Vitamin D deficiency may be the most common medical problem in the world| From Explorations | By Cynthia K. Buccini
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Barbara Gilchrest, a School of Medicine professor and former chair of dermatology, and Michael Holick, a MED professor of medicine, physiology, and biophysics, discuss the risks and benefits of the sun. Illustration by Grady McFerrin
Researchers have known for decades that vitamin D is crucial for healthy bones, but recent studies have shown that the vitamin has an important role in myriad functions in the human body. It regulates insulin production in the pancreas as well as the genes that control cell growth, according to Michael F. Holick, a School of Medicine professor of medicine, physiology, and biophysics. It has a marked effect on vascular smooth muscle, and therefore is important in regulating blood pressure and preventing type 2 diabetes, cardiovascular disease, and stroke. It also impacts the immune system, helping it to fight infectious diseases like tuberculosis and influenza and reducing the risk of autoimmune diseases, including Crohn’s disease, multiple sclerosis, rheumatoid arthritis, and type 1 diabetes.
“Every tissue and cell in your body has a vitamin D receptor,” says Holick, who has been studying how our skin makes vitamin D for more than thirty years. “We estimate that as many as 2,000 genes — up to one-sixth of the total human genome — are directly or indirectly regulated by vitamin D.”
And yet, says Holick, half of all people in the United States don’t get enough of the vitamin. “It’s estimated that about a billion and a half to two billion people worldwide are vitamin D–deficient,” he says. “It’s certainly the most common nutritional deficiency and likely the most common medical problem in the world.”
We get vitamin D from our diet and from supplements, but the principal source is the sun. When sunlight penetrates the skin, says Holick, it converts the prohormone 7-dehydrocholesterol to vitamin D-3, which enters the bloodstream. When it reaches the liver, it becomes 25-hydroxyvitamin D — the circulating form of the vitamin, which is what doctors measure to determine whether a patient is deficient. Next, it goes to the kidneys, where it is converted to the biologically active form, called 1,25-dihydroxyvitamin D. From there, it moves into the small intestine, interacts with a vitamin D receptor, and stimulates the absorption of calcium. “If you’re vitamin D–deficient, you absorb only 10 to 15 percent of the calcium in your diet,” says Holick. “If you’re vitamin D–sufficient, 30 to 40 percent.”
Vitamin D also goes to your bones, where it stimulates cells to remove calcium if you are not getting enough from your diet. “It does that,” says Holick, “because the ultimate function of vitamin D throughout evolution is to maintain blood calcium in a normal range in order to maintain brain, heart, and neuromuscular function. Only when you have enough calcium and phosphorus will you mineralize the skeleton. That’s why vitamin D has always been thought of as important for bone health.”
Michael Holick Photo by Vernon Doucette
Holick says low levels of vitamin D can exacerbate osteoporosis and cause osteomalacia, a painful softening of the bones (called rickets in children), increasing risk of fracture. It can also put us at risk for a host of other problems, including autoimmune diseases such as multiple sclerosis and rheumatoid arthritis, high blood pressure, diabetes, and colon, prostate, breast, and other cancers.
Adults, he says, need 2,000 IUs (international units) of vitamin D a day, a level we can’t get from the foods we eat and from most supplements. A glass of milk or vitamin D–fortified orange juice, for example, has 100 IUs. A common multivitamin might have only 400 IUs. “We did a study last year in a healthy adult population,” he says. “We gave them 1,000 units of vitamin D-2 or vitamin D-3 through the wintertime. Not one person became vitamin D–sufficient.”
Holick argues that another reason we are deficient is that we don’t get enough sun; we spend too much time indoors or slathered with sunblock. It’s especially a problem for residents of northern latitudes. “We showed that in Boston you can’t make any vitamin D in your skin from November through March no matter how long you stay outside,” he says. “In the summertime, you can’t make any vitamin D at eight in the morning or at five in the afternoon.”
He recommends that adults take a supplement with 2,000 units of vitamin D every day and that teenagers and children over a year take 1,000 units per day. He also recommends spending some time in the sun, which has him at odds with dermatologists. The American Academy of Dermatology recommends getting your vitamin D through a healthy diet, which may include vitamin supplements, rather than spending time in the sun unprotected.
