Vitamin D

Vitamin D is commonly referred to as the "sunshine" vitamin because it can be manufactured in the skin through the action of sunlight. This fat-soluble vitamin that functions both as a hormone and a vitamin, occurs in two primary forms: ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Cholecalciferol is formed in the skin by exposure to sunlight and found chiefly in fish liver oils, while ergocalciferol is found in irradiated yeast. Ergocalciferol is the form most commonly added to food and nutritional supplements. Both vitamins D2 and D3 are converted in the liver to 25-hydroxyvitamin D and then to 1,25-dihydroxycalciferol in the kidney. Vitamin D plays a critical role in regulating the metabolism of calcium and phosphorous, which are necessary for several body functions including normal growth and development of bones and teeth.

Even with adequate calcium and phosphorous intake, if our vitamin D intake is low, we will have poor calcification of our bones, whereas with good vitamin D intake, we will have better calcification, even in the presence of low calcium and phosphorous intake. Clinically, vitamin D is most useful for preventing and treating bone softening diseases like rickets, osteomalacia and osteoporosis. Vitamin D is also necessary for maintaining the integrity of the nervous and musculoskeletal systems, normal heart function and normal blood clotting.

Daily Requirement

  • Adequate Intake: 200 IU (5 mcg) for adult men and women.
  • Daily Optimal Intake: 800-1,000 (20-25 mcg) for adult men and women.
  • Current guidelines from the National Institute of Health recommend a dose of 400 IU vitamin D daily for people ages 51-70 years, and 600 IU vitamin D daily for those over age 70.
  • Anything which blocks ultraviolet light such as darkly pigmented skin, smog, windows, sunscreen and hats can interfere with vitamin D production in the body.
  • An easy way to ensure adequate amounts of vitamin D in the body is by exposing the face and arms to sunlight for fifteen minutes three times a week. During the winter months, we usually require additional vitamin D from either food or supplements.

Supplement Forms

  • Natural: Cholecalciferol (vitamin D3)
  • Synthetic: Ergocalciferol (vitamin D2)
  • 1, 25-Dihydroxycholecalciferol: Biologically active form useful for patients unable to convert vitamin D into its active form.

Special Instructions

  • As with all fat-soluble vitamins (A, D, E and K), vitamin D should be taken with meals to increase its absorption.

Toxicity

  • Vitamin D is considered by many authorities to be the most potentially toxic vitamin. Symptoms of toxicity can occur from ingesting large amounts of vitamin D from food or supplements, or from excessive exposure to sunlight. 
  • Toxic effects of vitamin D have been observed in adults using doses in excess of 1,000-1,500 IU for a period of one month. Vitamin D in doses of 5,000-10,000 IU daily can lead to hypercalcemia, hypercalciuria, kidney stones and soft tissue calcification.
  • Elevated serum calcium levels (12-16 mg/dL) are a constant finding associated with vitamin D toxicity. Frequent determination of serum calcium (first weekly, then monthly) should be made in all patients receiving high doses of vitamin D. 
  • There is also evidence to suggest that excessive intake of vitamin D may lead to heart attacks and atherosclerosis in certain individuals.

Adverse Reactions

  • Many of these symptoms will decrease or clear up after high doses of vitamin D are discontinued. However, if kidney damage or metastatic calcification has occurred, it may be irreversible.
  • Calcification of soft tissues- i.e. blood vessels, kidneys, liver, lungs, muscles, etc...
  • Anorexia
  • Vomiting
  • Headaches
  • Excessive thirst
  • Frequent urination
  • Weakness
  • Fatigue
  • Nervousness
  • Itchy skin
  • Impaired kidney function
  • Sore eyes
  • Bone pain
  • Osteoporosis

Precautions

  • Vitamin D supplements should not be given to those with high calcium or phosphorous levels, and should be given with caution to those suffering from cardiac or kidney disease.
  • Individuals prone to kidney stone formation should avoid all dairy products fortified with vitamin D. Vitamin D increases urinary calcification concentration, thus greatly increasing the risk of stone formation.

