Vitamin D deficiencies—especially in African-Americans and people with darker skin tones—could raise the risk for developing conditions that include cancer, diabetes and cardiovascular disease, according to several new studies.
As many as 36 percent of Americans are vitamin D deficient, according to the National Center for Health Statistics. That number could be more than double for African-Americans, according to geneticist Rick Kittles, associate professor at the University of Chicago in the Biological Sciences Division.
“Individuals who have moderate to high dark skin color make much less vitamin D,” Kittles said. “There have been some interesting studies recently which suggest that almost 75 percent of African Americans are vitamin D insufficient, which has a lot of implications as it relates to health of African-Americans.”
Vitamin D deficiency is called a “hidden epidemic” for darker-skinned people who have more melanin in the skin. High levels of melanin reduce the body’s ability to make vitamin D from sunlight exposure. In African-Americans it is called eumelanin.
“The brown-black pigment which is in our skin and gives us eye color and hair color is a protector of our skin cells from too much ultraviolet radiation. So it protects the skin from damage, DNA damage for the most part. The wavelength that melanin absorbs is the same wavelength that is needed to produce vitamin D,” Kittles said. “Those individuals with darker skin block that wavelength and so there’s less synthesis of vitamin D occurring.”
With a grant from the National Cancer Institute, Kittles is currently studying serum vitamin D and its effect on prostate cancer risk with respect to genes, UV exposure, skin color and diet.
Vitamin D is primarily produced by exposure to the sun’s ultraviolet rays. In the second layer of the skin, previtamin D is activated and transformed into vitamin D when exposed to UV rays. It is estimated that 15 minutes of daily sun could provide adequate vitamin D, although research is still being conducted.
Vitamin D appears to interact with virtually every tissue in the body. People living in areas such as Chicago, with limited sun exposure several months of the year, often are not manufacturing enough of the vitamin to sustain healthy living.
Kittles, as a dark-skinned African-American, said he takes 3,000 international units daily. He recommends people who live gloomy climates take upwards of 1,000 international units.
As of yet, there are no official recommended doses of vitamin D. But many scientists are trying to determine just how much people should get daily, either by taking supplements, eating more vitamin D-rich foods or from sun exposure. Studies published in the December 2008 issue of the American Journal of Clinical Nutrition recommended 600 international units of daily vitamin D intake. This is higher than the 400 international units generally found in multivitamins.
Kittles is in favor of supplements. He said taking the vitamin in pill form is as good as sun exposure.
“The supplement is actually vitamin D3 and that’s the form that is converted to the active form in the body. From the time we take it, it’s absorbed and it’s converted,” Kittles said. “It’s pretty much similar to the equivalent of the vitamin D that you would make from sunlight exposure.”
Dr. Rohit Arora, a cardiologist and professor at Rosalind Franklin University of Medicine and Science in North Chicago, addressed the issue of vitamin D insufficiency and the correlation with cardiac problems in a 2009 article featured in the American Journal of Therapeutics. After compiling a series of studies and controlled trials, Arora said location can make a big difference.
“In some cases, people must rely on diet and supplements to get the necessary amount of vitamin D as exposure to sunlight just may not be adequate, particularly in the Northern part of North America for example,” he said.
“There’s been a lot of investigative work done on this area,” he said. “Basically, it boils down to the transference of calcium from the bones into the vascular system, which can be detrimental. Build up of that calcium increases the risk of rupture, heart attack and death.”
Arora points out that more research is necessary “to come to a clear conclusion addressing serum vitamin D levels with overall and cardiovascular mortality.”
Deficiencies could also be linked to genetics.
“Risk of deficiencies is pertinent to multiple factors such as genes —particularly in certain racial or ethnic mixes—the oral intake of vitamin D, and the exposure to sunlight,” he said.
Some experts believe that adults should take between 800 and 1,000 international units a day to adequately prevent bone loss and protect against chronic disorders.
Suggestions of increased sun exposure have sparked an intense debate about skin cancer risks.
“You want people to have higher levels of vitamin D so you say the natural way of doing it is just going outside and exposing yourself. However individuals with fair skin color are more prone to skin cancer because of the increased exposures,” Kittles said.
In addition to supplements, the Mayo Clinic suggests fatty fish, egg yolks and other fortified foods as good dietary sources of vitamin D.
Experts, including Arora and Kittles, recommend patients consult with their doctors to see if they are deficient and learn what they can do about it.
“We can do a laboratory test and can look at the various breakdowns of vitamin D, which can tell us if the patient is deficient,” Arora said.