Vitamin D

Also indexed as: 1,25-dihydroxyvitamin D, Calciferol, Calcipotriol, Cholecalciferol, Ergocalciferol, Irradiated Ergocalciferol

What is it?

The fat-soluble vitamin D’s most important role is maintaining blood levels of calcium, which it accomplishes by increasing absorption of calcium from food and reducing urinary calcium loss. Both effects keep calcium in the body and therefore spare the calcium that is stored in bones. When necessary, vitamin D transfers calcium from the bone into the bloodstream, which does not benefit bones. Although the overall effect of vitamin D on the bones is complicated, some vitamin D is necessary for healthy bones and teeth.

Vitamin D plays a role in immunity and blood cell formation and also helps cells "differentiate"—a process that may reduce the risk of cancer. From animal and human studies, researchers have hypothesized that vitamin D may protect people from multiple sclerosis,¹ auto-immune arthritis, and juvenile diabetes.²

Vitamin D is also needed for adequate blood levels of insulin.³ Vitamin D receptors have been found in the pancreas where insulin is made, and preliminary evidence suggests that supplementation may increase insulin secretion for some people with adult-onset (type 2) diabetes.⁴

Where is it found?

Cod liver oil is an excellent dietary source of vitamin D, as are vitamin D-fortified foods. Traces of vitamin D are found in egg yolks and butter. However, the majority of vitamin D in the body is created during a chemical reaction that starts with sunlight exposure to the skin. Cholecalciferol (vitamin D3) is the animal form of this vitamin.

Vitamin D has been used in connection with the following conditions (refer to the individual health concern for complete information):

Science Ratings	Health Concerns
	Crohn’s disease Cystic fibrosis Osteoporosis Rickets/osteomalacia
	Burns (severe) Coeliac disease (for deficiency only) Depression Hypertension (for deficiency only) Prostate cancer Seasonal affective disorder Type 1 diabetes Type 2 diabetes
	Alcohol withdrawal support Amenorrhoea (calcium for preventing bone loss) Breast cancer (reduces risk) Cardiac arrhythmia Colon cancer (reduces risk) Migraine headaches Multiple sclerosis Parkinson’s disease Vitiligo (topical calcipotriol only)
Reliable and relatively consistent scientific data showing a substantial health benefit. Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit. For a herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support and/or minimal health benefit.

Who is likely to be deficient?

In adults, vitamin D deficiency may result in a softening of the bones known as osteomalacia. This condition is treated with vitamin D, sometimes in combination with calcium supplements. Osteomalacia should be diagnosed, and its treatment monitored, by a doctor. In people of any age, vitamin D deficiency causes abnormal bone formation. It occurs more commonly following winter, owing to restricted sunlight exposure during that season. Living in an area with a lot of atmospheric pollution, which can block the sun's ultraviolet rays, also appears to increase the risk of vitamin D deficiency.⁵

Vitamin D deficiency is more common in strict vegetarians (who avoid vitamin D-fortified dairy foods), dark-skinned people,⁶ alcoholics, and people with liver or kidney disease. People with liver and kidney disease can make vitamin D but cannot activate it.

Vitamin D deficiency is more common in people suffering from intestinal malabsorption, which may have occurred following previous intestinal surgeries, or from coeliac disease.⁷ People with insufficient pancreatic function (e.g., those with pancreatitis or cystic fibrosis) tend to be deficient in vitamin D. Vitamin D deficiency is also common in individuals with hyperthyroidism (Graves' disease), particularly women.⁸

In children, vitamin D deficiency is called rickets and causes a bowing of bones not seen in adults with vitamin D deficiency. Vitamin D deficiency is common among people with hyperparathyroidism, a condition in which the parathyroid gland is overactive. In a study of 124 people with mild hyperparathyroidism, vitamin D levels were below normal in 7% of them and suboptimal in 53% of them.⁹ Vitamin D deficiency is also common in men with advanced prostate cancer. In one study, 44% of 16 men with advanced prostate cancer had decreased blood levels of vitamin D.¹⁰

One in seven adults has been reported to be deficient in vitamin D.¹¹ In one study, 42% of hospitalised patients under age 65 were reported to be vitamin D deficient.¹² In this same study, 37% of the people were found to be deficient in vitamin D, despite the fact they were eating the currently recommended amount of this nutrient. Vitamin D deficiency is particularly common among the elderly. Age-related decline in vitamin D status may be due to reduced absorption, transport, or liver metabolism of vitamin D.¹³

How much is usually taken?

People who get plenty of sun exposure do not require supplemental vitamin D, since sunlight increases vitamin D synthesis when it strikes bare skin. Although the recommended dietary allowance for vitamin D is 200 IU per day for adults, there is some evidence that elderly people need 800 to 1,000 IU per day for maximum effects on preserving bone density and preventing fractures.¹⁴ ¹⁵ ¹⁶ ¹⁷ Sun-deprived people should take no less than 600 IU per day and ideally around 1,000 IU per day.¹⁸

Are there any side effects or interactions?

People with hyperparathyroidism should not take vitamin D without consulting a physician. People with sarcoidosis should not supplement with vitamin D, unless a doctor has determined that their calcium levels are not elevated. Too much vitamin D taken for long periods of time may lead to headaches, weight loss, and kidney stones. Rarely, excessive vitamin D may even lead to deafness, blindness, increased thirst, increased urination, diarrhoea, irritability, children’s failure to gain weight, or death.

