It is even known to extend the life of diabetics so they live longer than healthy people.
No, it is known to correlate with living longer. But some or all of that correlation seems to be due to the sickest diabetics being switched from metformin to other drugs.
How could it explain that diabetics lived longer than healthy people?
If all of the sickest diabetics are switched to other drugs, then the only people taking metformin are the ‘healthy diabetics’, and it is possible that the average healthy diabetic lives longer than the average person (who may be healthy or unhealthy).
This would give the observed effective without metformin having any effect on longevity.
No, it is known to correlate with living longer. But some or all of that correlation seems to be due to the sickest diabetics being switched from metformin to other drugs.
How could it explain that diabetics lived longer than healthy people?
Anyway, we need a direct test on healthy people to know if it works or not.
If all of the sickest diabetics are switched to other drugs, then the only people taking metformin are the ‘healthy diabetics’, and it is possible that the average healthy diabetic lives longer than the average person (who may be healthy or unhealthy).
This would give the observed effective without metformin having any effect on longevity.