Researchers suggest a huge bump in recommended daily levels as the vitamin's benefits extend to helping fight diabetes, cancer and cardiovascular disease.
By Susan J. Landers, AMNews staff. Posted April 20, 2009.
Vitamin D's star is on the rise and physicians who have studied it say it's about time.
Recent research has found that higher D levels are beneficial in fighting ills ranging from colds to cancer. And, on March 26, the Institute of Medicine's Food and Nutrition Board began reviewing those studies and many others with an eye to revising the recommended dietary intake of vitamin D and its close companion in maintaining bone health -- calcium. A report is expected within two years.
Vitamin D has long been recognized as essential to promoting calcium absorption to allow for bone growth and remodeling. Now, its role in health maintenance is expanding in other directions. Some researchers say if we dramatically increase amounts either absorbed from the sun, or ingested in supplements or fortified foods, a corresponding drop could occur in many rapidly proliferating illnesses, including diabetes and cardiovascular disease.
Since sun exposure is itself considered a cancer risk and people often use sunscreen to block it, supplements and fortified foods may be the best routes. So food manufacturers also have their eyes on the IOM Board's work to see whether a boost in fortification will be allowed.
But you would have to eat a lot of fortified foods to get the amounts of D urged by its fans. For example, some physicians who study the vitamin consume 2,000 International Units daily, well beyond the 200 to 400 units per day currently recommended for older teens and adults up to age 70.
Last fall the American Academy of Pediatrics recommended infants, children and adolescents double the amount of D they ingest each day from 200 IUs to 400 IUs. New research shows the higher amount would not only prevent rickets but treat it, said the AAP recommendation.
Is "D" even a vitamin?
Still, a lot is not known about vitamin D. First, it's actually a hormone. "Vitamin D is probably one of the oldest hormones on earth," said Michael Holick, MD, PhD, professor of medicine, physiology and biophysics at Boston University Medical Center.
"Back in the 1970s we realized we could make it in our skin so it couldn't be a vitamin," he added. But Dr. Holick is OK with calling it a vitamin. "People are afraid of hormones."
And the last thing he wants is for people to neglect their vitamin D. His hope is the IOM board will conclude its current Dietary Reference Intakes -- and those for calcium -- are woefully inadequate. He would like to see a minimum daily intake of 1,000 units per day for adults, with 1,500 to 2,000 units preferable.
It is difficult to get too much D, he said, noting that mankind evolved in the sun, thus ensuring adequate amounts before its rays' harmful effects were noted.
The last time the IOM set the intake limits was in 1997 and Dr. Holick was on the panel. "Even then we knew they were inadequate, but there was no literature to support a higher recommendation," he said -- a circumstance that has since changed.
David Klurfeld, PhD, who leads the Human Nutrition Program at the Dept. of Agriculture agrees. Hundreds of studies have been released on vitamin D since the last intake rates were established, he told the board.
The IOM review is being sponsored by the Agriculture Dept., the Dept. of Health and Human Services and the Dept. of Defense as well as Health Canada and the Public Health Agency of Canada.
Danielle Brule, PhD, director of research for Health Canada, told the board the amount of vitamin D people can absorb at her nation's far northern latitudes is too low. Plus, people who have darker skin have more trouble absorbing adequate amounts of sunlight to gain sufficient D.
Despite the increased focus on the need for higher vitamin D levels, people are actually getting less, researchers concluded in a March 23 Archives of Internal Medicine study. They compared the vitamin D levels in blood collected from participants in the National Health and Nutrition Examination Survey between 1988 and 1994 with the D in blood levels of participants in the 2001-2004 survey.
They found the amount of 25-hydroxyvitamin D had dropped from 30 nanograms per milliliter, the amount generally considered necessary for optimal health, to 24 ng/mL.
The main reason for the drop is that people are less likely to go out in the sun, said lead author Adit Ginde, MD, MPH, assistant professor of emergency medicine at the University of Colorado School of Medicine in Denver.
He and his colleagues also concluded that current recommendations are inadequate to address the "growing epidemic of vitamin D deficiency." They advocate increasing intakes to 1,000 IUs per day or more -- especially during the winter and at higher latitudes -- and allowing for judicious sun exposure. They suggest large randomized controlled trials be conducted to evaluate the effects of the increased dose.
Meanwhile, John Whitcomb, MD, medical director for patient access at Aurora Health Care, a nonprofit Wisconsin health care system based in Milwaukee, isn't waiting for the IOM board to make its decision. He's already an enthusiastic booster of increased vitamin D uptake, recommending that people take 1,000 IUs to 2,000 IUs per day.
He called the evidence supporting this increase, "the most critical public health advance in 30 years. We can reduce diabetes, coronary artery disease and cancer. We can drive down the cost of health care in America." He has spread the word of the virtues of D supplements throughout the Aurora system and beyond. "We want everyone in the state of Wisconsin to take vitamin D during the winter."
The print version of this content appeared in the April 27, 2009 issue of American Medical News.
ADDITIONAL INFORMATION:
Who needs more vitamin D
The National Institutes of Health Office of Dietary Supplements compiled a list of people who may require dietary supplements to meet their daily allowance. Among them are:
Breastfed infants: Vitamin D requirements cannot be met by human milk alone. The American Academy of Pediatrics recommends that exclusively and partially breastfed infants be supplemented daily with 400 International Units of this nutrient.
People age 50 and older: This group is at increased risk for vitamin D insufficiency. As people age, their skin is less efficient in synthesizing the vitamin and the kidney is less able to convert it to its active hormone form.
People with limited sun exposure: This population includes the homebound, those living in northern latitudes and individuals who wear long robes and head coverings.
People with dark skin: Greater amounts of the pigment melanin result in darker skin and reduce the skin's ability to produce vitamin D from sunlight.
People with fat malabsorption: Vitamin D requires some dietary fat in the gut for absorption. Individuals who have a reduced ability to absorb dietary fat might require supplements. Fat malabsorption is associated with conditions including pancreatic enzyme deficiency, Crohn's disease, cystic fibrosis, celiac disease, surgical removal of part of the stomach or intestines and some forms of liver disease.
People who are obese: Individuals with a body mass index equal to or greater than 30 typically have a low concentration of the vitamin in the blood.
Source: National Institutes of Health Office of Dietary Supplements (ods.od.nih.gov/factsheets/vitamind.asp)
Weblink
"Dietary Supplement Fact Sheet: Vitamin D," National Institutes of Health Office of Dietary Supplements (ods.od.nih.gov/factsheets/vitamind.asp)
"Dietary Reference Intakes for Vitamin D and Calcium," a project of the Food and Nutrition Board of the Institute of Medicine (www.iom.edu/cms/3788/61170.aspx)
"Demographic Differences and Trends of Vitamin D Insufficiency in the U.S. Population, 1988-2004," abstract, Archives of Internal Medicine, March 23 (archinte.ama-assn.org/cgi/content/abstract/169/6/626)
