Experts said combining healthy habits boosts the chances of staving off conditions like Alzheimer’s disease.
They created a chart of six beneficial behaviours, with a healthy diet deemed as eating at least seven out of 12 food groups (fruits, vegetables, fish, meat, dairy, salt, oil, eggs, cereals, legumes, nuts and tea).
Taking part in writing, reading, playing cards or other games at least twice a week is another area of healthy behaviour.
Other areas are drinking no alcohol, exercising for more than 150 minutes a week at moderate intensity or more than 75 at vigorous intensity, and never having smoked or being an ex-smoker.
Social contact at least twice a week was the sixth healthy behaviour, such as visiting loved ones, attending meetings or going to parties.
Researchers analysed data from 29,000 adults aged at least 60 (average age 72) with normal cognitive function who were part of the China Cognition and Aging Study.
At the start of the study in 2009, memory function was measured using tests and people were checked for the APOE gene – the strongest risk factor gene for Alzheimer’s disease.
Follow-up assessments were then carried out over the next 10 years.
The people in the study were analysed according to how many healthy behaviours they had, with those with four to six healthy behaviours being put in the most favourable group.
After accounting for a range of factors likely to affect the results, the researchers found that each individual healthy behaviour was associated with a slower-than-average decline in memory over 10 years.
A healthy diet had the strongest effect on slowing memory decline, followed by cognitive activity (writing, reading, playing games) and then physical exercise.
People with the APOE gene who had healthy lives on the whole also experienced a slower rate of memory decline than those with APOE who were the least healthy.
Overall, people with the healthiest (four to six healthy behaviours) or even average healthy lifestyles (two to three healthy behaviours) were almost 90% and almost 30% less likely to develop dementia or mild cognitive impairment relative to those who were the least healthy.
Writing in the British Medical Journal (BMJ), the team said more research is needed but concluded that “a healthy lifestyle is associated with slower memory decline, even in the presence of … APOE.”
Dr Susan Mitchell, head of policy at Alzheimer’s Research UK, said: “Too few of us know that there are steps we can all take to reduce our chances of dementia in later life.
“This is a well-conducted study, which followed people over a long period of time, and adds to the substantial evidence that a healthy lifestyle can help to support memory and thinking skills as we age.
“While the genes we inherit play an important part in our chances of dementia as we age, importantly, this research found a link between healthy lifestyle and slower cognitive decline even in people who carry a key Alzheimer’s risk gene.
“So it’s not either/or – this study suggests making lifestyle changes can help all of us reduce our risk, whatever genetic cards we’re dealt…
“There is no sure-fire way to prevent dementia – nobody brings it on themselves or is ever to blame for a disease like Alzheimer’s. The best we can do is improve our chances of living longer with better cognitive health.”
Alzheimer’s disease affects an estimated one in 14 people over the age of 65 and one in six people over 80.
The experts included staff from the National Centre for Neurological Disorders in Beijing.
