Vitamin D is a group of five fat soluble compounds, although the D2 and D3 types are the most significant for people. Vitamin D2, or ergocalciferol, is obtained from food and through supplementation. Vitamin D3, or cholecalciferol, is produced within the skin in reaction to ultraviolet-B radiation from sunlight. Lack of adequate sun exposure combined with insufficient dietary consumption results in vitamin D deficiency, which often causes tiredness and sore joints, among other symptoms.
Adequate Amounts
The U.S. Department of Agriculture recommends 200 IU of vitamin D daily for adults to age 50 and 400 IU beyond that age, which are levels meant to avoid acute deficiency symptoms. However, an exposed light-skinned body produces about 10,000 IU of vitamin D3 in 20 to 30 minutes when subjected to midday, summer sun. This physiological capability suggests the body may require more than 400 IU of vitamin D daily to thrive and be healthy. Dark-skinned people block more ultraviolet-B radiation because of the high melanin content of their skin, so they require up to six times longer in the sun to produce similar amounts of vitamin D3.
Causes of Deficiency
Vitamin D does not occur naturally in many food sources, although dairy products, orange juice and breakfast cereals are often fortified with it. Thus, inadequate nutrition is a cause of vitamin D deficiency, especially in geographical regions that do not receive ample solar radiation. In sunnier climates, vitamin D deficiency is much less common, but it still occurs due to indoor jobs and lifestyles, fear of skin cancer and sunscreen use. In general, people not exposing themselves to the sun, or not supplementing, or not eating vitamin D rich foods are likely suffering from deficiency symptoms.
Initial Deficiency Symptoms
Vitamin D deficiency symptoms usually begin when serum levels of calcidiol fall below 37.5 nanomoles per liter. The first symptoms of vitamin D deficiency can take many months to manifest, but usually includes heavy sweating, anxiety, tiredness not relieved by sleep and muscle cramps. These symptoms slowly progress towards depression, achy pain in the muscles and joints, muscle weakness and hypertension.
Advanced Deficiency Symptoms
Long-term vitamin D deficiency causes bone malformation often described as "soft bones." In children, soft bones are referred to as rickets, whereas in adults it is called osteomalacia. Deformed spinal curves and bowed legs are common signs of advanced vitamin D deficiency. Other advanced symptoms include muscle wasting, chronic back pain, reduced cognition, psychiatric disorders, inflammatory arthritis and macular degeneration.
Sources of Vitamin D
Sunshine, especially during summer months, is the best and cheapest source of vitamin D3. Animal based sources of vitamin D include fish, cod liver oil, beef liver, shrimp and egg yolks. Fortified sources include milk, orange juice, yogurt, cereals, some breads and cheeses. For supplementation, many believe vitamin D3 is better than the D2 type because it is better assimilated and more hormonally active in the body.
References
- U.S. Department of Agriculture: Food and Nutrition Information Center: Vitamin D Dietary Reference Intake
- "Biochemical, Physiological and Molecular Aspects of Human Nutrition"; Martha Stipanuk; 2006
- "Human Biochemistry and Disease"; Gerald Litwack; 2008
- "Professional Guide to Diseases: Ninth Edition"; Springhouse Publishing; 2009
- "American Dietetic Association Complete Food and Nutrition Guide"; American Dietetic Association; 2006
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