BU Today

Health & Wellness + In the World

Sunny Dispositions and Vitamin D

Best of Medical: Deficiency may be the most common medical problem


Get the Flash Player to see this media.

In the video above, 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.

Researchers have known for decades that vitamin D is crucial for healthy bones, but recent studies have shown that the vitamin plays an important role in myriad functions in the body.

It regulates insulin production in the pancreas as well as in 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, 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 has a vitamin D receptor,” says Holick, who has been studying how skin makes vitamin D for more than 30 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—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,” he says. “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. 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.”

He says low levels of vitamin D can exacerbate osteoporosis and cause osteomalacia, a painful softening of the bones (called rickets in children). It can also put us at risk for a host of other problems, including 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 food. A glass of milk or vitamin D–fortified orange juice, for example, has 100 IUs. A common multivitamin might have 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 take 1,000 units per day. He also advises spending some time in the sun, which puts him at odds with dermatologists. The American Academy of Dermatology recommends getting vitamin D through a healthy diet, which may include vitamin supplements, rather than spending unprotected time in the sun.

“I don’t advocate tanning,” Holick says. “But I do advocate sensible sun exposure. I tell people to wear some protection on your face. Arms and legs—10 to 15 minutes of sun a couple of times a week between 10 and 3, depending on the season, latitude, and skin pigmentation—is usually adequate.”

Holick, whose book The Vitamin D Solution will 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 believes, 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.”

This story originally ran March 8, 2010. Thumbnail by Gillian Wach (COM’09).

Cynthia K. Buccini can be reached at cbuccini@bu.edu.


4 Comments on Sunny Dispositions and Vitamin D

  • cynthia on 07.30.2010 at 4:46 am

    what lack of vitamin D did to me...

    while i wont say i am an active our outdoor person, i am still surprised my doctor diagnosed me as having vitamin d deficiency. is there any chance that this might be caused by our consumption of overly processed food too? after consuming extra dosage of vitamin D3 for a few months, i noticed the pains and aches were no longer there…and i do feel much more energized too…

  • Felecia on 01.17.2013 at 4:24 pm

    I have a problem with what the professor said……. “we have a healthy developed world living into the 80’s”. From what I see, we are spending many years before our 80’s slowly dying. That doesn’t seem “healthy” to me. How many seniors do you know dont take a boatload of meds and constant doctors appointments. Also she said “theres no shortage of the next generation”. Well the next generation will be the first to NOT out live the previous generation. I think the chances of getting skin cancer are far less than getting the problems you might get from lack of sun and low vitamin D. My friend healed her fibromyalgia with vitamin D although her “specialist” wanted to put her on dangerous drugs instead. Thank god her primary doctor told her to try getting her D level up before going the drug route. Also my husband has chronic back pain which is now much less since I talked him into taking D. I’ll try D before toxic drugs any day.

  • Cindy Harrington on 01.17.2013 at 5:05 pm

    I am 45 years old and live near Philadelphia. Last winter I began to become achey and tired all the time. In April, we discovered my D3 blood level was 16. Since I cannot tolerate the supplement, I have been using a safe tanning bed as advocated by Dr. Mercola and others in the medical profession. I am very careful to *never* burn or overdo it. My blood level has gradually risen to adequate levels and I have never felt better! While everyone around me is falling ill to the flu and other viruses, I continue to stay well. I realize now I have spent my entire adult life, as long as I can remember, catching every virus that goes around in the fall/winter/early spring. I’ve been chronically tired and low on energy except in the summer. I now believe my other chronic health problems may be related to a lifetime of D3 deficiency. I respectfully disagree with Dr. Gilchrest. And also, to both doctors, sitting outside two times per week and exposing some skin is *not* enough to bring up blood levels to a safe level when deficient. I tried consistently last summer and to my dismay, my level went up only minimally. Everyone this far from the equator needs to know their blood level first, proceed from there, and retest later so they can gauge how their body responds to supplementation or sun exposure.

  • Kathy Richmond on 01.17.2013 at 6:47 pm

    I live in Fairbanks, Alaska, 150 miles from the Arctic Circle. I’ve been taking Vit. D suppliments for years after my doctor told me that she started testing all her patients and virtually all her patients were deficient. So she just started prescribing Vit D suppliments routinely instead of testing. Our local health fair began offering Vit D testing a couple of years ago. This past year I discovered that after taking 10,000 per day for over six months, I reached 60, still with normal limits. I worry about doctors only prescribing 1,000mg per day as I don’t think that is sufficient for most people in northern climes.

Post Your Comment

(never shown)