Obesity phenotypes in midlife linked to cognitive decline in old age

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Key study points:

1.     Obese-metabolically normal and obese-metabolically abnormal patients had similar cognitive levels during baseline and cognitive decline after 10 years

2.     In the metabolically abnormal group, the decline in global cognitive score (reasoning, memory and verbal fluency) was significantly greater in obese patients than in normal patients over the 10-year period (p = 0.03), even though there was no difference at baseline (p = 0.74).

Primer: Obesity is the number one growing health problem in the world. In 2008, the WHO estimated that over 500 million men and women were clinically defined as obese. Not only does it have implications on cardiovascular health, but obesity has also has been associated with many different diseases such as diabetes and increased risk of certain cancers. Recently, interest has turned to how obesity can affect cognitive function. Research has found that higher BMIs were associated with a poorer cognitive function and with a faster decline in cognitive performance in healthy men and women. Furthermore, it has been shown that obesity during middle-age is positively correlated with an increased risk of dementia. In this study, the authors wanted to distinguish whether an unfavorable metabolic profile regardless of BMI could be associated with decreases in cognitive capacity.

Background Reading:

1.     Cournot M, et al. Relation between body mass index and cognitive function in healthy middle-aged men and women. Neurology 2006;67:1208-1214.

This [prospective cohort] study: Data were collected from the Whitehall II cohort study, which included 10,308 British civil servants (67% men) in 1985. Only 6,401 individuals (71.2%) were included in this study. Individuals were stratified based upon their BMI (normal, overweight, obese) and metabolic profile (normal or abnormal). Individuals were defined as metabolically abnormal if they had 2 or more of hypertriglyceridemia, hypertension, diabetes or low HDL. The patients also underwent 3 series of cognitive testing between 1997-2009. These tests examined their memory, reasoning and verbal fluency and were aggregated to form a global score.

The study demonstrated that increased BMI was inversely correlated with cognitive functions in the metabolically normal group at baseline. However, there was no difference in cognitive capacity in the metabolically abnormal group. Over the 10-year period, the study revealed that a larger BMI was significantly associated with a decline in the global score only in individuals who were metabolically abnormal (p = 0.03).

In sum: The study was a large cohort study that examined the relationship between cognitive function, body mass index and metabolic profiles. The study concluded that BMI was positively correlated with a decline in cognitive function in patients with metabolic abnormalities, but obese patients had similar cognitive defects regardless of their metabolism. This study elucidates one of the many ongoing sequelae of obesity, metabolic disease and their interactions.  Plausible explanations for the associations seen include vascular disease as well as the accelerated aging seen in obese individuals.

There were several limitations to this study. As a cohort study, only associations, not causal relationships, could be inferred from the data. Furthermore, the data from this study is not representative of the British community since unemployed and blue-collar professionals were not included in the analysis. However, the strengths of study were its large sample size, and the comprehensive cognitive testing. Further research in this field should assess whether the duration of metabolic abnormalities affects the changes in cognitive function over time.

Click to read the study in Neurology

By JC and MP

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