Vitamin C and survival among women with breast cancer: A Meta-analysis
Introduction
Breast cancer is the most commonly diagnosed cancer in women worldwide [1] and in the United States (US) alone there are approximately 2.9 million breast cancer survivors [2]. Multivitamin and supplement use is common among cancer patients with a prevalence reported to range from 75% to 87% among breast cancer survivors [3]. Vitamin C is one of the most commonly consumed supplements [4], however, the safety and benefits of oral vitamin C supplement use among cancer survivors has not been established [5], [6], and few studies have specifically examined vitamin C supplement use among women with breast cancer [7], [8], [9], [10], [11]. The association between dietary vitamin C intake and breast cancer survival is inconsistent, with some studies reporting a reduced risk of mortality with increasing intake [6], [7], [9], [12], [13], [14], [15], [16], and others reporting no association [17], [18], [19], [20], [21]. The purpose of this study was to summarise results from prospective studies on the association between vitamin C supplement use and dietary vitamin C intake and breast cancer survival.
Section snippets
Search strategy and study selection
We conducted a literature search through February 6, 2014 using the PubMed database (http://www.ncbi.nlm.nih.gov/pubmed ) without restrictions on language. The following search terms were used: ‘vitamin C’ or ‘vitamin C supplements’ or ‘supplements’ and ‘breast cancer’ or ‘breast cancer mortality’ or ‘breast cancer survival.’ In addition, we reviewed the reference lists from retrieved articles to identify additional studies.
To be included in the meta-analysis the following criteria had to be
Study characteristics
We identified 15 papers with data from 11 prospective observational studies that were potentially eligible for inclusion into the meta-analysis [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21]. Two were excluded because they did not report RRs or CIs for vitamin C intake [12], [21], three were excluded because they only reported results for total vitamin C intake (food + supplements) [13], [16], [19], and one had more recent results available within the
Discussion
In this meta-analysis, dietary vitamin C intake and post-diagnosis oral vitamin C supplement use were statistically significantly associated with a reduced risk of total mortality and breast cancer-specific mortality.
There are several mechanisms through which intake of vitamin C may influence mortality among women with breast cancer. Vitamin C exhibits antioxidant actions including the neutralisation of free radicals which may impact cancer progression [29], [30]. At higher doses it may also
Role of the funding source
The funding source had no role in the study design, collection, analysis, and interpretation of data, in the writing of the manuscript or in the decision to submit the manuscript for publication.
Conflict of interest statement
None declared.
Acknowledgement
This work was supported by the Swedish Cancer Foundation.
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