On the flip side, meeting the physical activity recommendations seemed to compensate for sleep-related health risks.
“It doesn’t undo them but it does attenuate them quite considerably,” says senior author of the study, Professor Emmanuel Stamatakis from the Charles Perkins Centre at the University of Sydney.
Stamatakis explains that often health behaviours are examined in isolation and the idea of this latest research was to better understand the synergies between different behaviours.
“The combined effect of health behaviours is not necessarily the sum of the separate parts,” he says. “There is a synergistic effect – something else is at play and our findings basically confirm that.”
Although this study wasn’t designed to understand the mechanics behind such a synergy, previous research provides clues.
There is evidence showing that regularly not getting enough sleep or having insomnia disturbs metabolic function, causes inflammation and stimulates the stress response via our sympathetic nervous system (SNS).
It is this SNS activation, Stamatakis explains, that is to blame for the feeling of being wired and having a racing heart when we haven’t slept.
Professor Peter Cistulli, a co-author on the paper and the ResMed Chair in Sleep Medicine at the University of Sydney, explains that they believe the biological pathways that are affected when we don’t sleep well are the same ones affected when we exercise.
“We think exercise attenuates the pathway or reverses it to alleviate that risks,” says Cistulli.
So, in theory, exercise helps to restore metabolic function, reduce inflammation and calm the SNS response affected by poor sleep.
But, there does seem to be a threshold effect in that people who exceeded the exercise guidelines did not enjoy the risk reduction if they also experienced poor sleep regularly.
“A speculative explanation but a plausible explanation is that if the body is compromised already from a lack of sleep, by giving a larger dose of exercise, you may be doing some benefit but you may also be doing some harm,” Stamatakis says.
While the findings are observational and the researchers say further studies are needed to understand the relationships, there are several takeaways.
Firstly, it is to acknowledge that the last thing people with chronic sleep problems feel like doing is exercise. This complicates the advice, according to Stamatakis.
He also stresses that the findings are not an excuse to stay up until 3am watching Netflix so long as you go for a walk the next day.
With these caveats, he says that physical activity predicts better sleep and better sleep predicts more physical activity. Now the synergistic health effects of the two are known, it is yet another reason to get up and move as much as you can.
“These results give more reason for people to be physically active especially in the presence of any compromised sleep patterns,” Stamatakis says.
He adds that for health professionals who routinely deal with sleep problems, it is worth thinking about prescribing physical activity and understanding the breadth of the health benefits.
“There are the direct benefits on health outcomes, improving other behaviours like sleep and emerging evidence that physical activity mitigates the health risks that comes from other behaviours.”
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