Atrophic gastritis
Historically, PA was considered to be the major cause of vitamin B12 deficiency, but it was a fairly rare condition, perhaps affecting 1 percent to a few percent of elderly populations. More recently it has been suggested that a far more common problem is that of hypochlorhydria associated with atrophic gastritis, where there is a progressive reduction with age of the ability of the parietal cells to secrete hydrochloric acid.
It is claimed that perhaps up to onequarter of elderly subjects could have various degrees of hypochlorhydria as a result of atrophic gastritis. It has also been suggested that bacterial overgrowth in the stomach and intestine in individuals suffering from atrophic gastritis may also reduce vitamin B12 absorption. This absence of acid is postulated to prevent the release of protein-bound vitamin B12 contained in food but not to interfere with the absorption of the free vitamin B12 found in fortified foods or supplements.
Atrophic gastritis does not prevent the reabsorption of bilary vitamin B12 and therefore does not result in the negative balance seen in individuals with PA. However, it is agreed that with time, a reduction in the amount of vitamin B12 absorbed from the diet will eventually deplete even the usually adequate vitamin B12 stores, resulting in overt deficiency.
It is claimed that perhaps up to onequarter of elderly subjects could have various degrees of hypochlorhydria as a result of atrophic gastritis. It has also been suggested that bacterial overgrowth in the stomach and intestine in individuals suffering from atrophic gastritis may also reduce vitamin B12 absorption. This absence of acid is postulated to prevent the release of protein-bound vitamin B12 contained in food but not to interfere with the absorption of the free vitamin B12 found in fortified foods or supplements.
Atrophic gastritis does not prevent the reabsorption of bilary vitamin B12 and therefore does not result in the negative balance seen in individuals with PA. However, it is agreed that with time, a reduction in the amount of vitamin B12 absorbed from the diet will eventually deplete even the usually adequate vitamin B12 stores, resulting in overt deficiency.
When considering recommended nutrient intakes (RNIs) for vitamin B12 for the elderly, it is important to take into account the absorption of vitamin B12 from sources such as fortified foods or supplements as compared with dietary vitamin B12. In the latter instances, it is clear that absorption of intakes of less than 1.5–2.0 μg/day is complete – that is, for intakes of less than 1.5–2.0 μg of free vitamin B12, the intrinsic factor – mediated system absorbs all
of that amount. It is probable that this is also true of vitamin B12 in fortified foods, although this has not specifically been examined. However, absorption of food-bound vitamin B12 has been reported to vary from 9 percent to 60 percent depending on the study and the source of the vitamin, which is perhaps related to its incomplete release from food. This has led many to estimate absorption as being up to 50 percent to correct for bio-availability of absorption from food.
References
Carmel, R. 1996. Prevalence of undiagnosed pernicious anaemia in the elderly. Arch. Intern. Med., 156: 1097-1100.
Food and Nutrition Board, Institute of Medicine, National academy of Sciences. 1998. Dietary reference intakes for thiamin, riboflavin, niacin, vitamin B6, folate, and vitamin B12, pantothenic aid, botin, and choline. National Academy Press Washington DC, USA.
of that amount. It is probable that this is also true of vitamin B12 in fortified foods, although this has not specifically been examined. However, absorption of food-bound vitamin B12 has been reported to vary from 9 percent to 60 percent depending on the study and the source of the vitamin, which is perhaps related to its incomplete release from food. This has led many to estimate absorption as being up to 50 percent to correct for bio-availability of absorption from food.
References
Carmel, R. 1996. Prevalence of undiagnosed pernicious anaemia in the elderly. Arch. Intern. Med., 156: 1097-1100.
Food and Nutrition Board, Institute of Medicine, National academy of Sciences. 1998. Dietary reference intakes for thiamin, riboflavin, niacin, vitamin B6, folate, and vitamin B12, pantothenic aid, botin, and choline. National Academy Press Washington DC, USA.
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