Increasing evidence suggests that being active can reduce a person's risk of dementia. Dementia is the name for the effects of Alzheimer's disease, stroke and other brain disorders. People may be considered to have dementia if they lose abilities in two or more areas such as memory and language skills. Other signs of dementia include a loss of ability to think clearly or control emotions. The World Health Organization says about thirty-five million people worldwide are living with dementia. Most studies of exercise and dementia depend on self-reporting -- asking people to report their levels of physical activity. Laura Middleton is a researcher at the Sunnybrook Research Institute and the University of Waterloo in Canada. She says there are problems with self-reporting. "It does a very good job of capturing jogging, or biking or tennis but does a relatively poor job of capturing low-intensity activity like walking or daily chores, which may also be important to the risk of cognitive impairment."So, Professor Middleton led a team in a new study to measure activity levels scientifically. The study lasted five years. Almost two hundred people took part. Their average age was seventy-five. The people drank small amounts of what scientists call doubly labeled water. It contains forms of hydrogen and oxygen that can mark, or label, these elements within body water. This way scientists can measure energy use through urine tests. The research showed that the greater the level of activity, the greater the reduction in the risk of memory loss and other cognitive impairment. The study is published in the Archives of Internal Medicine. In a second study, French researchers reported on exercise and dementia in women with heart risks like obesity or diabetes. Marie-Noel Vercambre of the Foundation for Public Health in Paris led the study. The findings suggest that even a half-hour walk at a quick speed every day could lower the risk of cognitive impairment.Dr. Eric Larson of the Group Health Research Institute in Seattle, Washington, wrote a commentary about the studies. "It's not obvious to people that exercise would make your brain healthier," he says, but the latest findings add to the evidence that it does.

For VOA Special English, I'm Carolyn Presutti. For more health news and to learn English, go to voaspecialenglish.com.