Vitamin C causes cancer: retro health scare

October 31, 2008 at 8:47 pm (Bad Science, Media, Supplements) (Antioxidants, Cancer, DNA adducts, Food Supplements, Nature, nutritionists, Podmore et al, Prooxidant, Vitamin C)

In 1998, Ian Podmore and others had a paper published in Nature. This quote is from the paper:

Vitamin C is marketed as a dietary supplement, partly because of its ‘antioxidant’ properties. However, we report here that vitamin C administered as a dietary supplement to healthy humans exhibits a pro-oxidant, as well as an antioxidant, effect in vivo.

Here’s an idea of what the press ran with

TOO MUCH VITAMIN C CAN GIVE YOU THE BIG C; SCIENTISTS THINK IT HARMS DNA; TOO MUCH VITAMIN C CAN TRIGGER CANCER WARN SCIENTISTS [headline and sub-headlines from the Daily Mirror report; April 9th 1998]; TOO much vitamin C could trigger cancer and other diseases, scientists warned yesterday [from the body of the Mirror story]; LARGE doses of vitamin C may not be such a healthy option, research at Leicester University has suggested. Far from preventing diseases such as cancer and heart disease, vitamin C in large amounts might help trigger them [The Times; April 9th 1998]

Here’s some extracts from the published responses

“Because the reported changes in levels of 8-oxoguanine and 8-oxoadenine occurred in lymphocytes, the relevant vitamin C concentrations are not those in plasma but those in lymphocytes; however, these data were not presented”; “…because 500 mg is a saturating dose of vitamin C, the initial plasma vitamin C concentration was roughly 50 mM (refs 5,6). However, at this concentration lymphocytes are already saturated…”; “The concentrations of 8-oxoguanine reported by Podmore et al are 25–120 times more than those reported by others” [Mark Levine and others]

“Artefactual oxidation ex vivo in their study cannot be excluded and hence their results are difficult to interpret”; “the study design is without randomization or true placebo control”; “Third, Podmore et al. did not mention whether any of their subjects smoked. Fourth, the authors did not reference relevant previous studies.” [Poulsen and others]

Here’s a few bits from the authors’ reply to the above mentioned responses

“The suggestion made above by Poulsen et al. and Levine et al. that artefactual oxidation has occurred during lymphocyte isolation and DNA extraction is based entirely on the measurement of a single marker, 8-oxoguanine. […] we have measured 8-oxoguanine in DNA samples from healthy volunteers by two additional assays […] All three assays show the same decrease in 8-oxoguanine on vitamin C supplementation.”

“We disagree with Poulsen et al. about the need for randomization or a double-blind study, as we were not reporting a clinical trial requiring a subjective interpretation of efficacy.”

“We do not consider the references cited by Poulsen et al. to be relevant to our study on human volunteers (all of whom were non-smokers, as smoking is known to reduce levels of plasma ascorbate).”

“Levine et al. argue that lymphocytes saturate when plasma ascorbate levels reach 50 mM. We do not find their argument compelling as it seems to be based on a depletion–repletion study of seven healthy volunteers”

“we observe highly significant positive and negative correlations between plasma ascorbate concentration and levels of 8-oxoadenine and 8-oxoguanine, respectively, which we believe suggests that vitamin C is influencing levels of both markers in a divergent manner (Cooke, M. S. et al., manuscript in preparation). This differential effect, which cannot be explained as methodological artefact”

This next bit is interesting in light of the media articles: “In conclusion, our results show a definite increase in 8-oxoadenine after supplementation with vitamin C. This lesion is at least ten times less mutagenic than 8-oxoguanine, and hence our study shows an overall profound protective effect of this vitamin.” [my italics]. So, not quite the “Vit C gives you the Big C!” story that appeared in the newspapers then. What a surprise.

Sadly, and I genuinely mean this, I have been unable to find (so far) any record of a response from the food supplements industry – nothing from HSIS, HFMA or the CRN. I’m sure this is due to my piss-poor research skillz rather than any lack of response but the entire comedy value of this post relied upon there being something from a trade body giving us half-truths or red herrings that have no bearing on the study findings or soliciting opinion from such experts on health as Cliff Richard. Who, of course, you will all remember had his say on the Cochrane review of antioxidant supplements. The responses to the article and the replies from the author are great. Levine, Poulsen and their respective colleagues bring up points that are relevant to the study and the authors answer these points. They discuss the methodology, results and interpretation of the study and they look at what factors have and have not been taken into consideration. I actually remember reading a response to the Nature paper from an industry spokesman and am incredibly annoyed that I can’t find it. I’m almost certain that the spokesman made no comment relating to the techincal apsects of the study, no criticism of the methodology… basically said nothing at all that was relevant. The responses to the Cochrane review are even more egregious examples of the inability of the food supplements-nutritionist industrial complex to engage with the evidence and so I have linked to them to shine a bit of light on the willingness of the vast, corporate incarnate, $50bn food supplement industry. No member of which, incidentally, appears to have spoken out yet about Matthias Rath. Never gonna happen.

I like to think I’ve managed to make the points that the newspapers don’t accurately report scientific papers and that nutritionists and the $50bn food supplements industry don’t engage with evidence in the way that academics do. Next up: Pope is Catholic, bears shit in woods [Except during hibernation, when they use a butt plug made of hair and faeces to cork their cornholes. Apparently.] and quite possibly a stunning revelation that Russell Brand can be a bit rude sometimes. That or something on the disgraceful way that the media represents mental health issues.

Links

The Podmore paper: if you’re willing to pay, that is… ; Link to PDF of responses: podmore-et-al-vitamin-c-as-pro-oxidant ;