Vitamin D: Declining Levels Troubling, May Presage Serious Health Problems

Vitamin D plays diverse and profound roles in health -- it lowers the risk of weak muscles and bones, cancer, heart disease, and depression. But the latest -- and very troubling -- news is that the average blood levels of vitamin D among Americans are decreasing and heading toward outright deficiency.

That's the finding of two recent studies in major medical journals.

Adit Ginde, MD, MPH, of the University of Colorado School of Medicine, Denver, and his colleagues analyzed data from two large studies of people, one conducted between 1988 and 1994 and the other between 2001 and 2004. The first study included information of vitamin D levels in 18,883 people, and the second study included data from 13,369 people.

From about 1994 to 2004, the number of Americans with normal levels of vitamin D (30 ng/mL or higher) decreased from 45 percent to 23 percent--meaning that three-fourths of Americans do not have optimal levels of the vitamin. In addition, the percentage of people with a severe deficiency (less than 10 ng/mL) increased from 2 percent to 6 percent during this time.

In addition, African American and Hispanic men and women had substantially lower vitamin D levels compared with Caucasian men and women. Darker complexions limit the skin's production of vitamin D after exposure to sunlight.

In the second study, Sandy Saintonge, MD, of the Weill Cornell Medical College, New York City, analyzed vitamin D levels in 2,955 people ranging from 12 to 19 years old. She reported that low levels of vitamin D were widespread among teenagers, particularly among African Americans, Hispanics, girls, and those who were overweight.

Overall, about 11 percent of African American teenagers were deficient in vitamin D. However, Saintonge wrote that if the standard for deficiency was changed from 11 ng/mL to 20 ng/ mL--as many experts have recommended--50 percent of African American teenagers would be considered deficient, as would 14 percent of teenagers in general.

Current recommendations call for every infant, child, and adult to supplement with 1,000 IU daily, with a doubling of that amount for people with dark complexions.

References: Ginde AA, Liu MC, Camargo CA. "Demographic differences and trends of vitamin D insufficiency in the US population, 1988-2004." Archives of Internal Medicine, 2009;169: 626-632. Saintonge S, Bang H, Gerber LM. "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;123:797-803.