Seasonal variation of glycated haemoglobin and estimated average glucose in temperate South Africa

Abstract

Background: Glycated haemoglobin (HbA1c) is a useful biomarker for the monitoring and diagnosis of diabetes mellitus. In the northern hemisphere, there is evidence of seasonal fluctuations in HbA1c with values being higher in cooler months and lower in warmer months. In the southern hemisphere, there is one description from Australia. It is not known if this would also pertain in other temperate climates. We explored the relationship between seasons, HbA1c and estimated average glucose in South Africa.

Methods: This was a retrospective analysis. HbA1c data were obtained from January 2016 to December 2020 from two different provinces with different climates. The mean HbA1c values and mean monthly temperatures were compared for each year.

Results: We show seasonal variation for HbA1c and estimated average glucose (eAG) in both provinces (p < 0.01). The population was further subdivided and evaluated based on gender and age. Glycated haemoglobin was higher in cooler months and lower in the warmer months for all the data and for both the categories (age and gender; p < 0.01).

Conclusion: South Africa shows demonstrable seasonal variation in glycated haemoglobin that needs to taken into account when managing diabetes mellitus.

Contribution: Awareness of this seasonal effect may assist in more efficient use of HbA1c to monitor and diagnose diabetes mellitus and will assist in modifying therapeutic targets for achieving good glycaemic control.