Harvard Health Letter

Ask the doctor: Vitamin B12 essential for thinking skills

Q. Why is vitamin B12 important, and should I check if mine is low?

A. We get vitamin B12 in the diet, primarily from animal sources—meat, eggs, milk and other dairy products. For our bodies to absorb vitamin B12 we eat, our stomach enzymes need to "shake it loose" from the foods that it is attached to. Then, the vitamin needs to attach itself to a protein that is made in our stomach, called intrinsic factor. Once attached, it can be absorbed into the body.

Vitamin B12 is essential. Someone who doesn't have enough in the blood can develop serious blood and neurological problems. In a relatively uncommon disease, pernicious anemia, the stomach does not make intrinsic factor, so the body absorbs very little B12. A much more common problem, however, is difficulty that some of us have as we grow older in "shaking loose" the B12 from food. This also can cause abnormally low levels of vitamin B12 in the blood, and related health problems.

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