“I don’t advocate tanning,” Holick says. “But I do advocate sensible sun exposure. I tell people to wear some protection on your face. But arms and legs — ten to fifteen minutes of sun a couple of times a week between ten and three, depending on the season, latitude, and skin pigmentation, is usually adequate.”
Holick, whose book The Vitamin D Solution is to be published in April, says he’s begun doing studies on varying amounts of vitamin D in the body and its impact on health outcomes. “We’re asking the question, how does your body know it’s getting enough vitamin D?” he says.
The bottom line, he says, is that there is no downside to increasing our intake of vitamin D. “If you think of it evolutionarily, it’s the oldest hormone on this Earth. I don’t think that this is going to be a flash in the pan.”
You Asked, We Answered
Readers took advantage of our invitation to ask Dr. Michael Holick about vitamin D. Here are some of those questions, along with Holick's responses. Learn more about vitamin D at DrHolicksDsolution.com and in Michael Holick’s book The Vitamin D Solution.
QI read that you can take or get too much vitamin D. If that's true, how much is too much? Thank you. — Steve Sailor
ADear Steve, Yes you can take too much of vitamin D. However, in a study that we conducted, we found that 10,000 IU of vitamin D a day for five months did not cause toxicity. Therefore, we recommend that people should not take more than 10,000 IU of vitamin D a day unless prescribed by a doctor.
QIn this article, you gave recommended supplementation for adults and teenagers, but what about children? Since this population probably has the highest compliance rate with sunscreen (from parents protecting their skin) and a higher incidence of milk allergies, therefore reducing vitamin D-fortified foods, how much supplementation would you suggest? — Michelle Mix (COM’03)
ADear Michelle, I recommend that all children be on at least 400 IU of vitamin D a day as has been recommended by the American Academy of Pediatrics. However, I believe that all children should increase their total intake to at least 1,000 IU of vitamin D a day to take advantage of the other health benefits of vitamin D in reducing risk of chronic diseases later in life.
QHow long does the body store vitamin D? I take 5,000 IU a day (I find it helps with inflamed joints) and am wondering if, for ease of dispensing, I could give that amount to my 10- and 12-year-old children, perhaps every other day. Would this, in effect, amount to an average daily dose of 2,500 IUs? And is that too much for them? Thank you. — Anonymous
A Vitamin D intoxication usually occurs in people taking more than 10,000 IU of vitamin D a day for at least half a year. It causes an elevated blood calcium, which can increase thirst, urination, kidney stones, elevated blood calcium, and calcification of the kidneys. Vitamin D intoxication is one of the rarest medical conditions in the world.
QAre there any interactions with other vitamins, or with taking too much calcium? Thank you. — Al (ENG)
AThe recommendation is that adults up to the age of 50 should take 1,000 mg of calcium a day and adults over 50 years 1,200 mg a day from supplements and dietary sources. These amounts will not have any interaction with other vitamins.
QFor individuals found to be vitamin D-deficient, do you agree with a 12-week course of 50,000 IUs once a week? — C. Scott (SAR’03)
AI recommend 50,000 IU of vitamin D once a week for eight weeks to fill up the empty vitamin D tank and then to be on 50,000 IU of vitamin D once every two weeks to maintain a normal vitamin D status. Twelve weeks should be okay.
QIs there a difference between vitamin D2 and D3? How can vegans obtain their required vitamin D? — Barbara Lamagna (SPH’94)
AVitamin D2 is equally as effective as vitamin D3. Ultraviolet irradiated mushrooms and sun-dried mushrooms is a good source of vitamin D2.
QDr. Holick, I really enjoyed this article. I have started my own research recently on vitamin D and this article could not have come out at a better time. Do you have an opinion about light boxes and vitamin D production? My wife is vitamin D deficient, and I was thinking about purchasing one to use over the winter months. Any thoughts would be appreciated. — Mike Haynes (CAS’01)
ADear Mike, Your wife can easily maintain her vitamin D status by increasing her vitamin D intake to 3,000 IU of vitamin D a day during the winter. If she's unable to absorb vitamin D, there is a vitamin D producing lamp called the Sperti lamp that you can find at sperti.com.
QI'm told 2,000 units of vitamin D are a beneficial antidepressant, though I don't see it listed among the advantages itemized in the story. Most people are 'happier' when it's warm and sunny. Please comment. — Joe F. (SMG’79)
ADear Joe, Vitamin D deficiency has been associated with depression. Also people who were vitamin D deficient do not feel well and often have aches and pains in their bones and muscles; correcting their vitamin D deficiency improves their feeling of well-being as well as their aches and pains in their bones and muscles.
