What are the benefits of metformin 1000 mg per day for a a 64 year old male?

For a 64-year-old man with type 2 diabetes, metformin 1000 mg/day offers real but modest blood sugar control, with a known trade-off in vitamin B12 depletion that gets worse the longer you take it.

The strongest evidence for metformin's benefit comes from the UKPDS trial, where overweight patients newly diagnosed with type 2 diabetes who started metformin early saw a 33% reduction in heart attack risk and a 42% drop in diabetes-related deaths compared to diet alone [1]. That benefit persisted for years after the trial ended [5]. For a 64-year-old man, those are meaningful numbers. But the same trial also shows metformin causes less weight gain than sulfonylureas or insulin — about 1-2 kg versus 5-7 kg [1] — which matters for long-term metabolic health.

The catch is that metformin's effect on blood sugar is not huge. In one 1980 study of older patients, adding 1000 mg/day of metformin to a maximal sulfonylurea dose only dropped fasting blood glucose by about 1.1 mmol/L [4]. A more recent review confirms metformin reduces HbA1c by roughly 1% from baseline [3]. That is useful but not transformative.

Now the part the doctor may not mention: metformin depletes vitamin B12. A 2026 Ugandan study of adults on metformin found that 10% were B12 deficient overall, but at the 1000 mg/day dose the rate was 10%, and at 2000 mg/day it jumped to 36% [2]. Longer use made it worse — 27% deficiency after 10+ years versus 7.5% before that [2]. B12 deficiency is not trivial: in that same study, deficient patients had much higher rates of peripheral neuropathy (77% vs 47%) and neuropsychiatric symptoms (50% vs 29%) [2]. For a 64-year-old man, nerve damage and cognitive decline are serious risks.

The evidence also raises a flag about overtreatment in older adults. A 2018 Australian study of people 75 and older with type 2 diabetes found that those on metformin who achieved very tight control (HbA1c below 6.5%) had higher all-cause mortality than those with moderate control [6]. That suggests pushing blood sugar too low in older patients may backfire.

My call: metformin 1000 mg/day is a reasonable first-line drug for a 64-year-old man with type 2 diabetes, but it is not a free lunch. The blood sugar benefit is real but modest, the cardiovascular benefit from early use is the strongest argument, and the B12 depletion is a predictable, dose-dependent cost that demands monitoring and likely supplementation. Do not take it without checking B12 levels every year, and do not assume tighter control is better — the mortality data says otherwise for older patients. Confidence: moderate — the benefit is proven in trials, but the B12 risk is under-discussed and the optimal target HbA1c for this age is not settled.