ABSTRACT
Reports that aging slows down in space prompted this investigation of anti-aging effects in humans by analyzing astronauts’ heart rate variability (HRV). Ambulatory 48-hour electrocardiograms from 7 astronauts (42.1 ± 6.8 years; 6 men) 20.6 ± 2.7 days (ISS01) and 138.6 ± 21.8 days (ISS02) after launch were divided into 24-hour spans of relative lower or higher magnetic disturbance, based on geomagnetic measures in Tromso, Norway. Magnetic disturbances were significantly higher on disturbed than on quiet days (ISS01: 72.01 ± 33.82 versus 33.96 ± 17.90 nT, P = 0.0307; ISS02: 71.06 ± 51.52 versus 32.53 ± 27.27 nT, P = 0.0308). SDNNIDX was increased on disturbed days (by 5.5% during ISS01, P = 0.0110), as were other HRV indices during ISS02 (SDANN, 12.5%, P = 0.0243; Triangular Index, 8.4%, P = 0.0469; and TF-component, 17.2%, P = 0.0054), suggesting the action of an anti-aging or longevity effect. The effect on TF was stronger during light (12:00–17:00) than during darkness (0:00–05:00) (P = 0.0268). The brain default mode network (DMN) was activated, gauged by increases in the LF-band (9.7%, P = 0.0730) and MF1-band (9.9%, P = 0.0281). Magnetic changes in the magnetosphere can affect and enhance HRV indices in space, involving an anti-aging or longevity effect, probably in association with the brain DMN, in a light-dependent manner and/or with help from the circadian clock.
INTRODUCTION
Aging is the inevitable time-dependent decline in physiological organ function and a major risk factor for cardiovascular disease, cancer and Alzheimer’s disease. Novel treatments and translational approaches have been tried to prevent, delay, alleviate or even reverse age-related diseases. Maximal longevity, however, appears unchanged. Space research is bringing insight on how to directly intervene against the aging hallmarks and prevent age-related diseases. This possibility may exist because spaceflight has complex effects on the physiology of organisms, such as reduced gravity and different electromagnetic surroundings, which induce changes to almost every system in the body.
The Sun markedly affects most activities on Earth, including its solid, liquid and gas states. Whether life started on Earth or in the cosmos (panspermia hypothesis), it evolved following long physical/chemical processes, so that life on Earth matches what this planet requires1,2. Now, humans plan to live on the moon or Mars3,4. Spaceflight opens new opportunities to learn about capabilities of the human body that could not be studied on Earth. Spaceflight is known to dramatically alter cardiovascular dynamics5,6,7,8,9,10,11, also posing significant risks, such as an overall greater than 10-fold faster onset and time course of muscle and bone atrophy12,13,14,15. Microgravity is one of the crucial contributors to these observed physiological changes.
How microgravitational space environments affect aging is not well understood16,17. Honda et al.18 reported that spaceflight in Caenorhabditis elegans suppressed the formation of transgenically-expressed polyglutamine aggregates, which normally accumulate with increasing age. Inactivation of each of the seven genes that were down-regulated in space was found to extend lifespan on the ground. Aging in Caenorhabditis elegans seemed to be slowed through neuronal and endocrine responses to space environmental cues.
Whether similar anti-aging effects apply to astronauts during long-term missions in space is investigated herein by analyzing heart rate variability (HRV) on quiet versus magnetically-disturbed days. Exposure to weak geomagnetic fields is associated with biological effects1,19,20,21,22. Previously we showed that magnetic disturbances suppress HRV primarily in the very-low frequency region, which is clinically important since its reduction is a predictor of morbidity and mortality from cardiovascular disease23,24. HRV in the minutes to hours (very-low to ultra-low frequency) range is also a powerful predictor of longevity in clinically healthy people.
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