Dr. Keith Roach

DEAR DR. ROACH: How much vitamin B12 should I take as a diabetic? — T.H.

ANSWER: Many people have strong feelings that vitamin B12 can dramatically improve their health, but it only helps to take vitamin B12 if you are deficient. Vitamin B12 deficiency isn’t too common. Still, there are a few situations where supplemental vitamin B12 should be considered, and two of them are specific for people with diabetes.

People with Type 1 diabetes, which usually presents itself during childhood, are at a high risk for other autoimmune diseases, including pernicious anemia — an autoimmune destruction of the cells in the stomach that make a protein called intrinsic factor. This protein is necessary for the absorption of vitamin B12. Multiple autoimmune diseases are often diagnosed in the same person.

People with Type 2 diabetes who take metformin are at risk for vitamin B12 deficiency due to poor absorption. I recommend testing vitamin B12 in people who have been on metformin for a long time. Proton-pump inhibitors (like omeprazole) may also reduce B12 absorption to the point of deficiency.

People who are very strict with avoiding any type of animal products will develop B12 deficiency over the years unless they use supplements. Finally, people who can’t absorb nutrients for a variety of reasons (such as bariatric surgery, Crohn’s disease, celiac disease, bacterial overgrowth, fish tapeworm, and disease of the pancreas) may all become B12-deficient.

Treatment of B12 deficiency depends on the underlying cause. For example, a vegan only needs about 1 mcg a day to avoid B12 deficiency. By contrast, people with pernicious anemia need 1,000 times the usual oral dose of B12 or B12 injections. Measuring B12 levels to ensure adequate supplementation is wise in people who have difficulty absorbing it.

For healthy people (apart from the above and a few other rare conditions) with a non-vegan diet, it is not necessary to supplement B12, nor is testing necessary. B12 toxicity is essentially unheard of since the body simply excretes the B12 that you don’t need.

Apart from severe absorption problems like pernicious anemia, the dosing of B12 supplementation is the same whether a person has diabetes or not. Fifty micrograms a day is almost always more than enough.

DEAR DR. ROACH: Is the Naltrexone shot (for alcohol abstinence) more effective when given on one side of the body compared to the other? A person I know who receives the shots feels that it’s only effective when they receive it on their right buttock. Is this possible, or could they be noticing a placebo effect? — C.M.

ANSWER: Naltrexone is an effective treatment for people with alcohol dependence. The exact effectiveness depends on the setting, but people who use naltrexone are less likely to relapse on their drinking.

Of course the drug will be absorbed just as well from the left side as the right. However, our expectations can have a huge influence on the effectiveness of a treatment. When there is an expectation of benefit, there is a placebo effect. (When there is an expectation of harm, it’s called a nocebo effect.) The placebo effect isn’t as critical in a situation like antibiotics for pneumonia but can be of immense importance when the desired effect is a decrease in alcohol cravings.

If I were this person’s doctor, I would keep giving the injection on their right side.

Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu.