Exercise results in a healthier brain, prevents cognitive decline and in some studies has cut the incidence of Alzheimer's disease in half, says an eminent Harvard University professor of psychiatry.

A big study in the early 1990s showed exercise was one of three major factors - with low caloric content and continuous learning - that prevented the onset of the progressive brain disease, said Dr. John J. Ratey.

“;It threw a little wrench into thinking because no one could explain it,”; he said in an interview. “;It was by far the most powerful of preventive factors.”;

A clinical researcher and prolific author of papers and books, Ratey gave a series of talks in Honolulu last week about the huge benefits of exercise for health and fitness, especially for children and seniors.

He said “;God's gift to us”; is BDNF (brain-derived neutrophic factor), a protein that affects areas essential for memory and thinking.

He calls it “;Miracle Gro”; for the brain: “;It acts like fertilizer. Things that challenge our brain like exercise, Sudoku, crossword puzzles, even low caloric intake, cause our brain cells to get stronger and more resilient and actually make things work better.”;

Author of “;Spark - The Revolutionary New Science of Exercise and the Brain,”; Ratey said the revolution is that “;exercise causes our brain to get healthier and stay healthier.”;

Studies have shown that even in middle age, people who hadn't been exercising and started three times a week could push back cognitive decline 10 to 15 years, he said.

“;The ability of the brain to maintain itself and still be active and do what it is supposed to do - learning, having memories, being able to recover memories, being able to think through problems - all of that is maintained through a steady diet of exercise and play.”;

Tai chi, yoga and any of the martial arts are very good for balance and concentration, he said, noting a Nintendo Wii fitness video game is being used in many assisted living facilities to improve balance.

Ratey practices what he preaches. He works out for an hour every morning at a gym, does weight training and has a personal trainer on Saturdays. He played squash three times a week for 25 years until ruining his shoulder but still skis, he said.

He tried paddle boarding in Waikiki and on the North Shore but said, “;Every wave that would come along, boom. It knocked me off. I thought my balance was pretty good but I have to go back and work harder.”;