DEAR DR. DONOHUE: I am 73 and in good health. I take the multivitamin Centrum Silver, low-dose aspirin, vitamin C and cod-liver oil. My problem is diarrhea. It started more than a month ago. I took Imodium. The doctor took me off Imodium and put me on lactobacillus. I’ve been on it for 22 days. I am also off all dairy products. I still have this problem. What’s next? – P.

ANSWER: Diarrhea that lasts less than two weeks is “acute” diarrhea, and most often caused by bacteria or viruses. Sometimes antibiotics are used for bacterial diarrheas, but time usually cures both kinds.

You’re past the acute stage. You have “chronic” diarrhea, the kind that lasts for a month or longer. Rarer infections, like giardia and amebic dysentery, can produce protracted diarrhea. So can things like milk sugar (lactose) intolerance, so stay off dairy products. Anything that upsets the pancreas’s production of digestive enzymes leads to chronic diarrhea. Celiac disease, which is sensitivity to gluten – a protein found in wheat, barley and rye – is another consideration. Ulcerative colitis and Crohn’s disease cause long-term diarrhea. An overactive thyroid gland is a possibility. The list goes on and on, and you’ll likely have to undergo many more tests to find the cause. Colonoscopies, X-rays, scans, examination of the stool and testing the intestinal tract’s function will be in store if this doesn’t stop.

In the meantime, stop the cod-liver oil. You’re getting far too much vitamin A, and that can cause diarrhea. The recommended amount of vitamin A for someone your age is 900 mcg (3,000 IU) or slightly more. One teaspoon of cod-liver oil has 1,360 mcg (4,500 IU). In addition, one Centrum Silver tablet contains a little more than 900 mcg. The upper limit for daily ingestion is 2,000 mcg (6,600 IU). You’re over the limit.

If your doctor agrees, Pepto-Bismol might slow things down for you. Codeine has a long record for combating diarrhea. Keep yourself hydrated. That is most important.

DEAR DR. DONOHUE: I have been waiting for some time now for you to address “markers” in the blood and how they relate to cancer. – C.R.

ANSWER: You’re speaking of tumor markers, products in the blood made by cancers. A raft of such markers exists, but there is not one that absolutely proves the presence of cancer. PSA – prostate specific antigen – is an example of a tumor marker, much in use, that’s helpful in detecting prostate cancer. Yet conditions other than cancer can make it rise – prostate enlargement, for example. Alpha-fetoprotein often increases with cancer of the testicle. At one time, CA-125, another tumor marker, was believed to be a foolproof way for detecting ovarian cancer. It isn’t, but it is useful in following successful treatment for that cancer. I could go on with many more examples.

When the day comes that a tumor marker provides irrefutable evidence of cancer in all people having that cancer, we can all rejoice.

DEAR DR. DONOHUE: I appreciate that you have a large volume of mail, but this is the fourth time I have written you. I am again enclosing copies of my latest blood work. Is this an accepted alternative to a hands-on physical?

Please, give me a break. It is less than 100 days to my 80th birthday. I’m not sure how much longer I can wait for an answer. – F.O.

ANSWER: OK, F.O., here goes. Your blood potassium is normal. Potassium keeps the heart beating, muscles contracting and nerves firing. Creatinine is an indicator of kidney health. Your level is fine. ALT, alanine aminotransferase, is a liver enzyme. It too is great. No trouble with your liver. Your RBS (random blood sugar) and HBA1c (hemoglobin A1c), both diabetes tests, are perfect. No diabetes. Your triglycerides are excellent. They’re fats, and they can gunk up arteries with cholesterol. Your total cholesterol is very good, as is your HDL (high density lipoprotein) cholesterol. HDL cholesterol protects against heart disease. Your LDL cholesterol, so-called bad cholesterol, is at an acceptable level. All in all, your lab report is like an all-A report card. It appears you’re going to be around far longer than I am.

Lab tests are not a substitute for a hands-on physical examination.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com