Metformin is a great drug. I've heard of top researchers in the field who are healthy take it daily. I hear it reduces gluconeogenesis in the liver and may be effective in preventing cancer (or killing off existing cancer cells).
AFAIK, i don't need to take it but I may discuss with my doctor next time if it might be useful to take as a preventive type of measure.
As I read it is prescribed for people who are obese and where diet and exercise no longer adequately control glucose levels so for those past that magical point of no return
For those not there yet, there are lot of studies on how, in addition to healthier eating as we all discussed, resistance exercise and developing muscle (not body builder but normal muscle) helps because muscles can take up glucose easily without the aid of insulin or muscles adapt to become more sensitive ot insulin due to the need to store glucose and therefore will better regulate blood levels.
With cancer being discussed as a metabolic disease, anything to keep glucose uptake in check does lower risk factors for cancer.
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