Treatment allocation
Using a double‐blind, placebo‐controlled study design, older adults were randomized to either placebo or metformin groups and were sex‐matched. Randomization was performed by an individual who was not involved in the experimental implementation or data analyses. Treatment allocation was performed using sequentially labeled envelopes, opened after verifying participants' eligibility. Metformin and placebo control pills were encapsulated to prevent the visual identification of the treatment assignment.