Vitamin D deficiencies are usually the result of dietary inadequacy, impaired absorption and utilization, increased requirement, or increased excretion (loss). A deficiency of vitamin D can occur: when usual intake is below recommended levels , when there is limited exposure to sunlight, when the kidney cannot convert vitamin D to its active hormone form, and when someone cannot adequately absorb vitamin D from the digestive tract.
The classic vitamin D deficiency diseases are rickets and osteomalacia. In children, vitamin D deficiency causes rickets. Rickets is a bone disease characterized by a failure to properly mineralize bone tissue. Rickets results in soft bones and skeletal deformities. The most common causes of rickets are vitamin D deficiency from a vitamin D deficient diet, lack of sunlight, or both.
In adults, vitamin D deficiency can lead to osteomalacia, which results in muscular weakness in addition to weak bones.. Symptoms of bone pain and muscle weakness may indicate vitamin D deficiency, but symptoms may be subtle and go undetected in the initial stages. A deficiency is accurately diagnosed by measuring the concentration of a specific form of vitamin D in blood. Adults aged 19-50 are recommended to get 200 IU of vitamin D per day. Adults 51 – 70 are recommended to get 400 IU of vitamin D per day. The easiest way to get Vitamin D is through exposure to natural sunlight. In general, 10-15 minutes of exposure to sunlight on exposed skin 3 times a week is enough. The exactly amount varies by individual. Americans age 50 and older are believed to be at increased risk of developing vitamin D deficiency. As people age, skin cannot synthesize vitamin D as efficiently and the kidney is less able to convert vitamin D to its active hormone form. It is estimated that as many as 30% to 40% of older adults with hip fractures are vitamin D insufficien. Therefore, older adults may benefit from supplemental vitamin D.
In a review of women with osteoporosis hospitalized for hip fractures, 50 percent were found to have signs of vitamin D deficiency. Daily supplementation with 20 μg (800 IU) of vitamin D may reduce the risk of osteoporotic fractures in elderly populations with low blood levels of vitamin D.
Besides natural production through sunlight exposure, Vitamin D is also found in foods such as dairy products (particularly milk), fish, oyesters, and fortified cerals.
|Food||International Units(IU) per serving||Percent DV*|
|Cod liver oil, 1 Tablespoon||1,360||340|
|Salmon, cooked, 3½ ounces||360||90|
|Mackerel, cooked, 3½ ounces||345||90|
|Tuna fish, canned in oil, 3 ounces||200||50|
|Sardines, canned in oil, drained, 1¾ ounces||250||70|
|Milk, nonfat, reduced fat, and whole, vitamin D fortified, 1 cup||98||25|
|Margarine, fortified, 1 Tablespoon||60||15|
|Pudding, prepared from mix and made with vitamin D fortified milk, ½ cup||50||10|
|Ready-to-eat cereals fortified with 10% of the DV for vitamin D, ¾ cup to 1 cup servings (servings vary according to the brand)||40||10|
|Egg, 1 whole (vitamin D is found in egg yolk)||20||6|
|Liver, beef, cooked, 3½ ounces||15||4|
|Cheese, Swiss, 1 ounce||12||4|
Too much Vitamin D results in toxicity can cause nausea, vomiting, poor appetite, constipation, weakness, and weight loss. It can also raise blood levels of calcium, causing mental status changes such as confusion. High blood levels of calcium also can cause heart rhythm abnormalities. Calcinosis, the deposition of calcium and phosphate in the body’s soft tissues such as the kidney, can also be caused by vitamin D toxicity. Sun exposure is unlikely to result in vitamin D toxicity. Diet is also unlikely to cause vitamin D toxicity, unless large amounts of cod liver oil are consumed. Vitamin D toxicity is much more likely to occur from high intakes of vitamin D in supplements. The Food and Nutrition Board of the Institute of Medicine has set the tolerable upper intake level (UL) for vitamin D at 25 μg (1,000 IU) for infants up to 12 months of age and 50 μg (2,000 IU) for children, adults, pregnant, and lactating women..