In recent years, healthy people have been bombarded by stories in the media and on web sites health warning about the dangers of too low levels of vitamin D, and urging the high doses of supplements to protect against everything from hypertension to hardening of the arteries to diabetes.
However, new research from Johns Hopkins University found that blood levels of the “sunshine vitamin” that are higher than the top of the range suggested by the Institute of Medicine confer any benefit additional. This finding, together with the results of a previous study by the same group observing damage potential of higher levels of vitamin D in healthy people, has urged researchers to prescribe caution.
“Healthy people these pills have been popping up, but they should continue taking vitamin D supplements without control,” says study leader Muhammad Amer, MD, MHS, assistant professor in the Division of General Internal Medicine Johns Hopkins Medicine. “At one point, more vitamin D no longer confer any survival benefit, so take these expensive supplements is at best a waste of money.”
Amer emphasizes that there are some groups of people – the elderly, postmenopausal women and people with kidney disease – who benefit from the highest blood levels of an essential vitamin for bone health. Such groups may need to take supplements.
In an article published online in The American Journal of Medicine, Amer and Rehan Qayyum, MD, MHS, also of Johns Hopkins, describe their review of data from more than 10,000 participants in the National Survey Health and Nutrition examination Survey (NHANES) from 2001 to 2004. They matched this data with mortality data from the National death Index through December 2006.
When examined deaths from all causes and cardiovascular disease in particular, those with blood levels of 21 nanograms per milliliter of 25-hydroxyvitamin D – at the top of the range IOM considers “adequate” and at the lower end of “normal” – lower your risk of death in half. Above 21 nanograms per milliliter, the data suggest that the protective effect seems to disappear.
The main source of vitamin D is the sun, and while it is found naturally in very few foods, commercially sold milk is usually fortified with it. Amer says that people spend more time indoors and slather their bodies with sunscreen when outdoors, concern is growing that many are deficient in vitamin D. But he says no amount of management system supplements that can bring someone up to 21 nanograms per milliliter, for how to process vitamins varies.
In research published in January 2012 in the American Journal of Cardiology, Amer and Qayyum found that increased levels of vitamin D in the blood are associated with lower levels of a popular marker for inflammation cardiovascular – C-reactive protein (also known as CRP). Beyond blood levels of 21 nanograms per milliliter, any further increase in vitamin D was associated with increased CRP, a factor related to the rigidity of blood vessels and increased risk of cardiovascular problems. unpublished research team also suggests a link between excess vitamin D and high levels of homocysteine, another warning sign for cardiovascular disease.
Individuals should consult with their doctors, Amer says, before starting vitamin D supplements and should have their blood levels checked. However, he says, “most healthy people are unlikely to find that supplementation prevents cardiovascular diseases and extends their life,” and there is no consensus among doctors about what is the right level of vitamin D in the blood of people healthy.
“There are a lot of myths out there and there are insufficient data,” he concludes.
Qayyum is supported by a grant from the National Heart, Lung and Blood Institute (1K23HL105897-01).