Blood is often described as the river of life. If blood flow to any part of our bodies is reduced, the cells dependent on the oxygen and nutrients that our blood delivers cannot function as well, and if blood supply is cut off entirely for even a few minutes, those cells will begin to die.
While every tissue and organ in the body is dependent on our red river of life flowing freely, every second of the day, our brains are particularly sensitive to changes in blood flow. And this makes the findings of a study published in the Journal of Alzheimer’s Disease in August 2020 incredibly concerning.
The study, titled ‘Patterns of Regional Cerebral Blood Flow as a Function of Obesity in Adults‘, reported an analysis of over 35 000 functional neuroimaging scans from nearly 18 000 individuals aged 18–94, across weight categories from underweight to morbidly obese.
The brain scans used single-photon emission computerized tomography (SPECT) to measure blood flow to various regions of the brain, and activity within those regions, both when participants were at rest and when they were engaged in the Connors Continuous Performance Test II, which measures the ability to concentrate and pay attention.
In every brain region, both blood flow and brain activity decreased, in a linear fashion, as body weight increased.
In other words, the higher the individual’s body weight, the more his or her brain was starved of the vital oxygen and nutrients supplied by blood, both when at rest and when attempting to concentrate on a task.
Here is the effect of body weight on blood flow to the temporal lobes, a brain region involved in processing input from our senses, especially hearing, so that we can understand speech, form memories and process our emotions:
And here’s the effect on the parietal lobes, which important for processing and interpreting somatosensory input.
And on the hippocampus, which is primarily involved with memory and spatial navigation:
And the posterior cingulate, which plays a role in awareness, memory retrieval and pain recognition, and is believed to mediate interactions between emotion and memory:
And finally, the precuneus, which is involved in numerous complex functions including memory recall, integration of information relating to perception of the environment, forming mental images, and emotional responses to pain.
There were no brain regions in which blood flow was higher in overweight or obese participants; the compromised blood flow patterns were remarkably consistent.
The researchers were particularly interested in the implications of their findings on the risk of Alzheimer’s disease. Our understanding of Alzheimer’s has changed dramatically in the last few years, with the realisation that, far from being simply a distressing but inevitable consequence of aging, Alzheimer’s disease is a lifestyle disease – just like type 2 diabetes and coronary artery disease, with which it shares major risk factors.
Our brains are not magically protected from the devastating metabolic effects of excess body fat. In fact, they are exquisitely sensitive to these effects.
Obesity, and even milder degrees of overweight, unquestionably compromise blood supply to the brain. In the short run, this compromised blood supply impairs brain function, making it more difficult to concentrate and pay attention to challenging tasks.
And in the long run, compromised blood flow shrinks the brain and promotes Alzheimer’s disease, a devastating condition which – quite rightly, in my opinion – the majority of people fear more than death.
With over two thirds of Australian adults and nearly 3 in 10 children currently classified as overweight or obese, the findings from this study, which add to a growing body of evidence linking excess body fat to impaired cognitive function and brain health, should be a wake-up call to us all.
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