DEAR DR. DONOHUE: Please explain HDL cholesterol. What makes it “good”? What’s considered a normal value for it? How important is it to have a high number? How can you raise it if it’s low? – L.T.

ANSWER: In truth, there is no good or bad cholesterol. It’s all the same stuff. Like fat, cholesterol doesn’t mix well with liquids. In order for it to swim around in the blood, the body has to wrap it with a substance called lipoprotein. Lipoproteins are part fat and part protein, and they make it possible for cholesterol to mix with blood. It’s the lipoprotein wrapping around cholesterol that makes it good or bad.

HDL – high-density lipoprotein – cholesterol vacuums cholesterol stuck to artery walls and dumps it in the liver for disposal. That’s why it’s called good cholesterol. LDL – low-density lipoprotein – cholesterol has a wrapper that makes it stick to artery walls. LDL is bad cholesterol.

A high HDL number confers protection against heart attacks. A reading of 60 mg/dL (1.6 mmol/L) or higher is desirable.

A low HDL value is a risk for a heart attack. A level less than 40 (1.0) for men and 45 (1.16) for women raises the chances for a heart attack. If a person raises the HDL by 11 percent, the risk for a heart attack drops by 34 percent – or so some investigators say. Others dispute such a dramatic statement.

How do you raise HDL cholesterol? Thirty minutes a day of brisk walking or equivalent exercise can do it. Introducing monounsaturated fats such as olive or canola oil into the diet also boosts HDL cholesterol. Weight loss, when indicated, ups it, as does moderating the amount of alcohol drunk.

If the level is very low and if the doctor feels it poses a health threat, then medicines such as niacin (nicotinic acid) or Lopid can be prescribed.

For more details on cholesterol and its treatment, readers can obtain a copy of the cholesterol pamphlet by writing: Dr. Donohue – No. 201, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.50 U.S./$6.50 Can. with the recipient’s printed name and address. Please allow four weeks for delivery.

DEAR DR. DONOHUE: For more than a year, my mother complained about being short of breath. She couldn’t do much more than wash the dishes. Doctors told her she had congestive heart failure, but she really has idiopathic pulmonary fibrosis. How is this treated, and how long has she got to live? She’s 72. – V.S.

ANSWER: “Fibrosis” refers to scar tissue, and “pulmonary” locates the scar tissue in the lungs. “Idiopathic” is a common medical word meaning the cause is undiscovered.

Usually this condition comes on between the ages of 40 and 60, and it is often mistaken for another condition, such as congestive heart failure. Breathlessness and a dry cough are the usual complaints, and they are the same complaints voiced in congestive heart failure. The reason for both is that scarred lungs are a barrier against the passage of oxygen into the blood. Pulmonary fibrosis patients, therefore, are in a state of oxygen depletion. That’s why they struggle for air. Cough is another consequence of lung scarring.

Prednisone, a cortisone drug, is the medicine that is usually picked for treatment, and it’s often used in conjunction with azathioprine.

Supplemental oxygen is almost always needed.

In some patients, lung transplantation is a consideration.

I am not dodging your question about longevity, but I can’t give you a reasonable estimate without knowing more details about your mother’s condition. Her doctors are the ones who can best answer that question for you.

DEAR DR. DONOHUE: What do you think of taking thyroid hormone for weight loss? A friend is doing this, and she has lost 30 pounds. I’m jealous. – M.M.

ANSWER: Don’t be jealous. It’s a foolish way to lose weight. Thyroid hormone speeds metabolism, and calories are burned. However, unneeded thyroid hormone can be harmful to the heart and many other body organs. For weight loss, stick with calorie restriction and exercise.

DEAR DR. DONOHUE: My father, 81, lives with us and has been quite active until the past month, when he began falling. He hasn’t broken any bones, but I worry about that happening. Have you any suggestions about what might be going on? – R.T.

ANSWER: Older people fall due to both serious and relatively innocent conditions. Even if the cause is innocent or if no cause can be found, the person still requires proactive protection for the very worry you state – broken bones. So, at the outset, your dad should be wearing hip protectors, available at medical-supply stores, and all booby traps in the home, like throw rugs and electrical cords haphazardly spread across the floor, should be removed.

Muscle weakness is often a cause for falls and unstable gait. The “get up and go” test is a simple and dependable way to assess a person’s muscle strength, with emphasis on leg muscles. The tested person is told to rise from a chair that has no arms, so the legs do all the work in getting the person to the vertical position. An armless dining-room chair is fine. After rising, the person is then told to quickly take about five steps, turn and return to the chair within 15 seconds. If the person passes the test, muscle strength needs no more investigation. If he or she fails, then that person is likely to benefit from a conditioning program supervised by trained personnel.

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.