Obesity is linked to reduced cranial blood flow, a condition that is a key imaging predictor of Alzheimer's disease and other mental health conditions, according to a new study published in the Journal of Alzheimer's Disease—findings that suggest "[w]eight hurts the brain," the study's lead author said.

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Researchers tie obesity to increased Alzheimer's risk

For the study, researchers measured the blood flow and brain activity of 17,721 participants, average age 41, by analyzing more than 35,000 functional neuroimaging scans using single-photon emission computerized tomography.

The scientists looked for low brain blood flow, which is associated with mental health conditions including depression, ADHD, bipolar disorder, and schizophrenia, as well as traumatic brain injuries. It is also the number one brain imaging predictor of Alzheimer's disease, according to a press release on the study.

The researchers categorized the participants into weight categories based on their body mass index (BMI):

• Underweight, or those with a BMI of less than 18;
• Normal, including those with a BMI of 18.5 to 24.9;
• Overweight, including those with a BMI of 24.9 to 29.9;
• Obese, including those with a BMI greater than 30; or
• Morbidly obese, including those with a BMI greater than 40.

The researchers found that participants classified as overweight, obese, and morbidly obese had lower blood flow to virtually all brain regions, including areas of the brain that are particularly vulnerable in Alzheimer's disease—namely, the temporal lobes, parietal lobes, hippocampus, posterior cingulate, and the precuneus. In addition, the researchers found that blood flow to the brain progressively worsened as BMI increased.

According to the researchers, low blood flow was observed both while participants were in a resting state and while they were performing concentration tasks. And the connection between BMI and low blood flow remained even after the researchers controlled for substance use disorders, traumatic brain injury, bipolar disorder, and other conditions that can affect blood flow.

'Weight hurts the brain'

Daniel Amen, lead author of the study and founder of Amen Clinics, said the study results reveal "that being overweight or obese seriously impacts brain activity and increases the risk for Alzheimer's disease as well as many other psychiatric and cognitive conditions."

George Perry—editor-in-chief of the Journal of Alzheimer's Disease and a Semmes Foundation distinguished university chair in neurobiology at The University of Texas at San Antonio, who was not involved in the study—said the study provides "compelling evidence that obesity alters blood supply to the brain to shrink the brain and promote Alzheimer's disease."

Stating that "Alzheimer's disease is a lifestyle disease, little different than other age-related diseases," Perry added that the study's findings are "a major advance because it directly demonstrates how the brain responds to our body."

For his part, Amen said the study highlights the importance of developing health initiatives that address obesity to improve brain function, especially given that 72% of Americans are overweight. "One of the most important lessons we have learned through 30 years of performing functional brain imaging studies is that brains can be improved when you put them in a healing environment by adopting brain-healthy habits, such as a healthy calorie-smart diet and regular exercise," he said.

In fact, according to Amen, the findings support the idea that, when it comes to the risk of developing Alzheimer's disease, people "have way more control than [they] may think."

He continued, "Weight hurts the brain. I want people to care enough about their brains that they will work to get their bodies healthy" (Science Daily release, 8/5; Bakalar, New York Times, 8/18; Romero, Philly Voice, 8/6).