Excess visceral fat tissue generates chronic inflammation via a range of mechanisms, including an accelerated creation of senescent cells. Most of the commmon age-related conditions have an inflammatory component, and thus people who are overweight or obese suffer a raised risk of age-related disease, higher lifetime medical costs, and a shorter life expectancy. This is illustrated here in yet another study showing that greater BMI and waist circumference (the latter a better measure of visceral fat burden) correlate with greater risk of dementia.
Researchers collected data from 6,582 people in a nationally representative sample of the English population aged 50 years and over, from the English Longitudinal Study of Ageing. Three different sources were used to ascertain dementia: doctor diagnosis, informant reports and hospital episode statistics. It was found that people whose BMI was 30 or higher (at obese level) at the start of the study period had a 31% greater risk of dementia, at an average follow-up of 11 years, than those with BMIs from 18.5-24.9 (normal level).
There was also a significant gender difference in the risk of dementia associated with obesity. Women with abdominal obesity (based on waist circumference) had a 39% increased risk of dementia compared to those with a normal level. This was independent of their age, education, marital status, smoking behaviour, genetics (APOE ε4 gene), diabetes and hypertension - and yet this association was not found among the male participants. When BMI and waist circumference were viewed in combination, obese study participants of either gender showed a 28% greater risk of dementia compared to those in the normal range.
Prior evidence suggests that obesity might cause an increased risk of dementia via its direct influence on cytokines (cell signalling proteins) and hormones derived from fat cells, or indirectly through an adverse effect on vascular risk factors. Some researchers have also suggested that excess body fat may increase dementia risk through metabolic and vascular pathways that contribute to the accumulation of amyloid proteins or lesions in the brain. "It is possible that the association between obesity and dementia might be potentially mediated by other conditions, such as hypertension or anticholinergic treatments. While not explored in this study, the research question of whether there an interactive effect between obesity and other midlife risk factors, such as hypertension, diabetes, and APOE ε4 carrier status, in relation to dementia will be investigated in upcoming work."