Vitamin D is a fat-soluble vitamin that promotes the absorption of calcium and phosphorus from the intestines and into the bloodstream. A vitamin is a molecule required by the body in sufficient amounts for proper health, nearly always obtained from external sources. Vitamin D is unique in its categorization as a vitamin, since it can sometimes be produced by the skin. There are two forms of vitamin D, both of which are important for nutrition. The first is produced by plants, and consumed in the diet. This form of vitamin D is most commonly found in fish liver oils, fatty fish, and fortified dairy products. Since many higher latitude locations do not receive enough sunlight -- particularly during the winter -- milk and other foods are fortified with vitamin D to avoid widespread deficiency. The second form of Vitamin D is produce by the skin after exposure to ultraviolet sunlight triggers its synthesis.

Effects of vitamin D deficiency

In deficiency syndromes, calcium and phosphate levels in the blood decrease because they cannot be absorbed without the synergistic aid of vitamin D. This may lead to bone disorders, rickets in children, or osteomalacia in adults. Breast milk contains low levels of vitamin D, so infants who lack exposure to sufficient sunlight or lack proper nutritional supplementation may develop rickets. Older adults, whose skin may not synthesize sufficient quantities of vitamin D, or who do not get enough sun exposure or proper supplementation in their diet, may be at risk for osteomalacia or osteoporosis. Recent studies have indicated that vitamin D deficiency may also be linked to diseases such as cancer, chronic pain, weakness, fatigue, multiple sclerosis, diabetes, high blood pressure, periodontal disease, and irritable bowel syndrome. The recommended daily allowance for adults is 200 IU up to the age of 50, 400 IU for ages 51 to 70, and 600 IU over age 70.

Can you consume too much vitamin D?

Excessive intake of vitamin D over several months can cause toxicity, with symptoms including loss of appetite, nausea and vomiting, excessive thirst, weakness, nervousness, and high blood pressure. Overdose is very rare.