DEAR DR. ROACH: A reader recently asked you about taking niacin for lowering cholesterol and what side effects might be expected. Your reply did not include the very serious side effect of diabetes. Although it may occur only rarely, it did happen to me, and to my brother. We had totally different experiences, but the same outcomes.

After a friend told me that niacin would lower my high cholesterol, I began taking approximately 1,000-1,200 mg daily in my early 60s. Because I had not done thorough research on possible side effects, when I began to have high blood sugar levels, I did not associate it with the niacin. No diet changes, weight loss or exercise lowered my blood sugar, and in my late 60s, I was diagnosed with Type 2 diabetes. A disturbing fact is that numerous physicians also did not associate taking the niacin with having diabetes. I had elevated liver enzymes, and no one knew the reason.

My brother, who is three years older, was taking a little higher dosage than I was under his doctor’s care. He never had any problems with elevated blood sugar. After more than five years, he suddenly was diabetic. But because his doctor was aware of the possibility of diabetes with high dosages of niacin, he took him off of niacin right away. We were diagnosed with Type 2 diabetes within three months of each other.

I am now 73 years old and prediabetic. Although my brother and I no longer have to take diabetic medications, we still struggle with blood sugar levels that are higher than they should be. My thought is that damage was done that cannot repair itself. But now my concern is that many physicians are either unaware of this danger or maybe think that it is too rare to be concerning. I am hoping that you will spread the word that it is a very real possibility. — L.T.

ANSWER: It is a very common side effect that niacin, in the doses necessary to change blood cholesterol, can affect the liver, seen by elevated liver enzymes in the blood. The increase in blood sugar is not as well known, but it is common, and usually of small magnitude. However, in a person who is at risk for Type 2 diabetes due to it running in the family (genetic risk), the niacin can be enough to make a predisposition become overt.

Most experts feel that niacin doesn’t cause the underlying metabolic defect in diabetes, but rather makes it show up.

Because of the toxicities of niacin, and especially because of the questionable benefits in terms of preventing heart disease, I no longer have any patients on niacin.

It’s important to note that statins, which have clear benefits in reducing heart attacks in those whose risk is higher-than-average, also can affect blood sugar and likelihood of developing diabetes. This occurs in approximately one person for every thousand people taking statins for a year. However, in that same group, we would expect five people to have a heart attack or death prevented by taking the statin, so there is clearly more benefit than harm, if the people taking statins are of appropriate risk to do so.

I agree with you that both patients and doctors need to be aware of these risks, both before deciding to take the medication and while monitoring treatment.

Diabetes has become epidemic in North America. The booklet on it provides insight on its diagnosis and treatment. Readers can order a copy by writing: Dr. Roach Book No. 402, 628 Virginia Dr., Orlando, FL 32803. Enclose a check or money order (no cash) for $4.75 U.S./$6 Can. with the recipient’s printed name and address. Please allow four weeks for delivery.

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 or request an order form of available health newsletters at 628 Virginia Dr., Orlando, FL 32803. Health newsletters may be ordered from www.rbmamall.com.