Vitamin D supplementation should not be one-size-fits-all, report researchers. Vitamin D recommendations should vary because risk for vitamin D deficiency varies widely. For example, African-American men who live in areas with low sunlight are more likely to suffer vitamin D deficiency than European-American men living in the same environment, according to a study conducted in Chicago.
When researchers looked at 25 hydroxyvitamin D [25(OH)D] levels in 492 men age 40 to 79 who lived in Chicago, Illinois, they found that 93% of African-American men and 69.7% of European-American men were vitamin D-deficient, with 25(OH)D levels of less than 30 ng/mL. (According to the National Oceanic and Atmospheric Administration, Chicago gets 54% sunshine, compared with Yuma, Arizona, which gets 90%.)
"This study shows that across the board, vitamin D recommendations just won't work for everybody," Adam B. Murphy, MD, MBA, clinical instructor in the Department of Urology at Northwestern University Feinberg School of Medicine, Chicago, said in a statement. He reported on the study at the Fourth American Association for Cancer Research (AACR) Conference on the Science of Cancer Health Disparities (SCHD).
Vitamin D levels were low in not only African-American men but those with lower incomes and people with higher body mass indexes. Although low sunlight exposure is a known factor in lower levels of vitamin D, researchers found that African-American men also had lower levels of vitamin D in sunnier seasons as well.
Dr. Murphy, who was the lead investigator on the study, attributed the lower vitamin D levels to higher levels of melanin pigment in the skin, which prevents ultraviolet radiation rays from being absorbed and reduces the amount of vitamin D produced.
Race, Exposure to Sunlight Affect Vitamin D Requirements
"I think the IOM's [Institute of Medicine's] recent recommendation is a complete farce," one researcher, Rick Kittles, PhD, associate professor of medicine and epidemiology and biostatistics at the University of Illinois at Chicago, told Medscape Medical News. The IOM recommended raising the recommended dietary allowance from 400 to 600 IU of vitamin D for people aged 1 to 70. But Dr. Kittles contends that still is not enough to increase the levels of vitamin D in people of color.
Many more criteria need to be taken into account when devising vitamin D recommendations, he said, including skin tone, occupation, geographic location, and weight. "Someone of light complexion living in Florida may not need to take as much vitamin D as someone living in Chicago, where there's poor sunlight," Dr. Kittles said. Having a blanket recommendation of 600 IU doesn't make sense, he stated.
In defense of the IOM recommendations, JoAnn Manson, MD, MPH, PhD, toldMedscape Medical News that the IOM committee assumed minimal to no sun exposure in deriving the recommended dietary allowances (RDAs). She was a member of the IOM committee and is chief of the Division of Preventive Medicine at Brigham and Women's Hospital and professor of medicine at Harvard Medical School in Boston, Massachusetts.
The RDAs apply to intakes during all seasons, all latitudes, all sunscreen use behaviors, and clothing practices, she said. An extreme example is that they are supposed to apply during winters in Antarctica. The IOM committee also believed that the appropriate cutoff point to use for sufficient serum 25(OH)D was 20 ng/mL or greater, not 30 ng/mL or greater.
The IOM report does offer a lengthy discussion of several groups who may need higher intakes of vitamin D to achieve the recommended 25(OH)D threshold level of 20 ng/mL. In fact, many African Americans will need higher amounts of vitamin D, Dr. Manson noted. However, there is not enough evidence to conclude that a serum 25(OH)D level of 30 ng/mL or greater will confer greater health benefits than levels of 20 ng/mL or greater for any demographic group, she contended. Randomized trials are in progress (such as the VITamin D and OmegA-3 TriaL) to test these hypotheses.
Dr. Kittles said that modifiers of serum vitamin D levels, such as skin pigmentation, diet, body mass index, ultraviolet radiation exposure, and genes must be taken into account in the trials; if not, there would be multiple confounding variables and the study, like earlier ones, would fall short of being definitive.
Even for people with lighter skin color and the ideal physical location and body weight, the IOM-recommended intake of 600 IU is still low, Dr. Kittles asserted.
He recommends an intake between 1000 and 3000 IU a day for the general population. When you see that 80% of African Americans and around 57% to 60% of whites are vitamin D-deficient, he said, that should be cause for concern, given that we know that vitamin D is playing a role in many different diseases. Vitamin D deficiency has been linked to many diseases, such as breast cancer, prostate cancer, diabetes, rheumatoid arthritis, and multiple sclerosis, which explains why the researchers believe the recommended intake should be adjusted to reflect the differences between African Americans and European Americans.
Fourth American Association for Cancer Research Conference on the Science of Cancer Health Disparities (SCHD); Abstract #B54. Presented September 20, 2011.
Dr. Murphy, Dr. Kittles, and Dr. Manson have disclosed no relevant financial relationships.
Sandra Yin • Medscape Medical News © 2011 WebMD, LLC