Herbs & Supplements:
Vitamin D
Supplement Forms / Alternate Names
•
Cholecalciferol (Vitamin D3), Ergocalciferol (Vitamin D2)
Principal Proposed Uses
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Preventing and Treating Osteoporosis
Other Proposed Uses
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Cancer Prevention, Polycystic Ovary Syndrome, Psoriasis, Diabetes (Prevention)
Vitamin D is both a vitamin and a hormone. It's a vitamin because your body cannot absorb calcium without it; it's a hormone because your body manufactures it in response to your skin's exposure to sunlight.
There are two major forms of vitamin D, and both have the word calciferol in their names. In Latin, calciferol means "calcium carrier." Vitamin D3 (cholecalciferol) is made by the body and is found in some foods. Vitamin D2 (ergocalciferol) is the form most often added to milk and other foods, and the form you're most likely to use as a supplement.
Strong evidence tells us that the combination of vitamin D and calcium supplements can be quite helpful for preventing and treating osteoporosis.
Requirements/Sources
As with vitamin A, dosages of vitamin D are often expressed in terms of international units (IU) rather than milligrams. The official U.S. and Canadian recommendations for daily intake of vitamin D are as follows:
- Infants 0–12 months, 200 IU (5 mcg)
- Males and females 1–50 years, 200 IU (5 mcg)
51–70 years, 400 IU (10 mcg)
71 years and older, 600 IU (15 mcg) - Pregnant women, 200 IU (5 mcg)
- Nursing women, 200 IU (5 mcg)
However, growing evidence suggests that these recommendations may be too low. For example, a study of veiled Moslem women living in Denmark found that 600 IU of vitamin D daily was insufficient to raise vitamin D levels in the blood to normal levels.1 The authors of this study recommend that sun-deprived individuals should receive 1,000 IU of vitamin D daily. However, this idea has not been universally accepted.
There is very little vitamin D found naturally in the foods we eat (the best sources are coldwater fish). In many countries, vitamin D is added to milk and other foods like breakfast cereals and margarine, contributing to our daily intake.
By far the best source of vitamin D is sunlight. However, current recommendations which stress sun avoidance and the use of sunblock may have the unintended effect of increasing the prevalence of vitamin D deficiency. Severe vitamin D deficiency was common in England in the 1800s due to coal smoke obscuring the sun. During that time, cod liver oil, which is high in vitamin D, became popular as a supplement for children to help prevent rickets. (Rickets is a disease caused by vitamin D deficiency in which developing bones soften and curve because they aren't receiving enough calcium.)
Vitamin D deficiency is known to occur today in the elderly (who often receive less sun exposure) as well as in people who live in northern latitudes and don't drink vitamin D–enriched milk.5,6,7 The consequences of this deficiency may be increased risk of hypertension, osteoporosis, and several forms of cancer.8
Additionally, phenytoin (Dilantin), primidone (Mysoline), and phenobarbital for seizures; corticosteroids; cimetidine (Tagamet) for ulcers; the blood-thinning drug heparin; and the antituberculosis drugs isoniazid (INH) and rifampin may interfere with vitamin D absorption or activity.9–27
Therapeutic Dosages
For therapeutic purposes, vitamin D is taken at the nutritional doses described in Requirements/Sources (and sometimes in even higher amounts). If you wish to exceed nutritional levels of vitamin D intake, physician supervision is recommended (see Safety Issues).
Therapeutic Uses
Without question, if you are concerned about osteoporosis, you should take calcium and vitamin D. The combination definitely helps prevent bone loss.28,29 This is true even if you are taking estrogen or any other treatment for osteoporosis; after all, you can't build bone without calcium, and you can't properly absorb and utilize calcium without adequate intake of vitamin D.Other uses of vitamin D are less well documented. Some evidence suggests that getting adequate vitamin D may help prevent cancer of the breast, colon, pancreas, prostate, and skin, but the research on this question has yielded mixed results.30–49 Adequate vitamin D might also reduce the risk of hypertension.50–53
One preliminary study suggests that supplementation with vitamin D and calcium may be helpful for women with polycystic ovary syndrome.54
Vitamin D is sometimes mentioned as a treatment for psoriasis. However, this recommendation is based on Danish studies using calcipotriol, a variation of vitamin D3 that is used externally (applied to the skin).55 Calcipotriol does not affect your body's absorption of calcium, so it is a very different substance from the vitamin D you can purchase at a store.
