We don't give much thought to exercising for the sake of our brains (at least not until we're old enough to worry about Alzheimer's). But there's growing evidence that brains thrive on regular physical activity all the way from childhood to old age, say researchers at Deakin University's Institute for Physical Activity and Nutrition.
Childhood and adolescence may turn out to be critical for influencing brain health in later life, says Dr Helen Macpherson whose recent review of research linking physical activity to brain health was published in . although we need more research to determine this.
"Physical activity in the early years may set up long term behaviours that promote healthier brains over the lifespan. At any age it may be important to consider the benefits of a healthy lifestyle for maintaining a healthy brain, rather than focusing on the impact on our waistlines," she points out.
Besides paying off with a lower risk of dementia and Parkinson's disease in older age, a lifelong exercise habit – especially one that includes building strength – can benefit the brain at different life stages and even have direct effects on its structure and function.
These benefits may also be different depending on whether you're a child, a mid-lifer or over 60, says Macpherson.
In childhood, for instance, there's evidence that regular physical activity is good for young brains in ways that optimise the rapid development of brains at this age and may enhance learning.
"Imaging studies have found that in fitter children, the parts of the brain involved in attention and memory are larger and some studies have also found that more physically active teenagers have better academic outcomes," she says.
While there's no evidence that being more physically active protects against ADHD, some studies have also shown a link between increased physical activity and reduced symptoms of ADHD, as well as better cognition in children with ADHD, she adds.
Although we need more research to confirm this, being more physically active in your teens could also pay off in your 70s – physical activity in the teenage years was the strongest protective factor against cognitive impairment at 71, according to one study.
If you're in the mid-life zone between 40 and 60 these may be important years for building defences against dementia. Some of the brain changes that can lead to dementia can appear 20 years before someone has memory problems, Macpherson says. But regular exercise to prevent high blood pressure and type 2 diabetes – both of which can damage the brain's delicate blood vessels over time – can reduce the risk of dementia.
Yet protecting these blood vessels is only part of what exercise can do, especially when you combine aerobic exercise – like brisk walking, jogging or cycling – with resistance exercises that build strength.
"We used to think that we're born with all the brain cells we'll ever have but we now know that in the hippocampus – the part of the brain involved with memory – brain cells can regenerate throughout life and that exercise can promote new growth," explains Macpherson. "One benefit of resistance training is that it increases production of a growth hormone called IGF, (insulin-like growth factor) which can have a big influence on memory.
"IGF crosses into the brain and has two effects – it supports the growth of brain cells and also helps to insulate these cells and improve communication between them."
But the pace of this physical activity matters – and pushing up the heart rate to the point where it's hard to hold a conversation is more effective. The exceptions here may be tai chi and dancing which also appear to enhance cognition – although they're done at a slower pace, they do make the brain work harder, she says.
So what if you're an ageing couch potato who's made a lifelong habit of not exercising? It's not too late to start, stresses Macpherson. It's true that older adults who spend a lot of time sitting have an increased risk of dementia but even starting exercise later in life can slow brain shrinkage in people over 60.
"Studies have found that 70- to 80 year-olds who've been involved in moderate to vigorous physical activity for 150 minutes a week in the previous five or more years have a 40 per cent lower chance of developing dementia," she says.