Zinc: an alternative path away from type 2 diabetes?

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.