Primary prevention
The recommended dietary allowance (RDA) for vitamin B12 is 2.4 micrograms/day in men and women aged 14 years and above.[58] During pregnancy and lactation, the RDA is 2.6 and 2.8 micrograms/day, respectively.[58][59]
Most vitamin B12 is obtained through ingestion of meat and dairy products, and body stores of vitamin B12 remain for years. Food fortification policies may reduce risk of vitamin B12 deficiency.[60]
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Countries with a high prevalence of vitamin B12 depletion and deficiency may consider the inclusion of vitamin B12 when staples are fortified with folic acid. This may help to prevent unintended consequences of excess folic acid consumption.[61][62]
Vegans and strict vegetarians may be at risk of vitamin B12 deficiency, and should supplement their diet with vitamin B12-fortified foods or a multivitamin containing a minimum of 2.4 micrograms of vitamin B12 per day. Those with a history of gastric bypass surgery or gastrectomy should supplement their diet with additional vitamin B12.[63]
Secondary prevention
Vegans, strict vegetarians, and older people are at risk of vitamin B12 deficiency without multivitamin supplementation or vitamin B12-fortified foods. Optimal dosing of vitamin B12 supplementation is uncertain, but older people may need oral dosages of >500 micrograms/day for optimal absorption.[115] Most vegans and strict vegetarians should absorb free vitamin B12 in standard multivitamins or fortified foods without difficulty, and minimal target intake should meet the recommended dietary allowance (2.4 micrograms/day). In vegans and vegetarians with marginal vitamin B12 stores, one study demonstrated improvement of stores with 50 micrograms/day of sublingual vitamin B12 or 2000 micrograms/week of sublingual vitamin B12.[93] The results support the use of a sublingual supplement at low doses in this population.[93]
In patients with diagnosed pernicious anemia (due to lack of intrinsic factor), endoscopic follow-up is advised in view of their increased risk of developing gastric cancer. A two to threefold excess risk of gastric cancer has been noted in patients with pernicious anemia.[81]
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