A fairly long open access commentary on metformin and its effects on slowing aging in mice: "A recent study [may] certainly establish that metformin should be defined as geroprotective or gerosuppressant rather than bona fide [calorie restriction mimetic]. Long-living female mice from the outbred SHR strain were fed metformin in drinking water beginning at 3, 9 or 15 months of age and they were then analyzed for reproductive aging, mean and maximal lifespan and incidence of malignant tumors ... In female SHR mice, [researchers] now confirm that metformin treatment, if started early in life, notably increases by 21% the mean lifespan of tumor-free mice. In contrast, if started late in life, metformin treatment appears to significantly reduce (by 13%) the mean lifespan of tumor-free mice. ... It is perhaps relevant to note that, if started early in life, metformin treatment decreased the risk of death compared to the control group whereas similar treatment with metformin at older ages did not affect the relative risk of death in SHR female mice. Metformin's ability to increase the mean lifespan of tumor-free mice while simultaneously decreasing the risk of death in an age-related manner somewhat recapitulate metformin's ability to reduce cancer incidence among type 2 diabetic individuals."