Recent studies show an alarming lack of vitamin D, also called cholecalciferol, in American children and adolescents.
Vitamin D is important for the development of strong bones. Vitamin D deficiency can lead to rickets (weak, deformed bones) in infants and children. It also contributes to osteoporosis(thinning of the bones) in post-menopausal women. Vitamin D deficiency may also contribute to high blood pressure, diabetes and certain cancers, although no definite causal link has been proven.
Vitamin D Made in the Skin from Sunlight
Vitamin D is available to the body in two different ways. Sun exposure helps the skin make vitamin D. Ultraviolet B (UVB) waves help formation of vitamin D in the skin, but UVB rays are also responsible for the burning effects of the sun.
Not surprisingly, vitamin D deficiency is more common in northern parts of the country, where there is less sunlight. Melanin, the pigment in the skin, as well as sunblock applied to skin, can decrease the absorption of vitamin D. The more melanin in the skin, the darker the pigment of the skin, and the less vitamin D that is absorbed.
Regular application of sunblock to the skin will also decrease absorption of sun. The American Academy of Dermatology does not recommend stopping the use of sunblock to allow the absorption of vitamin D, since the ultraviolet B rays can increase the risk of skin cancers.
Vitamin D can be Absorbed in the Stomach
200 IU (international units) of vitamin D is the daily recommended intake of vitamin D in children and adolescents. Post-menopausal women should have at least 400 IU a day to prevent thinning of the bones. Many experts feel that this recommendation is too conservative, and that post-menopausal women need at least 1000 IU daily to prevent/treat osteoporosis.
Fish, vegetables, and milk and cereal fortified with vitamin D are all good sources of vitamin D. However, a child would have to drink the equivalent of half a liter of milk a day to get recommended amounts of vitamin D. Vitamin D is important because it helps the absorption of calcium by the gut.
Vitamin D is Converted into 25 Hydroxyvitamin D, 25 (OH) D (Calcidiol)
Once vitamin D is absorbed by the skin or in the stomach, it is converted to a molecule called 25 hydroxyvitamin D (shortened as 25 (OH) D or calcidiol), in the liver. Although it is not routinely checked, 25 (OH) D can be measured by a blood test. 25 (OH) D is then converted to another molecule in the kidney. So it is not surprising that children and adults with kidney failure are prone to severe thinning of the bone. Vitamin D is then stored in the fat in the body once it is converted by the liver and kidney.
Vitamin D Deficiency is Common in Children and Adolescents
Currently, a level of < 11 ng/ml is defined as vitamin D deficiency. Many experts feel that this threshold is too low, and that the negative effects of vitamin D deficiency on bones can occur at levels of 20 ng/l or higher. A number of studies have shown that vitamin D deficiency is more common than previously thought. Three main factors play a role in vitamin D deficiency in children and adolescents: race, gender and body-mass index (BMI, a measure of obesity). Girls are twice as likely as boys to have vitamin D deficiency. Darker pigmented children are more likely to have vitamin D deficiency. 25 (OH) D levels decrease as BMI (weight) increases.
The Highest Rate of 25 (OH) D Deficiency is Seen in Overweight African American Adolscents
In the United States, up to 2 % of all children have levels of 25 (OH) D less than 11 ng/ml, and 14 % have less than 20 ng/ml. Even more concerning, 11-50 % of African American teenagers in the United States may have 25 hydroxy D deficiency (depending on how deficiency is defined). This is a startling statistic. In one study, African American adolescents were found to be twenty times as likely as Caucasion adolescents to have vitamin D deficiency. The risk of vitamin D deficiency in Hispanic and Asian adolescents is also higher than in Caucasions. Being overweight increases the risk of vitamin D deficiency by 75 %. The highest rate of 25 (OH) deficiency is seen in overweight African American adolescent girls.
Vitamin D Supplementation in the Diet
It is unclear how vitamin D deficiency in adolescents will affect health when they become adults. Interestingly, in post-menopausal women, thin Caucasians are at highest risk for osteoporosis and bone fractures. It seems prudent to maximize food intake of vitamin D or to consider taking a vitamin D supplement if not enough vitamin D is consumed in the diet. In the future, it may be useful to measure 25 (OH) D levels in high risk adolescents.
Saintonge, Sandy, Bang, Heejung, Gerber, Linda. Implications of a New Definition of Vitamin D Deficiency in a Multiracial US Adolescent Population: The National Health and Nutrition Examination Survey III. Pediatrics 2009; Vol. 123, Number 3: 797.
Legal Disclaimer: This article is for informational purposes only and should not substitute for medical advice from your healthcare provider. The author is not providing personal medical opinion, diagnosis or course of treatment. Do not delay or substitute this information for medical treatment if you have any medical concerns.
Updated January 6, 2011 by Dr. Vee