Randy Weadon walks six miles each day around the perimeters of his retirement community, Greenspring in Springfield. He also does crossword puzzles daily.

“During tax season, I walk around the halls and mentally do my income taxes in my head,” said Weadon, a retired Coast Guard officer. “If I had not started walking, I don’t know if I’d be alive. I am 86-and-a-half years old, but I don't feel that age at all.”

Geriatric experts say healthy lifestyle habits like regular exercise, eating a nutritious diet and brain challenges can help preserve mental health as we age.

“The one thing that I always tell my patients is that if you don’t use it, you lose it. I recommend crossword puzzles, mentally challenging games and reading, especially about current events,” said Dr. Lisa Calusic, a psychiatrist at Inova Behavioral Health Services in Alexandria, and an Arlington, resident.

Researchers Pamela Greenwood and Raja Parasuraman, professors at the Department of Psychology at George Mason University in Fairfax, have spent more than 20 years studying the way the human brain ages with a focus on Alzheimer’s disease. The two wrote a book, “Nurturing the Older Brain and Mind,” in which they explore ways middle-aged people can stave off mental deterioration.

“We know that if we can put off dementing illnesses, even by a year or two through lifestyle changes, that will reduce the number of people with Alzheimer’s disease, which is reaching epidemic proportions,” Parasuraman says.

The duo says that preventing and staving off mental deterioration is more important than ever now that workers are staying employed longer for economic reasons. Physical activity is an important tool as well.

“Exercise [is] the ‘lifestyle’ factor with the strongest effect,” said Greenwood. “A number of different research groups have found benefits of aerobic exercise on both brain structure and function, and on cognitive performance.”

Joel Martin, a professor of kinesiology at George Mason, agrees: “Regular exercise has been proven to slow the aging process,” he said. “People have their actual age, which they can't do anything about, and their biological age. Someone could be 40 years old, live a very inactive lifestyle and not eat very well, which may cause them to be closer to 60 in terms of their biological age. Vice versa: Someone who is 60 could be very active and eat a healthy diet and feel like they are much younger, perhaps a biological age closer to mid-40s.”

As an octogenarian, Weadon credits his sharpness to regular mental challenges. Martin agrees. “Regularly engaging in activities requiring cognitive function is important,” said Martin. “Most tissues in the body respond to stress placed on it by becoming stronger or adapting to handle the stimulus you place on it. If you lift weights, your muscles get bigger and stronger. If you don't do any sort of physical activity to stimulate your muscles, then they get smaller and become weaker. The brain is the same way, it needs regular stimulation to maintain its function.”

Experts also say not to rule out the importance of good nutrition. “The antioxidants in foods, especially fruits and vegetables, can help to preserve and protect tissues from damage that occurs as part of the natural aging process,” said Martin.