Background/objectives: This study investigates the predictors of serum cobalamin concentrations in community-dwelling older adults and the relationship between serum cobalamin and plasma homocysteine.
Subjects/methods: Serum cobalamin and plasma homocysteine were measured by SimulTRAC-SNB radio assay and HPLC, respectively. Linear multiple regression analyses were performed with cross-sectional data of 352 participants aged 60-90 years to examine (1) the predictors of serum cobalamin and (2) the association between cobalamin and homocysteine status. Age, sex, body composition, diet, supplement use, smoking, serum folate, serum pyridoxal 5´-phosphate, serum creatinine, and selected diseases were considered as potential predicting/confounding factors.
Results: Median values of serum cobalamin, plasma homocysteine, and dietary cobalamin intake were 256 pmol/L, 9.7 µmol/L, and 5.7 µg/day, respectively. In multiple regression analysis, cobalamin intake, sex, body composition, serum creatinine and smoking did not predict serum cobalamin (all P > 0.05). In contrast, age (β = 0.111, P = 0.031), serum folate (β = 0.410, P < 0.001) and diagnosis of chronic inflammatory bowel disease (IBD) (β = 0.101, P = 0.037) were positively and cancer diagnosis (β = -0.142, P = 0.003) was negatively associated with serum cobalamin. The model explained 23% of the variability of serum cobalamin. After exclusion of subjects with IBD/cancer diagnosis and/or vitamin B/multi-vitamin supplementation, only serum folate remained as positive predictor of serum cobalamin (β = 0.407, P < 0.001). Serum cobalamin was positively associated with inverse-transformed plasma homocysteine before (β = 0.298, P < 0.001) and after (β = 0.199, P < 0.001) multiple adjustments.
Conclusions: Serum folate but not cobalamin intake or age proves to be a main predictor of cobalamin status. Nevertheless, independent of serum folate and other potential confounders, serum cobalamin is inversely associated with plasma homocysteine.