To stave off dementia, should you sleep an extra 30 minutes or exercise?

It’s hardly surprising to hear that six hours of sleep and 30 minutes of moderate exercise are the foundations of a healthy life, helping minimise our risk of developing diseases, such as dementia. In a perfect world, we’d get both every day.

But we don’t live in a perfect world. Realistically, life happens, and we need to prioritise our time, often being forced to decide whether to sleep in or get up and move our body.

Surely, it’s better to do the latter? Well, it depends.

A new study from Monash University has found that the optimal combination of sleep and exercise to ward off dementia depends on how much sleep you get in the first place.

Most of the existing research into dementia prevention looks at factors such as sleep and exercise in isolation. This is why researchers – led by Professor Matthew Pase and Dr Stephanie Yiallourou from the Turner Institute for Brain and Mental Health and School of Psychological Sciences – wanted to investigate the relationship between sleep and physical activity across the full span of a person’s day, considering the reality that increasing time spent doing one will come at the expense of the other, and how that might affect dementia risk.

It’s important that we think about our life more holistically, and the trade-offs we make each day, Pase explains. “It’s all very well for a doctor to say you could exercise more, but at what cost?”

For the study, published in BMC Medicine, researchers examined the sleep and exercise data of 87,490 participants. They tracked their activity over 24 hours for seven days, and then kept tabs on them for roughly eight years to determine who went on to develop dementia. The average age of the participants was 63.

“It’s all very well for a doctor to say you could exercise more, but at what cost?”

Professor Matthew Pase

They found that individuals with very short sleep, high inactivity and low moderate to vigorous activity had the highest rates of dementia and evidence of accelerated brain ageing on MRI.

The findings reiterate the importance of considering lifestyle behaviours together when it comes to dementia prevention, says Associate Professor Stephanie Rainey-Smith, from the Centre for Healthy Ageing at Murdoch University and deputy director of research at Alzheimer’s Research Australia.

“We need to think of them as being pieces of a puzzle that need to be put together in order to optimise our chance of healthy ageing and decreasing likelihood of developing dementia,” she says.

And this puzzle will look different for everyone.

How to stave off dementia when you’re a short sleeper

To figure out your optimal ratio, we should start with a baseline understanding of our sleep.

For instance, are you a short sleeper (who gets less than six hours of sleep) or a normal sleeper (who gets between six and nine hours)?

If you’re a short sleeper, the study found that increasing sleep duration was associated with a lowering of dementia risk when at the expense of inactivity or light activity, but not when at the expense of moderate to vigorous physical activity.

Specifically, increasing sleep by 30 minute instead of engaging in inactivity or light activity was associated with a 9 per cent and 19 per cent reduction in dementia risk, respectively.

This may seem counterintuitive; if you’re going to sleep more, you’d think it’s better to do so in place of doing nothing, compared to doing some light activity.

But Pase and the researchers hypothesise that although inactivity sounds bad, it’s not necessarily. “People could be reading a book, which is stimulating for the brain, or sitting having dinner with friends, which has some social element, which is good for the brain,” he says.

When you’re a normal sleeper

For those who get a normal amount of sleep, the effect of increasing or decreasing sleep duration on dementia risk differs based on what you’re substituting it for.

Increasing sleep at the expense of time spent doing moderate to vigorous exercise was associated with greater dementia risk, while increasing moderate/vigorous exercise at the expense of sleep was associated with lower dementia risk.

What’s missing from the findings, Pase says, is considerations like sleep quality.

“Sleep is obviously way more complex than just the duration, and there are elements of quality and regularity and all kinds of things which we didn’t delve into in this particular study.”

Rainey-Smith agrees, adding that she’d like to see more work done with younger people.

“It’s really important that all of us in the research field look much earlier in the piece, well before someone has overt symptoms,” she says.

Make the most of your health, relationships, fitness and nutrition with our Live Well newsletter. Get it in your inbox every Monday.