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It measured concentrations and deficiency incidence, not clinical deficiency syndromes.\nexposure: 850 mg metformin three times daily for 4.3 years versus placebo\nevidence_span: {\"source_cache\": \"artifacts/metformin-research/20488910.abstract.txt\", \"locator\": \"Indexed abstract; zero-based, end-exclusive Unicode character offsets\", \"file_sha256\": \"6c9e09d44fe1103e6927321e925e69e31c38d1a688fd2ac18ea96927098de922\", \"start_char\": 0, \"end_char\": 2518, \"text_sha256\": \"6c9e09d44fe1103e6927321e925e69e31c38d1a688fd2ac18ea96927098de922\"}\n[metformin-p20488910] Long term treatment with metformin in patients with type 2 diabetes and risk of vitamin B-12 deficiency: randomised placebo controlled trial. 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