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).
Fruit and vegetable consumption is a focus of research and nutrition education, but there is no universal agreement on the meaning of 'fruits and vegetables'. Foods that require specific instruction include rice, dried beans, potatoes, tomatoes and fruits and vegetables in mixtures and condiments.
Fruit and vegetables are important components of a healthy diet, and their sufficient daily consumption could help prevent major diseases. A recently published WHO/FAO report recommends a minimum of 400g of fruit and vegetables per day (excluding potatoes and other starchy tubers) for the prevention of chronic diseases such as heart disease, cancer, diabetes and obesity, as well as for the prevention and alleviation of several micronutrient deficiencies.
Fruits and vegetables are universally promoted as healthy. The Dietary Guidelines for Americans 2010 recommend you make one-half of your plate fruits and vegetables.
Fruits and vegetables include a diverse group of plant foods that vary greatly in content of energy and nutrients. Fruits and vegetables supply dietary fiber, vitamins and minerals to the diet and are sources of phytochemicals (phytonutrients) that function as antioxidants, phytoestrogens, and antiinflammatory agents and through other protective mechanisms.