Quest Diagnostics, Lab Corp. of America and the Mayo Clinic—three of the largest diagnostic testing labs in the United States—have all reported a sharp rise in vitamin D testing in response to growing public and physician awareness of vitamin D deficiencies among the U.S. population, according to a July 14 USA Today article. Data from the National Center for Health Statistics shows that as many as 36% of all Americans lack vitamin D. In addition, 40% of infants and toddlers tested below the optimal blood threshold for this crucial nutrient, the Archives of Pediatrics and Adolescent Medicine reports.

Research has been mounting regarding the numerous health problems associated with vitamin D deficiencies, including an increased risk of heart attack in men and lower survival rates for women with breast cancer. Orders for vitamin D testing—once rarely used by doctors, especially primary-care physicians—jumped 80% from May 2007 to May 2008 at Quest Diagnostics in Madison, New Jersey and 90% at Burlington, North Carolina-based Lab Corp. of America from 2007 to 2008, USA Today reports. Testing orders have also been rising at the Mayo Clinic in Rochester, Minnesota, which expects to process more than half a million vitamin D tests by the end of this year.

Supplementation is key to preventing vitamin D deficiencies, and many doctors now recommend adults take 1,000 IUs daily of the sunshine nutrient. According to SPINS data, vitamin D sales spiked 91.9% in 2007.