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Vitamin D

What is Vitamin D?

Vitamin D is unique among vitamins in that it can be provided to your body through food or from exposure to the sun or tanning bed. Sunshine is a significant source of vitamin D because UV rays from sunlight triggers vitamin D synthesis in the skin. Vitamin D functions as an important hormone by sending a message to your intestines to increase the absorption of calcium by as much as 80%. Vitamin D is well known for maintaining normal calcium levels, but it is involved in so much more! Please read on.

Vitamin D Deficiency


In infants and children, severe vitamin D deficiency results in the failure of bone to mineralize. Rapidly growing bones are most severely affected by rickets. The growth plates of bones continue to enlarge, but in the absence of adequate mineralization, weight-bearing limbs become bowed. Although fortification of foods has led to complacency regarding vitamin D deficiency, nutritional rickets is still being reported in cities throughout the world.


Although adult bones are no longer growing, they are in a constant state of turnover. In adults with severe vitamin D deficiency, the collagen bone matrix is preserved but bone mineral is progressively lost, resulting in bone pain and osteomalacia (soft bones) ...more on Osteomalacia

Muscle Weakness and Pain

Vitamin D deficiency causes muscle weakness and pain in children and adults. In a cross-sectional study of 150 patients referred to a clinic in Minnesota for the evaluation of persistent, muscle and bone pain, 93% had vitamin D deficiency!

Muscle pain and weakness was a prominent symptom of vitamin D deficiency in a study of Arab and Danish Moslem women living in Denmark.

Another trial found that supplementation of elderly women with 800 IU/day of vitamin D and 1,200 mg/day of calcium for three months increased muscle strength and decreased the risk of falling by almost 50% compared to supplementation with calcium alone.

Risk Factors for Vitamin D Deficiency

If you find yourself in any of the categories below, you would be well advised to get a blood test to determine your vitamin D levels.

Dark Skin

People with dark skin synthesize less vitamin D on exposure to sunlight than those with light skin. The risk of vitamin D deficiency is particularly high in dark-skinned people who live far from the equator.

Breast Fed Infants

Infants who are exclusively breast fed are at high risk of vitamin D inadequacy, particularly if they have dark skin and/or receive little sun exposure.Human milk generally provides 25 IU of vitamin D per liter, which is not enough for an infant if it is the sole source of vitamin D. Older infants and toddlers exclusively fed milk substitutes and weaning foods that are not vitamin D fortified are also at risk of vitamin D deficiency.The American Academy of Pediatrics recommends that all infants that are not consuming at least 500 ml (16 ounces) of vitamin D fortified formula or milk be given a vitamin D supplement of 200 IU/day.


The elderly have reduced capacity to synthesize vitamin D in the skin when exposed to UVB radiation, and are more likely to stay indoors or use sunscreen. Institutionalized adults are at extremely high risk of vitamin D deficiency without supplementation.

Inflammatory Bowel Disease

If you suffer from inflammatory bowel disease like Crohn’s disease you may be at increased risk of vitamin D deficiency, especially if you have had small bowel surgery.29

Fat Malabsorption Syndromes

Cystic fibrosis and cholestatic liver disease impair the absorption of dietary vitamin D.


If you are overweight, it increases your risk of vitamin D deficiency. Once vitamin D is synthesized in the skin or ingested, it is deposited in body fat stores, making it less bio-available if you have large stores of body fat.

Vitamin D Sources

Sunlight is the best source of vitamin D. It can provide you with your entire vitamin D requirement. Children and young adults who spend a short time outside two or three times a week will generally synthesize all the vitamin D they need. If you are older, you have diminished capacity to synthesize vitamin D from sunlight exposure and possibly use sunscreen or protective clothing in order to prevent skin cancer and sun damage, so you should consider getting your vitamin D from food and supplements.

The application of sunscreen with an SPF factor of 8 reduces production of vitamin D by 95%. In latitudes around 40 degrees north or 40 degrees south (Boston is 42 degrees north), there is insufficient UVB radiation available for vitamin D synthesis from November to early March. Ten degrees farther north (Edmonton, Canada) this "vitamin D winter" extends from mid October to mid March. According to Dr. Michael Holick, as little as 5-10 minutes of sun exposure on arms and legs or face and arms three times weekly between 11:00 am and 2:00 pm during the spring, summer, and fall at 42 degrees latitude should provide a light-skinned individual with adequate vitamin D and allow for storage of any excess for use during the winter with minimal risk of skin damage.

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