Vitamin D is a hormone produced by the human body in response to sun exposure. Vitamin D is also found naturally in food sources such as fish, eggs, cod liver oil and fortified milk. Vitamin D helps keep bones strong by aiding in the absorption of calcium and helps to maintain blood levels of calcium and phosphorous.
Normal Values
Blood values of vitamin D are assessed by testing the amounts of 25-hydroxy vitamin D in the blood stream; 25-hydroxy vitamin D is an inactive form of the vitamin that is changed to the active form in the kidney. To test for vitamin D status, individuals must fast for four hours prior to the test. Blood is drawn from the back of the hand or the inside of the elbow. The normal range is from 30.0 to 74.0 nanograms per ml. Lower-than-normal values indicate deficiency while higher-than-normal values may indicate hypervitaminosis D. This condition can eventually cause severe damage to bones, kidneys and soft tissues.
Deficiency
Vitamin D deficiency is determined by blood testing and is characterized by low serum vitamin D levels. Deficiency occurs when ipeople do not get appropriate exposure to the sun's ultraviolet-B rays. There are several risk factors associated with vitamin D deficiency. As we age, our skin becomes less responsive to sunlight, making it more difficult to produce vitamin D. Obesity, breastfeeding and dark skin pigmentation are also listed as risk factors. There are no specific symptoms associated with deficiency because everyone is affected slightly differently. Chronic pain, weakened bones and fatigue could be present. Deficiency can lead to a variety of health conditions.
Sun
As little as 10 to 15 minutes of sun exposure three times each week is sufficient for the production of adequate levels of vitamin D. Although this seems easy to achieve, many people need additional supplementation because they do not get recommended levels of sunlight exposure. Season, time of day, length of day, cloud cover and sunscreen application can all affect vitamin D synthesis.
Supplements
Supplemental vitamin D comes in two forms: vitamin D2 and vitamin D3, with D3 being the form that should be used to treat deficiency. Both forms will raise serum levels of vitamin D when used for supplementation. Breastfed infants and older adults are often encouraged to have vitamin D supplementation because they generally do not meet adequate levels. Any supplementation should be discussed with your doctor prior to beginning.
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