Those experiencing pernicious anemia (an auto-immune reaction to either the parietal cells or intrinsic factor) go on to develop vitamin B12 deﬁciency through malabsorption if untreated. Deﬁciency could develop within 1–3 years in those experiencing malabsorption.
Patients having surgical alteration of the distal ileum, Crohn’s disease, and using metformin are also at an increased risk for malabsorption.
Herbert (1994) estimates that deﬁciency could take as long as 20–30 years to develop in persons having normal absorption/reabsorption and suddenly ceasing to include substantial amounts of vitamin B12 in their diet during adulthood. This is due to the large amount of vitamin B12 that can be stored in the body and recycled through enterohepatic reabsorption.
The prevalence of vitamin B12 deﬁciency increases with age and is associated with a number of conditions and treatments.
The main causes of vitamin B12 deﬁciency are
- poor dietary intake (as in vegetarianism),
- poor absorption (occurring in achlorhydria, pernicious anemia, Helicobacter pylori (H. pylori) infection, Crohn’s disease, and metformin use),
- poor distribution (genetic predisposition for aberrant proteins that are inefﬁcient in transport or cellular uptake of vitamin B12).
Isaac Bashevis Singer
What do they know-all these scholars, all these philosophers, all the leaders of the world - about such as you? They have convinced themselves that man, the worst transgressor of all the species, is the crown of creation. All other creatures were created merely to provide him with food, pelts, to be tormented, exterminated.
Undernutrition is a form of malnutrition. (Malnutrition also includes overnutrition).
Undernutrition can result from:
- inadequate ingestion of nutrients,
- impaired metabolism,
- loss of nutrients due to diarrhea,
- increased nutritional requirements.
Undernutrition progresses in stages: it may develop slowly when it is due to anorexia or very rapidly. First, nutrient levels in blood and tissues change, followed by intracellular changes in biochemical functions and structure. Ultimately, symptoms and signs appear. Diagnosis is by history, physical examination, body composition analysis, and sometimes laboratory tests.
Undernutrition from micronutrient deficiencies, or "hidden hunger", affects over 2 billion people globally and can lead to reduced growth and cognitive development, birth defects, blindness, and overall poor health. Vitamin A deficiency, iron deficiency anaemia and iodine deficiency disorders are among the most common forms of micronutrient malnutrition.