Nearly 1 billion people worldwide may have deficient or insufficient levels of vitamin D due to chronic disease and inadequate sun exposure related to sunscreen use, according to a study in the Journal of the American Osteopathic Association.

The study also found that 95 percent of African American adults may have vitamin D deficiency or insufficiency.

"People are spending less time outside and, when they do go out, they're typically wearing sunscreen, which essentially nullifies the body's ability to produce vitamin D," says study author Kim Pfotenhauer, DO, assistant professor at Touro University in Vallejo, Calif., in a news release.  "While we want people to protect themselves against skin cancer, there are healthy, moderate levels of unprotected sun exposure that can be very helpful in boosting vitamin D."

Dr. Pfotenhauer also said chronic diseases like Type 2 Diabetes and those related to malabsorption, including kidney disease, Crohn's and celiac disease greatly inhibit the body's ability to metabolize vitamin D from food sources.

Increasing and maintaining healthy vitamin D levels can be as easy as spending 5–30 minutes in midday sun twice per week, according to the study authors. It is important to forgo sunscreen during these sessions because SPF 15 or greater decreases vitamin D3 production by 99 percent, they write.

"Science has been trying to find a one-to-one correspondence between vitamin D levels and specific diseases," says Dr. Pfotenhauer. "Given vitamin D's ubiquitous role in the body, I believe sufficient vitamin D is more about overall health. Our job as osteopathic physicians is to recognize those patients that need to be tested and treat them accordingly."

Currently, insufficiency is defined as between 21 and 30 ng/ml and deficiency is considered below 20ng/ml by the Endocrine Society.