Vitamin B12 deficiency: epidemiological trends and risk factors

Vitamin B12 (cobalamin) can only be obtained from animal food sources and is important for several functions, including DNA synthesis, haematopoiesis and myelination. It is one of the most common micronutrient deficiencies worldwide. Accurate estimates of the global burden remain difficult to ascertain because studies differ in the biomarker used (total serum/plasma B12, holotranscobalamin, or methylmalonic acid) and in the diagnostic cut-off applied, and because countrywide, longitudinally comparable data remain limited. This narrative review conducted following a defined literature search and selection strategy described in Section 1.1-synthesizes the current epidemiology of vitamin B12 deficiency, compares India's experience with other nations, and examines how reported prevalence has changed over the past 50 years. Pooled meta-analytic estimates indicate that approximately 50% of the Indian population is affected by vitamin B12 deficiency, among the highest rates reported worldwide. Reported prevalence rises across the life course, from 14% to 17% to 31% to 48% to 62% in pre-schoolers, school-aged children, adolescents, adults and the elderly respectively, with substantial regional heterogeneity within India (Section 2.8). Prevalence among pregnant women has been reported to range from 40% to 70%. The most consistently reported associated factors are dietary pattern (vegetarianism), low socioeconomic status, advancing age and female sex; because the underlying studies are predominantly cross-sectional, these should be read as associations rather than established causal pathways. Reported prevalence has remained high across every assessment period from the 1970s to the present, though this pattern is reconstructed from independent cross-sectional studies rather than a single longitudinal cohort (Section 4). We conclude that improved, harmonized diagnostic criteria, targeted screening, and reconsideration of current food-fortification standards are needed, while noting the implementation and evidentiary challenges that fortification scale-up in India still faces (Section 5).