Scheduled hypometabolism and hypothermia at the crossroads of deep space manned mission and longevity

Spaceflight is a mysterious ageing/rejuvenation transition. It is associated with factors of evolutionary unfamiliar to the earth's inhabitants — microgravity, cosmic rays and solar wind irradiation, failure of circadian rhythms and numerous other singularities. For still unknown reasons, spaceflight provokes quick acceleration of almost all hallmarks of ageing and age-related diseases. The alterations have a transitory character and disappear in the post-landing adaptation period. The posited ageing/rejuvenation transition could be repeated over multiple flights. This should be confirmed by epigenetic or other types of ageing clocks. Hypometabolism and hypothermia are considered efficient protectors from the hazards of space missions while saving energy and food intake. The two most discussed approaches are based on the idea of dormancy (synthetic torpor) or excessive sleeping (shallow metabolic depression). We suggest another model of metabolic depression induced by a rebreathing hypoxic-hypercapnic environment (HHE), which is accompanied by ‘voluntary’ calorie restriction. Crewmembers' work schedules can be designed to allow crewmembers to maintain normoxic levels during energy-demanding activities and transition to HHE during rest periods. A computerized tracking system can harmonize daily schedules with personalized HHE. The resulting scheduled hypometabolothermia (SHMT) could optimise energy expenditure without compromising productivity and be applicable during spaceflight and upon arrival at a destination and subsequent planetary exploration. We envision SHMT as a major human lifestyle on Earth as well. Of course, only further thorough explorations will reveal all the advantages and pitfalls of HHE and SHMT on Earth and in space. ________________________________________________________________________________________Keywords: hypoxia and hypercapnia; metabolic suppression; food consumption; space mission; longevity