Data from the National Health and Nutrition Examination Surveys (NHANES) indicate that vitamin D levels are falling in general, particularly among adult men.
Anne C. Looker, PhD, from the National Center of Health Statistics, and colleagues compared serum 25-hydroxyvitamin D (25[OH]D) concentrations in the U.S. population measured in 18,158 participants in 1988-1994 with that of 20,228 in 2000-2004. These findings were considered alongside information on milk intake, sun protection, and BMI.
The analysis revealed that age-adjusted mean serum 25(OH)D concentrations were 5-20 nmol/L lower in the more recent NHANES group than in the earlier one. Differences in the assays used to test vitamin D levels in the two periods accounted for most of the discrepancy, but the remaining difference “appears to represent a true decline in the vitamin D status of the population since NHANES III,” note the investigators (Am J Clin Nutr. 2008;88:1519-1527). This decrease was particularly pronounced in men (with the exception of Mexican Americans). When groups from the two time periods were compared, vitamin D levels were significantly lower—by 5-9 nmol/L—in most men but not in most women.