Do you feel tired and weak all the time? You should find out if you have pernicious anemia. The blood disorder occures when you can't make enough red blood cells to take oxygen to your cells due to lacking B12.
Lack of B12 in the diet may be due to lack of intrinsic factor. To understand how this might happen, it’s important to understand just how cobalamin is absorbed. Cobalamin (B12) is taken up by R-binder, found in the saliva, after its released in the stomach from meat and dairy products that you eat (1). The bound complex then gets to the intestine where the cobalamin is released and binds to intrinsic factor (1). Cobalamin needs intrinsic factor to be absorbed because absorption only occurs when intrinsic factor binds to receptors of the distal ileum. Then cobalamin is released and taken up by a transport protein called transcobalamin II (1).
The lack of intrinsic factor can be caused by an autoimmune attack on intrinsic factor and the parietal cells producing it (1). Or it may be due to a possible mutation of intrinsic factor caused by mutation of intrinsic factor gene(2). In either case, dietary B12 from meat and dairy is unlikely to help with the anemia (1). B12 injections or sublingual dosages are necessary.
1. Nowak TJ, Handford AG. Pathophysiology: Concepts and Applications for Health Professionals. New York: McGraw-Hill, 2004.
2. Remacha AF, Del RE, Sarda MP, Canals C, Simo M, Baiget M. Role of (Glu --> Arg, Q5R) mutation of the intrinsic factor in pernicious anemia and other causes of low vitamin B12. Ann Hematol 2008;87:599-600.