DEAR DR. ROACH: My stepdad is 84 years old and having problems with B12 deficiency. He is taking B12 shots, 1,000 mcg once a week, in addition to taking a 5000 mcg B12 vitamin daily. The numbers come back below 200. None of our doctors can figure it out. Any advice on to what is causing this? - R.B.
ANSWER: Vitamin B12 deficiency can be caused by low intake, although this is unusual. It's seen occasionally in very strict adherence to a vegan diet without taking supplements. Otherwise, the major cause is poor absorption, especially by an autoimmune disease called pernicious anemia. Treatment can be either with B12 injection or very high dose of oral B12, and either is usually effective. Your stepfather is being treated with both, and his level below 200 in the blood confirms the lack of effect.