The Food and Nutrition Board says, “Since 10 – 30% of older people may malabsorb food-bound B12, it is advisable for those older than 50 to meet their RDA mainly by consuming foods fortified with B12 or a B12-containing supplement.” This could be due to decreased digestive enzyme production and/or decreased stomach acid (1). Decreased stomach acid reduces enzyme action on protein-bound B12 and/or allows bacterial overgrowth in the stomach and small intestine. Some types of bacteria use B12 for themselves (2).
Approximately 2% of older adults do not produce enough intrinsic factor to prevent pernicious anemia (1). In order to know whether someone suffers from such a problem, people should have their B12 status tested every 5 years starting after age 50.
Because older adults (vegan or not) may not produce much intrinsic factor or gastric acid, chewable tablets and sublingual supplements may be the best way for them to obtain B12. People over 50 years should consider occasionally taking a sublingual B12 supplement of 500-1,000 µg.
There is evidence that people over 65 years old should take at least 500 µg per day of vitamin B12 in order to optimize their B12 status—see People Over 65 Years.
References
1. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academy Press; 2000.
2. Selhub J, Bagley LC, Miller J, Rosenberg IH. B vitamins, homocysteine, and neurocognitive function in the elderly. Am J Clin Nutr. 2000 Feb;71(2):614S-620S.