- Older people who expend more energy on physical activity each week tend to have more gray matter in their brains than less active peers, according to a recent U.S. study.

Exercise, including activities like walking and running, is linked to preserved brain structure, even among individuals with mild and severe symptoms of mental decline, said coauthor James T. Becker, professor of psychiatry at the University of Pittsburgh School of Medicine.

"The volumes of these critical brain regions themselves predict the transition from normal cognition to some degree of impairment (mild or severe)," Becker told Reuters Health by email.

The researchers analyzed data from a long-term cardiovascular health study of 876 people, aged 65 years and older when they enrolled, who underwent cognitive assessments, volumetric brain imaging and answered questionnaires about their activities.

Researchers estimated weekly energy expenditure based on the questionnaires, and used total calories burned as a proxy for how much physical activity participants got. About half the participants were over age 78 when the brain scans measured their gray matter volume.

After accounting for other factors that could affect brain volume, including head size, age, sex, white matter lesions in the brain, mild cognitive impairment and Alzheimer's status, the researchers found that higher energy output in leisure time activities was associated with larger gray matter volumes in many regions of the brain, according to the results the Journal of Alzheimer's Disease.

Energy expenditure may be related to the release of a substance known as brain-derived neurotrophic factor (BDNF), which promotes the growth and differentiation of new neurons in the brain, Becker said.

The volume of gray matter in the brain typically shrinks with age. But past research has suggested that increased BDNF as a result of exercise may help to preserve a more youthful amount of gray matter.

"Activity, and the resulting sparing of brain structure, likely acts by supporting the brain and cognitive reserve," Becker said. "Thus, in the presence of a degenerative disorder such as Alzheimer's disease, the higher brain reserve extends the 'dementia free' time."

The more activity, the better, both for heart and brain health, Becker said.

"Our data suggest that it may not matter so much what we do, so long as we burn a lot of calories doing it," since the biggest impact was seen in the upper 25 percent of calorie expenditure, he said.

Being active in a social setting may be more effective than just walking on a treadmill alone, he said.

The study team acknowledges that for some participants reduced physical activity could be a result of an overall health decline associated with dementia. They also did not look at whether the greater gray matter volume associated with exercise had any protective effect on cognitive function.

"Physical activity is multidimensional, not only energy expenditure but also social, mental and emotional activities are involved," said Leandro Fornias Machado de Rezende of the department of preventive medicine at the University of Sao Paulo School of Medicine in Brazil, who was not part of the new research.

"In this sense, prevention of Alzheimer's disease through physical activity should be understood in a broad view," Rezende told Reuters Health by email.

SOURCE: bit.ly/1XmOHxy Journal of Alzheimer's Disease, online March 11, 2016.