When applying different previously used exposure metrics for night work.We found that estimates showed a slight(10%-30%) but nonsignificant increase of risk for breast cancer exposure categories.
By using consecutive night shifts as the exposure parameter,we observed significantly elevated breast cancer risks in the range of 1.7-1.8 in nurses who worked 5 or more years in jobs including ≥6 consecutive night shifts, compared with nurses who never worked night shifts.To our knowledge ,this is the first study to reveal an association between a higher number of consecutive night shifts and breast cancer risk.the study is based on a large cohort of nurses educated from 1950 to 1984 and includes a high number of breast cancer cases. Compulsory reporting of all cancer cases to the national cancer registry made in possible to identify all breast cancer cases in the cohort for the period 1990-2007. However ,a several validity questions have to be addressed.The study is based on living, prevalent cases. Selection bias might affect the results when deceased cases are excluded ,However, a subanalysis of cases diagnosed in 2004-2007 showing approximately the same estimates as for all suggests that it is unlikely that the inclusion of long-term survivors has biased the results.Although the participation rate is considered fairly high in both group, differential recruitment between group, together with the 9% higher response rate among cases than controls
might also have contributed to selection bias. Responders and nonresponders were, however similar with respect to socioeconomic status, occupation, age distribution,and sex.
A detailed occupational history with information on lifetime night work experience and data on well-known and suspected risk factors was obtained by telephone interviews.
When applying different previously used exposure metrics for night work.We found that estimates showed a slight(10%-30%) but nonsignificant increase of risk for breast cancer exposure categories.
By using consecutive night shifts as the exposure parameter,we observed significantly elevated breast cancer risks in the range of 1.7-1.8 in nurses who worked 5 or more years in jobs including ≥6 consecutive night shifts, compared with nurses who never worked night shifts.To our knowledge ,this is the first study to reveal an association between a higher number of consecutive night shifts and breast cancer risk.the study is based on a large cohort of nurses educated from 1950 to 1984 and includes a high number of breast cancer cases. Compulsory reporting of all cancer cases to the national cancer registry made in possible to identify all breast cancer cases in the cohort for the period 1990-2007. However ,a several validity questions have to be addressed.The study is based on living, prevalent cases. Selection bias might affect the results when deceased cases are excluded ,However, a subanalysis of cases diagnosed in 2004-2007 showing approximately the same estimates as for all suggests that it is unlikely that the inclusion of long-term survivors has biased the results.Although the participation rate is considered fairly high in both group, differential recruitment between group, together with the 9% higher response rate among cases than controls
might also have contributed to selection bias. Responders and nonresponders were, however similar with respect to socioeconomic status, occupation, age distribution,and sex.
A detailed occupational history with information on lifetime night work experience and data on well-known and suspected risk factors was obtained by telephone interviews.
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