The American Diabetes Association 71st Scientific Sessions:

Multiple Studies Link Low Vitamin D Levels for Both Types of Diabetes, but Researchers Still Want Randomized Trials

Thirteen studies linking vitamin D deficiency to increased risks of both type 1 and type 2 diabetes and their complications were presented at the 2011 American Diabetes Association meeting.

But without a single randomized trial yet published in the field, researchers remained divided on whether to recommend supplementation to their patients.

“I do not recommend it yet because we do not have positive randomized trials looking at safety and efficacy,” said co-author of one of the larger studies presented (abstract 117-OR), Joanna Mitri, MD, an endocrinology fellow at Tufts Medical Center in Boston, Massachusetts.

Still, she said, “Definitely anyone who has a [serum 25-hydroxy D] level below 10 [ng/mL] needs to have a higher level. The serum level recommended by the Institute of Medicine is 20.”

The senior author of that paper agreed that the apparent role of vitamin D levels seen in numerous studies may yet turn out to be simply a marker for some confounding variable as yet unknown.

Even so, “Vitamin D supplementation is easy and inexpensive,” said Anastassios G. Pittas, MD, co-director of Tufts Medical Center’s Diabetes Center. “If these findings are confirmed by randomized trials, it would have important public health implications.”

Some endocrinologists are not waiting for those randomized trials to recommend the vitamin to their patients.

“I don’t know what people are waiting for,” said Elena Christofides, MD, FACE, an endocrinologist in private practice in Columbus, Ohio. “We’re seeing single-digit levels [of serum 25-hydroxy D] when we measure our patients. I give 50,000 units of D3 daily for six months and then re-test. Many patients’ biggest complaint before I treat is loss of muscle strength and a subjective sense of respiratory distress. And it all resolves.”

The paper on which Dr. Mitri and Dr. Pittas collaborated examined 2,039 patients who were at risk of developing type 2 diabetes when randomized to receive either intensive lifestyle training or placebo as part of the diabetes prevention program. During a mean of 3.2 years follow-up, and after multivariate analysis, participants in the highest tertile of 25 OHD had a hazard ratio of 0.74 (95% CI 0.59 to 0.93) for progression to type 2 diabetes, compared to those in the lowest tertile.

Type 1 diabetes was also studied in relation to vitamin D levels in 2 papers presented at the meeting.

Australian researchers reported that risk of retinopathy was more than doubled in children and adolescents with type 1 diabetes who had 25 OHD deficiency (abstract 1209-P). The 2-year cross-sectional analysis of 517 subjects found that the risk of developing retinopathy was 18% in those deficient in 20 OHD, compared to 9% in those with normal levels (p = 0.02). Having vitamin D deficiency was associated with a 2.25 odds ratio (95% CI 1.09 to 4.65) of developing retinopathy, the study found.

Another study (abstract 430-PP) found that vitamin D might cut the risk of developing type 1 diabetes in half. The paper analyzed 265 US military personnel who developed type 1 diabetes between 1992 and 2008, and whose serum had been stored prior to diagnosis in the Department of Defense Serum Repository. Each case was matched against 2 controls with similar demographics. Non-Hispanic whites whose 25 OHD level was at least 75 nmol/L had a 54% lower risk of developing type 1 diabetes (RR – 0.46, 95% CI 0.29 to 0.74, p = 0.001) than those whose vitamin D level was lower. No significant association, however, was found for blacks or Hispanics.

Other papers finding an association between low levels of 25 OHD and increased risk of type 2 diabetes, or morbidities associated with it, included abstracts 2669-OP, 2512-OP, 1260-P, 809-P, 799-P, 631-P, and 325-OR.

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