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We'd all like to about keep our brains as sharp as possible as we age. But what are the best ways to do this, asks Michael Mosley.

Ask anyone over the age of 40 what worries them most about growing older and the answer that comes back is almost always the fear of losing your memory. I worry about the fact that I find it harder than ever to remember names and that without my phone to remind me, I would forget many of my daily appointments.

There are some fairly obvious things to avoid if you want to maintain good brain health. These include smoking, becoming overweight and developing Type 2 diabetes. But what can you positively do to enhance your brain?

Find out more Trust Me I'm A Doctor, with Michael Mosley, Gabriel Weston and Dr Chris van Tulleken, is broadcast on BBC Two at 20:00 BST on Wednesday 15 July Watch the programme on BBC iPlayer

With the help of Newcastle University we recruited 30 volunteers to find out.

Before we began our experiment all our volunteers were subjected to a barrage of tests that measured things like memory, ability to problem solve and general psychomotor speed (reaction times).

Everyone was then fitted with an activity monitor to measure how much and when they were moving.

The volunteers were then randomly allocated to three groups and asked to do a particular activity for the next eight weeks.

One group we simply asked to walk briskly, so that they were just out of breath, for three hours a week. The idea is that walking - in fact any form of vigorous exercise - will keep your brain fed with lots of oxygen-rich blood. This was not a popular choice with some.

"Walking is my least favourite activity," sighs Ann. (Newcastle does have punishingly steep hills.)

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The second group were asked to do puzzles, such as crosswords or Sudoku. Again they had to do it for three hours each week. The reasoning behind this approach is that your brain, like a muscle, benefits from being challenged. Use it or lose it.

The final group were asked to stare at a naked man for three hours a week. Or, to be more accurate, they were asked to take part in an art class which also happened to involve drawing a naked man, Steve.

The results

By the end of our eight-week trial almost everyone in the walking group noticed a big improvement in their general health - how much easier they found managing a particular hill.

Some of the puzzler group had found the puzzles hard at first, but by the end of the eight weeks many were hooked and swapping Sudoku tips.

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The most enthusiastic group, however, was undoubtedly the art class. Although a few found attending a class once a week daunting, all of them commented on how much they enjoyed it.

"I have become a compulsive drawer of everything," says Simone. "I have been out to buy myself some pastel pencils and even a book on 'How to'."

So, art equals pleasure, but which group enjoyed the greatest improvements in brain power?

Our scientists redid their battery of cognitive tests and the results were clear-cut. All the groups had got a bit better, but the stand-out group was those who had attended the art class.

It seems the naked man, Steve, had made a big impression.

Image caption Gabriel Weston with life model Steve

But why should going to an art class make a difference to things like memory? Clinical Psychologist Daniel Collerton, one of our experts from Northumberland, Tyne and Wear NHS Trust and Newcastle University, says that part of the benefit came from learning a new skill. "Learning something new," he says, "engages the brain in ways that seem to be key. Your brain changes in response, no matter how many years you have behind you."

Learning how to draw was not only a fresh challenge to our group but, unlike the puzzlers, it also involved developing psychomotor skills. Capturing an image on paper is not just intellectually demanding. It involves learning how to make the muscles in your hand guide the pencil or paintbrush in the right directions.

An additional benefit was that going to the art class meant that for three hours a week they had to stand while drawing or painting. As we've shown before on Trust Me I'm a Doctor, standing for longer periods is a good way of burning calories and keeping your heart in good shape.

The art class was also the most socially active, another important thing to bear in mind if you want to keep your brain sharp. This group met regularly outside class, were keen to exchange emails and there was a definite social aspect to this intervention.

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All of which meant that this group enjoyed a triple benefit when it came to boosting brain health. One of our volunteers, Lynn, says that learning to draw had produced other, unexpected benefits.

"Part of my job involves writing and pitching bids, which is a difficult and lengthy process," she explains. "I am dyslexic which is an added hurdle. But having done the art class I found that my writing now flows and my ability to concentrate has improved. It seems to have opened my mind. I'm not sure I can explain it properly, I just know it made a difference."

It is likely that any group activity which involves being active and learning a new skill will help boost your brain. Ballroom dancing, anyone?

Trust Me I'm A Doctor begins its new series on BBC Two at 20:00 BST on Wednesday 15 July - or watch on BBC iPlayer

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