Objective: Assessment of functional vitamin B(12) status in a subset of the respondents in the British National Diet and Nutrition Survey of people aged 65 y and over.
Setting: National Diet and Nutrition Survey: a British nationwide cross-sectional sample of people aged 65 y and over, living either in the community or in institutions such as nursing homes, during one calendar year spanning 1994-1995.
Methods: Methylmalonic acid (MMA) concentrations were measured in plasma samples from 313 subjects (ca 14% of those originally enrolled in the survey). The results were compared with those for serum vitamin B(12), vitamin B(12) intakes and other status and intake estimates and with socio-demographic indices.
Results: Of the NDNS participants overall, 20% had serum vitamin B(12) concentrations<150 pmol/l. In the subset studied here, 24% of free-living and 46% of institution-living participants had MMA>0.5 micromol/l. Geometric mean MMA increased with age, from 0.25 micro mol/l in people aged 65-74 y to 0.38 micro mol/l in people aged 85+y. There was little evidence for any gender difference in MMA. It was inversely correlated with serum vitamin B(12) and with red blood cell folate; it was positively correlated directly with total homocysteine, but not significantly with serum folate or with vitamin B(12) intake. Among respondents with high MMA, a subgroup had normal serum vitamin B(12) but higher-than-average plasma urea and creatinine. Socio-demographic co-variates of MMA included receipt of State income benefits, social class of head of household, and educational attainment. These indices were not correlated with serum vitamin B(12).
Conclusions: The progressive increase in MMA with age is metabolic evidence for increasing risk of functional vitamin B(12) deficiency with increasing age in older people. There is evidence that renal function is linked to high MMA in some older people. Age and renal function are thus both important when establishing upper reference limits for MMA. The socio-demographic observations suggest a link between poverty and poor functional vitamin B(12) status in older British people.