Exercising for at least 45 minutes several times a week can boost brain power in the over-50s, research suggests.
Several types of exercise help improve thinking, attention, memory skills and executive function (mental skills that help people get things done), a new analysis of 39 studies found.
Aerobic exercise such as swimming, cycling and jogging; resistance training including weights, multicomponent training (such as combined aerobic and weight training) and tai chi were all "similarly effective", experts writing in the British Journal of Sports Medicine said.
"Positive benefits to cognition occurred with an exercise intervention that included tai chi, or resistance and aerobic training, prescribed either in isolation or combined," they said.
And the benefits were irrespective of the current state of an individual's brain health, they added.
An ideal exercise "prescription" for the over-50s would include an "exercise programme with components of both aerobic and resistance-type training, of at least moderate intensity and at least 45 min per session, on as many days of the week as possible", the team from the University of Canberra in Australia said.
While only a small number of studies examining tai chi were included, the team said the findings on this were "important" as it may be the type of exercise chosen by less mobile people who cannot take on more challenging exercise.
While previous studies have shown that exercise helps boost brain power, the researchers said theirs is the most comprehensive study to date.
Dr Allison Smith, head of strategy and development for Royal Voluntary Service, said: "Resistance-based exercise is critical as we get older, particularly following a period of illness, surgery or accident as we are most at risk of losing of muscle mass and strength.
"We know from a growing body of evidence that improved mobility helps older people to live more independent, fulfilled and happier lives".
She said the charity's own eight-month project with 44 people with an average age of 81 showed that resistance training improved physical function and well-being.
It more than halved the numbers reporting they were lonely, improved happiness and reduced the number saying they were extremely or very anxious.
Dr Doug Brown, director of research at Alzheimer's Society, said: "The benefits of regular exercise to keep a sharp mind are becoming clearer.
"Previous studies show that people who exercise are less likely to develop dementia, but more research is needed to find out exactly what type and how much exercise is best to help reduce your risk of the condition."
He said the present study did not aim to look specifically at dementia but did show that exercise improved performance on tests of thinking skills.
Dr Justin Varney, from Public Health England, said: "Any physical activity is good for your brain and your body. Whilst every 10 minutes of exercise provides some benefit, doing 150 minutes a week cuts the chances of depression and dementia by a third, and boosts mental health at any age.
"You can incorporate more aerobic activity into your daily routine by cycling or walking to work, and improve your strength with simple resistance exercises, like carrying heavy shopping bags. Doing both aerobic and strengthening exercises lead to a greater variety of health benefits."