Effect of different levels of acute hypoxia on subsequent oral glucose tolerance in males with overweight: a balanced cross-over pilot feasibility study

Previous research has shown that ≤60 minutes hypoxic exposure improves subsequent glycaemic control, but the optimal level of hypoxia is unknown and data are lacking from individuals with overweight. We undertook a cross-over pilot feasibility study investigating the effect of 60-minutes prior resting exposure to different inspired oxygen fractions (CON F_IO₂=0.209; HIGH F_IO₂=0.155; VHIGH F_IO₂=0.125) on glycaemic control, insulin sensitivity and oxidative stress during a subsequent oral glucose tolerance test (OGTT) in males with overweight (mean(SD) BMI=27.6(1.3) kg/m²; n=12). Feasibility was defined by exceeding predefined withdrawal criteria for peripheral blood oxygen saturation (SpO₂), partial pressure of end-tidal oxygen or carbon dioxide and acute mountain sickness (AMS), and dyspnoea symptomology. Hypoxia reduced SpO₂ in a stepwise manner (CON=97(1)%; HIGH=91(1)%; VHIGH=81(3)%, P<0.001), but did not affect peak plasma glucose concentration CON=7.5(1.8) mmol∙L^-1; HIGH=7.7(1.1) mmol∙L^-1; VHIGH=7.7(1.1) mmol∙L^-1; P=0.777; η2=0.013), plasma glucose area under the curve, insulin sensitivity, or metabolic clearance rate of glucose (P>0.05). We observed no between-conditions differences in oxidative stress (P>0.05), but dyspnoea and AMS symptoms increased in VHIGH (P<0.05), with one participant meeting the withdrawal criteria. Acute HIGH or VHIGH exposure prior to an OGTT does not influence glucose homeostasis males with overweight, but VHIGH is associated with adverse symptomology and reduced feasibility.