All entries tagged with “vitamin d”
Posted by Dr. Micah Eimer on Sunday Oct 16, 2011 11:50 am
Just like haircuts and clothing, vitamins will from time to time become fashionable in maintaining health and preventing disease. Vitamins E, C and folate seem to have had their time and the focus lately has been on Vitamin D.
The body’s requirement for Vitamin D is met in two ways – 95% is derived from the exposure to ultraviolet B radiation, which creates Vitamin D in the skin, while the remainder is obtained from foods. Many foods are fortified with Vitamin D including dairy products, cereals and orange juice. A potent natural source of Vitamin D is oily fish such as salmon, mackerel, tuna and sardines.
Depending on the normal cut-off value for Vitamin D, it is estimated that 25-60% of the United States population is deficient in Vitamin D. Risk factors for deficiency include increased distance from the equator ( the atmosphere filters the needed ultraviolet radiation), lack of sunshine, darker pigmentation, smoking, obesity, physical inactivity and certain medications.
Originally recognized for its importance in bone development, it has recently been discovered that Vitamin D acts more like a hormone in that there are Vitamin D receptors located throughout the body; including white cells, nerve cells, heart cells and the pancreas cells that release insulin. The exact role of Vitamin D in these non-bone cells is the subject of much current research.
Most of the available data on the consequence of Vitamin D deficiency is derived from population based observation studies in which Vitamin D levels were correlated with various outcomes including cardiovascular disease and death. For example, in the NHANES III study, patients with the lowest 25% of Vitamin D levels had a 26% higher risk of dying in the 9 years of follow up. In the Intermountain study, patients with low Vitamin D levels had an increased risk of having diabetes, high blood pressure, high cholesterol and also an increased risk of heart attack or stroke. Another recent study looking at patients who came to the hospital with heart attacks found that 96% were deficient in Vitamin D.
While these are interesting findings they do not answer the key question- does giving Vitamin D reduce these risks? That requires a prospective, randomized double blind trial in which neither patients or investigators know who is receiving Vitamin D. One obvious obstacle is that it is impossible to restrict Vitamin D in the placebo arm as sunlight is everywhere. Nonetheless, about 18 studies have attempted to do just this with varying results. When the studies are pooled together, Vitamin D does appear to impart a modest (7%) reduction in the risk of dying.
Is there any harm in having too much Vitamin D? The answer at this time appears to be yes. The population based studies demonstrate that there is a “U shaped” curve for Vitamin D, meaning that at high levels it may increase the risk of dying.
There is currently a major trial sponsored by the NIH called the VITAL study which seeks to answer many of these questions. Until those results are released it seems prudent to try and maintain Vitamin D levels in a physiologic range by consuming foods rich in Vitamin D, living a healthy lifestyle as well as ensuring adequate exposure to sunlight.
|
