Vitamin B-12 is essential for normal brain and nervous system function; and it helps make red blood cells and DNA. It also forms the genetic material in cells; produces energy; and converts folate to its active form.

How Much: Recommended dietary allowance (RDA) = 2.4 mcg (micrograms) daily. 

Too Much: There is no tolerable upper limit (UL) for vitamin B-12. 

Too Little: Too little vitamin B-12 can cause exhaustion, cognitive difficulties, nerve damage and anemia. The ability to absorb vitamin B-12 from food decreases with age. Most experts recommend older adults get this vitamin from supplements or fortified foods.

Foods: Vitamin B-12 occurs naturally in animal foods, especially liver, clams, egg yolks and salmon. Easier-to-absorb synthetic forms are added to supplements and some cereals, pastas and breads.

Interactions: Antacids; drugs for indigestion and reflux disease; cholesterol-lowering medications and the diabetes medication metformin.

Research Note: Vitamin B12 reduces homocysteine, an amino acid found at high levels in people with rheumatoid arthritis (RA). Even moderately elevated homocysteine is associated with an increased risk of fractures in older adults. Methotrexate and protein pump inhibitors (drugs that reduce stomach acid) such as omeprazole (Prilosec) interfere with B12 absorption..