Determinants of urinary methylmalonic acid concentration in an elderly population in the United Kingdom

An age-related deterioration of vitamin B-12 status has been well documented. The early detection of deficiency may prevent the development of serious clinical symptoms, but plasma vitamin B-12 concentration is known to be an imperfect measure of vitamin B-12 status. Urinary methylmalonic acid (MMA) may be a more informative biomarker of vitamin B-12 status; however, biochemical, dietary, and other lifestyle determinants are not known.

We identified determinants of urinary MMA concentrations in free-living men and women aged ≥65 y in the United Kingdom.

A cross-sectional study in 591 men and women aged 65-85 y, with no clinical evidence of vitamin B-12 deficiency, was conducted to determine the demographic, clinical, and lifestyle determinants of urinary MMA concentration expressed as the ratio of micromoles of MMA to millimoles of creatinine (uMMA ratio).

Twenty percent of subjects had plasma vitamin B-12 concentrations <200 pmol/L. Seventeen percent of the variation in the uMMA ratio could be explained by plasma holotranscobalamin and sex; total vitamin B-12 intake and measures of renal function and gastric function made only a small contribution to the model. The uMMA ratio was lower in people with moderately impaired renal function.

Plasma holotranscobalamin and sex were the most important determinants of uMMA ratio in elderly people with no clinical diagnosis of renal impairment. This biomarker might underestimate vitamin B-12 deficiency in a population in which renal impairment is prevalent. This trial was registered at www.controlled-trials.com as ISRCJN83921062.