Stopping smoking, a healthy diet and avoiding harmful use of alcohol were also among the recommendations of the WHO’s report, entitled “Risk reduction of cognitive decline and dementia”.
Treatment for hypertension, high cholesterol and diabetes also lower the risks, the report said.
Neerja Chowdhary, a WHO expert, said that the study had not looked at smoking marijuana and did not include environmental factors, although there was some evidence of a link with pollution, and there was too little evidence of a link with poor sleep to include it in the recommendations.
Vitamins and supplements were not useful and could even be harmful if taken in high doses, she said.
But there was less evidence that cognitive training or social activity would stave off the onset of dementia, and insufficient evidence that antidepressant medicines or hearing aids could help.
Dementia affects around 50 million people globally, with nearly 10 million new cases annually a figure that is set to triple by 2050, while the cost of caring for dementia patients is expected to hit $2 trillion by 2030, WHO Assistant Director-General Ren Minghui wrote in the report.