Does exercise in cool water cause a higher risk of hypoglycaemia than in thermoneutral conditions in type 1 diabetes?

AIMS/HYPOTHESIS The aim of this study was to test the hypothesis that exercise in cool water results in a greater decrease in blood glucose concentration than in thermoneutral water or on land in individuals with type 1 diabetes. METHODS Eight overnight-fasted individuals (aged 18-40 years) with type 1 diabetes completed 3 × 60 min cycling sessions on an ergometer at 40% of their on-land V ˙ O 2peak under the following conditions: while immersed in cool water (22°C) or in thermoneutral water (32°C) or on land at thermoneutrality (22°C). At time intervals, the following variables were measured: concentration of blood glucose and plasma insulin, skin blood flow, skin temperature and rate of carbohydrate and fat oxidation. RESULTS Blood glucose concentration did not change in response to cycling while immersed in cool or thermoneutral water (p>0.05) but decreased during cycling on land (p<0.05). The concentration of plasma insulin decreased during and early after cycling in cool water (p<0.05). During 60 min of on-land recovery (at 24°C) after cycling in cool water, blood glucose concentration increased significantly (~2 mmol/l, p<0.05), but not after cycling in thermoneutral water or on-land. CONCLUSIONS/INTERPRETATION Exercise at 40% V ˙ O 2peak performed in a basal insulinaemic state in cool water in people with type 1 diabetes does not cause a greater decrease in blood glucose concentration than in thermoneutral water or on land, but blood glucose increases early during on-land recovery, probably as a result of a transient fall in plasma insulin.