Effect of zinc supplementation on insulin secretion: interaction between zinc and SLC30A8 genotype in Old Order Amish.

SLC30A8 encodes a zinc transporter in the beta cell; individuals with a common missense variant (rs13266634; R325W) in SLC30A8 demonstrate a lower early insulin response to glucose and an increased risk of type 2 diabetes. We hypothesised that zinc supplementation may improve insulin secretion in a genotype-dependent manner. We evaluated the early insulin response to glucose (using frequently sampled intravenous glucose tolerance testing) by R325W genotype before and after 14 days of supplementation with oral zinc acetate (50 mg elemental zinc) twice daily in healthy non-diabetic Amish individuals (N = 55). Individuals with RW/WW genotypes (n = 32) had the lowest insulin response to glucose at 5 and 10 min at baseline (vs RR homozygotes [n = 23]). After zinc supplementation, the RW/WW group experienced 15% and 14% increases in the insulin response to glucose at 5 and 10 min, respectively (p ≤ 0.04), and, compared with RR homozygotes, experienced a 26% (p = 0.04) increase in insulin at 5 min. We observed reciprocal decreases in proinsulin:insulin in the RW/WW (p = 0.002) vs RR group (p = 0.048), suggesting a genotype-specific improvement in insulin processing. Zinc supplementation appears to affect the early insulin response to glucose differentially by rs13266634 genotype and could be beneficial for diabetes prevention and/or treatment for some individuals based on SLC30A8 variation. ClinicalTrials.gov NCT00981448.