Most people take 400 IU per day, a safe amount for adults. Some researchers believe that amounts up to 10,000 IU per day are safe for the average healthy adult, although adverse effects may occur even at lower levels among people with hypersensitivity to vitamin D (e.g. hyperparathyroidism).¹⁹ In fact, of all published cases of vitamin D toxicity for which a vitamin D amount is known, only one occurred at a level of intake under 40,000 IU per day.²⁰ Nevertheless, people wishing to take more than 1,000 IU per day for long periods of time should consult a physician. People should remember the total daily intake of vitamin D includes vitamin D from fortified milk and other fortified foods, cod liver oil, supplements that contain vitamin D, and sunlight. People who receive adequate sunlight exposure do not need as much vitamin D in their diet as do people who receive minimal sunlight exposure.

Vitamin D increases both calcium and phosphorus absorption and has also been reported to increase absorption of aluminium. Increased blood levels of calcium (which may be a marker for vitamin D status) have been linked to heart disease.²¹ Some,²² but not all,²³ research suggests that vitamin D may slightly raise blood levels of cholesterol in humans.

Are there any drug interactions?
Certain medicines may interact with vitamin D. Refer to drug interactions for a list of those medicines.

References
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1. Hayes CE, Cantorna MT, Deluca HF. Vitamin D and multiple sclerosis. Proc Soc Exp Biol Med 1997;216:21–7 [review].

2. Cantorna MT. Vitamin D and autoimmunity: is vitamin D status an environmental factor affecting autoimmune disease prevalence? Proc Soc Exp Biol Med 2000;223:230–3 [review].

3. Labriji-Mestaghanmi H, Billaudel B, Garnier PE, Sutter BC. Vitamin D and pancreatic islet function. I. Time course for changes in insulin secretion and content during vitamin deprivation and repletion. J Endocrinol Invest 1988;11:577–87.

4. Boucher BJ. Inadequate vitamin D status: does it contribute to the disorders comprising syndrome ‘X’? Br J Nutr 1998;79:315–27.

5. Agarwal KS, Mughal MZ, Upadhyay P, et al. The impact of atmospheric pollution on vitamin D status of infants and toddlers in Delhi, India. Arch Dis Child 2002;87:111–3.

6. Kyriakidou-Himonas M, Aloia JF, Yeh JK. Vitamin D supplementation in postmenopausal black women. J Clin Endocrinol Metab 1999;84:3988–90.

7. Basha B, Rao S, Han ZH, Parfitt, AM. Osteomalacia due to vitamin D depletion: neglected consequence of intestinal malabsorption. Am J Med 2000;108:296–300.

8. Yamashita H, Noguchi S, Takatsu K, et al. High prevalence of vitamin D deficiency in Japanese female patients with Graves' disease. Endocr J 2001;48(6):63–9.

9. Silverberg SL, Shane E, Dempster DW, Bilezikian JP. The effects of vitamin D insufficiency in patients with primary hyperparathyroidism. Am J Med 1999; 107:561–7.

10. Van Veldhuizen PJ, Taylor SA, Williamson S, Drees BM. Treatment of vitamin D deficiency in patients with metastatic prostate cancer may improve bone pain and muscle strength. J Urol 2000;163:187–90.

11. Chapuy MC, Preziosi P, Maamer M, et al. Prevalence of vitamin D insufficiency in an adult normal population. Osteoporos Int 1997;7:439–43.

12. Thomas MK, Lloyd-Jones DM, Thadhani RI, et al. Hypovitaminosis D in medical inpatients. N Engl J Med 1998;338:777–83.

13. Harris SS, Dawson-Hughes B, Perrone GA. Plasma 25-hydroxyvitamin D responses of younger and older men to three weeks of supplementation with 1800 IU/day of vitamin D. J Am Coll Nutr 1999;18:470–4.

14. Dawson-Hughes B, Harris SS, Krall EA, Dallal GE. Effect of calcium and vitamin D supplementation on bone density in men and women 65 years of age or older. N Engl J Med 1997;337:670–6.

15. Dawson-Hughes B. Calcium and vitamin D nutritional needs of elderly women. J Nutr 1996;126(4 Suppl):1165–7S.

16. Chapuy MC, Arlot ME, Duboeuf F, et al. Vitamin D3 and calcium to prevent hip fractures in the elderly women. N Engl J Med 1992;327:1637–42.

17. Dawson-Hughes B, Harris SS, Krall EA, et al. Rates of bone loss in postmenopausal women randomly assigned to one of two dosages of vitamin D. Am J Clin Nutr 1995;61:1140–5.

18. Glerup H, Mikkelsen K, Poulsen L, et al. Commonly recommended daily intake of vitamin D is not sufficient if sunlight exposure is limited. J Intern Med 2000;247:260–8.

19. Vieth R. Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety. Am J Clin Nutr 1999;69:842–56.

20. Vieth R. Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety. Am J Clin Nutr 1999;69:842–56.

21. Lind L, Skarfors E, Berglund L, et al. Serum calcium: a new, independent prospective risk factor for myocardial infarction in middle-aged men followed for 18 years. J Clin Epidemiol 1997;50:967–73.

22. Heikkinen AM, Tuppurainen MT, Komulainen M, et al. Long-term vitamin D3 supplementation may have adverse effects on serum lipids during postmenopausal hormone replacement therapy. Eur J Endocrinol 1997;137:495–502.

23. Scragg R, Khaw KT, Murphy S. Effect of winter oral vitamin D3 supplementation on cardiovascular risk factors in elderly adults. Eur J Clin Nutr 1995;49:640–6.

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The information presented in Healthnotes is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or chemist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires March 2007.

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