I've been warning for years about the danger of metformin, the most commonly prescribed drug for diabetes, and the need to monitor homocysteine levels and B12 status. Now, a trial, published the British Medical Journal today, which gave 850 mg of metformin to 196 of the study’s participants and a placebo to the other 194 people three times daily for more than four years, confirms this. People who had taken the metformin were found to have a 19% reduction in their vitamin B-12 levels, compared with people who had taken a placebo, who had almost no change in their levels during the study.
In addition, the reduction of levels of vitamin B-12 by metformin was not temporary, but persisted and became more apparent over time. There was also a significant rise in the number of people with deficient levels of vitamin B-12 over the period of the study if they had been taking metformin, from three patients to 19. The equivalent number for the placebo group rose from four patients to five. Compared with people taking a placebo, people taking metformin also had a 5% increase in homocysteine, but their folate levels were the same. Homocysteine levels increased especially in individuals in whom vitamin B-12 levels decreased - showing that the decrease in vitamin B-12 levels were functionally meaningful.
The authors say: “Our study shows that it is reasonable to assume harm will eventually occur in some patients with metformin-induced low vitamin B12 levels.” Raised homocysteine is associated with increased risk for strokes, cardiovascular disease, osteoporosis, depression and age-related memory loss. Current guidelines indicate that metformin is a cornerstone in the treatment of type 2 diabetes, but make no recommendations on the detection and prevention of vitamin B-12 deficiency during treatment, they add. “Our data provide a strong case for routine assessment of vitamin B-12 levels during long term treatment with metformin.” My recommendation is to use chromium instead of metformin.
At doses of 600mcg a day (most supplements provide 200mcg, so that means three a day) chromium is more effective than metformin at stabilising blood sugar levels. A systematic review in the top journal Diabetes care says "“Among participants with type 2 diabetes, chromium supplementation improved glycosylated hemoglobin levels and fasting glucose. Chromium supplementation significantly improved glycemia among patients with diabetes.” Cinnamon also has benefits and supplements combining high dose chromium with cinnulin, a specific extract of cinnamon, are my favourite. If you are on metformin do check your homocysteine level. If raised you need to supplement more B12. The RDA is far too low. A basic level to supplement for everybody is 10mcg a day. A good multivitamin needs to provide this. But if you are low, or your homocysteine level is high, you'll need more like 500mcg to correct deficiency. B12 is increasingly poorly absorbed as you age and is only found in animal products.