Vitamin D is a collective name for five fat-soluble substances called secosteroids. The types that are most essential for human biochemistry are vitamins D-2 and D-3. Vitamin D-2, or ergocalciferol, is obtained from dietary sources or through supplementation. Vitamin D-3, or cholecalciferol, is produced in the skin in response to the sun's ultraviolet-B rays. According to "Contemporary Nutrition," up to 75 percent of Americans are not getting their adequate daily doses of vitamin D, causing numerous deficiency symptoms.
Adequate Daily Dose
The National Institutes of Health Office of Dietary Supplements states that 400 IU of vitamin D per day is adequate for children up to their first year, 600 IU daily for adults up to the age of 70 and 800 IU for adults older than 70. These recommended levels are meant to avoid acute deficiency symptoms and are not necessarily high enough to meet the demands of healthy, active people. According to "Biochemical, Physiological and Molecular Aspects of Human Nutrition," the body has the physiological capacity to produce thousands of international units D-3 per hour when exposed to adequate UV-B solar radiation, suggesting the body may require higher levels to thrive.
Symptoms of Vitamin D Deficiency
Vitamin D is essential for immune system function and healthy bones, but indoor lifestyles and fear of the sun is causing deficiencies. According to "Human Biochemistry and Disease," vitamin D deficiency starts to cause symptoms when serum levels of calcidiol drop below 37.5 nanomoles per liter. Early symptoms of lack of vitamin D include profuse sweating, anxiety, fatigue and muscle cramps. Later symptoms include depression, muscle aches, joint pain and hypertension. Advanced vitamin D deficiency leads to bone malformation, which is termed rickets in children, and osteomalacia in adults. The immune system is also compromised by chronic vitamin D deficiency, leading to infections, inflammatory arthritis and macular degeneration.
The Sun as a Source of Vitamin D
Given the right climate, the sun is the most abundant source of vitamin D-3. Vitamin D-3 is produced within the skin when exposed to UV-B radiation between the wavelengths of 270 and 300 nm. These wavelengths are common when the UV index is greater than three, which happens daily in tropical climates, daily during spring and summer in temperate climates and rarely in arctic climates. Although 10,000 IU of vitamin D-3 can be produced by exposed Caucasian skin within 20 minutes, darker skin requires up to six-times longer to produce similar amounts, as cited in "Vitamins: Fundamental Aspects in Nutrition and Health."
Other Sources of Vitamin D
Not many foods contain vitamin D, which makes it difficult to intake recommended daily amounts in climates that lack sunshine. According to the "American Dietetic Association Complete Food and Nutrition Guide," natural sources of vitamin D-2 mainly include fish, such as salmon, mackerel, cod and tuna, cod liver oil, beef liver and egg yolks. Vitamin D-2 fortified foods include milk, margarine, some flours, some breakfast cereals and some brands of juice, particularly orange juice. Both vitamin D-2 and D-3 can be taken as supplements, with doses often ranging from 400 IU to 1,000 IU daily. Up to 10,000 IU per day of supplemental vitamin D is considered safe.
References
- "Contemporary Nutrition"; Gordon M. Wardlaw; 2010
- The National Institutes of Health: Office of Dietary Supplements: Vitamin D
- "Biochemical, Physiological and Molecular Aspects of Human Nutrition"; Martha Stipanuk; 2006
- "Human Biochemistry and Disease"; Gerald Litwack; 2008
- "Vitamins: Fundamental Aspects in Nutrition and Health"; G. Combs; 2008
- "American Dietetic Association Complete Food and Nutrition Guide"; American Dietetic Association; 2006
Member Comments