According to Dr. Michael Holick, director of the Vitamin D, Skin and Bone Research Laboratory and professor of Medicine, Dermatology, Physiology, and Biophysics at Boston University Medical Center, most of us are vitamin D deficient. If we live north of Los Angeles or Atlanta, the low angle of the winter sun doesn’t provide enough ultraviolet light (UVB) for our skin to make adequate vitamin D from November through February. If we live more than 50 degrees from the equator (in much of Canada, for example), we can’t get enough D from the sun from September through March. Even when the sun is strong in March or April, we’re likely to have our skin covered for warmth in colder climate, plus skin becomes less efficient at making active vitamin D as we age. Even when the angle of the sun is high, many of us protect our skin with sun block or clothing. Finally, there is little vitamin D in most foods.
“General population studies indicate that at least one in three people are vitamin D deficient,” according to Dr. Kenneth Saag. Holick thinks the number is much higher. A study from Massachusetts General Hospital in Boston evaluated vitamin D status of patients who were hospitalized for problems unrelated to vitamin D. Of 290 patients admitted on 2 days (one in spring when vitamin D levels are lowest and one in late summer when vitamin D levels are highest), 57% were vitamin D deficient (less than 15 nanograms per milliliter of blood) and 22% were severely deficient (less than 8 ng/mL). Optimal levels are 30-50 ng/mL.
The recommended intake of vitamin D varies with age. Holick found that giving healthy young and middle-aged adults in Boston1000 units of vitamin D a day at the end of winter raised their blood levels of D to optimal levels. He suggests healthy individuals take at least 1000 IU of vitamin D daily, but this amount may be inadequate for people who have little sun exposure or are older than 30.
According to Holick, the toxicity of vitamin D has been exaggerated, although he suggests taking no more than 2000 IU a day without medical supervision. Studies suggest that taking 5000-10,000 IU a day under medical supervision doesn’t cause toxicity. Holick’s vitamin D deficient patients receive as much as 50,000 IU once a week for 8 weeks and then receive this dose once or twice a month to maintain healthy levels. Holick hasn’t seen symptoms of toxicity even at these high levels, but he monitors blood levels carefully.
Vitamin D in Food and Supplements
It’s not easy to get adequate vitamin D from food. An 8-ounce glass of fortified milk or orange juice has about 100 international units (IU). Many processed cold cereals are fortified with small amounts of D. The best dietary source is cod liver oil which contains 1360 IU of vitamin D per tablespoon, but who takes cod liver oil? Three ounces of the following fish provide substantial amounts: halibut 650 IU, herring 750 IU, salmon 425 IU, and sardines 250 IU.
Nutritional Supplements: Vitamin D3 (cholicalciferol) from supplements is well-absorbed at all ages.
Vitamin D from the Sun
Dr. Holick describes the mechanism for vitamin D conversion in this way: “When the highest energy ultraviolet light, called UVB, penetrates the skin, it converts a precursor into vitamin D which becomes 25-hydroxyvitamin D in the liver. This is then activated to 1,25-dihydroxyvitamin D in the kidneys.” (Nutrition Action Healthletter, Dec. 2003, p. 3) As you can see, the mechanism requires healthy skin, liver, and kidney function.
We have developed sun aversion in recent years because of fear of skin cancer, but protecting our skin has caused a new problem. If we use a sunscreen rated SPF 8 (and who uses one this low?), it reduces our ability to make vitamin D by more than 90%. Holick suggests that exposure to strong sun on untreated skin is healthy, but only if the exposure is brief and doesn’t cause burning or reddening of the skin.
As we age, our bodies become less efficient at producing active vitamin D. At age 70, skin makes ¼ the active vitamin D it does at age 20 with same amount of sun exposure. Still, if older individuals in southern climates expose their skin to the sun for 20 minutes a few times a week, they maintain healthy vitamin D levels. A nursing home inEnglandkept vitamin D levels optimal in their residents by putting UVB light fixtures in the ceilings.
Vitamin D and Disease Prevention
Osteomalacia is the technical name for vitamin D deficiency. Osteomalacia is known for causing rickets in children. In adults, symptoms are muscle weakness, bone ache and bone pain, as well as a risk of low bone density. According to Holick, many people who are diagnosed with arthritis, vascular disease or fibromyalgia have vitamin D deficiency. Gregory A. Plotnikoff, MD, of the University of Minnesota Medical School found a high incidence of vitamin D deficiency in his patients of all races, skin colors, and age groups with unexplained muscle and skeletal pain. Men and women are at equal risk for osteomalacia, although it more often leads to osteoporosis in women because they begin with smaller, less dense bones than men.
Osteoporosis is thought of as a women’s disease, but it’s also a problem for men as life-expectancy increases. Adequate vitamin D increases bone density and decreases fracture risk by increasing calcium absorption and the activity of bone cells that lay down bone matrix. With inadequate vitamin D levels, you absorb as little as 10-15% of the calcium you consume.
