Increased insulin requirements during exercise at very high altitude in type 1 diabetes

Abstract

Objective: Safe, very high altitude trekking in subjects with type 1 diabetes requires understanding of glucose regulation at high altitude. We investigated insulin requirements, energy expenditure, and glucose levels at very high altitude in relation to acute mountain sickness (AMS) symptoms in individuals with type 1 diabetes.

Research design and methods: Eight individuals with complication-free type 1 diabetes took part in a 14-day expedition to Mount Meru (4,562 m) and Mount Kilimanjaro (5,895 m) in Tanzania. Daily insulin doses, glucose levels, energy expenditure, and AMS symptoms were determined. Also, energy expenditure and AMS symptoms were compared with a healthy control group.

Results: We found a positive relation between AMS symptoms and insulin requirements (r = 0.78; P = 0.041) and AMS symptoms and glucose levels (r = 0.86; P = 0.014) for Mount Kilimanjaro. Compared with sea level, insulin doses tended to decrease by 14.2% (19.7) (median [interquartile range]) (P = 0.41), whereas glucose levels remained stable up to 5,000 m altitude. However, at altitudes >5,000 m, insulin dose was unchanged (36.8 ± 17 vs. 37.6 ± 19.1 international units [mean ± SD] P = 0.75), but glucose levels (7.5 ± 0.6 vs. 9.5 ± 0.8 mmol/L [mean ± SD] P = 0.067) and AMS scores (1.3 ± 1.6 vs. 4.4 ± 4 points [mean ± SD] P = 0.091) tended to increase. Energy expenditure and AMS symptoms were comparable in both groups (P = 0.84).

Conclusions: Our data indicate that in complication-free individuals with type 1 diabetes, insulin requirements tend to increase during altitudes above 5,000 m despite high energy expenditure. This change may be explained, at least partly, by AMS.

Figure 1

Mean insulin dosage (black circles; top), mean glucose from CGM (black squares; middle), and mean AMS score per day (black triangles: downward: diabetes group, upward: control group; bottom) during the expedition; left Y axis. Altitude profile of expedition (gray line, shaded area); right y-axis. Note: Altitude presented on expedition days is the highest altitude reached that specific day. AMS scores comprise seven subjects with type 1 diabetes. Data are presented as means ± SD.

Figure 2

Relative change in daily insulin dose compared with sea level doses during the expedition (mean ± SD; %).

Figure 3

Energy expenditure per day of the type 1 diabetes group (black circles) and the control group (black squares) (left y-axis) during the expedition in relation to the altitude profile (gray line, shaded area; right y-axis). Day 6 is a day of rest in between ascents.