Professor of Medicine and Epidemiology Department of Medicine, Rutgers Robert Wood Johnson Medical School, New Brunswick, NJ New Brunswick, United States
Background: Heat can induce changes in metabolism and hemodynamics and potentially cause alterations in insulin sensitivity. Older diabetic adults who are on exogenous insulin or insulin secretagogues might be particularly sensitive to such effects and develop serious hypoglycemia.
Objectives: To determine the association between ambient heat and severe hypoglycemia among older adults on insulin, insulin secretagogues, or metformin monotherapy.
Methods: We conducted a time-stratified case-crossover analysis among older Medicare adults (aged >= 65) eligible for Parts D during the summer months (May - September) from 2016 to 2019 (N = 23 million). We identified cases of severe hypoglycemia among insulin or sulfonylurea users as well as metformin monotherapy users as a negative control. Severe hypoglycemia was defined as ED visits or hospital admissions with primary ICD-10 diagnosis codes of hypoglycemia. Ambient heat was categorized into percentile categories of the local warm season distribution of heat index (HI): ≥99, 95-98, 85-94, 75-84, 25-74, and < 25th %tiles. We estimated relative risks (RR) for the HI percentile categories and their 95% confidence intervals (CI) using conditional logistic regression.
Results: Among 2 million insulin users, we identified 32,461 serious hypoglycemia cases (26 per 1000 person-years). Of the 32,461 cases (mean age 73 years, 41% male, 72% White), the RR for HI >99%tile, 95-98%tile, 85-94%tile, 75-84%tile was 1.42 (CI, 1.31-1.53), 1.16 (CI, 1.10-1.22), 1.14 (CI, 1.10-1.18), 1.10 (CI, 1.06-1.14), respectively, compared to the 25-74%tile. Among 92,472 cases from sulfonylurea users, RR for ≥99%tile, 95-98%tile, 85-94%tile, 75-84%tile was 1.41 (CI, 1.24-1.58), 1.16 (CI, 1.08-1.25), 1.15 (CI, 1.08-1.21), 1.11 (CI, 1.05-1.17), respectively. Among 505 cases from metformin users, RR for the same four HI %tile categories ranged from 0.94 -1.21 with CIs crossing 1.
Conclusions: Among older diabetic adults on insulin and insulin secretagogues, a higher heat index was associated with an increased risk of serious hypoglycemia, potentially due to heat-related increases in insulin sensitivity. Patients and providers should be aware of the risk of hypoglycemia from mildly to extremely elevated ambient temperature.
