In 1700 Bernardino Ramazzini, an Italian doctor known as the “father of occupational diseases,” published the first book on occupational epidemiology. He found that certain diseases were associated with specific exposures, including metals and dust that may be associated with cancer in miners and industrial workers, poor posture in mining workers and pain, and a high incidence of breast cancer but not cervical cancer among nuns.
Rashcini’s most important contribution was his observation in 1713 that nuns were more likely to develop breast cancer than cervical cancer, compared with the general population of women living in Padua (his hometown), a result he had not expected. At the time, one theory about breast cancer was that it was caused by “intense sexual intercourse.” He then had to come up with an alternative theory to explain the phenomenon: that breasts are sexual organs, and without regular sexual activity, they rot, leading to cancer. However, this theory obviously doesn’t explain why the nun doesn’t have a cervix. Now, this theory is very funny. Nevertheless, he was the first to suggest that lifestyle was closely related to cancer. The high incidence of breast cancer and low incidence of cervical cancer among nuns are related to the lifestyle of living alone.
Then why is the nun’s breast cancer so prevalent? Modern medical research has found that after a woman becomes pregnant, her body’s hormones will change dramatically, and estrogen levels will drop significantly. You know, estrogen is associated with the development of breast cancer. Falling estrogen levels during pregnancy can reduce the risk of breast cancer. Indeed, research now shows that women who conceive for the first time before age 30 have a lower risk of breast cancer than those who conceive for the first time after age 35.
Why is that nun’s cervical cancer incidence low? This is because almost all cases of cervical cancer (> 99%) are caused by the human papillomavirus (HPV), which is a sexually transmitted disease. Since the nun lived alone, she had never been infected with the virus and never developed cervical cancer.
Either way, these two observations are the first to identify lifestyle factors as a possible cause of cancer. Today, we still use this method of observation. For example, smoking is a lifestyle, and the role of smoking in the development of lung cancer is widely accepted. So, even though Ramazcini’s hypothesis about the incidence of breast and cervical cancer among nuns is wrong, this is still a great early epidemiological study and shows how epidemiology can help us prevent disease.
The lesson of this story is that to reduce the risk of breast cancer, it may be a good idea to get pregnant and have a baby, and early. If you want to reduce the risk of cervical cancer, you need to reduce HPV infection, and the best way to do that now is to get the HPV vaccine.