Type 1 Diabetes: In Finland where the high latitude increases the risk for childhood rickets, 10,000 children were followed for 30 years in a vitamin D study. The children who received a supplement of 2,000 IU vitamin D a day during the 1st year of life had 80% lower risk of developing diabetes than those who received no vitamin D. (Hypponen)
In Multiple Sclerosis (MS), antibodies destroy the myelin sheath that covers nerves. Mice who received activated vitamin D did not develop the myelin sheath-destroying antibodies. In humans, population studies show that the further you live from the equator (making it more likely you’ll have vitamin D deficiency), the higher the risk of MS. In the Nurse’s Health Study, women who supplemented with at least 400 IU of vitamin D a day had significantly less risk of MS. (Holick and Munger)
Congestive Heart Failure (CHF): In preliminary studies, 54 patients with CHF were compared with 34 healthy people. It was found that the CHF patients had vitamin D levels up to 50 percent lower than healthy patients. The more severe the vitamin D deficiency, the worse the heart failure symptoms were. (Zittermann)
Some Cancers: In test tube studies, active vitamin D is a potent hormone for inhibiting cell proliferation in breast, colon, lung, and prostate cancer cells. Researchers are now using vitamin D analogs on liver cancer (hepatoma) and prelimary results look good. (Holick)
Colon Cancer: A vitamin D intake greater than 645 IU/day was linked to a 40% lower risk of colon cancer in a study published in the New England Journal of Medicine. (Lieberman)
Blood Pressure: In a preliminary study, exposing vitamin D deficient people with mild hypertension to enough sunlight to normalize vitamin D blood levels made blood pressure normal, and normal blood pressure was maintained for 9 months. Holick theorizes that vitamin D decreases renin production in the kidney, since increased renin causes hypertension. (Holick)
Rheumatoid Arthritis (RA): The Iowa Women’s Health Study followed almost 30,000 women, aged 55 to 69, for 11 years. During the trial, 152 of the women developed RA. Women whose diets were highest in vitamin D had the lowest incidence of RA. Women who got less than 200 international units (IU) of vitamin D in their diets each day were 33% more likely to develop RA than women who got higher levels. (Saag)
Getting The Vitamin D You Need
Holick suggests taking a supplement of at least 1000 IU a day, and more if you’re vitamin D deficient. He also recommends a few minutes of daily sun exposure without sunscreen when weather permits. TheAmericanAcademyof Dermatology expressed deep concern about this recommendation because of the danger of sun exposure causing skin cancer.
“The trick is getting just enough sun to satisfy your body’s vitamin D requirement, without damaging the skin,” Holick says. “It is difficult to believe that this kind of limited exposure significantly increases a person’s risk of skin cancer.” A light-skinned person in a bathing suit can get the vitamin D they need in 5-10 minutes exposure to summer sun between 10 am and 2 pm 2-3 times a week. In FL, the summer exposure time should be 2-3 minutes. Exposure should be short enough to avoid burning. There is no need to expose head or hands or other areas that suffer skin damage from frequent sun exposure throughout life.
Testing Your Vitamin D Levels
A simple blood test gives you reliable information, but make sure you are tested for 25-hydroxyvitamin D, not 1,25-dihydroxyvitamin D. Holick suggests that blood levels should be at least 30-40 ng/mL in a healthy person. Some researchers suggest that patients with diseases related to osteomalacia, such as osteoporosis, should have levels as high as 50 ng.
Holick, Michael F., Director of theVitamin D, Skin and Bone Research Laboratory and Professor of Medicine, Dermatology, Physiology, and Biophysics at Boston University Medical Center, interview in Nutrition Action Healthletter, Center for Science in the Public Interest, December 2003, 3-6.
Hypponen E, Laara E, Reunanen A, Jarvelin MR, Virtanen SM, “Intake of vitamin D and risk of type 1 diabetes: a birth-cohort study,” Lancet. 2001 Nov 3;358(9292):1500-3.
Lieberman DA, Prindiville S, Weiss DG, Willett W, “Risk factors for advanced colonic neoplasia and hyperplastic polyps in asymptomatic individuals.” JAMA. 2003 Dec 10; 290(22): 2959-67.
Munger KL, Zhang SM, O’Reilly E, Hernán MA, Olek MJ, Willett WC, Ascherio A, “Vitamin D intake and incidence of multiple sclerosis,” Neurology, 2004;62:60-65.
Saag K, Arthritis and Rheumatism, January 2004; vol. 50: pp. 72-77.
Plotnikoff G, Mayo Clinic Proceedings, December 2003; vol. 78: pp. 1463-1470.
Thomas MK, Lloyd-Jones DM, Thadhani RI, et al, “Hypovitaminosis D in Medical Inpatients,” New England J Medicine 338 (12):777-783 (Mar 19, 1998).
Zittermann A, Schleithoff SS, Tenderich G, Berthold HK, Korfer R, Stehle P., “Low vitamin D status: a contributing factor in the pathogenesis of congestive heart failure?” J Am Coll Cardiol. 2003 Jan 1;41(1):105-12.