Keeping physically fit can reduce age-related changes in the brain, new research reveals.

Researchers at the University of Arizona analyzed aerobic fitness levels and neural differences among 123 men and women between the ages of 50 and 89, and found a clear relationship between exercise and healthier aging brains.

"Better brain aging is associated with better physical fitness," said psychologist Gene Alexander who led the study team.

Our brains shrink as we age, as genes related to brain functioning become less active. Neural circuitry goes slightly haywire as nerve sheaths become thinner. Other recent research has shown that aerobic exercise can aid cognitive functioning as we age, and the new findings confirm the relationship between being physically fit and fewer changes to an aging brain.

Those over the age of 60 worldwide are expected to outnumber the young by 2025, according to United Nations population figures. An estimated 2 billion people are currently coping with effects of aging.