Researchers conducted a study of 93 adults in Hawaii who self-reported sun exposure of 29 hours per week and found 51 percent had low levels of vitamin D, according to the study published in the June issue of the Journal of Clinical Endocrinology & Metabolism.

"Low vitamin D status is very common and can contribute to the development of osteoporosis and rickets," lead author Dr. Neil Binkley, of the University of Wisconsin in Madison, said in a statement. "Low levels of vitamin D may also play a role in certain cancers, multiple sclerosis, hypertension and diabetes."

The researchers suggest the common clinical recommendation to allow sun exposure to the hands and face for 15 minutes a day may not assure vitamin D sufficiency.