The main source of vitamin B12 (cobalamin) in humans is the consumption of meat, poultry and dairy products. Its deficiency can be caused by decreased ingestion (poor dietary intake), impaired absorption (failure to release B12 from protein, intrinsic factor deficiency, chronic pancreatic disease, intestinal parasites, other intestinal diseases), or impaired use (congenital enzyme deficiencies, lack of transcobalamin II, administration of nitrous oxide). The recommended daily intake varies with age and is about is 2 mcg/day in adults; 2.6 mcg/day in pregnant and lactating women; and 0.7 mcg/day in children.The prevalence of B12 deficiency in the general population has not been well established because a universally accepted normal B12 level has not been defined. Prevalence in the general population varies from 3% to 5%, and from 5% to 20% among people older than 65 years. Vitamin B-12 deficiency is a worldwide problem, particularly in the newborn period due to the combined effects of poor maternal diet and congenital deficiencies of transcobalamin. Pernicious anemia is a common cause of megaloblastic anemia especially in persons of European or African descent. Dietary vitamin B12 deficiency is a serious problem in India, Mexico, Central America, South America, and some areas of Africa. The increase in vegetarianism is related to an increase in vitamin B12 deficiency, especially concerning in breastfed infants of vitamin B12–deficient mothers.In India, a hospital population radio assay study with a cutoff of 200 pg/ml found a vitamin B12 deficiency in 0.88% of patients, with borderline values in 3.8%. Some evidence suggests South Asians, lacto vegetarians, and in particular South Asians who are lacto-vegetarians are at greater risk of B12 deficiency. One study found that about 38% of people in western India followed a lacto-vegetarian diet and that 47% of the study population (60% of vegetarian and 39% of non-vegetarian people) was B12 deficient. Another study found that South Asian men in the United Kingdom had lower mean B12 levels than European controls (270 pmol/L vs 357 pmol/L). In Asia, Indians had lower B12 levels than Chinese or Malays.Some Indian studies on this topic are as below:
Indian SeriesYearVit.B12 def. (%)Bhende et al19657.0Mittal et al196922.4Sarode et al198976.4Gomber et al199850.0Gomber et al199836.6Chaudhry MW200119.0Chandra et al200232.0Khanduri et al200533.0