How much vitamin D is enough? That’s a question often asked by people of all ages, and a team of University of Washington researchers undertook the task of answering it regarding the level needed in the blood to lower the risk of a major medical event in older adults. What they found may surprise you.
The researchers collected and evaluated blood samples from 1,621 white adults who were enrolled in the Cardiovascular Health Study in the early 1990s. Over an 11-year follow-up period, the investigators looked at each individual’s blood vitamin D levels and when a defining medical event occurred: heart attack (186), cancer (335), death (360), and hip fractures (137).
The risk of these medical events occurring among older adults rose when their vitamin D concentration dropped lower than 20 ng/mL (nanograms per milliliter). According to the study’s leader, Dr. Ian de Boer, assistant professor of medicine in the Division of Nephrology, “This target level for adults is considerably lower than that set by other expert panels.”
In fact, the Vitamin D Council recommends individuals take sufficient vitamin D to ensure their blood levels are between 50 ng/mL and 80 ng/mL, which is the range determined as necessary for optimal health.
Everyone should have a blood test to identify their vitamin D level before starting vitamin D supplementation to determine how much they need to take to reach optimal blood levels.
The University of Washington study also pointed out that an association between low blood concentration levels of vitamin D and the risk of a major medical condition varied by season. That’s because people are more likely to get vitamin D from the sun during summer months, which is when blood levels tend to be higher, and to have the lowest blood levels in the winter.
de Boer IH et al. Serum 25-hydroxyvitamin D concentration and risk for major clinical disease events in a community-based population of older adults. Annals of Internal Medicine 2012 May 1; 156:627-34