This is a plain English summary of an original research article
People who carry excess weight in midlife have an increased risk of developing dementia, suggests new research from the long-running English Longitudinal Study of Ageing (ELSA).
This study included people aged over 50 and followed them for an average of 11 years. Overall, those who were obese at the start of the study had a risk of dementia one-third higher (34% increase) than people with normal weight. Women who carried extra weight around their waistline were particularly vulnerable.
Rates of obesity are rising around the world. The findings emphasise the need for public health initiatives to prevent and manage the many factors that contribute to its development.
What’s the issue?
Dementia is one of the major health challenges of the 21st century. People with the condition typically have problems with memory loss, in processing information and in communication; these symptoms get worse over time. Dementia now accounts for one in eight deaths in England, and rates are expected to rise as the population ages.
Some known risk factors for dementia, such as genetics, are hard to address. Health experts, therefore, argue that we must identify risk factors that that can be modified. Obesity is believed to be one of these factors. Excess body fat increases inflammation which might contribute to the build-up of damaging proteins in the brain.
But the results of previous studies have been mixed and the association between obesity at older ages and dementia is unclear. Some results have even suggested that obesity could protect against dementia in elderly people.
This study analysed data on around 6000 people aged 50 or over in England. They are part of ELSA, a representative sample of older adults in England.
When they entered the study, people had their height and weight measured to give an approximate measure of body fat (body-mass index or BMI) and determine whether participants were obese, overweight or normal weight. A waist circumference of more than 88 cm in women, or 100 cm in men, was the measure of excess weight around the middle.
The study included 6582 people who were free of dementia. More than one in four (28.7%) were obese. After an average of 11 years, 453 (6.9%) had developed dementia. These people were more likely to have genes associated with dementia (APOE-E4).
The researchers took into account factors linked with both obesity and dementia, such as being physically inactive, having no educational qualifications, and having high blood pressure and diabetes. After correcting for these factors, the link between obesity and dementia remained.
The study found:
- those who were obese at the start of the study were 31% more likely to develop dementia than those of a normal weight
- women who carried weight around their middle had a 39% greater risk of dementia, but there was no link between waistline and dementia in men
- those with both obesity and a high waist circumference showed a 28% increased risk of dementia
- the increased risk of dementia could not be explained by differences in age, marital status, smoking behaviour or health conditions, including diabetes and high blood pressure.
Why is this important?
The study shows that carrying excess weight in middle-age is linked to an increased risk of developing dementia. This poses a serious public health problem as more than a third of adults are now overweight. It could help explain why the global rates of dementia almost tripled between 1975 and 2016.
The study demonstrated the link between obesity and dementia in a group of people over time. But an observational study cannot definitively conclude that obesity causes dementia. However, the authors say that it is the most likely explanation.
Unlike some recognised risk factors for dementia, such as genetics, obesity is considered a lifestyle factor that can be targeted and reduced by policy makers. In other words, the study provides another reason why people should be encouraged to eat a healthier diet and to take exercise, particularly as they age.
The study adds to the already overwhelming evidence that obesity is a growing and serious problem for individuals and society. It emphasises the need for campaigns, information and actions to convince people to maintain an optimal weight and adopt healthier lifestyles – eating a more balanced diet and taking regular exercise.
The link with dementia has not often been stressed in public health campaigns on healthy eating. Only a few countries have national dementia plans, and most focus on lifestyle factors rather than obesity. This study suggests that active intervention for reducing obesity should be targeted at the groups most at risk of dementia, including women carrying excess weight around the waist.
Further research is needed to explore outstanding questions about the link between obesity and dementia. In this study, the researchers recruited people aged 50 and over, many of whom were already obese. It would be helpful to track younger people for longer periods of time to see if becoming obese earlier in life has an impact on the risk of dementia. Longer follow up of the group in this study would also be helpful; it would increase the numbers of people with dementia and allow further analysis of early risk factors.
Studies are also needed to unpick the biological mechanism that relates obesity to dementia, such as the possible role of inflammation in allowing harmful proteins to pass into the brain.
You may be interested to read
The full study: Ma Y, and others. Higher risk of dementia in English older individuals who are overweight or obese. International Journal of Epidemiology. 2020;49:1353-1365
Review of the link between obesity and dementia: Anjum I, and others. Does Obesity Increase the Risk of Dementia: A Literature Review. Cureus. 2018;10:e2660
Funding: This project was funded by the National Institute on Aging, the Economic and Social Research Council, the Office for National Statistics, and an NIHR Post Doctoral Fellowship Award.
Conflicts of Interest: The study authors declare no conflicts of interest.
Disclaimer: NIHR Alerts are not a substitute for professional medical advice. They provide information about research which is funded or supported by the NIHR. Please note that views expressed in NIHR Alerts are those of the author(s) and reviewer(s) and not necessarily those of the NHS, the NIHR or the Department of Health and Social Care.