Yuxian Ma, Olesya Ajnakina, Andrew Steptoe and Dorina Cadar
Dementia is a major health challenge that could steal away the opportunity for successful ageing of the population. A priority is to identify lifestyle factors that may reduce the risk of dementia, or even prevent it. The modifiable risk factors for vascular diseases — such as smoking, excessive alcohol intake, lack of physical activity, low intake of antioxidants and high intake of saturated fats — are receiving greater attention in this area because of their association with cognitive impairment and dementia in older people.
Obesity, which is linked to lifestyle behaviours, is an important modifiable risk factor. In our recent study carried out at the UCL Department of Behavioural Science and Health, we found that being overweight or obese was associated with a greater risk of developing dementia.
Obesity might increase the risk of dementia either through its direct influence on cytokines and adipocyte-derived hormones or indirectly through an associated increased risk of hypertension, high cholesterol levels, diabetes and other vascular risk factors. Despite inconclusive findings, several epidemiological studies have previously suggested that midlife obesity is associated with an increased risk of dementia in older ages. Some evidence has shown that higher body mass index (BMI) could be a marker for change in energy metabolism that could have an impact on dementia risk.
It has also been suggested that excess body fat increases the risk of dementia in later life through metabolic and vascular pathways, contributing to the accumulation of brain amyloid and lacunar lesions. However, conflicting findings from different studies have shown that the association between obesity at older ages and dementia remains unclear, and obesity may even be a protective factor for dementia among older people.
Our study used up to 15 years of data from the English Longitudinal Study of Ageing for 6582 people who comprised a nationally representative sample of the English population aged 50 years or older. We used BMI and waist circumference to determine obesity and abdominal obesity, respectively. Three different sources — doctor diagnosis, informant reports and hospital episode statistics — were used to ascertain dementia.
More than a quarter of the study participants (28.7%) were obese. The obese participants were more likely to have no educational qualifications, be smokers and be physically inactive; they also had a higher prevalence of hypertension and diabetes than the other participants.
We found that people who had a BMI in the obese range had a 31% higher risk of dementia than those with a BMI in the normal range. Interestingly, women with abdominal obesity had a 39% increased risk of dementia (independently of their age, educational status, marital status, smoking, APOE ε4 carrier status, diabetes and hypertension), compared with women without abdominal obesity, while this association was not found among the men.
Finally, obese participants who also had a high waist circumference had a 28% greater risk of dementia than those with normal BMI and waist circumference. In some populations, such as Asian Americans, waist circumference is a better indicator than BMI of relative disease risk. It may be that waist circumference also assumes greater value for estimating risk of obesity-related disease in midlife and older ages.
The evidence from our study suggests that maintaining a healthy BMI — and a healthy waist circumference — might be important to protect against dementia.
It is possible that the association between obesity and dementia might be mediated by other conditions, such as hypertension or anticholinergic treatments. Although not explored in this study, the question of whether there is an interactive effect between obesity and other risk factors in midlife, such as hypertension, diabetes and APOE ε4 carrier status, will be investigated in upcoming research.
An example is the investigation of how physical inactivity contributes to obesity and further dementia risk. Previous research showed that vigorous-intensity physical activity was associated with about a 20% lower risk of becoming overweight or obese, which could be an important precursor, depending on the initial BMI or body weight status. However, research into the potential for physical exercise to reduce the risk of dementia is continuing.
Taken together, these findings provide new evidence that obesity may have important implications in terms of preventing dementia or delaying its onset. Close monitoring of both BMI and waist circumference should start earlier in life for men and women, when they are aged in their 40s or 50s. Reducing weight to optimal levels — by adopting healthy and balanced patterns of eating, such as the Mediterranean diet, and appropriate physical exercise throughout the adult lifespan — is recommended.
Public health interventions designed to prevent obesity could also prevent onset or progression of dementia and would translate into public health and societal benefits for successful ageing.
Ma Y, Ajnakina O, Steptoe A, Cadar D. Higher risk of dementia in English older individuals who are overweight or obese. Int J Epidemiol 2020; 23 June. doi: 10.1093/ije/dyaa099.
Yuxian Ma is an MSc student at UCL Institute of Epidemiology & Health Care.
Olesya Ajnakina is a Research Associate in Genetic Epidemiology at UCL Institute of Epidemiology & Health Care and a Research Fellow in Precision Medicine in the Department of Biostatistics and Health Informatics at King’s College London.
Andrew Steptoe is a Professor of Psychology and Epidemiology and Head of the Department of Behavioural Science and Health at UCL Institute of Epidemiology & Health Care, and the Director of the English Longitudinal Study of Ageing.
Dorina Cadar is a Senior Research Fellow in Dementia at UCL Institute of Epidemiology & Health Care, working with an international multidisciplinary team to implement the Healthy Cognitive Ageing Project within the English Longitudinal Study of Ageing.