In her doctoral dissertation, Katuwal modeled the dual effect theory of parity on breast cancer risk. Her findings among around 19,000 Finnish women with breast cancer and their population controls confirmed the dual effect theory of pregnancy, which concludes that although childbirths have a long-term protective against breast cancer, there is short-term increase in the risk immediately after each pregnancy. She observed that the risk of breast cancer soon after the first childbirth was two-fold as compared to women without birth. The respective excess risk was only 20% after the 5th birth.
“In the current era, increasing number of women are career-oriented and therefore it is more essential than ever to understand the factors in occupational settings as well as the effects of modern work life such as, increasing sedentary work, the demand of longer education and career planning which may lead to postponement of childbirth and thus, increase risk of breast cancer risk.”, states Katuwal.
In her dissertation Sushmita Katuwal studied the variation in breast cancer risk by occupation and association of occupational physical activity using five-country data of the Nordic Occupational Cancer Study which included follow up of 7.5 million women resulting in 373,361 breast cancer cases. She says that occupational sedentariness was associated with somewhat increased breast cancer risk but not so much as has been suggested in studies which do not take into account other factors which are associated both with physical activity and with breast cancer risk.
Katuwal also exemplified a situation where direct information on individual’s reproductive, social and lifestyle history is not available. This is still common in developing countries and in developed countries with poor registries or practices which make it difficult to use data for research. In such situation, e.g., the information on causes of death of the breast cancer patients could be used as a surrogate for obtaining the information on possible risk factors of the diseases. In one of her studies, she observed that the risk factors associated with the causes of death among breast cancer patients were also the risk factors for breast cancer.
“We observed significantly higher risk of stomach cancer death among breast cancer patients and since alcohol consumption is a well-established risk factor of stomach cancer, we can assume that alcohol consumption might have played a role in breast cancer causation as well”, says Katuwal.
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The dissertation is available online at