Does metformin lower your risk of cancer or dementia?
In people with diabetes there are indications that metformin lowers overall cancer risk, but the evidence varies or is absent depending on the specific cancer type. Based on the available studies, no conclusions whatsoever can be drawn regarding dementia.
Metformin has been the most widely prescribed drug for type 2 diabetes for decades. Observational research in diabetic patients shows that users develop cancer less often and die from cancer less often than non-users. That pattern is intriguing, but the precise mechanism is not yet well understood. Moreover, the evidence comes almost exclusively from observational research, which is susceptible to bias: people who take metformin differ from people who do not in a wide variety of ways.
The picture varies by cancer type. For breast cancer the evidence is frankly contradictory: some studies found a lower risk, but a summary of 15 studies found no statistically demonstrable difference in women with type 2 diabetes (the risk was around 0.82, but the margin of uncertainty ran from 0.60 to 1.12, meaning the effect could be zero). For prostate cancer the picture is even clearer: a summary of more than 52,000 cases showed no association whatsoever. For lung cancer the evidence is too thin to draw any conclusion.
On the subject of dementia, the available studies give us nothing to go on. No studies were provided that examined that association, so presenting metformin as protection against dementia is an overclaim.
What is well supported: metformin is safe, well tolerated, and extremely inexpensive. That makes it interesting as a potential agent outside of diabetes, but demonstrable clinical benefit in healthy people or as a preventive agent against cancer has not yet been established. Anyone without diabetes who is considering using metformin for life extension or cancer prevention is doing so without evidential support. Always discuss this with your doctor first.
All claims are based on observational (epidemiological) research and meta-analyses of cohort studies. No RCTs were provided demonstrating cancer prevention in non-diabetic patients. No sources on dementia are available in this source file.
Does exercise lower my risk of cancer?
Regular physical activity is associated with a clearly lower risk of several cancers in large population studies. Alongside that, aim to reduce the number of hours you spend sitting during the day, and use sun protection if you do a lot of outdoor sport.
Does working with pesticides increase your risk of cancer?
Working with pesticides is associated in multiple studies with an increased risk of several types of cancer, including bladder, bowel, and blood cancers. Avoiding unprotected contact is sensible, especially if you are pregnant or planning to become pregnant.
Does drinking less alcohol meaningfully reduce your cancer risk?
Drinking less alcohol meaningfully reduces your risk of several cancer types, although it takes years before the full effect becomes visible. Stopping sooner yields greater health gains.
Which lifestyle factors reduce your cancer risk the most?
Not smoking, a healthy weight, regular exercise and little or no alcohol have the strongest and best-supported protective effect. Combining all these factors lowers cancer risk the most, even when a hereditary predisposition is present.
Does metformin help you live longer in good health?
For people with diabetes, metformin has a reasonably well-supported health benefit, but as an anti-ageing agent for healthy people it has not yet been proven. Wait for the results of the TAME study before drawing conclusions.
Does metformin help with weight loss?
Metformin helps with weight loss, but the effect is modest: expect a few kilograms, not a dramatic transformation. Lifestyle changes work better in the short term, but weight loss with metformin remains stable over the long term. Discuss it with your doctor if you want to know whether it suits your situation.