Scientists from University College London (UCL), who conducted the research, say this risk may be particularly high for women who have abdominal obesity.
The researchers said the findings, published in the International Journal of Epidemiology, suggest keeping body mass index (BMI) under control could play a “significant role” in reducing the risk of dementia. Dr Dorina Cadar, from UCL’s Institute of Epidemiology and Health Care, and the senior author on the study, said: “These findings provide new evidence that obesity may have important implications in terms of dementia risk.
“Both BMI and waist circumference status should be monitored to avoid metabolic or vascular complications.
“Hence, reducing weight to optimal levels is recommended by adopting healthy and balanced patterns of eating, such as the Mediterranean diet, appropriate physical exercise and reduced alcohol consumption throughout the course of the entire adult life span.”
The research team analysed data gathered from more than 6,500 people who were part of the English Longitudinal Study of Ageing, a representative database of over-50s in England that stores information about health, wellbeing and economic circumstances in several time periods.
The participants did not have dementia at the start of the study. Compared with those with BMIs at normal levels (between 18.5 to 24.9), the team found people whose BMI was 30 or higher at the start of the study period had a 31 per cent greater risk of dementia, at an average of 11 years later.
Women with abdominal obesity, based on waist circumference, were found to have a 39 per cent increased risk of dementia compared with those who were not obese.
When BMI and waist circumference were viewed in combination, obese study participants of either gender showed a 28 per cent greater risk of dementia compared with those in the normal range, the researchers said.
UCL Professor Andrew Steptoe, director of the English Longitudinal Study of Ageing, said: “Dementia is one of the major health challenges of the 21st century that could threaten successful ageing of the population.
“Our findings suggest that rising obesity rates will compound the issue.”