The sperm of men who smoke, compared to those who don’t, have more damaged DNA, fewer active energy-generating mitochondria and more proteins indicating a revved-up immune response, according to a small study.

Past research has found that smokers tend to have more abnormal sperm in terms of number, motility, shape and acrosomes that help sperm penetrate an egg.

“We knew that smoking leads to decreased sperm DNA integrity, decreased mitochondrial activity and decreased acrosome integrity,” said senior author of the new study Ricardo Pimenta Bertolla of Sao Paulo Federal University in Brazil. “Sperm from these men are thus less capable of achieving fertilisation, and, due to high rates of DNA fragmentation, are more likely to lead to early embryo loss and even to consequences in the offspring.”

DNA damage in a father’s sperm has been tied to a child’s risk of childhood cancer, he said.

“All these effects were known by previous studies from our group and from other groups as well,” but the new study confirms this with new patients, and helps to demonstrate how these alterations happen, Bertolla said.

Smoking cigarettes may change protein manufacture in the sperm, increasing some and decreasing others, which indicates inflammation in the testicles and other glands, he and his coauthors write in BJU International.

“Excessive seminal inflammation, thus, seems to be one of the mechanisms through which smoking alters sperm,” Bertolla said.

The researchers tested the functional quality of sperm from 20 nonsmoking men with normal semen quality and from 20 men who said they smoked at least 10 cigarettes per day. They tested semen volume, pH, sperm concentration, motility and shape. They also observed DNA damage and activity in the mitochondria.

For women, smoking has been tied to earlier menopause, higher risk of miscarriage and ectopic pregnancy and less success with in-vitro fertilisation, he said.