Low level of hemoglobin A1c and the increased incidence of herpes zoster: longitudinal study.

Little is known about the association between glycemic status and herpes zoster. The aim of this study was to evaluate whether glycemic status, including both high and low hemoglobin A1c(HbA1c), is associated with subsequent herpes zoster. We conducted a retrospective longitudinal study in a large teaching hospital in Tokyo, Japan, from 2005 to 2016. We included all participants who underwent voluntary health check-ups at the hospital. Our primary outcome was the incidence of herpes zoster in groups of individuals stratified by HbA1c levels, which were compared using the generalized estimating equation (GEE), adjusting for participants' demographic characteristics, social history, body mass index, and comorbidities. A total of 81,466 participants were included in this study. The mean age (standard deviation) was 46.5 (12.1), and 39,643 (48.7%) participants were male. Among them, 1751 (2.1%) were diagnosed with diabetes prior to their first visits. After a median follow-up of 1784 [interquartile range (IQR), 749-3150] days, 673 (0.8%) participants developed herpes zoster. The incidence of herpes zoster was 1.45 per 1000 person-years. Compared with the reference group (HbA1c of 5.0-6.4%), the lowest HbA1c group (HbA1c of < 5.0%) had a significantly higher adjusted odds ratio (OR) (OR 1.63; 95% confidence interval (CI), 1.07-2.48) of developing herpes zoster. The group with an HbA1c of ≥ 9.5% had a higher but nonsignificant OR than the reference group (OR 2.15; 95% CI, 0.67-6.94). Our longitudinal study demonstrated that individuals in the lowest (< 5.0%) HbA1c group had a significantly higher risk of developing herpes zoster than the reference group (HbA1c of 5.0-6.4%) after adjusting for covariates.