Low vitamin D levels greatly increase a teenager’s risk of diabetes and heart disease, Johns Hopkins researchers find. It is becoming clear that adults who get too little vitamin D are at higher risk for diabetes and heart disease. Now, it appears vitamin D levels also affect these risks earlier in life, say Johns Hopkins researchers Jared P. Reis, PhD, and colleagues. The researchers analyzed data from 3,577 adolescents aged 12 to 19 enrolled in National Health and Nutrition Examination surveys from 2001 through 2004.