Regular exercise makes everything better: it's one of the only presently widely available strategies backed by a weight of evidence to show that it slows the biochemical changes of aging in humans. The other being calorie restriction, of course. Here are a couple of articles on the interaction of exercise and the common neurodegenerative condition of Alzheimer's disease:
"The benefits [of exercise] tend to be on the order of a 20 to 30 percent reduction in being diagnosed with Alzheimer's disease and other such diseases," Kramer said. "And again, this isn't universal but this is found in an increasing number of studies."
Kramer said researchers also tend to consider studies that show what exercise does for animals.
"There are improvements in the chemistry of the brain in terms of the molecules that protect the brain, increases in the number of connections between neurons, which allows us to encode new learning and memory, and even the birth of new neurons in one region of the brain that supports memory," he said.
This study follows on from previously published work by the research team which revealed that walking for two and a half hours per week for 24 weeks significantly improved memory and thinking ability in Australians who were 50 years and older and who reported problems with their memory.
Associate Professor Gerard Byrne, Head of Psychiatry at The University of Queensland and Director of the Older Persons Mental Health Service at the Royal Brisbane & Women's Hospital said: "It is becoming increasingly evident that regular physical exercise is not only important for physical health, but may also be an important part of maintaining a person's memory and thinking ability."
The main hypothesis of this study is that participants with mild to moderate Alzheimer's Disease who participate in the personalised training program for 24 weeks will experience significantly less difficulty with their memory and thinking ability by the end of the program than participants who undertook their usual exercise activity.
Bear in mind that in terms of its progression, risk factors, and even some of its biochemistry, Alzheimer's looks a lot like type 2 diabetes. If you are sedentary and fat, you are more likely to suffer from Alzheimer's disease. Notice that exercise doesn't just protect to some degree from degeneration, but if taken up in later life, it can also to some limited extent reverse current degeneration.
This is all far less than what we know to be possible in the future of medical science. But if you keep yourself fit, you stand a greater chance of living to see that future in good enough shape to benefit from it.