-hydroxy-vitamin D, abbreviated 25(OH)D.

The researchers tested 25(OH)D concentrations from a biorepository of blood samples of 1,621 Caucasian adults. These adults had enrolled in the early 1990s in the Cardiovascular Health Study, originally designed to look at risk factors and progression of heart disease in people age 65 and over. The participants lived in one of four areas in the United States: Forsyth County, North Carolina; Sacramento, County, California; Washington County, Maryland; and Philadelphia, Pennsylvania.

Over about an 11-year follow-up, researchers looked at the association between each individuals 25(OH)D test results and the time that a first defining medical event occurred. Among the participants, 1,018 had such an event. There were 137 hip fractures, 186 heart attacks (myocardial infarctions), 335 incidences of cancer, and 360 deaths.

Levels of the sunshine vitamin rise during the bright days of summer.

Levels of the sunshine vitamin rise during the bright days of summer.Alice Gray

“In evaluating health risk,” the researchers concluded, “Season-specific targets for 25(OH)D blood concentration may be more appropriate than a static target when evaluating patients health risk.

”Future research in this area, de Boer said, will require clinical trials. Researcher will look, for example, at the health effects of attempts to raise 25(OH)D in patients whose levels fall below the target. Interventions might include supplements, dietary changes and increasing outdoor activity.

“Sun exposure is tricky,” de Boer said, “because people have to protect themselves from skin cancer and other sun damage.” Sunscreen blocks the UVB waves responsible for producing Vitamin D. Food sources for Vitamin D are milk, fortified juice and cereal and oily fish like salmon, mackerel, cod and herring.

Vitamin D provides many different beneficial effects on health because it is actually not a vitamin, but a prohormone. It can suppress the hormonal systems that cause fluid to be retained and blood pressure to go up, modulate the function of immune cells, and stop abnormal cells from overgrowing.

In addition to de Boer, other UW authors of the research paper, “Serum 25-hydroxy vitamin D concentrations and risk of major clinical disease events in a community-based population” are Gregory Levin and Mary L. Biggs, Biostatistics; Cassianne Robinson-Cohen, Epidemiology; Andy Hoofnagle, Laboratory Medicine; David Siscovick, Cardiovascular Health Unit and Medicine and Epidemiology; and Bryan Kestenbaum, Nephrology, Kidney Research Institute and Epidemiology.

The research was funded by grants from the National Institutes of Health, including the National Heart, Lung and Blood Institute, the National Institute of Neurological Disorders and Stroke, the National Institute on Aging, and the National Institute of Diabetes and Kidney Disease.