Cognitive decline: being overweight damages the brain

Excess weight can also affect cognitive function, with inflammation possibly playing a role, a new Canadian study has found. People with excess body fat scored lower for processing speed in cognitive tests. Physical exercise, which increases blood flow to the brain, can help limit cognitive impairment, even in people with a high body mass index (BMI).

It is widely known that excess body weight is associated with many health problems. Now researchers have found a link between adiposity, having too much fatty tissue in the body, and cognitive impairment.

On the occasion of a new study, published in the JAMA Network Open, Canadian researchers determined the adiposity of more than 9,000 participants. They measured both total body fat and visceral adipose tissue (VAT): the fat that is mostly found around organs in the abdominal cavity.

Previous studies have already associated visceral fat with increased morbidity and a higher risk of mortality. Visceral fat increases the risk of many conditions, such as:

– heart disease, including heart attacks
– type 2 diabetes
– high blood pressure
– strokes
– breast cancer and colorectal cancer
– Alzheimer’s disease.
This latest study suggests that excess fat can have mental as well as physical effects.

Slower cognitive tests

All participants took two cognitive tests, the Numerical Symbol Substitution Test (DSST) and the Montreal Cognitive Assessment (MoCA), to assess a range of cognitive functions. The researchers adjusted the scores for cardiovascular risk factors, education level and vascular brain damage detected by MRI, which is known to be associated with cognitive impairment. The researchers found that higher total fat mass and VAT were both significantly associated with lower DSST and MoCA scores. This association was stronger for the DSST, which assesses processing speed, than for the MoCA, which is a multidimensional cognitive test.

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Compared to people in the lowest group (25%) of adiposity, the performance of people in the highest group was equivalent to three additional years of cognitive aging.

These results are not unexpected, it is already known that greater adiposity and body fat are associated with an increase in cardiovascular risk factors and that these are associated with an increased risk of cognitive decline. This study found that excess adiposity was a risk factor for lower cognitive scores, independent of cardiovascular risk factors, education level, and vascular brain injury.

This study reinforces the findings of a previous study of older adults in Dublin, which found an association between adiposity, particularly central adiposity, and reduced cognitive function.

Effect of inflammation on the brain

The authors suggest that inflammation may play a role in cognitive impairment in overweight or obese people. A recent study of over 15,000 people found elevated levels of plasma C-reactive protein (an inflammatory marker) in people with a high BMI and high waist-to-hip ratio. Pro-inflammatory cytokines from adipose tissue could also potentially contribute to tissue damage through inflammation.

Hypertension and reduced blood flow

There are also other potential mechanisms. For example, adiposity can often go hand in hand with other chronic conditions, such as hypertension, which could be a separate mechanism. Obesity may be associated with reduced blood flow to the brain, which may increase the risk of vascular microcellular damage. This could lead to a reduction in cognitive test scores. In another study, scientists found that a one centimeter increase in waist circumference resulted in the same reduction in blood flow as a year of aging.

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Fight cognitive decline

This study supports previous findings that overweight and obesity are associated with cognitive impairments.

Several measures that can help: Weight loss, exercise, both aerobics and resistance training, control of diabetes/glucose intolerance, or cognitive training at the speed of treatment are some of the measures to put in place to curb cognitive decline. People with a high BMI or a high waist-to-hip ratio and doing little physical activity have significantly lower cerebral blood flow. Since physical activity could potentially moderate obesity/blood flow associations, increasing physical activity could be an effective and relatively easy way to help mitigate the negative impact of obesity.


Evaluation of Adiposity and Cognitive Function in Adults

Subcutaneous adipose tissue & visceral adipose tissue

The relationship between adiposity and cognitive function in a large community-dwelling population: data from the Trinity Ulster Department of Agriculture (TUDA) aging cohort study

Obesity impairs cognitive function via metabolic syndrome and cerebrovascular disease: an SEM analysis in 15,000 adults from the UK Biobank

Obesity is associated with reduced cerebral blood flow – modified by physical activity


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