A unique study involving 20 men that remained in bed for two months straight demonstrates the damaging impact long-term immobility can have on the body’s metabolic health, with potential consequences for future space missions and life back on Earth.
What happens if you put 20 young men in bed without any physical activity for two months? Despite reducing food intake to avoid gaining weight, long-term inactivity significantly increases blood sugar levels, reports a new study from the University of Bath [1].
A team from the University’s Centre for Nutrition, Exercise and Metabolism carried out the research as part of an ESA (European Space Agency) bed rest study. For 60 days, 20 young, fit and healthy male participants remained in bed with their feet above their heads as international researchers evaluated numerous health measures. Individuals remained in bed while eating, showering and going to the restroom.
The Bath team’s research focused on participants’ metabolic health – how well their bodies control their blood sugar levels. The same team demonstrated in 2018 that exercise impacts blood sugar in the short term, even when done in short bursts.
Researchers wanted to understand what happens when there is no physical activity or movement for weeks or months. The participants were fed a much-reduced diet to make up for their physical activity and stop them from gaining weight.
According to the findings published in Clinical Nutrition on February 16, inactivity negatively affected blood sugar levels even when food intake was decreased to match participants’ much lower energy consumption during bed rest.
Blood glucose levels are affected
During the day, blood sugar levels rose by around 6%, while at night they rose by 10%. It was found that their ability to dispose of blood sugar – for instance, to take up blood sugar into muscles, decreased by almost a quarter (24%). Participants struggled to control their blood sugar, a significant risk factor in developing conditions such as cardiovascular disease or type II diabetes.
Researchers found that reducing calorie intake further reduced blood sugar levels. Their blood sugar levels would have spiked even higher if they had eaten the same amount as usual because of their reduced ability to dispose of sugar.
The bed rest study was conducted to better understand the health effects of future astronaut crewed space missions. However, the researchers say the effects are also significant for life back here on Earth, where millions of people face periods of long-term inactivity due to poor lifestyles, chronic conditions, ill health or injury.
Dylan Thompson, professor of human physiology at the University of Bath, led the study. During the course of nearly two months, 20 young fit and healthy men were put through a series of tests in which they stayed in bed without doing any physical activity, he explained. Deconditioning as a model for microgravity can be studied using such bed rest studies, and this one was among the longest to date.
According to Thompson, “results reveal that the withdrawal of physical activity profoundly impacts physiological health over and above the impact of controlling diet.” Although participants’ blood sugar levels increased naturally due to their inactivity, resulting in a decrease in their ability to take up and process sugar, although the changes were not as significant as anticipated if participants maintained the same calorie intake.
Thus, adjusting diet alone cannot overcome all the adverse effects of reducing physical activity – even if you succeed to avoid weight gain.
Dr Angelique Van Ombergen, discipline lead for life sciences at the ESA, added, “Our spaceflight analogs, of which bedrest is the golden standard, don’t only allow us to do research that can directly benefit our astronauts, but they also allow us to apply this knowledge for people on Earth such as the elderly and the immobilized.” This newly released study from Thompson and his team is a good example of that. Currently, ESA is planning two bedrest studies where multiple countermeasures will be tested.
Aside from helping people on Earth who are bedridden, the Bath team is also exploring countermeasures in space. In extreme cases where individuals do not have mobility, electrical stimulation of leg muscles might replicate some of the benefits of exercise on blood sugar control.
In addition Thompson said this study underscores the importance of physical activity for metabolic health. Long-term inactivity without movement increases the risk of diabetes and other chronic conditions. Technology could impact muscular contraction for blood sugar control, even in extreme cases where individuals have lost all movement.
[1] https://medicalxpress.com/news/2023-02-day-bed-rest-dangers-long-term.html
