Vitamin B12 deficiency in relation to functional disabilities.

This study was designed to assess whether symptoms, functional measures, and reported disabilities were associated with vitamin B12 (B12) deficiency when defined in three ways. Participants, aged 60 or more years of age, in 1999-2002 National Health and Nutrition Examination Surveys (NHANES) were categorized in relation to three previously used definitions of B12 deficiency: (1) serum B12 < 148 pmol/L; (2) serum B12 < 200 pmol/L and serum homocysteine > 20 μmol/L; and (3) serum B12 < 258 pmol/L or serum methylmalonic acid > 0.21 μmol/L.