Oxidative stress is a key factor that is involved in many chronic neurodegenerative diseases, including the main form of dementia, Alzheimer's disease [97, 98]. Oxidative stress is also viewed as a primary mechanism linking obesity and metabolic disorders [99]. Therefore, oxidative stress may be a common mechanism for these complex diseases. Increased evidence indicates that there is an association between obesity and nervous system disorders (cognitive deficits, neurodevelopmental disorders, neurodegenerative diseases, and psychiatric disorders), including dementia and major depression. The conditions of chronic obesity and overweight status are risk factors for lower cognitive performance, cognitive decline, cognitive deficit, and dementia; on the other hand, lower cognitive performance early in life itself may be a risk factor for an increase in body weight over time [100]. Childhood overweight and obesity and their psychosocial and cognitive consequences have been investigated in a nationally representative sample of children. The association between BMI and academic performance was not significant after adjusting for parental/familial characteristics. However, the associations between BMI and cognitive functioning remained significant, and severe overweight correlates with lower cognitive functioning [101].
