Previous studies have shown that being overweight and obese can increase the risk for developing cognitive decline, mild cognitive impairment, and dementia in later life. This is particularly true for middle aged individuals, as it is believed that the effects of obesity on cognition occur over a prolonged period of time. Obesity increases the risk of developing several other health problems and these include type 2 diabetes, high blood pressure, high cholesterol, and arthritis. As a result, obesity is considered by some in the healthcare field to be a risk factor for cardiovascular disease. Despite this, there have been some recent studies that have shown that obese individuals who do not have the other cardiovascular risk factors are not at increased risk of heart disease or stroke. However, the evidence that metabolically normal obese individuals do not carry increased cardiovascular risk is not conclusive. We have previously discussed that individuals with type 2 diabetes have increased risk for developing cognitive decline and dementia. The effects of obesity on cognitive function and the development of dementia are only now being studied.
Researchers, lead by Dr. Archana Singh-Manoux from the Institut National de la Santé et de la Recherche Médicale in France, have found that individuals with obesity in midlife exhibit accelerated cognitive decline when compared to normal weight individuals. The results of their research were published online in the journal Neurology. The researchers studied 6,401 adults aged 39 to 63 years who were enrolled in the Whitehall II cohort study. The study participants were followed longitudinally for a 10 year period and were assessed according to body mass index (BMI), cognitive function, and metabolic status (high triglycerides, high blood pressure, diabetes, and high density lipoprotein). In the obese group, the cognitive function at baseline and throughout the study showed similar rates of decline in both the metabolically normal and abnormal subgroups. In the metabolically normal group, global cognition declined over the 10 year period similarly in the normal, overweight, and obese groups. However, in the metabolically abnormal group, the rate of decline in global cognitive function was faster in the obese group when compared to normal weight individuals.
The authors wrote, “There is considerable evidence from single studies and meta analyses to suggest that obesity in midlife is associated with poorer cognition and greater risk of dementia in later life. The extent to which these associations are causal remains unclear …given the rapid increase in obesity levels globally, it is important to estimate its impact on health from a public health point of view. If the concept of [metabolically healthy obese] holds, then the estimation of the negative impact of obesity on health needs to be revisited. Our data suggest no such heterogeneity in the impact of obesity on cognitive performance in early old age, because obese individuals who are otherwise metabolically healthy have a risk of poor cognition similar to that of their obese metabolically unhealthy counterparts”. The authors concluded, “In these analyses the fastest cognitive decline was observed in those with both obesity and metabolic abnormality”.
The investigators theorized that the accelerated cognitive decline observed for obese individuals could be due to vascular pathologies such as white matter lesions, lacunar infarcts, hypoperfusion, blood vessel inflammation, and cerebrovascular disease. Some other possible mechanisms for the observed accelerated cognitive decline were theorized to be secretions of adipose tissue containing leptin and adiponectin, which can adversely affect the brain with age. Ultimately, this study shows that even obese individuals who do not have any metabolic disorders, such as high lipids, diabetes, or high blood pressure, are at increased risk of cognitive decline and dementia in later life. This is another reason to lose weight and attempt to establish a normal BMI – optimal brain function is dependent on a normal body weight.
Archana Singh-Manoux et al. “Obesity phenotypes in midlife and cognition in early old age: The Whitehall II cohort study” Neurology August 21, 2012 vol. 79 no. 8 755-762 doi: 10.1212/WNL.0b013e3182661f63