Women diagnosed as having breast cancer are more likely to survive if they take large doses of vitamin C. And yes, they can take vitamin C in supplement form, Swedish nutritionists at the Karolinska Institutet concluded after carrying out a meta-study. Every 100 mg vitamin C that women with breast cancer consume daily reduces their chance of dying by a quarter, the researchers discovered.
Vitamin C and breast cancer
Is taking extra vitamin C good or bad for people who’ve been treated for cancer? Researchers can’t agree on the answer to this question.
Most scientists think that cancer survivors should be careful about taking vitamin preparations. These are good for healthy cells they say, but may be even better for cancer cells that have survived chemotherapy, radiation and hormone therapy. Scientists point to in-vitro studies for example in which an analogue of vitamin C protects breast cancer cells – see one here above – against the cancer medicine tamoxifen. [J Cell Mol Med. 2014 Feb;18(2):305-13.]
Tamoxifen blocks the effect of estradiol. Women who have the kind of breast cancer in which the cancer cells need estradiol to grow are given tamoxifen for a number of years after surgery, chemotherapy and radiation treatment.
According to an in-vitro study done at the Universiti Putra Malaysia vitamin C undermines the effect of tamoxifen, but it’s worth noting that the researchers only used the vitamin C analogue dehydroascorbic acid. In the body there is a balance between the vitamin C analogues dehydroascorbic acid and ascorbic acid.
If you also know that a) ascorbic acid can have similar effects as free radicals in cells [because when it’s converted into dehydroascorbic acid hydrogen peroxide is released] and b) that healthy cells generally react to this but cancer cells don’t and c) that dehydroascorbic acid does not have such a radical effect, can you conclude from the Malaysian study that breast cancer survivors should not use extra vitamin C? We don’t.
The Swedes approached the problem in a different way. They gathered data from 10 epidemiological studies in which researchers had followed a total of 17696 women for a number of years after their treatment, and kept track of how much vitamin C the women consumed daily.
In 6 of the studies the researchers looked at the use of supplements. And guess what: The women who used supplements containing vitamin C had higher chances of survival than women who had not taken any supplements.
The researchers also noticed a similar effect when they looked at total vitamin C intake: the more vitamin C the women consumed on a daily basis, the better their survival chances.
“Results from this meta-analysis suggest that post-diagnosis vitamin C supplement intake did not have a negative impact on breast cancer survival and may be associated with a reduced risk of mortality”, the Sweeds write. “Dietary vitamin C intake was also associated with a reduced risk of total mortality and breast cancer-specific mortality. More studies of post-diagnosis supplement use, including vitamin C, are warranted.”
Vitamin C and survival among women with breast cancer: a meta-analysis.
The association between dietary vitamin C intake and breast cancer survival is inconsistent and few studies have specifically examined vitamin C supplement use among women with breast cancer. 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-specific mortality and total mortality.
Studies were identified using the PubMed database through February 6, 2014 and by examining the references of retrieved articles. Prospective studies were included if they reported relative risks (RR) with 95% confidence intervals (95% CIs) for at least two categories or as a continuous exposure. Random-effects models were used to combine study-specific results.
The ten identified studies examined vitamin C supplement use (n=6) and dietary vitamin C intake (n=7) and included 17,696 breast cancer cases, 2791 total deaths, and 1558 breast cancer-specific deaths. The summary RR (95% CI) for post-diagnosis vitamin C supplement use was 0.81 (95% CI 0.72-0.91) for total mortality and 0.85 (95% CI 0.74-0.99) for breast cancer-specific mortality. The summary RR for a 100mg per day increase in dietary vitamin C intake was 0.73 (95% CI 0.59-0.89) for total mortality and 0.78 (95% CI 0.64-0.94) for breast cancer-specific mortality.
Results from this meta-analysis suggest that post-diagnosis vitamin C supplement use may be associated with a reduced risk of mortality. Dietary vitamin C intake was also statistically significantly associated with a reduced risk of total mortality and breast cancer-specific mortality.
PMID: 24613622 [PubMed – indexed for MEDLINE]