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).
Vitamin C, or L-ascorbic acid, or ascorbate, is an essential nutrient for humans, a water-soluble vitamin. Humans, unlike most animals, are unable to synthesize vitamin C, so it is an essential dietary component.
- Vitamin C is required for the biosynthesis of collagen (an essential component of connective tissue), L-carnitine, and certain neurotransmitters, it is also involved in protein metabolism.
- Vitamin C is also an important physiological antioxidant and has been shown to regenerate other antioxidants within the body, including alpha-tocopherol (vitamin E). Vitamin C regenerates vitamin E by reducing vitamin E radicals formed when vitamin E scavenges the oxygen radicals.
- Vitamin C plays an important role in immune function and improves the absorption of nonheme iron, the form of iron present in plant-based foods.
Approximately 70%–90% of vitamin C is absorbed at moderate intakes of 30–180 mg a day. At doses above 1 g a day, absorption falls to less than 50% and absorbed, unmetabolized ascorbic acid is excreted in the urine.
Insufficient vitamin C intake causes scurvy, which is characterized by fatigue or lassitude, connective tissue weakness, and capillary fragility.
Cells accumulate vitamin C. The total body content of vitamin C ranges from 300 mg (at near scurvy) to about 2 g.
- High levels of vitamin C are maintained in cells and tissues, and are highest in leukocytes (white blood cells), eyes, adrenal glands, pituitary gland, and brain.
- Relatively low levels of vitamin C are found in extracellular fluids, such as plasma, red blood cells, and saliva.