A large percentage of Americans are low in vitamin D. The U.S. Centers for Disease Control and Prevention (CDC) set out to determine if and how vitamin D status across the United States has changed since 1988. Blood levels of vitamin D were assessed in 38,700 citizens during 1988 to 2006, then again in 12,446 citizens in 2007 to 2010. Weighted averages and the prevalence of blood vitamin D levels above and below a cutoff concentration were calculated to evaluate long-term trends. Results showed no changes in vitamin D levels between 1988 and 2006. However, a trend upwards was noted in the second half of the study. Those people who showed improved vitamin D status tended to be older, female, Caucasian, and vitamin D supplement users. During the entire study, the proportions of people with vitamin D levels below 40nmol/L were 14-18% overall, up to 60% for non Hispanic blacks, up to 28% for Mexican Americans, and up to 10% for non-Hispanic whites.
In Perspective: Vitamin D is produced by the body when exposed to UV sunlight, but that production diminishes with age, sunscreen use, and dark skin. Dietary sources of the vitamin are limited to primarily fortified foods, such as milk. It is difficult to meet recommended intake levels without supplementation. This study shows that people who supplement are the ones mostly likely to meet minimum recommended blood levels of the vitamin. Interestingly, this study found considerably fewer Americans deficient in vitamin D than has been found in previous studies, with estimates they are as high as 80%.
Schleicher R, Sternberg M, Lacher D, et al: The vitamin D status of the US population from 1988-2010 using standardized serum concentrations of 25-hydroxyvitamin D shows recent modest increases. American Journal of Clinical Nutrition 2016;July 6th.