Multiple studies have signaled brain atrophy in relationship with obesity, particularly in elderly cohorts. Initially, this relationship was shown in the Cardiovascular Health Study in 94 cognitively normal participants in their late 70s who remained cognitively normal 5 years after their brain MRI scan.
The findings of brain atrophy in relation to higher BMI were replicated in the separate Alzheimer's Disease Neuroimaging Cohort and then in a larger Cardiovascular Study Cohort. However, what makes the present study different from that work, is the focus on brain perfusion, that shows greater sensitivity and earlier changes related brain dysfunction than atrophy.
These changes have been demonstrated even in cognitively normal individuals, as well as persons with mild cognitive impairment and Alzheimer's disease. Regional cerebral blood flow has also been used to track obesity-related brain abnormalities.
A SPECT scan monitors level of biological activity at each place in the 3-D region analyzed. Emissions from the radionuclide indicate amounts of blood flow in the capillaries of the imaged regions. Because blood flow in the brain is tightly coupled to local brain metabolism and energy use, the radionuclide is used to assess brain metabolism regionally, in an attempt to diagnose and differentiate the different causal pathologies of dementia. SPECT imaging is performed by using a gamma camera to acquire multiple 2-D images (also called projections), from multiple angles. A computer is then used to apply a tomographic reconstruction algorithm to the multiple projections, yielding a 3-D data set.
Recent studies have shown the accuracy of SPECT in Alzheimer's diagnosis may be as high as 88%. SPECT was superior to clinical exam and clinical criteria in being able to differentiate Alzheimer's disease from vascular dementias. This latter ability relates to SPECT's imaging of local metabolism of the brain, in which the patchy loss of cortical metabolism seen in multiple strokes differs clearly from the more even or "smooth" loss of non-occipital cortical brain function typical of Alzheimer's disease.
The authors have previously utilized SPECT functional neuroimaging to review and identify patterns of abnormality relevant to the diagnosis of traumatic brain injury, depression versus dementia classification , marijuana-related influences in the brain , omega-3 fatty acid associated improved cerebral blood flow , gender-related differences in the brain , and brain aging.
The purpose of their current article is to identify potential brain perfusion abnormalities in adults related to being overweight or obese.
A large psychiatric cohort of 35,442 brain scans across 17,721 adults were imaged with SPECT. ANOVA was done to identify patterns of perfusion abnormality in this cohort across BMI designations of underweight, normal weight, overweight, obesity, and morbid obesity.
With over 35,000 functional neuroimaging scans across more than 17,000 individuals, this study is one of the larger studies linking obesity with brain dysfunction, as evidenced here by quantifiable regional perfusion.
In particular, brain areas noted to be vulnerable to Alzheimer's disease: the temporal and parietal lobes, hippocampus, posterior cingulate gyrus, and precuneus were found to have reduced perfusion along the spectrum of weight classification from normal weight to overweight, obese, and morbidly obese.
While the work presented here focused on body tissue adiposity and cerebral perfusion in a large cohort, other studies have suggested a negative relationship between BMI, obesity, and the brain, particularly with neuroimaging as a proxy of structure or function.
Across adulthood, higher BMI correlated with decreased perfusion on both resting and concentration brain SPECT scans. These are seen in virtually all brain regions, including those influenced by AD pathology such as the hippocampus.
Perfusion is the passage of fluid through the circulatory system or lymphatic system to an organ or a tissue, it usually refers to the delivery of blood to a capillary bed in tissue. Cerebral perfusion may therefore warrant further study as a biomarker of caloric restriction in related efforts to improve brain health.
Overall, the scientists have found a strong set of relationships between being overweight and obese and brain hypoperfusion across a large adult cohort spanning young adults to late life.
The persistence of these abnormalities despite adjusting for demographic and psychiatric factors further highlights the need to address obesity as a target for interventions designed to improve brain function, be they Alzheimer's disease prevention initiatives or attempts to optimize cognition in younger populations.
