• Cholecalciferol (Vitamin D 3 ) , Ergocalciferol (Vitamin D 2 )
• Preventing and Treating Osteoporosis
• Cancer Prevention, Diabetes (Prevention) , Hypertension (Prevention) , Polycystic Ovary Syndrome, Psoriasis, Seasonal Affective Disorder
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 D 3 (cholecalciferol) is made by the body and is found in some foods. Vitamin D 2 (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. Other potential uses of vitamin D have little supporting evidence.
As with vitamin A , dosages of vitamin D are often expressed in terms of international units (IU) rather than milligrams. The official US 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. In a study of military personnel in submarines, use of 400 IU of vitamin D daily was inadequate to maintain bone health, while six days of sun exposure proved capable of supplying enough vitamin D for 49 sunless days. 89 In addition, a study of veiled Islamic 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.
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.
As indicated by the study of submarine personnel noted above, 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. 5,7 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
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 ).
Without question, if you are concerned about osteoporosis , you should take calcium and vitamin D. The combination appears to help prevent bone loss. 28,29 This is true even if you are taking other treatments 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. Interestingly, vitamin D may also help prevent the falls that lead to osteoporotic fractures .
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. 30-49,90 One study suggests that combined use of calcium plus vitamin D, but not either supplement separately, can help reduce risk of colon cancer. 84
One preliminary study suggests that supplementation with vitamin D and calcium may be helpful for women with polycystic ovary syndrome. 54
A meta-analysis (formal statistical review) of published studies found some evidence that use of vitamin D at recommended levels may reduce overall mortality. 102 This article suggested, but did not attempt to establish, just how vitamin D might accomplish this.
Vitamin D is sometimes mentioned as a treatment for psoriasis . However, this recommendation is based on Danish studies using calcipotriol, a variation of vitamin D 3 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.
It has been suggested that since vitamin D levels in the body drop in the wintertime, vitamin D supplements might be helpful for seasonal affective disorder ("winter blues"). A small double-blind, placebo-controlled trial conducted during winter on 44 people found that vitamin D supplements produced improvements in various measures of mood. 79 However, a double-blind, placebo-controlled study of 2,217 women over 70 failed to find benefit. 91 It has been hypothesized that light therapy (used successfully for SAD) works by raising vitamin D levels, but there is some evidence that this is not the case. 92
Vitamin D supplements also do not appear to help enhance growth in healthy children. 80
What Is the Scientific Evidence for Vitamin D?
Individuals with severe osteoporosis often have low levels of vitamin D. 56,58 Supplementing with vitamin D alone is probably no more than minimally helpful, at best, 59,60,81,99,100 but the combination of calcium and vitamin D is probably more effective. (See the Calcium article for more information.)
Interestingly, vitamin D may offer another benefit for osteoporosis in seniors: most (though not all) studies have found that vitamin D supplementation improves balance in seniors (especially female seniors) and reduces risk of falling. 77,78,82,83,85-87,93-97,99,103,104 Since the most common adverse consequence of osteoporosis is a fracture due to a fall, this could be a meaningful benefit. Why vitamin D should offer this benefit, however, remains a mystery.
Supplementation with vitamin D plus calcium may aid healing after a fracture has occurred. 88
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. At an intake level of about 40,000 IU daily (about 100 times the recommended daily intake) vitamin D can cause dangerous elevations in blood calcium levels. 101 Doses five times higher than this were consumed by a few individuals due to a manufacturing error; the resulting toxicity was severe and may have caused death in one individual. 101
However, short of these vastly excessive dosages, it is not clear at what level vitamin D becomes toxic. The official safe upper limits for vitamin D daily intake are 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)
Note, however, that some authorities believe these upper limits have been set a bit too low. 66,68 Their arguments closely parallel those discussed in the Requirements/Sources section regarding nutritional needs.
There is no disagreement that 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 drugs in the calcium-channel blocker family. 69 It is very important that you consult your physician before trying this combination.
The combination of calcium, vitamin D, and thiazide diuretics could potentially lead to excessive calcium levels in the body. 70,72 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
- You may need extra vitamin D if you are taking antiseizure drugs, such as:
- If you are taking calcium-channel blockers , do not take high-dose vitamin D (with calcium) except under physician supervision.
- If you are taking thiazide diuretics , do not take calcium and vitamin D supplements unless under a doctor's supervision.
21. Buckley LM, Leib ES, Cartularo KS, et al. Calcium and vitamin D3 supplementation prevents bone loss in the spine secondary to low-dose corticosteroids in patients with rheumatoid arthritis. A randomized, double-blind, placebo-controlled study. Ann Intern Med. 1996;125:961-968.
42. Hofer H, Ho GM, Peterlik M, et al. Biological effects of 1alpha-hydroxy- and 1beta-(hydroxymethyl)-vitamin D compounds relevant for potential colorectal cancer therapy. J Pharmacol Exp Ther. 1999;291:450-455.
43. Tong WM, Kallay E, Hofer H, et al. Growth regulation of human colon cancer cells by epidermal growth factor and 1,25-dihydroxyvitamin D3 is mediated by mutual modulation of receptor expression. Eur J Cancer. 1998;34:2119-2125.