Intriguing preliminary evidence suggests that adequate vitamin D intake may help reduce the risk of diabetes.74-76
What Is the Scientific Evidence for Vitamin D?
Osteoporosis
Individuals with severe osteoporosis have low levels of vitamin D.56,57,58 Supplementing with vitamin D alone may not be helpful,59,60 but the combination of calcium and vitamin D can slow down or even reverse osteoporosis. However, calcium and vitamin D use must be continual. Improvements in bone rapidly disappear once the supplements are stopped.61
One double-blind study followed 249 women in Boston for 1 year; the location of this study is important because your body can't produce significant amounts of vitamin D from sunlight during the winter in Boston.62 These were postmenopausal women with an average age of 61, none of whom were taking estrogen or other medications for bone loss. Half of the women received a calcium citrate malate supplement (400 mg daily) plus a vitamin D supplement (400 IU daily), while the other half received placebo. The women in this study who were taking the vitamin D and calcium experienced a net increase in spinal bone mass (0.85%), while the placebo group showed no net change—a significant difference.
Another double-blind placebo-controlled study enrolling 3,270 women (nearly all of whom had never been on estrogen-replacement therapy) found that higher dosages of vitamin D produced even better results. For a period of 1.5 years, participants received either placebo or 1,200 mg of calcium and 800 IU of vitamin D. At the end of the study period, the researchers found that the bone density in the hips of the women who had taken calcium and vitamin D had increased by 2.7%, while the hip bone density of the women who had taken placebo decreased by 4.6%. The calcium/vitamin D group also had 43% fewer hip fractures. A reduced fracture rate was also seen in another large, double-blind placebo-controlled study.63
There is also good evidence that the use of calcium combined with vitamin D can help protect against the bone loss caused by corticosteroid drugs (such as prednisone). A recent review of five studies covering a total of 274 participants reported that calcium and vitamin D supplementation significantly prevented bone loss in corticosteroid-treated individuals.64
For example, in a 2-year double-blind placebo-controlled study that followed 65 individuals with rheumatoid arthritis taking low-dose corticosteroids, daily supplementation with 1,000 mg of calcium and 500 IU of vitamin D reversed steroid-induced bone loss, causing a net bone gain.65
Interestingly, vitamin D may offer another benefit for osteoporosis: studies have found that when older individuals take vitamin D supplements, they have less of a tendency to sway while standing or walking, and may therefore be less likely to fall.77,78 Since the most common adverse consequence of osteoporosis is a fracture due to a fall, this could be a meaningful benefit.
Safety Issues
When taken at recommended dosages, vitamin D appears to be safe. However, when used at considerable excess, vitamin D can build up in the body and cause toxic symptoms. However, the precise dosage at which intake becomes toxic is a matter of dispute.66,67,68Official safe upper limits for vitamin D daily intake have been set as follows:73
- Infants 0–12 months, 1,000 IU (25 mcg)
- Males and females 1 year and older, 2,000 IU (50 mcg)
- Pregnant and nursing women, 2,000 IU (50 mcg)
People with sarcoidosis or hyperparathyroidism should never take vitamin D without first consulting a physician.
Taking vitamin D and calcium supplements might interfere with some of the effects of calcium channel–blockers.69 It is very important that you consult your physician before trying this combination.
The combination of calcium, vitamin D, and thiazide diuretics can lead to excessive calcium levels in the body.70,71,72 If you are taking thiazide diuretics, you should consult with a physician about the right doses of vitamin D and calcium for you.
Interactions You Should Know About
If you are taking
View References
Last reviewed August 2002 by Medical Review Board
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