In testing older patients' blood vitamin D levels, there's 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.
Their findings are reported today, May 1, in the Annals of Internal Medicine. Dr. Ian de Boer, assistant professor of medicine in the Division of Nephrology and a member of the Kidney Research Institute, led the project. He also holds an appointment in the Department of Epidemiology, UW School of Public Health.
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 individual's 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.
Through their statistical analysis, the researchers concluded that the risk of these disease events rose when the concentration of 25(OH)D fell below 20 ng/milliliter o
|Contact: Leila Gray|
University of Washington