Vitamin D is actually a group of five fat-soluble molecules called secosteroids. The D2 and D3 forms are the most physiologically important. The D3 form, called cholecalciferol, is synthesized in the skin when the molecule, 7-dehydrocholesterol, is irradiated with ultraviolet-B from sunlight, according to MayoClinic.com. Vitamin D deficiency has multiple causes and can result in bone deformities and other serious conditions.
Lack of Essential Sunshine
The most common and direct cause of vitamin D3 deficiency is lack of essential sunshine, as noted in “Professional Guide to Diseases." Cloud cover can reduce 50 percent of the sun’s radiation, while pollution in large cities can create a haze that blocks out more. Modern lifestyles, in general, cause people to spend most of their time indoors, away from the sun. The growing fear of skin cancer and the common use of sunscreen also severely reduce exposure to essential sunshine.
Caucasian skin can produce approximately 10,000 IU of vitamin D3 in response to about 20 minutes of summer sun exposure, which is 50 times more than the 200 IU per day that the U.S. Department of Agriculture recommends for healthy adults. Although darker skinned people produce up to six times less vitamin D from sun exposure, the average levels produced in the human body in response to the sun dwarf what can be obtained from the diet. Consequently, assuming a person can process and use vitamin D3 internally, regular exposure to sunshine is the best approach to reduce the risk of deficiency.
As the National Institute of Health notes, when exposure to sunshine is limited due to geographical location, climate or lifestyle, then the diet must include sources of vitamin D or a deficiency often develops. Foods naturally rich in vitamin D3 include fish flesh, fish oils, liver, and egg yolks. Foods often fortified with vitamin D3 include milk, cheese, cereals and orange juice. Vitamin D deficiency is often associated with milk allergies, lactose intolerance and strict vegetarianism, although supplemental forms of vitamin D3 are widely available.
To be utilized effectively in the body, vitamin D3 needs other nutrients as co-factors, such as magnesium, zinc, vitamin K2, boron and vitamin A. Magnesium is the most important of these co-factors, and a dietary deficiency of magnesium can lead to a vitamin D deficiency.
Diseases That Inhibit Vitamin D Utilization
Even if a person eats vitamin D rich foods, takes supplements and seeks regular sunshine, some diseases and conditions inhibit the body’s use of vitamin D. Lowered absorption of fat-soluble vitamin D can occur with chronic pancreatitis, celiac disease, Crohn’s disease, cystic fibrosis, colitis, and biliary obstruction, according to "Professional Guide to Diseases." Liver or kidney disease can interfere with the formation of calciferol from vitamin D3 or its absorption. A malfunctioning parathyroid gland and reduced parathyroid hormone can interfere with activation of vitamin D3 in the kidneys.
The initial signs of vitamin D deficiency are profuse sweating, anxiety, fatigue and muscle cramps. Late stages of vitamin D deficiency include reduced immune response and altered bone formation, or soft bones, also called rickets in children and osteomalacia in adults.
- 'Professional Guide to Diseases, Eighth Edition"; Springhouse; 2005