Experts on new study on multi-vitamins and breast cancer

A new study published in the American Journal of Clinical Nutrition this month has raised concerns that the use of multi-vitamin supplements may increase the risk of breast cancer.

multivitaminsCoverage in the New Zealand Herald and on the Sciblogs websitelooks at this issue.

A copy of the paper can be accessed by logging into the resource library of the Science Media Centre website.

We asked New Zealand health and nutrition experts for their views on this new study and what the public health message is for women who might be currently taking multi-vitamin supplements.

Rod Jackson, Professor of Epidemiology at the University of Auckland, comments:

“This study is non-randomised, so I wouldn’t take too much from it. As vitamin supplements in otherwise healthy people are only likely to cause either small harms or small benefits, randomised controlled trials (RCTs) are essential to determine their effects. Cohort studies like this Swedish study are just too prone to biases to be very helpful.

“A Cochrane meta-analysis on anti-oxidant vitamins published in 2008 included all the high quality RCTs examining vitamin supplementation and mortality and demonstrated that there was either an increased risk of death or a tendency towards an increased risk of death among people taking these vitamins (Vitamin A, beta-carotene, Vitamin C and Vitamin E). Since the meta-analysis was published two further RCTs on B vitamins have also demonstrated an increased risk of death. While these studies were based mainly on individual vitamins, there is no reason to believe that combining them as multivitamins would make them safer.

“So the bottom line is that the best available evidence demonstrates that vitamin supplementation in otherwise healthy people increases the risk of death. While the Swedish study supports this conclusion, we already have much better evidence of harm. In my opinion, the only potential benefit of the Swedish study is to encourage people to seek out the best evidence which comes from the Cochrane meta-analysis.

“The main advice for the public at large is that based on the current best evidence (which doesn’t include the recent Swedish study), they should not take vitamin supplements unless they have a diagnosed deficiency.”

Dr Jan Pearson, health promotion manager from the Cancer Society comments:

“This study only found a modestly increased risk in those who were taking vitamin supplements compared to those who did not take multi-vitamin supplements.

“It is important to keep this in perspective of the well established risk factors for breast cancer – i.e. obesity, physical inactivity and drinking alcohol are much more significant risk factors for breast cancer.

“Women taking multi-vitamin supplements should not be alarmed, but should consider whether they need to take a multi-vitamin supplement. It is much more advisable to have a healthy diet with a variety of fresh fruit and vegetables than rely on getting our nutrients from multivitamin pills.”

New Zealand Registered Dietitian Angela Berrill comments:

“A recent study published in the American Journal of Clinical Nutrition found that women (aged 49 – 83 years) taking multi-vitamin supplements had nearly a 20% increased risk of developing breast cancer. Given that many people take multi-vitamins in an effort to fight off disease, this may seem alarming. However, before you start tipping the rest of your multivitamins down the sink, it is important to take a closer look at the research itself.

“The results from the trail were linked to women who took a multi-vitamin supplement everyday (or more regularly) for over 3 years. It is known that formulations of multi-vitamins can vary greatly. However, the types of multi-vitamin used was not recorded, meaning the multi-vitamins exact nutritional composition is unknown. Therefore, the research is unable to determine which multi-vitamins may increase they risk of breast cancer and even which specific nutrients may be responsible. While this was a well conducted large scale observational trial, the results only give us a snapshot of information.

“Therefore, we can not necessarily assume ’cause and effect’, like we could if a randomised double blind clinical trial had been conducted. In this type of trial design, participants would be given either a multivitamin or a placebo and then the results analysed to see if in-fact multi-vitamin use does cause cancer. In the trial, the researchers controlled for factors which were known to increase the risk of breast cancer. However, due to the study’s observational nature, those who took multivitamins may have also been a group which had other ‘unknown’ breast cancer risk factors.

“While the findings are interesting, and something to be aware of, more research is needed to establish whether or not multivitamin use does in-fact cause breast cancer. In the interim, and until such time as more research is available, women should try to ensure they meet their vitamin and mineral requirements through eating a healthy and balanced diet – including foods from all the main food groups. In such instances where diet alone is unable to meet nutrient an individual’s requirements, multivitamin use may still be warranted.”