Meditation doesn't just relax the mind - it could also keep it young.
Regular sessions knock seven and a half years off the middle-aged brain, a study found.
The researchers said that the combination of intense concentration and relaxation may trigger the growth of new brain cells. Although they did not look at whether the meditators were also smarter, brain shrinkage is linked to Alzheimer's and other brain diseases.
The scientists scanned the brains of 50 American men and women who regularly meditated and 50 non-meditators.
The scans were fed into a computer programme that analysed the images and provided an age for each brain based on its physical condition.
The results were striking. In general, the non-meditators' brain ages and actual ages were the same.
But the meditators' brains were younger than their years, with the average 50-year-old having a brain that belonged in a 42 or 43-year-old's body. The benefits were particularly great for older meditators. For every year over the age of 50, a youth spent meditating knocked an extra year off brain age, the journal NeuroImage reports.
Researcher Christian Gaser, a neuroscientist at Jena University Hospital in Germany, said: "These findings seem to suggest that meditation is beneficial for brain preservation, with a slower rate of brain ageing throughout life."
Dr Gaser, who collaborated with US and Australian scientists, said it is not clear how meditation protects the brain but that it is possible that the 'intense mental processes' trigger the growth of new cells and connections.
The chemicals behind the feel-good sensation produced by meditation may also provide a boost.
However, he cautioned that those who meditate may lead healthier lifestyles in general.
It is also possible that some inherent difference in brain structure makes some people more likely to take up meditating. Those studied had practised various types of traditional meditation for an average of 20 years. Some did seven sessions a week or had more than 40 years' experience under their belt.
It isn't clear from the results if shorter bursts are also beneficial and if mindfulness, the "meditation-lite" technique that is becoming increasing popular, would have the same effect.
Interestingly, the scans revealed that meditation isn't the only way to keep the mind youthful - being female also helps. The women's brains were, on average, three years younger than the men's, whether they meditated or not.
Meditation is credited with improving health in numerous ways, from boosting the immune system to easing loneliness.
But some scientists believe it can be linked to unpleasant side-effects. One study, from the University of California, found that 63 per cent of people who had been on meditation retreats suffered at least one side-effect, ranging from confusion to panic and depression. Other research has flagged up twitches and fits as possible effects.