48. Danielsson C, Torma H, Vahlquist A, et al. Positive and negative interaction of 1,25-dihydroxyvitamin D3 and the retinoid CD437 in the induction of human melanoma cell apoptosis. Int J Cancer. 1999;81:467-470.
52. O'Connell TD, Simpson RU. 1,25-dihydroxyvitamin D3 and cardiac muscle structure and function. In: Crass MF II, Avioli LV, eds. Calcium-Regulating Hormones and Cardiovascular Function. Boca Raton, FL: CRC Press; 1995:191-211.
57. Mezquita-Raya P, Munoz-Torres M, De Dios Luna J, et al. Relation between vitamin D insufficiency, bone density, and bone metabolism in healthy postmenopausal women. J Bone Miner Res. 2001;16:1408-1415.
60. Hunter D, Major P, Arden N, et al. A randomized controlled trial of vitamin D supplementation on preventing postmenopausal bone loss and modifying bone metabolism using identical twin pairs. J Bone Miner Res. 2000;15:2276-2283.
65. Buckley LM, Leib ES, Cartularo KS, et al. Calcium and vitamin D 3 supplementation prevents bone loss in the spine secondary to low-dose corticosteroids in patients with rheumatoid arthritis. A randomized, double-blind, placebo-controlled trial. Ann Intern Med. 1996;125:961-968.
71. Lemann J, Gray RW, Maierhofer WJ, et al. Hydrochlorothiazide inhibits bone resorption in men despite experimentally elevated serum 1,25-dihydroxyvitamin D concentrations. Kidney Int. 198528:951-958.
73. Dietary reference intakes for calcium, phosphorus, magnesium, vitamin D, and fluoride. 1997. National Academies Press website. Available at: http://www.nap.edu . Accessed October 4, 2001.
77. Pfeifer M, Begerow B, Minne H, et al. Effects of a short-term vitamin D and calcium supplementation on body sway and secondary hyperparathyroidism in elderly women. J Bone Miner Res. 2000;15:1113-1118.
81. Trivedi DP, Doll R, Khaw KT. Effect of four monthly oral vitamin D3 (cholecalciferol) supplementation on fractures and mortality in men and women living in the community: randomised double blind controlled trial. BMJ. 2003;326:469.
83. Latham NK, Anderson CS, Lee A, et al. A randomized, controlled trial of quadriceps resistance exercise and vitamin D in frail older people: the frailty interventions trial in elderly subjects (FITNESS). J Am Geriatr Soc. 2003;51:291-299.
85. Harwood RH, Sahota O, Gaynor K, et al. A randomised, controlled comparison of different calcium and vitamin D supplementation regimens in elderly women after hip fracture: The Nottingham Neck of Femur (NONOF) Study. Age Ageing. 2004;33:45-51.
86. Kenny AM, Biskup B, Robbins B, et al. Effects of vitamin D supplementation on strength, physical function, and health perception in older, community-dwelling men. J Am Geriatr Soc. 2003;51:1762-1767.
88. Doetsch AM, Faber J, Lynnerup N, et al. The effect of calcium and vitamin D(3) supplementation on the healing of the proximal humerus fracture: a randomized placebo-controlled study. Calcif Tissue Int. 2004 May 27. [Epub ahead of print]
92. Partonen T, Vakkuri O, Lamberg-Allardt C, Lonnqvist J. Effects of bright light on sleepiness, melatonin, and 25-hydroxyvitamin D(3) in winter seasonal affective disorder. Biol Psychiatry. 1996;39:865-872.
94. Bischoff-Ferrari HA, Orav EJ, Dawson-Hughes B, et al. Effect of cholecalciferol plus calcium on falling in ambulatory older men and women: a 3-year randomized controlled trial. Arch Intern Med. 2006;166:424-430.
95. Sato Y, Iwamoto J, Kanoko T, et al. Low-Dose Vitamin D Prevents Muscular Atrophy and Reduces Falls and Hip Fractures in Women after Stroke: A Randomized Controlled Trial. Cerebrovasc Dis. 2005 Jul 27. [Epub ahead of print].
96. Law M, Withers H, Morris J, et al. Vitamin D supplementation and the prevention of fractures and falls: results of a randomised trial in elderly people in residential accommodation. Age Ageing. 2006 Apr 26. [Epub ahead of print]
97. Bunout D, Barrera G, Leiva L, et al. Effects of vitamin D supplementation and exercise training on physical performance in Chilean vitamin D deficient elderly subjects. Exp Gerontol. 2006 Jun 21 [Epub ahead of print]
100. Lyons RA, Johansen A, Brophy S, et al. Preventing fractures among older people living in institutional care: a pragmatic randomised double blind placebo controlled trial of vitamin D supplementation. Osteoporos Int. 2007;18:811-818.
104. Pfeifer M, Begerow B, Minne HW, et al. Effects of a long-term vitamin D and calcium supplementation on falls and parameters of muscle function in community-dwelling older individuals. Osteoporos Int. 2008 Jul 16.
Last reviewed August 2008 by EBSCO CAM Review Board
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