Loneliness, too much television, and too little exercise could all raise the risk of developing dementia in later life, researchers say.

Having a complicated job and doing well at school have both been linked to a lower risk of dementia, while loneliness, excessive TV watching and low levels of physical activity could accelerate cognitive decline in later life.

The research was presented at an international conference on Alzheimer's in the US, which is also due to hear the results from trials on the first drug, Solanezumab, that is thought could halt the progression of the disease if caught early enough.

Delegates have already heard about a study which looked at 7500 people aged 65 and over in Sweden over 20 years.

Dementia rates were 21 per cent higher in those whose school grades were in the bottom fifth of the population, while they were 23 per cent lower among those with complex occupations involving data and numbers.

A second study saw 440 people aged 75 or over, also in Sweden, who were followed over nine years.

Those in the bottom fifth for school grades were found to have a 50 per cent increase in the risk of developing dementia over the course of the study.

Meanwhile, participants who reported complex jobs involving working with people had 60 per cent lower risk of dementia, but this was only true in women.

The Alzheimer's Association International Conference in Washington DC also heard how two-yearly assessments of more than 8300 over-65s participating in the US Health and Retirement Study found that the loneliest people involved also had accelerated cognitive decline - approximately 20 per cent faster - than people who were not lonely.

Another US study of more than 3200 adults aged 18 to 30 years over 25 years found participants who consistently reported low levels of physical activity (under 150 minutes of medium intensity exercise per week) or watched more than four hours of TV a day had significantly lower performance on the cognitive tests in middle age.

Those who reported both low physical activity and high television viewing were almost two times more likely to have poor cognitive function at the end of the study.

The conference is also expected to hear details of the first drug that could halt the progression of Alzheimer's disease, if caught early enough.

Trials have been ongoing into a new treatment called Solanezumab which appears to stop the degenerative brain disease in its tracks.