By Consuelo H. Wilkins, M.D., December 16, 2010
Over the past 5 years, the messages regarding vitamin D have been both confusing and conflicting and the Institute of Medicine’s (IOM) recent report has only made it more complex. Last month, the IOM, which sets the dietary reference intakes for nutrients, published new guidelines for calcium and vitamin D. Although the recommended dietary allowances (600-800 IUs, depending on age) and the upper limit of the vitamin D intake (4,000 IUs) are higher than the IOM’s 1997 recommendations, it is not as high as some experts, researchers and other health professionals had anticipated.
Why is there so much confusion? During the past decade, hundreds of papers on vitamin D have been published and many of them have linked low vitamin D levels to various health conditions including heart disease, stroke, diabetes, cancer, depression, and dementia. Given the reports, many have concluded or hypothesized that more vitamin D may prevent these illnesses. Countless media reports from CNN to Oprah’s O magazine have touted the promise of vitamin D as well. Yet the recent IOM report cautions about taking too much vitamin D.
Have we been misled? No. Although the individual studies are true and accurate, the IOM report and its recommendations are based on a review of more than 1,000 studies which include data that support the need for more vitamin D and studies that don’t. The IOM committee found that the research provides strong support for the importance of calcium and vitamin D for strong bones; however, the data supporting vitamin D for other health conditions was not conclusive. This doesn’t mean that vitamin D is not important in the other conditions but that additional studies are needed to establish this.
What does the new 2010 IOM report mean? Compared to the 1997 report, the Dietary Reference Intakes (DRI) established by the IOM provide higher recommended dietary allowances for vitamin D (600 IUs/day for children over 1 year and adults up to 70 years and 800 IUs/day for adults older than 70 years). The recommended upper level of vitamin D intake for adults and children over age 9 is 4,000 IUs/day.
What about the fine print? Although the IOM report states that most people have adequate vitamin D levels, the report clearly identifies groups that are at increased risk for having ‘too little’ vitamin D. The groups are older adults, especially those living in institutions (such as nursing homes) and people with darker skin pigmentation.
Why are there special considerations for these groups? One of the challenges with determining the appropriate amount of vitamin D needed in the diet is that vitamin D is actually made by the body. There is a substance in the skin, that when activated by ultraviolet (UV) light, is released into the bloodstream where it be goes through the liver and on to the kidney to become activated vitamin D. Exposure to sunlight allows the body to make large quantities of vitamin D, far more than one could consume in the diet. Skin changes in older adults make it more difficult to make vitamin D. People with darker skin have more melanin which blocks UV light and reduces the amount of vitamin D made.
What is meant by dark skin pigmentation? Melanin, the substance that is primarily responsible for skin color, helps protect the skin from sun damage by absorbing some of the UV light. The more melanin you have, the darker your skin. While protecting from sun damage, melanin consequently reduces the amount of vitamin D produced. The risk of having a low vitamin D is more common in African Americans, other people of African descent, and Hispanics, even in those with lighter skin (less melanin/pigmentation). African Americans are up to 10 times more likely to be vitamin D deficient.
So how much vitamin D should blacks consume? Healthy African Americans who don’t know their vitamin D level should consume a minimum of 600IUs/day (800 IUs/day if you are over 70) of vitamin D but can safely consume up to 4,000 IUs/day (per the IOM report). If you have vitamin D deficiency, you may require much higher doses to get to a normal level. Your doctor can monitor your vitamin D level with a blood test to be sure that you don’t get too little or too much vitamin D. If you are over the age of 65 or have low bone density, ask your health care provider to check your vitamin D level.
The IOM report on Dietary Reference Intakes for vitamin D and calcium can be found at http://tinyurl.com/IOMVitaminD.
Dr. Wilkins is an associate professor of medicine and psychiatry at Washington University School of Medicine. She has received funding from the National Institutes of Health to study vitamin D and she has published her research on vitamin D in numerous studies in scientific journals and has presented her research nationally and internationally.
– – – – –
Vitamin D deficiency is associated with worse cognitive performance and lower bone density in older African Americans. Full text on-line here
J Natl Med Assoc. 2009 Apr;101(4):349-54.