Are Low Vitamin D Levels a Cause of Health Disparities? 19 Feb 2013
Vitamin D is an exception in the vitamin world because it can – under some conditions – be produced by the body without the need for a dietary source. Adequate vitamin D is produced by the skin when exposed to UVB light of sufficient strength. This is good, because there are few good food sources of vitamin D (it is found naturally in mushrooms exposed to ultraviolet light, fatty fish, and in lower quantities in eggs, and also in some fortified foods). Vitamin D production is not the same in everyone, however. Individuals with darker skin produce less vitamin D. In fact, it is thought that darker skin color provides a survival advantage to people living in sunny climates because it protects from the negative effects of too much sun. The drawback occurs when year-round sunlight is not available, placing these people at higher risk of vitamin D deficiency. A nationally representative survey of the United States, a country with both high- and low-sunshine regions, found that darker skinned individuals are at greater risk of vitamin D deficiency (see the CDC’s National Report on Biochemical Indicators of Diet and Nutrition in the U.S. Population 2012). Since vitamin D deficiency is related to a diverse array of health-related conditions, Weishaar and Vergili recently analyzed the relationship between vitamin D status, skin color and health disparities in the United States.
The authors made use of the NHANES survey, a nationally representative sample of the US population’s health and nutrition status that is carried out on a continual basis. Data from 2003 to 2006 were used. The NHANES survey contains a wide array of data, but the authors were primarily interested in participants’ skin color, self-perceived health status and serum level of vitamin D.
One key finding was that the major US ethnic group with the lowest levels of vitamin D were those with the darkest skin color. As skin color lightened, the risk of vitamin D deficiency decreased. This supports the idea that due to few good food sources, a major determinant of vitamin D status is sunlight exposure. Of note, average vitamin D concentrations in African Americans living in the United States were around one fifth of that of Africans exposed to daily sunshine in equatorial Africa (data was based on Luxwolda and co-workers). The authors prepared models to account for other contributors to health status such as smoking, gender, age, body mass index, exercise participation and level of education.
The major finding was that both vitamin D status and socioeconomic status were independent predictors of self-reported measures of health. The data suggest that ending socioeconomic health disparities cannot be achieved unless the low vitamin D level due to skin color can also be eliminated. In the survey, participants with better vitamin D status is related to a better self-perception of health and this appears not to be the result of the effect of the major confounding factors used in the calculations.
Future health and nutrition policy documents should aim to address both reducing health disparities due to socioeconomic status, and also preventing vitamin D deficiency. -jb-
Tom Weishaar, MS, Joyce Marcley Vergili, EdD, RD. Vitamin D Status Is a Biological Determinant of Health Disparities. Journal of the Academy of Nutrition and Dietetics. http://dx.doi.org/10.1016/j.jand.2012.12.011