A growing number of people got their vitamin D blood levels checked in 2008, and vitamin D testing labs are gearing up for those numbers to skyrocket in 2009 and beyond.

According to LabCorp., a North Carolina-based testing lab, Vitamin D blood tests are now one of the fastest growing medical tests, with twice as many ordered in 2008 as in 2007. Other testing labs, such as Quest Diagnostics in New Jersey, are reporting similar increases. And yet, according to Vitamin D researchers, still relatively few people ever get their vitamin D blood levels checked.

Vitamin D leaders now recommend vitamin D blood levels of 40-60 ng/ml and a combined daily vitamin D intake of 2,000 international units — significantly higher than the national average of around 23 ng/ml and the current median recommendation of 400 IU.

Sunshine exposure to the skin is the body’s most reliable and natural source of vitamin D. A suntan can produce as much vitamin D as 100 glasses of whole milk.