Ten men at the University of Nottingham are lying down for science by taking to their beds for three days. No, it's not an exercise in leisure, but part of a study on the effects of weightlessness on astronauts' health on prolonged space missions. The "pillownauts" will provide medical data that could one day help astronauts avoid the risk of developing Type-2 diabetes due to a lack of gravity.

One of the depressing aspects of space medicine is that the more we know about the effects of weightlessness on the human body, the more we know how bad it is. In the early days of the Space Race, the worries about zero gravity were painted with pretty broad brush strokes. Could a person breathe without gravity? Was it possible to swallow? What about motion sickness?

As the first manned flights progressed, the first two problems turned out to be non-existent, while the third remains as much the bane of astronauts today as seasickness is for sailors. But to this has been added a catalog of health concerns. Weightlessness causes bones to lose calcium and muscles to lose mass as they atrophy. Spines stretch, causing back problems. Fluids rise into the head, resulting in nasal congestion, a loss of taste, and blurred vision as eyeballs are pressed out of shape. Even the autoimmune system is affected, as are certain basic cellular functions.

Another thing that has been observed is that returning astronauts show symptoms of pre-diabetes, indicating that they are at risk of developing Type-2 diabetes. This is due to the body developing a resistance to insulin under weightless conditions , causing the muscles and liver to absorb less glucose to regulate blood sugar levels.

Working in conjunction with a similar 60-day study by ESA at the MEDES facility in Toulouse, France, the Nottingham experiment uses the tried method of simulating the effects of zero gravity by having subjects lying flat in bed with their heads angled slightly down to allow fluids to flow to the head. In this case, the 10 healthy male volunteers will be tucked in for three days this month at the Queen's Medical Centre in Nottingham. There they will be subjected to baseline tests to determine weight, muscle mass, liver and pancreatic function as well as undergoing MRI scans and muscle biopsies.

"Over the period of bed rest, we will use the gold standard method to measure insulin resistance in our 10 participants, says Natalie Shur, PhD researcher on the project. "This is called an 'insulin clamp' and it shows us exactly how much glucose is being taken up by the muscles. We also use stable isotope tracers, administered both orally and intravenously, to show how glucose uptake by muscles changes over time as the bed rest progresses. We expect to find an accelerated onset of insulin resistance in the first three days of bed rest and we hope to answer significant questions about the rate and magnitude of that resistance and associated muscle wasting."

The team hopes that by gaining a better understanding of how fast the body develops insulin resistance, it will be possible to develop new exercise and diet regimes that will combat the effects of weightless in pre-diabetes – preferably during the first week in space while the body is adjusting to its new environment. Meanwhile, the French study will be testing the effects of an antioxidant cocktail versus a placebo in combating pre-diabetes.

"Non-weight-bearing has a major negative impact on health, including reduced muscle mass and sensitivity to nutrition," says study co-leader Paul Greenhaff. "Pre-diabetes is a very marked negative side effect and it is this aspect that we want to investigate as part of the wider ESA studies. This research has important implications for space flight, but will also provide important insight into the negative effects of inactivity on metabolic health in the general population. Indeed, many of the effects currently attributable to aging across our life course are most likely caused by decreasing physical activity levels that accompany aging."

Source: University of Nottingham