The Link Between Obesity and Incidence Of Dementia

Higher incidence of dementia tied to central obesity in English women.  

Dementia is attributed to numerous risk factors, with age being the strongest. Approximately 85% of dementia cases occur in individuals 75 years and older. Besides age, there are multiple modifiable risk factors associated with dementia; obesity is one of those risk factors. Overweight and obesity have become a public health priority worldwide due to the numerous health risks linked to them. Excess body fat is associated with the accumulation of brain lesions, changes in energy metabolism, and brain volume deficits, an early marker of neurodegeneration. However, the link between high body mass index (BMI) and dementia has never been clear. Different studies in older adults show conflicting results, leading to increased uncertainty in understanding the relationship between obesity and the risk of dementia in the elderly. On the other hand, some studies suggest that waist circumference (WC) is more related to dementia than BMI. 

A recent study in England examined the relationship between increased body weight and central obesity and the risk of developing dementia in adults 50 years and older, who were followed up from 2002 to 2017. The study aimed to prove that increased BMI and WC are associated with a higher incidence of dementia in the selected population during follow-up. A sample of men and women who participated in the English Longitudinal Study of Ageing and were dementia-free at baseline was selected. The population’s BMI was measured at baseline and divided into: 

• Normal weight (BMI 18.5-24.9) 
• Overweight (BMI 25-29.9) 
• Obese (BMI ≥ 30) 

Waist circumference was used to measure central obesity, which was defined as a WC of >88 cm in women and >102 cm in men.  

The researchers selected 6,582 participants for the BMI analysis and 5,538 participants for the WC analysis. Complete baseline data were collected, including dementia-free diagnosis, smoking status, BMI, WC, marital status, education, physical activity, apolipoprotein E-ε4, hypertension, and diabetes. Assessment of dementia was determined by: 

• A doctor diagnosis or reported by the participant 
• Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE) questionnaire 
• Records from the Hospital Episode Statistics identifying dementia patients  

Researchers identified the survival time as the time passed from the date of baseline interview of the participant to the date of dementia diagnosis, death, or the date of the most recent interview. The relationship between either baseline BMI or WC and the incidence of dementia was calculated using Cox proportional hazards regressions.  The joint association of BMI with the risk of dementia within WC strata was also assessed as follows: 

• Normal BMI + Normal WC 

• Normal BMI + High WC 
• Obese + Normal WC  
• Obese + High WC 

Four stepwise models were built according to the participants’ baseline characteristics to understand the role of covariates. According to the Cox proportional hazard regression, participants with baseline BMI of 30 or more were at a 35% higher risk of developing dementia (HR = 1.35, 95% CI 1.09–1.61, P < 0.05). Obesity was still associated with a higher risk of dementia when adjusted for education and marital status (HR = 1.31, 95% CI 1.04–1.58, P < 0.05), hypertension, and smoking status (HR = 1.34, 95% CI 1.07–1.61, P < 0.05).   

Additionally, women with high baseline WC (abdominal obesity) were at 39% higher risk of dementia (HR = 1.39, 95% CI 1.12–1.66, P < 0.05) compared with women with non-abdominal obesity. On the other hand, no association was observed among men (HR = 0.84, 95% CI, 0.55–1.19, P = 0.23).  Furthermore, participants with high BMI and high WC had a 1.28-fold increase in the risk of dementia (95% CI 1.03–1.53, P < 0.05). 

This study found an association between increased incidence of dementia and obesity in the elderly, especially in women with abdominal obesity. Nevertheless, further studies are needed given the rapidly growing rate of obesity worldwide. Identifying more modifiable risk factors associated with dementia is also a critical factor in preventing and managing dementia.  

Practice Pearls:  

• Multiple modifiable risk factors are associated with dementia, including obesity. 
• An English study found that there is a higher association between dementia and abdominal obesity in older women.  
• Further studies are needed to help identify high-risk individuals, which will ultimately reduce the risk of dementia.  

Yixuan Ma, Olesya Ajnakina, Andrew Steptoe, Dorina Cadar. Higher risk of dementia in English older individuals who are overweight or obese. Int J Epidemiol. 2020 June 23;dyaa099. 

Fairuz Afram, PharmD Candidate, University of Colorado, Skaggs School of Pharmacy and Pharmaceutical Sciences.