A new Johns Hopkins University School of Medicine study suggests low levels of vitamin D may be to blame for poor blood sugar control among diabetics.

Researchers reviewed the medical charts of 124 patients between the ages of 36 and 89 with type 2 diabetes who came to an endocrine outpatient clinic for specialty care from 2003 to 2008. All patients had a single measurement of their serum 25-hydroxyvitamin D levels as part of their evaluation at the clinic.

They found that 91 percent of patients had either vitamin D deficiency or insufficiency.

In addition, they found an inverse relationship between the patients’ blood levels of vitamin D and their hemoglobin A1c value, which is a measure of blood sugar control over the past several months.

"Since primary care providers diagnose and treat most patients with type 2 diabetes, screening and vitamin D supplementation as part of routine primary care may improve health outcomes of this highly prevalent condition," said study co-author Esther Krug, M.D.

Vitamin D is available in nutritional supplement form as well as in dietary sources like dairy products, fortified cereals, and fish such as salmon, tuna and mackerel.