Hi, psychologist here. Cognitive decline is not my specialty but I’ve taken doctoral level courses in it.

The problem with the “shorter higher quality life” position is that diet, exercise and health affect EVERYTHING. Exercise and diet are majorly implicated in both physical health decline and onset of dementia and Alzheimer’s. In fact, maintaining a healthy and active lifestyle is often found to be the number one protective factor against cognitive decline.

Unfortunately there’s no health strategy that reliably produces a shorter higher quality life. There’s only increasing health span through lifestyle.

Note: there are medical choices that increase lifespan but not health - medication and surgery that prolong unhealth. But that’s a whole different game than healthy lifestyle.