Americans Low on Vitamin D

Study Shows Rise in Number of Americans With Low Vitamin D Levels

By Jennifer Warner
WebMD Health News

Reviewed By Elizabeth Klodas, MD, FACC

March 25, 2009 -- Low vitamin D levels among adults are fast becoming a growing epidemic and could spell trouble for the future health of the nation, according to a new study.

Researchers found that not only has the number of Americans with low vitamin D levels increased, but average vitamin D levels among adults have also decreased from 1994 to 2004.

Vitamin D is produced by the skin in response to sunlight and is also found in vitamin D fortified foods, such as milk.

Low vitamin D levels are already known to cause rickets in children and weaken bones in adults. Recent studies also have linked low vitamin D levels with cancer, heart disease, infection, and other health problems.

Researchers say the results suggest that current recommendations for vitamin D supplementation may not be high enough to address the increasing health problem of low vitamin D levels.

The Institute of Medicine currently recommends vitamin D supplementation at the following levels:

  • 200 international units (IU) per day from birth to 50 years of age
  • 400 IU per day for adults aged 51 to 70
  • 600 IU per day for adults 71 and older.

Too Little Vitamin D

In the study, researchers compared vitamin D levels in blood samples from participants of the 1988-1994 and 2001-2004 National Health and Nutrition Examination Survey.

They found the average vitamin D level dropped from 30 nanograms per milliliter to 24 nanograms per milliliter from 1994 to 2004. In addition, the percentage of people with vitamin D deficiency (below 10 nanograms per milliliter) increased from 2% to 6%; fewer people had healthy vitamin D levels of 30 nanograms per milliliter or higher (45% vs. 23%) during the study period. The increase in prevalence of vitamin D deficiency was especially striking in non-Hispanic black Americans, rising from 9% to 29% in the same 10-year period.

Researchers say vitamin D levels may have dropped as a result of people spending less time outside and avoiding the sun.

"Current recommendations for dosage of vitamin D supplements are inadequate to address this growing epidemic of vitamin D insufficiency," write researcher Adit A. Ginde, MD, MPH, of the University of Colorado Denver School of Medicine and colleagues in the Archives of Internal Medicine. "Increased intake of vitamin D (greater than or equal to 1,000 IU/d) -- particularly during the winter months and at higher latitudes -- and judicious sun exposure would improve vitamin D status and likely improve the overall health of the U.S. population."

SOURCES: Ginde, A. Archives of Internal Medicine, March 23, 2009; vol 169: 626-632. News release, American Medical Association.

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