DEAR DR. ROACH: I hear about insulin resistance all the time. What is it and how do you prevent it? — M.E.

ANSWER: Insulin lowers blood sugar levels by moving the sugar into the cells that need it. Without insulin, cells starve for energy despite very high amounts of sugar in the blood.

A small amount of insulin should drop the blood sugar dramatically. In people with insulin resistance, the effect of insulin is blunted. In such people — like those with Type 2 diabetes or prediabetes — insulin blood levels are usually higher than they are in people without diabetes. This is often, but not always, in conjunction with obesity. However, there are several other causes of insulin resistance, including medications, stress, pregnancy, anti-insulin antibodies and genetic causes.

Glucocorticoids such as prednisone cause insulin resistance, and stress causes the body to release its own glucocorticoid (cortisol) as well as other hormones that oppose the action of insulin. There are many other drugs that can cause insulin resistance, predisposing people to weight gain and even overt diabetes. Among these, beta-blockers, niacin, birth control pills and HIV medications are among the most important.

Insulin resistance may not be completely preventable, but it can be minimized. The most important way to do this is by having a normal body weight. Exercise directly reduces insulin resistance, even if body weight stays the same. This is one reason exercise is frequently recommended: It can make big improvements in health, even if a person doesn’t lose a pound.

DEAR DR. ROACH: I found my water aerobics class very helpful. Would a water aerobics class be safe during the coronavirus pandemic? Do the chemicals in the water kill the virus? — A.

ANSWER: The primary way of spreading coronavirus is person-to-person via respiratory droplets. If you are a few feet from another person, and you are both breathing heavily from exertion (or singing), then there is a high risk of transmitting the virus. Being in a pool does little or nothing to reduce that risk. Wearing a mask in the pool is impractical, so I don’t think a water aerobics class with multiple people is advisable.

DEAR DR. ROACH: I’m 70 years old and do 400 push-ups every morning. I also lift weights two days a week. I have developed an epigastric hernia. It doesn’t bother me, and my primary doctor said leave it alone. Can I continue my exercise program without causing further damage? I do wear a brace during my workout and feel absolutely no pain. — R.S.

ANSWER: Epigastric hernias are fairly common, especially in men. They arise from a weakness in the abdominal wall in the midline, above the belly button, and are generally small. Surgery is needed only rarely, and if your doctor has said not to worry about it, that’s a very good reassurance.

If the exercise regimen isn’t bothering you or your hernia, there is no reason to stop. Four hundred pushups is pretty impressive! Keep up the great work.

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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 send mail to 628 Virginia Dr., Orlando, FL 32803.