Seasonal heat stress and glycaemic control in adults with type 2 diabetes in Cotonou, Benin

Urban humid heat may challenge glycaemic control in people with type 2 diabetes. This study assessed seasonal associations between heat stress and glycaemia and identified vulnerable profiles in Cotonou, Benin. A cohort of 240 adults with type 2 diabetes was followed for 12 months at three healthcare facilities. Daily meteorological data were linked to monthly fasting plasma glucose and seasonal glycated haemoglobin measurements. Seasonal differences were assessed using repeated-measures analysis of variance, followed by linear mixed models and logistic regression with generalised estimating equations. Mean fasting glucose was highest during the long dry season (1.56 g/L) and lowest during the short dry season (1.47 g/L), with a significant seasonal effect (F(3,717) = 39.74, p < 0.001). Each one-unit increase in Humidex was associated with a 0.014 g/L increase in fasting glucose and 12% higher odds of hyperglycaemia after adjustment. Hyperglycaemia occurred in 21.4% of measurements during the long dry season versus 12.5% during the short dry season. Associations were stronger among outdoor workers and participants reporting insufficient hydration. Seasonal humid heat was associated with poorer glycaemic control, supporting heat-adapted diabetes counselling and prevention in tropical settings.