Hitting the gym and kicking out the butts could prevent millions of cases of Alzheimer's disease worldwide, a new study released on Tuesday suggests.

The report, presented at a Paris conference and published online by the British journal Lancet Neurology, looked at how seven risk factors account for up to half of the 35 million cases of Alzheimer's worldwide.

Researchers used a mathematical model to estimate how the seven risk factors affect the likelihood of someone developing the disease. The factors are:

• Smoking
• Depression
• Low education
• Diabetes
• Too little exercise
• Obesity
• High blood pressure in mid-life

In the U.S., inactivity has the biggest impact on the number of cases because a third of the population is sedentary, Deborah Barnes, an associate professor of psychiatry at the University of California and lead author of the study, told The Associated Press.

Depression is also a key factor, followed by smoking and high blood pressure.

Worldwide the biggest risk factor was low education, because illiteracy and poor nutrition is so common, the study said.

"Education, even at a young age, starts to build your neural networks," so being deprived of it means less brain development, Barnes said.

Smoking and not exercising are the next leading risk factors around the world.

The mind-robbing disease has no cure and there's no treatment to reverse the effects of Alzheimer's, so preventing it is crucial.

"Prevention is a particularly attractive option given the state of therapy. That's why there's so much interest in it," William Thies, the Alzheimer's Association's chief scientific officer, said.

The study found that reducing these seven risk factors by 25 per cent could mean 3 million fewer cases of the disease in the world over the next 40 years and reducing by 10 per cent could translate to 1.1 million fewer cases.

"It gives us a little bit of hope about things we could do now about the epidemic that is coming our way," Barnes said.

Alzheimer cases are expected to triple to about 106 million worldwide by 2050.

With files from The Associated Press