These days, most health warnings about vitamins focus on the danger of overdose. For vitamin B12, though, it's more likely that people are getting too little. In fact, B12 deficiency is the most common nutritional deficiency in the developing world and possibly in the United States as well, reports the August issue of the Harvard Health Letter.
Sometimes the only symptoms of a B12 deficiency are subtle cognitive and neurological changes. More serious shortages can result in dementia or anemia. Breast-fed infants of mothers with a B12 deficiency are at risk for severe developmental abnormalities and irreversible neurological damage.
Vegans (people who don't eat any meat, dairy, or eggs) are most at risk for developing a B12 deficiency because, aside from fortified breakfast cereals, the only reliable dietary sources of vitamin B12 are animal-derived products. But even vegetarians who eat eggs and dairy products consume, on average, less than half the adult Recommended Dietary Allowance of 2.4 mcg of B12, notes the Health Letter.
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