It’s no surprise that smoking causes numerous health problems, including respiratory diseases. However, recent studies have shown that young female smokers are at an increased risk of developing a common type of breast cancer.

Researchers from the Fred Hutchinson Cancer Research Center in Seattle found that heavy smokers, or those who smoke at least one pack a day for 10 years, are at a 60 percent higher risk of developing estrogen receptor-positive breast cancer than lighter smokers.

The study found that women ages 20 to 44 years old who were classified as heavy smokers were at a much higher risk of developing this type of breast cancer than other members of the population. However, they were not as likely to develop triple-negative breast cancer, which is less common but more aggressive than the estrogen receptor-positive breast cancer.

Dr. Christopher Li, the study’s senior author, stated that “there is growing evidence that breast cancer is another health hazard associated with smoking.” Li and colleagues previously noted in the journal Cancer that there are links between smoking and breast cancer, but questions still remain as to whether smoking has been linked to some types of breast cancers but not others.

For the study, Li and his team of researchers analyzed data from young women around the Greater Seattle area who had received a breast cancer diagnosis between 2004 and 2010. The team found that of the women in the study, 778 were diagnosed with the more common type of breast cancer, estrogen receptor-positive type, while 182 were diagnosed with triple-negative type. To round out their study, the team also included information from 938 women without cancer. Another important finding is that women who smoked, but not as heavily, were 30 percent more likely to develop some sort of breast cancer when compared to women who never smoked.

No direct link was found between smoking and triple-negative type breast cancer, although recent or current female smokers who had smoked for at least 15 years were 50 percent more likely to have estrogen receptor-positive breast cancer than women who smoked for fewer years.

The researchers noted that certain substances in cigarettes act as estrogen, which could promote estrogen receptor-positive breast cancer. Li added, “There are so many different chemicals in cigarette smoke that can have so many kinds of effects.”