DEAR DR. DONOHUE: I am 68 and work hard at keeping my vitals under control. One way of doing so is to use margarine in place of butter to control my cholesterol. I recently received an e-mail that says margarine increases the risk of heart disease. Help! What’s your take on this? – M.D.

ANSWER: The butter versus margarine issue has been simmering on the back burner for quite some time now. Understanding it requires a little chemistry.

Saturated fat has received all the attention for controlling blood cholesterol. It primes the liver to pump out cholesterol. Saturated fats are found in dairy products and in and around animal meat. Their use should be minimized.

Trans fat starts out life as an oil. In order to improve its life span, hydrogen atoms are added to it. That changes it from an oil into a solid. Most shortenings used in baking are hydrogenated oils, as are most margarines. Both contain trans fats. Trans fats raise blood cholesterol levels even more than do saturated fats. Furthermore, they raise LDL cholesterol, the bad cholesterol that clings to artery walls, and they lower HDL cholesterol, the good cholesterol, the cholesterol that goes to the liver for disposal.

Calorie for calorie, margarine and butter are about equal, so if you are counting calories there is not much difference for you. A tablespoon of butter has about 100 calories; a tablespoon of margarine, between 50 and 100.

If your goal is to lower cholesterol and LDL cholesterol, then butter would be preferred to margarine with its trans fats.

If your goal is to lower total cholesterol, then margarines that contain plant stanols and sterols would be the better choice. Those plant products are not found in butter or ordinary margarine. They have a unique cholesterol-lowering effect. Take Control and Benecol are two examples.

The amount of trans fats in a food is about to be listed on the food’s label. For now, the word “hydrogenated” can be equated with trans fats.

DEAR DR. DONOHUE: I had an eye exam, and the doctor mentioned there were several floaters in my eyes. What are floaters? What causes them? Do they eventually cause problems? – S.A.

ANSWER: Floaters are bits of protein and other debris that float in the vitreous. The vitreous is the gelatinlike material that fills the back two-thirds of the eye. With eye movement, floaters dart across the field of vision like tiny insects.

Aging is one cause of floaters. Very nearsighted people – people who cannot see distant objects clearly – are prone to develop them.

Aside from their nuisance effect, floaters generally do not indicate serious eye trouble, nor do they foretell future eye trouble.

If there is a sudden shower of floaters, that is a danger warning. The retina might be detaching from the back of the eye. The retina is the light-sensitive eye layer that transmits images to the brain. A detaching retina has to be reattached promptly, or blindness could be the result.

DEAR DR. DONOHUE: What is the meaning of “elemental calcium”? The label of my multivitamin lists its calcium content as “elemental calcium.” – D.M.

ANSWER: Elemental calcium is the amount of pure calcium in the supplement. That is the number you want to know.

Calcium in nature comes with an attached twin. Often that twin is carbonate.

For a person keeping track of the daily calcium requirement, elemental calcium is the number to watch. The calcium carbonate weight is misleading.

DEAR DR. DONOHUE: Are sweet potatoes healthier than white potatoes? – B.R.

ANSWER: Contrary to popular opinion, a sweet potato has fewer calories than a white potato. It also has an exceptionally large supply of vitamin A. White potatoes are a rich source of potassium. Both are healthy. Potatoes find these comparisons odious.

DEAR DR. DONOHUE: I am lying in a hospital bed, recovering from acute pancreatitis. No one here will answer my questions, so I am writing to you. How did I get this? Does it ever come back? – L.J.

ANSWER: The pancreas has two important jobs. One is to provide insulin, the hormone that lowers blood sugar. The other is to produce enzymes that digest food so it can be absorbed.

Pancreatitis is a very painful inflammation of that organ. For some, it can be lethal. For most, it is a torture, but not a life-threatening one.

The inflammation can come about from a gallstone that blocks the pancreas’s drainage duct.

The pancreas and the gallbladder share a common duct. Alcohol can irritate and inflame the pancreas. High blood triglycerides (fats) can do the same.

An injury to the gland, such as one that comes from an auto accident, is another cause. Viral infections of the pancreas are on the list of causes, as are some medicines.

You appear to be making progress. You can anticipate a full recovery. About 10 percent of patients, however, have to contend with chronic pancreatitis, an inflammation that lingers on and on.

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.