Glycated haemoglobin index is a new predictor for all-cause mortality and cardiovascular mortality in the adults.

Glycosylated haemoglobin index (HGI) has been shown to correlate with the prognosis of metabolic diseases, but the relationship with mortality remains unclear. This study included 18,285 US adults who participated in the National Health and Nutrition Examination Survey (NHANES) between 1999 and 2018. During the median follow-up period of 115 months, a total of 2572 all-cause deaths and 671 cardiovascular disease (CVD) deaths occurred. The restricted cubic spline revealed a U-shaped correlation between HGI and all-cause and CVD mortality. After adjusting for all covariates, the optimal inflection point values in all-cause and CVD deaths were 0.17 and 0.02, respectively. In the left side of the inflection point, the risk of all-cause mortality and CVD mortality decreased by approximately 24% (HR 0.76, 95% CI 0.69, 0.84) and 25% (HR 0.75, 95% CI 0.60, 0.96) with the increase in HGI. Conversely, in the right of the inflection point, an increase of 1 unit in the HGI was linked with a 17% (HR 1.17, 95% CI 1.07, 1.27) and 31% (HR 1.31, 95% CI 1.15, 1.49) increase in all-cause and CVD mortality. Our study showed that HGI is an important tool for predicting the risk of all-cause mortality and CVD death in US adults and there is a U-shaped relationship between HGI and mortality.