10 million people are diagnosed with a form of dementia each year, which may triple the total number of patients by 2050, CNN reports.
The health body has published its first guidelines to reduce the risk of cognitive decline and dementia - a condition that affects nearly 350,000 Australians and 50 million people around the world. There's also little evidence that cognitive training has much benefit, and no evidence that treating depression or hearing loss reduces dementia risk.
Although age is the top risk factor, "dementia is not a natural or inevitable effect of aging", it says.
The scientific evidence gathered to draw up the guidelines, Tedros said, "confirm what we have suspected for some time, that what is good for our heart, is also good for our brain". Don't smoke. They're among the commonsense habits the World Health Organisation (WHO) says may keep your brain sharp and shield you from dementia as you age.
"There is now no evidence to show that taking these supplements actually reduces the risk of cognitive decline and dementia, and in fact, we know that in high doses these can be harmful", said the WHO's Dr Neerja Chowdhary.
"Genetic predisposition plays an important role in many people's risk of diseases like Alzheimer's, and while we cannot change the genes we inherit, taking the steps outlined in this report can still help to stack the odds in our favour".
Dementia is now incurable, but studies show a variety of things can affect the odds of developing it.
"Dementia carers are very often family members who need to make considerable adjustments to their family and professional lives to care for their loved ones", said Devora Kestel, director of the department of mental health and substance abuse at WHO.
The agency said its new recommendations could provide the key to delaying or slowing cognitive decline or dementia.
New guidelines based on analysis of decades of research found that physical inactivity, smoking, eating an unhealthy diet and drinking excessive alcohol significantly increased the threat of diseases such as Alzheimer's.
Medical conditions like hypertension, diabetes, high cholesterol, obesity and depression are also associated with increased risk of developing dementia, World Health Organization said.