Research suggests higher BMI in midlife is associated with lower cognitive function in later life. However, this association is not found to be consistently observed across age groups. In older age groups, measures such as BMI may not be the best methods to assess risk of dementia with increased body weight. Instead, other ways of measuring adiposity may be needed. Therefore, knowing when the change occurs will be important for informing the development of accurate protocols for calculating dementia risk in different age groups. These results will form a robust platform to develop new focused on predicting risk of cognitive decline not just in the old-old but also in young-old individuals. This is important for the development of intervention strategies focused on improvement/maintenance of cognitive function across different age groups.