Despite data showing that zinc helps promote the production and action of insulin, no randomized clinical trials have shown that zinc supplementation can prevent the onset of type 2 diabetes, suggest the investigators of a new systematic review of clinical studies on zinc and diabetes (Cochrane Database Syst Rev. 2007 Jan 24;[1]:CD005525).

They stress, however, that this does not necessarily mean that zinc has no role in diabetes prevention—only that eligible studies are lacking.

Of the 192 clinical studies involving zinc, insulin, and type 2 diabetes, only 1 study met all the inclusion criteria. In that study, 56 obese women who did not have diabetes were randomized to receive either 30 mg/day of oral zinc supplementation or placebo for 4 weeks.

Changes in insulin resistance, insulin concentration, fasting plasma glucose, and other measures associated with type 2 diabetes were monitored with blood tests. No significant differences between the zinc and placebo groups were found for any of the measures.

However, the investigators note that 4 weeks is an insufficient period to assess the development of glucose tolerance and diabetes.

“It is important to recognize that this systematic review…was left with 1 trial that treated 56 people with either zinc or placebo for 4 weeks and observed no effect,” said John Buse, MD, director of the Diabetes Care Center at the University of North Carolina School of Medicine. “The single trial is too small and too short to really tell us anything about the effectiveness of zinc.”

He added, “Basically we know nothing that can definitely guide clinicians in providing advice regarding zinc supplementation for the prevention of type 2 diabetes mellitus.”