QWhat foods do you recommend for those who cannot consume dairy products, but still need to get 1,000 IU or more of vitamin D in their diets? Is there any way to avoid supplements in winter-time? — John Anderson (GRS’62)
ADear John, Orange juices fortified with calcium and 100 IU of vitamin D, which is the same as in dairy products. Ultraviolet irradiated mushrooms and sun-dried mushrooms can also be a good source. Wild caught salmon is also a good source. However, it is next to impossible to get 1,000 IU of vitamin D a day for all dietary sources, and thus I recommend a supplement. Also note that a thousand IU of vitamin D a day in the winter will not satisfy adults’ vitamin D requirement.
QThank you very much for taking questions on vitamin D. Read your 'Sunny Dispositions' from my daughter's Bostonia - very interesting! Do older people have more trouble absorbing vitamin D than younger? Are older people's vitamin D requirements the same as a younger person's? — Bonnie Veninger (Parent of Alumnus, CAS’05)
ADear Bonnie, Older people do not have any problem absorbing vitamin D either from foods or supplements. They do make less of vitamin D when exposed to sunlight.
QIs there an optimal level for Vitamin D in the blood? I asked my primary care doc to test mine at my last physical exam. She sent me a copy of the results without any comment. I don't know any more now than before I asked her. The results read:
VIT D1,25-OH, TOTAL: 53 pg/mL
VIT D 1,25-OH,D3(o): 53 pg/mL
VIT D 1,25-OH,D2(o):: >8 pg/mL
Thank you for any advice you can provide. — Patricia Lipnick Hagopian (SAR)
ADear Patricia, Unfortunately, your doctor ordered the wrong vitamin D test. This test does not provide you with any information about your vitamin D status. Your doctor needs to order 25-hydroxyvitamin D. Once you have the results I will be happy to advise you about what they mean.
Q I really enjoyed the article, as several individuals whom I work with were found to be vitamin D deficient and felt much better on supplements. A relative had been taking a calcium/vitamin D supplement but was advised to stop it due to developing kidney stones. Does it make sense to take Vitamin D as a supplement if it stimulates the production of calcium, which is the most likely cause of the kidney stones? — Michele Bilodeau (CAS’76)
A Dear Michelle, In my opinion there is no evidence that increasing your vitamin D intake will increase risk of kidney stones.
Q I am a 54-year-old African-American male who was diagnosed with osteopenia about 3 years ago. I found out about this after consulting a doctor following the loss of a perfectly good tooth due to bone loss. I had a severe vitamin D deficiency, which requires 50,000 units per week. My vitamin D count is back to normal, however, I am told that I will have to continue this regimen for the rest of my life. I am an otherwise healthy person. Is there any explanation for what could be robbing my body of vitamin D? — Duane Turner (SMG’78)
A Dear Duane, All children and adults in the United States are at high risk for vitamin D deficiency. African-Americans are at particularly high risk because their skin pigment acts as a natural sunscreen and markedly diminishes the production of vitamin D from sun exposure. I recommend that all adults, no matter what their ethnicity, take between 2,000 and 3,000 IU of vitamin D a day to satisfy their vitamin D requirement. I treat vitamin D deficiency with 50,000 IU of vitamin D once a week for eight weeks to fill up the empty vitamin D tank and then maintained vitamin D status by keeping my patients on 50,000 IU of vitamin D once every two weeks forever. For my obese patients, they may require 50,000 IU of vitamin D once a week forever because fat absorbs the vitamin D and does not make it available to the body.
Q I am in stage 4 renal failure and take 2,000 units of vitamin D daily. I'd appreciate any comments or suggestions you might have for me. Thank you.— Nancy Powell, 1981
A Dear Nancy, It is recommended by the National Kidney Foundation that all patients with renal failure should maintain a 25-hydroxyvitamin D level greater than 30 ng/ML. To do this you need at least 2,000 IU of vitamin D a day and probably 3,000 IU of vitamin D a day is better. I typically treat my renal failure patients with 50,000 IU of vitamin D once a week for eight weeks followed by once every two weeks thereafter forever.