Vitamin D is critical in promoting bone health and may have broader health benefits but, according to a recent Institute of Medicine, or IOM, report, it is premature to begin taking significantly higher dosages of vitamin D supplements until more research is done. After an extensive review of vitamin D research in 2010, the IOM increased recommendations for vitamin D intake but did so conservatively.
What Is Vitamin D?
Vitamin D is a group of fat-soluble pro-hormones converted into active hormone forms that regulate the body's calcium and phosphorus. The primary natural source of vitamin D is synthesized when skin is exposed to sunlight. For light-skinned people, as little as 15 minutes of sun a few times a week is enough to generate adequate stores of vitamin D, although for darker-skinned people it may take double or triple that. Natural dietary sources of vitamin D are few but include fatty fish, meat and eggs. Most dairy producers fortify their products with vitamin D, and it is also added to some orange juices and cereals.
Research on Health Effects
Two lines of inquiry have generated considerable interest in vitamin D's potential. First, research over the past decade, reviewed by the IOM as well as the New York Times, suggest health benefits for vitamin D in protecting against breast, prostate and colon cancers, boosting the immune system and regulating high blood pressure and insulin metabolism.
Second, research reported in the Archives of Internal Medicine tracked serum Vitamin D levels over a 25-year period and found dramatic decreases in average levels of Vitamin D and increases in the percentages of persons with clear deficiencies. The researchers urged significant increases in the recommended levels of Vitamin D supplements to "address the growing epidemic of Vitamin D deficiency."
After reviewing both lines of inquiry, the IOM concluded that the research, while a promising basis for additional research, is incomplete, sometimes inconsistent, and failed to form the basis to support dramatically increasing the recommended intake levels.
IOM Recommendations
In November 2010, the IOM released revised recommendations that more than doubled the recommended vitamin D levels for women. IOM found adults up to age 70 need no more than 1,000 international units, or IUs, of vitamin D per day, and those 71 and older need 1,200 IUs to maintain health. For 14- to 18-year-olds who are pregnant or lactating, the recommended level is 1,300 IUs, and for those 19 to 50 the recommended level is 1,200 IU.
Considerations
Whether women should take a lot of vitamin D depends on what "a lot" means. It certainly makes sense to take at least what the IOM recommends. Some researchers, including Michael Holick, an endocrinologist and recent author of The Vitamin D Solution, believe, however, that adults should be taking 1,500 to 2,000 IU daily.
So far, the only unambiguous research supports vitamin D's role in promoting bone health, but even here there are gaps. For example, the optimal levels of vitamin D to prevent osteoporosis or to promote bone health are unknown. Results of clinical trials in older women to assess the protective impact of doses of Vitamin D from 400 IU per day to 4,800 IU per day are under way.
References
- National Academies Press: Dietary Reference Intakes for Calcium and Vitamin D; 2010
- National Institutes of Health: Office of Dietary Supplements; Vitamin D
- New York Times: What Do You Lack? Probably Vitamin D
- National Institutes of Health: Clinical Trials: Vitamin D Supplementation in Older Women
- Archives of Internal Medicine; "Demographic Differences and Trends of Vitamin D Insufficiency;" Adit, A; March 2009
Member Comments