Dear Dr. Roach: My husband (age 71) received a diagnosis of polycythemia vera a few years ago. I understand this variety of polycythemia isn’t caused by smoking, but we know that smoking does make it worse.

For most of his life, he’s had a history of smoking with some short periods of not smoking, and he continues to smoke several times every couple of months for a few days, or up to a week at a time.

I would like to get a sense of how destructive smoking is under this circumstance. Is there any way to quantify it? For example, each cigarette increases the blood thickness by a certain percent or the risk of stroke or heart attack by a certain amount. His blood work is usually within the normal parameters, and he tolerates hydroxyurea very well.

— A.N.

Answer: “Polycythemia” basically means “too many red blood cells.” Many conditions, including smoking, can cause polycythemia. Smoking reduces the oxygen in the blood due to carbon monoxide and other toxic substances in the smoke, causing the body to make more blood cells to compensate. However, polycythemia vera is a myeloproliferative disorder, a type of blood cancer caused by a mutation in the JAK2 gene. This causes excess development of red blood cells.

People with P. vera are at risk for blood-clotting, leukemia, and the gradual destruction of the bone marrow. However, the leading cause of death in people with P. vera is cardiovascular disease. This reflects the fact that effective treatment of P. vera allows people to die from other causes and that cardiovascular disease is increased in patients with P. vera.

Smoking then causes several distinct problems for people with P. vera; it worsens the production of red blood cells and damages the walls of the blood vessels, making heart attacks and strokes more likely. Smoking also reduces plasma volume, making the blood thicker and increasing the risk of stroke, which is of critical importance in P. vera.

Experts in P. vera make the strongest possible recommendation for those with the condition to quit smoking. Help with nicotine replacement therapy, group counseling, and medication like varenicline (Chantix) or bupropion (Zyban) can greatly improve cessation rates.

Quantifying the damage from cigarettes is tough. A good rule of thumb is that a smoker lives 8-12 years less than a nonsmoker. Another is that each cigarette steals 11 minutes of life from an otherwise healthy person. However, for your husband, the risk of smoking is at least triple this, in my rough estimation, due to his P. vera diagnosis.

Dear Dr. Roach: Can vasectomies be reversed?

— I.M.

Answer: A vasectomy should only be sought for men who are sure that they do not want children again. Still, there are times when men’s circumstances change, and they want to attempt a reversal of the vasectomy. Unfortunately, there are no guarantees.

When reversals were attempted within three years, 75% of men were able to father a child; whereas 15 years after the vasectomy, only 30% of couples were able to have a successful pregnancy.

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.