In China, those who retired earlier had lower scores on cognitive tests of delayed recall. This promotes the hypothesis that decreased mental activity or sense of purpose can lead to cognitive decline.

Accumulation of tau protein is associated with progression of Alzheimer's disease, as it leads to neuron death. While spreading of tau is not immediately harmful, it does disrupt cellular processes over time.

Reduced food intake has been shown to elongate life and improve health in mice, but calorie restriction doesn't show as many health benefits if started in older age, especially in terms of fat loss.

Dog ownership was linked to longer life and better outcomes for heart attack and stroke survivors. The benefits may be due to the increase in physical activity or a decrease in loneliness or depression.