Professor Carol Brayne, from Cambridge University's Institute of Public Health, said Alzheimer's could be tackled simply by becoming more active:
Simply tackling physical inactivity, for example, will reduce levels of obesity, hypertension and diabetes, and prevent some people from developing dementia as well as allowing a healthier old age in general - it's a win-win situation.
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The talks descended into crisis on Friday when Canada's trade minister Chrystia Freeland walked out of meetings.
Police in New York are still investigating what the substance is and whether it could be harmful.
The Sherlock actor made the comment while he received an award for his humanitarian work.