Multivitamin Use and Breast Cancer Incidence
The stated purpose of the paper Multivitamin use and breast cancer incidence in a prospective cohort of Swedish women (Lersson, Akesson, Bergkvist & Wolk, 2010) was whether there was a relationship between multivitamin use and breast cancer, as well as the status of both the progesterone receptor (PR) and the estrogen receptor (ER) of tumors. The study followed up 35,329 cancer-free women who had responded to a questionnaire concerning their use of multivitamins from January 1998 to December 2007, their cancer diagnosis or their death, whichever event came first. The authors found that there was a significant relationship between multivitamin use and breast cancer incidents, with multivitamin use increasing breast cancer risk by 19.5%. However, there was no significant relationship between multivitamin use and PR or LR status, which indicated that multivitamins did not influence the subtype of breast cancer.
Objective of the Article
The title of the article adequately defines the primary objective of the article, but does not mention the fact that PR and ER status of tumors was also being considered, which can be regarded slightly misleading. The article also does not contain an actual hypothesis statement, and the authors do not make it clear whether they expect a relationship to be present or not. The literature review section to this article is limited, and the authors dedicate two paragraphs to discussing previous literature on the topic. In this part of the article, seven articles are identified that examined the relationship between multivitamin use and breast cancer, and these had inconsistent results. The authors did not examine the limitations or strengths of any of these studies
Self-Administered Questionnaire
This study made use of a self-administered questionnaire to determine what the multivitamin habits of participants were, and these participants were followed to determine whether breast cancer was diagnosed. Because this study was not experimental, there were no treatment groups selected. Participants in this study were members of the Swedish Mammography Cohort, which is a cohort study that has been used in other research, making this a study based on secondary data. The authors made use of a questionnaire that was filled out by this cohort in 1997. All participants were female, and cohort members were excluded if they did not have a National Registration Number or if this was erroneous, if there was no information provided about supplement use or if they had a history of cancer. Because the information was collected as part of the cohort study, the authors did not give information about the validity of the instruments, testing procedures or how the original sample was obtained, which makes determining reliability of the methods difficult.
The authors made use of Cox proportional hazard models to determine risk factors, and adjusted the multivariable models based on a range of factors including history of breast cancer within the family, age at menopause, use of oral contraceptives, alcohol intake and body mass index. In addition, the authors also used stratified analyses and log-likelihood ratio test, using two-sided tests. The authors used a statistical significance level of 5% to determine whether tests were statistically significant. The authors briefly mention that the results from their study raise some concern, and should be studied further, however, this is not elaborated on, and the authors do not mention what type of research should be undertaken. In general, this research does not raise any significant ethical concerns, as the study was not risky or invasive for participants. However, some important ethical elements are not discussed. In particular, the authors do not go into detail about the methods that were used to recruit or test the original sample, or whether any approaches were used to ensure that participants’ information remained confidential.
Key Limitations of the Study
The authors identified two key limitations of the study. The first of these was the fact that the questionnaire was self-administered, which could potentially lead to incorrect estimates of the level of exposure to multivitamins for some patients. The second limitation was the use of an observational design. This design could have meant that there were potentially confounding factors that were not evident, which could have influenced the results of the study. However, despite these limitations, the data supports the conclusions of the authors. One of the reasons for this is that the study had more than 30,000 samples and considered a large number of potentially confounding factors. Because of this, the statistical tests used had a high amount of power and ability to detect effects. This means that the authors were able to effectively answer their research question, by showing that there was a relationship between the use of multivitamins and breast cancer, but that multivitamins do not influence the subtype of the breast cancer.
Overall, this was a well-researched paper that attempted to effectively address the issue of a relationship between multivitamin use and breast cancer risk. The authors considered many potentially confounding factors within their models and used a large sample size. Both of these factors helped to ensure that the statistical tests correctly determined whether there was any relationship present. The paper was well written and clearly presented, making use of appropriate language and tables that made the results easy to follow. However, the quality of the paper was compromised by the limited literature review, lack of hypothesis and failure to discuss implications for future research in detail.
