Physical activity, body mass index and prostate cancer : studies of risk, progression and mortality
Sammanfattning: Prostate cancer is the most common cancer among men in developed countries, but it is still unclear what causes the disease. Body mass index (BMI) and physical activity are modifiable lifestyle factors with the potential to influence the development and progression of prostate tumors and may provide alternative strategies for reducing both prostate cancer incidence and mortality. This thesis includes studies of the importance of body weight and physical activity on prostate cancer as well as methodological studies of how to assess physical activity in epidemiological studies. In Study I and II we aim to clarify the effect of BMI, weight change and physical activity on prostate cancer progression and mortality, while we in Study V aim to investigate the associations between BMI, serum prostate specific antigen (PSA) and the risk of prostate cancer. In Study III and IV we aim to assess the validity of the new web-based physical activity questionnaire Active-Q against three different reference methods. In Study I and II, we found that high BMI was associated with increased rates of overall mortality, but not progression or prostate cancer specific mortality, in men diagnosed with localized prostate cancer. An increase in body weight by >5% after diagnosis was associated with a higher prostate cancer specific mortality, while a weight reduction by >5% after diagnosis was associated with higher overall mortality. Frequent walking/bicycling and exercise were associated with lower prostate cancer specific and overall mortality, compared to a less active lifestyle. Moreover, high levels of total recreational activity and household work were associated with lower overall mortality. Study V showed that men with high BMI had lower serum PSA-levels, compared to men with normal BMI. Although BMI was not associated with overall prostate cancer risk, there was a suggested association between high BMI and high-grade prostate cancer. Active-Q was validated with regards to energy expenditure and total MET-hours against doubly labelled water and pedometers in Study III and with regards to time spent in different intensity levels of activity against accelerometers in Study IV. Active-Q showed moderate validity compared to the reference methods and good absolute agreement for energy expenditure while a somewhat lower agreement for time at different intensity levels was seen. When comparing repeated Active-Q assessments, the questionnaire showed high reproducibility. In conclusion, a physically active lifestyle after prostate cancer diagnosis is beneficial and associated with lower levels of both overall and prostate cancer specific mortality. Our results also showed that a large increase in body weight after diagnosis was associated with higher prostate cancer specific mortality, whereas weight reduction was associated increased higher overall mortality. Although we did not find a clear effect of BMI on overall prostate cancer risk, progression or prostate cancer specific mortality, we found that men with high BMI had lower levels of serum PSA, potentially hampering early detection of prostate cancer. Weight maintenance and a physically active lifestyle after diagnosis may complement prostate cancer treatment to improve survival. Also, Active-Q is a valid method for assessing energy expenditure and time spent at different intensity levels in future epidemiological studies.
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