The higher the body mass index, the more the brain suffers. Indeed, blood circulation in the brain decreases with increasing body weight, as brain scans of more than 17,000 test subjects now prove. This poor circulation could explain why people who are severely overweight or obese have a significantly higher risk of Alzheimer’s disease and other forms of dementia.

If the body is not healthy, the brain and mental performance also suffer. Studies have already shown that the first damage to the white brain substance is already apparent in obese adolescents. In old age, people with obesity have a 30 percent higher risk of dementia than normal weight people. But one can prevent the effects of obesity on the brain by practicing a sport. Exercises counteract the mental breakdown and increase the ability to think already in middle age.

Until now, however, it remained unclear how and why obesity affects the brain. Daniel Gamen of the Amen Clinic in California and his colleagues may have found an answer. For their study, they examined brain circulation in 17,000 men and women who had undergone single photon emission tomography (SPECT).

In this procedure, the subjects are given a slightly radioactive contrast agent, the distribution of which is tracked in the brain via the emitted gamma radiation. The repeated scans allow doctors to understand whether and how much blood is supplied to certain areas of the brain. In the tests, all participants were examined both at rest and during a concentration task.

The result: The researchers found a striking relationship between the subjects’ body mass index (BMI) and their cerebral circulation. The higher the obesity, the less well important areas of the brain were supplied with blood. This correlation can be detected both at rest and in thinking tasks and shows an almost linear decrease in blood flow even with mild obesity, says Amen and his team.

“This is particularly evident in areas of the brain that are considered susceptible to Alzheimer’s,” the researchers report. Among these is the temple, but also the hippocampus, which is important for memory, and the cingulate gyrus, which is also involved in learning and memory. Regardless of age and gender, blood flow decreased in all these areas with increasing BMI.

“Our findings could provide a possible physiological explanation for why obesity is a risk factor for Alzheimer’s,” the scientists say. If certain areas of the brain are no longer sufficiently blooded, this can lead to the degradation of the brain substance and to impairments of functionality in the long run.

However, the way in which obesity interferes with blood circulation, whether through chronic inflammatory processes or other mechanisms, has yet to be clarified. However, it is already known from adipose tissue that it can also promote low-threshold inflammation of the vessels. According to the researchers, the fight against severe obesity is in any case a worthwhile prevention also against mental degradation.

Angie Mahecha

An fitness addict passionate about all things nature and animals, Angie often volunteers her time to NGOs and governmental organizations alike working with animals in general and endangered species in particular. She covers stories on wildlife and the environment for the Scientific Origin.