What Is It?
Vitamin D is called the sunlight vitamin because the body produces it when the sun’s ultraviolet B (UVB) rays strike the skin. It is the only vitamin the body manufactures naturally and is technically considered a hormone. Essential for building strong bones and teeth, vitamin D also helps to strengthen the immune system and may prevent some types of cancer.
While just 10 to 15 minutes in the summer sun a few days a week supplies adequate amounts of vitamin D, those who can’t get out in the sun may need a supplement. In winter, people in northern climes who don’t get enough sun may also need additional amounts of the vitamin. Unfortunately, the body’s ability to manufacture vitamin D appears to decline with age, so older adults may need to get more vitamin D through diet (fortified milk and fatty fish have good amounts) or supplements, whether they’re exposed to sunlight or not.
Surprisingly, even younger adults may have inadequate stores of this nutrient: In one study involving almost 300 patients of varying ages who were hospitalized for different types of ailments, 57% were found to have low levels of vitamin D. This insufficiency occurred in a full one-third of the people who were getting the recommended amounts of vitamin D from their diet or supplements.
By promoting the absorption and balance of calcium and phosphorous in the body, vitamin D strengthens the bones and teeth and also fosters normal muscle contraction and nerve function. It is also useful for promoting immunity and blood cell formation. In addition, Vitamin D supplements may slow or even reverse some cancers.
Specifically, vitamin D may help to:
Prevent osteoporosis. The body cannot absorb calcium from food or supplements without an adequate intake of vitamin D. If calcium levels in the blood are too low, the body will steal the mineral from the bones and supply the muscles and nerves with the amount they need. Over time, the loss of calcium in the bones can lead to osteoporosis, a disease in which bones become porous and prone to fractures. After menopause, women are particularly at risk for developing this condition. Vitamin D taken along with calcium plays a critical role in maintaining bone density.
In a study of 176 men and 213 women over age 65 done at Tufts University, those who took 500 mg of calcium and 700 IU of vitamin D daily for three years experienced a decrease in bone density loss. Moreover, the incidence of fractures was cut in half. In another study, of 3,270 healthy elderly French women, a daily dietary supplement of 1,200 mg calcium plus 800 IU of vitamin D lowered the incidence of hip fractures by 43% in just two years.
Protect against certain types of cancer. Some studies indicate that vitamin D may be useful in preventing cancer of the breast, colon, and prostate. In a clinical trial of 438 men, researchers reported that participants with colon cancer had lower blood levels of vitamin D than those who did not have the disease. In addition, the men with the highest intake of vitamin D were the least likely to get colon cancer. More studies are needed to support this finding and to determine if it is applicable to women.
Slow joint damage due to arthritis. One recent study showed that taking 400 IU or more of vitamin D daily was effective in delaying or stopping the progression of osteoarthritis of the knees. It did not, however, prevent the disease from developing.
Ease back pain. Individuals who are prone to back problems may benefit from taking vitamin D because of its ability to promote strong bones and cartilage.
Protect against multiple sclerosis. Preliminary animal research suggests a possible connection between high vitamin D levels and immunity to this disabling nerve disorder. This hypothesis may explain why both in the tropics (where there is ample sun to boost vitamin D levels) and in coastal Norway (where sun is scarce, but fatty fish rich in this nutrient abound and are eaten by the local population), cases of MS are rare. More studies in humans are needed, however.
Relieve the symptoms of psoriasis. Because it plays a role in skin cell metabolism and growth, vitamin D may be helpful in treating the itching and flaking associated with this skin ailment. A few studies show that individuals with psoriasis have low levels of this vitamin. Don’t bother with over-the-counter vitamin D creams and supplements, however; they have little effect on psoriasis. Studies do show that a vitamin D3 derivative (1,25 dihydroxycholecalciferol), or activated vitamin D, which is available only by prescription in cream and supplement form, may be useful for psoriasis. It is thought to work by helping skin cells to replicate normally.
Note: Vitamin D has also been found to be useful for a number of other disorders. For information on these additional ailments, see our Dosage Recommendations Chart for Vitamin D.
The government recently reviewed goals for the daily intake of Vitamin D for men and women. Called AI (Adequate Intake), the figures supplant the old RDA (Recommended Daily Allowance) and represent the amount of daily Vitamin D that all individuals in the following age groups should try to meet.
–For men and women ages 19 to 50: 200 IU a day.
–For men and women ages 51 to 70: 400 IU a day.
–For men and women ages 71 and older: 600 IU a day.
For more information on Adequate Intake and other dietary guidelines, see Government Dietary Guidelines.
If You Get Too Little
Insufficient amounts of vitamin D can lead to the development of osteoporosis in adults. Other signs of a deficiency are nervousness, muscle twitches, insomnia, and diarrhea.
In children, a severe deficiency can cause a bone-weakening disease called rickets. Today it is rare to see a child with rickets in industrialized countries because milk is fortified with vitamin D. Moreover, most children get enough exposure to sunlight for their bodies to manufacture all the vitamin D that they need.
If You Get Too Much
Doses greater than 1,000 IU a day are not recommended; signs and symptoms of a toxic reaction include loss of appetite, headache, nausea, vomiting, diarrhea and excessive thirst and urination. Taking 10,000 to 15,000 IU a day regularly can cause weight loss, paleness, constipation, fever, and a number of serious complications. Long-term overconsumption of vitamin D at any dose greater than 1,000 IU day may cause high blood pressure and premature hardening of the arteries. Bones may weaken and a calcium buildup in muscles and other soft tissues may occur. Kidney damage may also develop.
General Dosage Information
Special tips: Getting 10 to 15 minutes of sunlight on your face, hands, and arms between 8 A.M. and 3 P.M. two or three times a week can supply all the vitamin D you need. However, you should consider taking a supplement if you are over age 50; rarely go outdoors at midday; always wear sunscreen (the skin manufactures vitamin D from the sun’s ultraviolet B rays); or don’t drink fortified milk or any other fortified beverage.
–If you need to take a supplement for any of the reasons noted above, many experts advise taking more than the government-recommended intake as long as it does not exceed 10,000 IU a day. Men and women ages 19 to 50 should take 1,000 – 2,000 IU a day. Those over age 50 should take 2,000 IU a day. And people over age 70 should get 2,000 IU a day. Women who are pregnant or breast-feeding should take an additional 2,000 IU daily.
For back pain: Take 2,000 IU daily.
For preventing and treating osteoporosis: Take 2,000 IU of vitamin D in combination with 600 mg calcium twice a day.
For osteoarthritis: Take 2,000 IU daily.
Guidelines for Use
To promote absorption, take this fat-soluble vitamin with food that contains some fat.
Vitamin D supplements should not be combined with antacids containing magnesium. Together, they can cause high blood levels of magnesium.
When taken with thiazide diuretics, such as hydrochlorothiazide, vitamin D can cause excessive–and possibly toxic–levels of calcium in the body, which can cause the kidneys to fail.
Women who are pregnant or breast-feeding should take no more than 2,000 IU of vitamin D daily. Higher doses during pregnancy may cause birth abnormalities.
The body efficiently eliminates any extra vitamin D it makes from sunlight. However, toxic reactions–some of them quite serious–can occur if you get more than 50,000 IU a day from supplements and vitamin D-fortified foods.
Arthritis 2,000 IU a day
Crohn’s Disease 2,000 IU once a day; should be covered by your daily multivitamin and antioxidant.
Osteoporosis 2,000 a day
Psoriasis 2,000 IU a day
David Edelberg, MD