Sources

  • Exposure to sunlight
  • Fish liver oils
  • Salmon
  • Mackerel
  • Halibut
  • Tuna
  • Oysters
  • Shrimp
  • Fortified milk
  • Egg yolks

Signs of Deficiency

  • Rickets in children
  • Osteomalacia in adults
  • Muscle weakness
  • Bony deformities
  • Tooth decay
  • Neuromuscular irritability causing muscle spasms of the larynx and hands

Causes of Deficiency

  • Poor exposure to sunlight
  • Inadequate dietary intake
  • Vegan diets
  • Malabsorption syndromes
  • Darkly pigmented skin
  • Intestinal surgery
  • Kidney disease
  • Liver disease
  • Alcoholism
  • Aging
  • Crohn's disease
  • Ulcerative colitis
  • Hypothyroidism
  • Cushing's syndrome
  • Antacids
  • Mineral oil laxatives
  • Diuretics
  • Anticonvulsants
  • Cholesterol lowering drugs
  • Corticosteroids
  • Barbituates
  • According to a recent report in the New England Journal of Medicine, health care providers should routinely screen their patients for vitamin D deficiency. Previous research has shown that as many as 50% of senior citizens and home-bound individuals are deficient in vitamin D. The current study found that 57% of 290 adult inpatients, mean age 62 years, were deficient in the vitamin. In a subgroup analysis of 77 patients, average age 44 years, 42% were found to have sub-optimal levels of vitamin D. A deficiency in vitamin D can lead to decreased absorption of calcium and a decrease in bone density, thereby increasing the risk of osteoporosis and fracture. In an accompanying editorial, Robert D. Utiger, M.D., deputy editor of the New England Journal of Medicine, stated that "sick adults, older adults, and perhaps all adults need 800-1,000 IU of vitamin D daily, substantially more than the newly established levels of adequate intake." N Engl J Med, 1998 338:777-83

Possible Therapeutic Uses

  • Prevention of bone softening diseases- osteoporosis, osteomalacia and rickets
  • Hypocalcemia
  • Diabetes
  • Osteoarthritis
  • Mental health
  • Rheumatoid arthritis
  • Psoriasis
  • Atherosclerosis
  • Cancer
  • Menopausal symptoms
  • Multiple sclerosis

Osteoporosis

  • It is estimated that 28 million Americans, mainly women, are at risk of developing osteoporosis. According to the National Osteoporosis Foundation, as many as 1.5 million fractures each year, including 300,000 hip fracturs, are associated with osteoporosis. Low vitamin D levels produce a rise in parathyroid hormone which causes the body to draw calcium from the bones, eventually leading to bone loss. Osteoporosis develops when the breakdown of bone exceeds the amount of bone being built. Several studies have shown that vitamin D is necessary for efficient absorption of calcium and for normal mineralization of bone. A trial was undertaken to evaluate the efficacy of synthetic vitamin D (calcitriol) in the treatment of osteoporosis. Fifty post-menopausal women were randomly assigned to receive either vitamin D or a placebo for two years. The results showed bone density of the spine increased 1.94% with vitamin D supplements and decreased 3.92% without vitamin D (placebo). Ann Intern Med, 1990 Nov;113(9):649-55

  • According to a study published in the Journal of the American Medical Association, older women who have a vitamin D deficiency may be at greater risk for fractures compared with their peers. The study involved 98 post-menopausal women who underwent hip replacement surgery to repair a fracture (30 women) or had joint replacement surgery (68 women). Of the women with hip fractures, it was found that 50% were deficient in vitamin D. Researchers believe that correction of vitamin D deficiency in post-menopausal women with hip fractures could prevent subsequent fractures. JAMA, 1999 Apr;281:1505-11

 

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