Previous research has associated both obesity and diabetes with cognitive decline. But a new study from the Medical College of Georgia at Georgia Regents University found that regular exercise or the surgical removal of belly fat reverses this effect in mice.
The findings were recently published in The Journal of Neuroscience.
According to the research team, including study author Dr. Alexis M. Stranahan, past studies in animals and humans have shown that obesity and diabetes can triple the risk of mild cognitive impairment and increase the risk of Alzheimer's disease.
To find out more, the investigators conducted a mice study to determine how fat, and inflammation in the brain's hippocampus as a result of diabetes, affected cognitive impairment.
Obesity increases levels of inflammatory cytokines
On analyzing mice that were single-gene altered to become obese and diabetic, the investigators found that the mice had significantly high levels of inflammatory cytokines - small proteins that target pathogens and trigger the body's immune response.
The researchers hypothesize that the cytokines see excess fat tissue as an external pathogen and this prompts an immune response.
Dr. Stranahan explains:
"These obese diabetic mice have very high levels of inflammatory cytokines and I think it's because their bodies are reacting to the invasion of fat into tissues where it does not belong."
Once the body has been cleared of pathogens, cytokine levels should naturally decrease. But the researchers found that in the obese diabetic mice, the fat appeared as the "chronic invader," therefore levels of the cytokine interleukin-1 beta and inflammation remained high.
The investigators explain that in the brain, interleukin-1 beta causes microglia - microphages that act as the first form of defense in the central nervous system - to "eat up" neuronal synapses. These synapses are crucial to the communication of brain cells.
Synaptic functions repaired with exercise and surgery
The researchers found that when mice ran 5-10 kilometers a week for 3 months, or around 15-20% of their body weight was surgically removed, their weight and levels of interleukin-1 beta reduced, meaning their synaptic function was repaired.
Researchers found that exercise and removal of belly fat reversed cognitive decline in obese diabetic mice.
Furthermore, the researchers discovered that a drug already used to treat rheumatoid arthritis helped the obese and diabetic mice to restore their cognitive abilities.
Although Dr. Stranahan says that exercise is the best option for overweight and obese patients, he notes that a similar pharmacological intervention could be an alternative for people who are unable to exercise, such as elderly and frail individuals.
He points out that liposuction is not likely to be a viable option for patients, as the mice in this study had significantly more belly fat removed than what humans would have with the procedure.
The investigators say they plan to initiate similar studies in mice with diet-induced obesity, as the mice in this study were desensitized to leptin - a hormone that triggers satiety. This meant they were always hungry.
Medical News Today recently reported on a study suggesting that eating grilled meat could increase the risk of diabetes and Alzheimer's disease.