The Nutrition Examination Research Digest (NERD) aims to provide rigorous, unbiased analysis of the latest and most important nutrition and supplementation studies. Click here to subscribe or login if already a subscriber .
Study under review: Zinc supplementation in prediabetes: A randomized double-blind placebo-controlled clinical trial.
Introduction
Prediabetes is a condition of elevated blood glucose that is above normal, healthy levels but not so high as to meet criteria for type 2 diabetes. Two definitions of prediabetes are summarized in Figure 1. Currently, the World Health Organization defines prediabetes[1] as having a fasting blood glucose level of 110-125 mg/dL (6.1-7.0 mmol/L) or a two-hour blood glucose value of 140-200 mg/dL (7.8-11.1 mmol/L) during an oral glucose tolerance test. The American Diabetes Association has similar criteria, with the the additional parameter of HbA1c being 5.7-6.4%.
Figure 1 - Two definitions of prediabetes

The Center for Disease Control reports approximately one in three U.S. adults to have prediabetes. The prevalence increases with age, to about 48% of adults 65 years or older. Rising levels of blood sugar have also been noted worldwide[2] in both developed and developing countries. Ultimately, about 70% of people with prediabetes will progress[3] to develop type 2 diabetes, making prediabetes a critical period for intervention.
Lifestyle interventions for prediabetes primarily target fat loss, but improvements to diet and increases in physical activity are also key[4] for preventing progression to diabetes. Although effective and cost-efficient, lifestyle interventions can be difficult for some people to adhere to.
Treatment with zinc may provide a cost-effective alternative. Zinc is thought[5] to have multiple effects, summarized in Figure 2, that could help with both diabetes and prediabetes. It plays an important role in beta-cell function, insulin signal transduction, and is involved in insulin biosynthesis[6]. Moreover, some people with type 2 diabetes[7] have low zinc absorption and high urinary zinc excretion. This may, in part, explain why people with type 2 diabetes[8] have lower levels of serum zinc.

A meta-analysis[9] of zinc supplementation studies in participants with type 2 diabetes reported significant benefits for glycemic control and blood lipids. These findings were supported by a separate meta-analysis[10] involving primarily patients with type 2 diabetes, but also insulin resistant and healthy adults. However, a systematic review[11] looking only at people with insulin resistance without diabetes reported no significant benefit from zinc supplementation. Limited research looking specifically at adults with prediabetes exists. One pilot study[12] reported that zinc supplementation benefits glycemic control in this population. The study under review sought to build upon this research to determine the effects of zinc supplementation in a large group of people with prediabetes over a 12-month period.
Prediabetes represents an important checkpoint on the path to type 2 diabetes. Zinc is involved in proper glucose metabolism and supplementation has been shown to benefit glycemic control in people with type 2 diabetes. Less certainty exists regarding its effects in people with prediabetes. The study under review sought to address this knowledge gap.
Who and what was studied?
What were the findings?
What does this study really tell us?
The big picture
Frequently asked questions
What should I know?
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Can whole eggs help make swole legs?
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