People who are physically and mentally active in middle age may reduce their risk of developing dementia decades later, the results of a new study suggest.

Swedish researchers followed the progress of 800 women with an average age of 47, for 44 years. All were asked at the beginning of the study about their physical and mental activities.

Mental activities included intellectual activities such as reading and writing, manual activities, such as sewing and artistic activities, such as singling in a choir or attending concerts.

Participants were given scores based on how often they undertook mental activities and based on this, they were divided into two groups - no/low activity and high activity.

When it came to physical activity, such as walking, running, cycling, swimming or taking part in competitive sports, the participants were divided into two groups - active and inactive.

The active group ranged from light physical activity, such as walking, for a minimum of four hours per week, to regular intense exercise several times a week.

During the study, almost 200 of the participants developed dementia, with over half developing Alzheimer's disease.

The study found that those who undertook a high level of mental activities were 46% less likely to develop Alzheimer's disease and 34% less likely to develop dementia overall compared to women who undertook low levels of mental activity.

Meanwhile, those who were physically active were 56% less likely to develop mixed dementia than inactive women. Mixed dementia is a condition in which abnormalities characteristic of more than one type of dementia occur at the same time.

The findings stood even when other factors that could affect dementia risk were taken into account, such as smoking, diabetes and high blood pressure.

The researchers also ran the results again after excluding women who developed dementia about halfway through the study. This was to rule out the possibility that these women may have unknowingly been in the early stages of dementia at the beginning of the study, with less participation in the activities as an early symptom.

However, the results were similar, except that physical activity was then associated with a 34% reduced risk of dementia overall.

"These results indicate that these activities in middle age may play a role in preventing dementia in old age and preserving cognitive health. It's exciting as these are activities that people can incorporate into their lives pretty easily and without a lot of expense," commented the study's author, Dr Jenna Najar, of the University of Gothenburg.

Details of these findings are published in the journal, Neurology.