Acute altitude-induced hypoxia suppresses plasma glucose and leptin in healthy humans

Abstract

To examine the effects of acute altitude-induced hypoxia on the hormonal and metabolic response to ingested glucose, 8 young, healthy subjects (5 men/3 women; 26±2 yrs; BMI, 23.1±1.0 kg/m2) performed two randomized trials in a hypobaric chamber where a 75 g glucose solution was ingested under simulated altitude (ALT, 4,300m), or ambient (AMB, 362m) conditions. Plasma glucose, insulin, c-peptide, epinephrine, leptin and lactate concentrations were measured at baseline and 30, 60, 90 and 120 min after glucose ingestion during both trials. Compared to AMB, the plasma glucose response to glucose ingestion was reduced during the ALT trial (P=0.04). There were no differences in the insulin and c-peptide responses between trials, or in insulin sensitivity based on HOMA-IR. Epinephrine and lactate were both elevated during the ALT trial (P<0.05), while the plasma leptin response was reduced compared to AMB (P<0.05). The data suggest that the plasma glucose response is suppressed at ALT, but this is not due to insulin per se, since insulin and c-peptide levels were similar for both trials. Elevated plasma epinephrine and lactate during ALT is indicative of increased glycogenolysis, which may have masked the magnitude of the reduced glucose response. We conclude that during acute altitude exposure there is a rapid metabolic response that is accompanied by a shift in the hormonal milieu that appears to favor increased glucose utilization.

Usefulness of combining intermittent hypoxia and physical exercise in the treatment of obesity

“…Similar to the effects of exercise, increased epinephrine during IHE, which was reported in healthy humans may have contributed to glycogen utilization via increases in cyclic adenosine monophosphate concentrations, potentially leading to post-treatment increased on insulin sensitivity [72].…”

“…Other trial 12 demonstrated that IHE glucose tolerance enhancement four hours after exposure can be attributed to improvements in peripheral insulin sensitivity in sedentary males with T2D. Therefore, it may improve short-term glycaemic control [85].Similar to the effects of exercise, increased epinephrine during IHE, which was reported in healthy humans may have contributed to glycogen utilization via increases in cyclic adenosine monophosphate concentrations, potentially leading to post-treatment increased on insulin sensitivity [72].Similarly, it has been described that both IHE and IHT programmes carried out in hypoxic conditions increased glucose transporter GLUT-4 levels [33].Hypoxia and exercise have shown an additive effect on insulin sensitivity [87], suggesting that insulin signalling and insulin-dependent glucose transport, might have been up-regulated following hypoxic exercise [33, 34]. This additive improvement could also be attributed to an increase in the relative intensity of the practised exercise in hypoxia [56].…”

Hypoxic training: Clinical benefits on cardiometabolic risk factors

“…In healthy subjects, acute exposure to high altitude ≥3000m resulted in a reduction in insulin sensitivity in some studies [10][11][12][13][14], although glucose metabolism was enhanced, as shown in two studies [9,15] that reported a 36%-60% improvement in glucose uptake. Chronic exposure of ≥21 days, at moderate levels of altitude (1,700m-2740m) [6,9] demonstrated improvements in fasting glucose levels [6,9].…”

“…It would also suggest that patients with issues with blood regulation should monitor their blood glucose status when participating in hypoxic training involving high exercise intensities or high levels of hypoxia. Secretion of epinephrine has been suggested to be responsible for the rise in blood glucose levels and reduction in insulin sensitivity [14,15], however in one study, epinephrine levels remained unchanged despite a rise in blood glucose, indicating alternative metabolic signalling pathways [17]. Additionally hormones such as oestrogen may affect the response to hypoxic training as seen with gender differences in glucose response to hypoxic training [17].…”

“…Adverse blood glucose regulation was noted in most studies with either acute exposure to high altitude (>4,000m) [11,13,14,16] or high intensive training. However, in chronic exposure to hypoxic conditions (≥3 weeks) with moderate levels of exercise intensity showed favourable blood glucose status [6,9,15]. This would suggest positive adaptive changes in blood regulation would require extended exposure to moderate levels of hypoxia.…”