The health of astronauts in space is, quite obviously, a vital form of research. There’s no point in us rushing to get humans to Mars if all our astronauts get incredibly sick or perish on the way there. Things like muscle atrophy, altered vision, and genetic alteration are all real and very complex issues that still need to be dealt with.
A fresh piece of research has found another curious biological wrinkle that emerges during microgravity: astronauts seem to have a higher core body temperature (CBT) than us Earthbound rubes. During long-duration flights, they appear to be roughly 1°C (1.8°F) warmer than expected.
This study, which looked at 11 different astronauts, found that gradually, over the course of 2.5 months, CBT rises occurred. These impairments in thermoregulation persist back on Earth for some time, too.
As reported in a new Scientific Reports study, the detection of what the team refers to as “space fever” isn’t good news.
Your core body temperature, unless you’re afflicted with some sort of illness, is 37°C (98.6°F). This temperature control – technically known as thermoregulation – is controlled by the hypothalamus, and its failure can be triggered by a temperature change of just a few degrees.
Too high, and you can suffer from heat stroke; too low, and you’ll get hypothermia, both of which can damage your internal organs. Fortunately, things like evapotranspiration through sweat, and heat retention through blood vessel constriction, allow us to cool down or keep warm, respectively.
This new study highlights that when gravity is distinctly lacking, thermoregulation gets a little tougher – specifically, cooling yourself down, which may seem a little paradoxical considering that these spacefarers are always inches away from temperatures nearing absolute zero.
Sweating is harder in space. Without gravity to help it drip off you, it just clumps to your body, and only a towel properly helps to remove it.
The study also points out that convection – an incredibly efficient way of cooling that relies on a fluid – doesn’t operate normally either. Taking place everywhere, from Earth’s slowly mobile-but-solid mantle to the air around you, the lack of gravity interferes with it.
The astronauts' space fevers could be partly explained by these mechanisms. Curiously, the higher CBTs also seem to correlate with inflammation in the body linked to microgravity – perhaps your body mistaking near-weightlessness for an infection of sorts – higher-than-average radiation rates, psychological stress, or a combination of all of the above.
At present, it’s not entirely clear what causes persistently higher CBTs in space, but it does put astronauts in a bit of a bind. If they don’t exercise regularly, the microgravity environment will weaken and degrade their muscles and bones.
This difficulty in cooling themselves down, though, may mean that they are more prone to suffering from potentially dangerous exhaustion after a particularly straining session on the low-grav bikes on the International Space Station, for example.
Some astronauts during exercise had CBTs reaching around or even exceeding 40°C (104°F). If this is sustained for too long, it can induce a medical emergency.
The international research team, which was led by Charité – the Berlin University of Medicine, conclude in their paper that “since even minor increases in CBT can impair physical and cognitive performance, both findings have a considerable impact on astronauts’ health and well-being during future long-term spaceflights.”