Linus Carl Pauling (1901 – 1994), the American scientist, peace activist, author, and educator who won two Nobel prizes, was one of the most influential chemists in history and ranks among the most important scientists of the 20th century. Linus Pauling’s work on vitamin C, however, generated considerable controversy. Pauling wrote many papers and a popular book, Cancer and Vitamin C. Vitamin C, we know today, protects cells from oxidative DNA damage and might thereby block carcinogenesis. Pauling popularised the regular intake of vitamin C; eventually he published two studies of end-stage cancer patients; their results apparently showed that vitamin C quadrupled survival times. A re-evaluation, however, found that the vitamin C groups were less sick on entry to the study. Later clinical trials concluded that there was no benefit to high-dose vitamin C. Since then, the established opinion is that the best evidence does not support a role for high dose vitamin C in the treatment of cancer. Despite all this, high dose IV vitamin C is in unexpectedly wide use by CAM practitioners.
Yesterday, new evidence has been published in the highly respected journal ‘Nature’; does it vindicate Pauling and his followers?
Chinese oncologists conducted a meta-analysis to assess the association between vitamin C intake and the risk to acquire lung cancer. Pertinent studies were identified by a searches of several electronic databases through December of 2013. Random-effect model was used to combine the data for analysis. Publication bias was estimated using Begg’s funnel plot and Egger’s regression asymmetry test.
Eighteen articles reporting 21 studies involving 8938 lung cancer cases were included in this meta-analysis. Pooled results suggested that highest vitamin C intake level versus lowest level was significantly associated with the risk of lung cancer. The effect was largest in investigations from the United States and in prospective studies. A linear dose-response relationship was found, with the risk of lung cancer decreasing by 7% for every 100 mg/day increase in the intake of vitamin C . No publication bias was found.
The authors conclude that their analysis suggested that the higher intake of vitamin C might have a protective effect against lung cancer, especially in the United States, although this conclusion needs to be confirmed.
Does this finding vindicate Pauling’s theory? Not really.
Even though the above-quoted conclusions seem to suggest a causal link, we are, in fact, far from having established one. The meta-analysis pooled mainly epidemiological data from various studies. Such investigations are doubtlessly valuable but they are fraught with uncertainties and cannot prove causality. For instance, there could be dozens of factors that have confounded these data in such a way that they produce a misleading result. The simplest explanation of the meta-analytic results might be that people who have a very high vitamin C intake tend to have generally healthier life-styles than those who take less vitamin C. When conducting a meta-analysis, one does, of course, try to account for such factors; but in many cases the necessary information to do that is not available, and therefore uncertainty persists.
In other words, the authors were certainly correct when stating that their findings needed to be confirmed. Pauling’s theory cannot be vindicated by such reports – in fact, the authors do not even mention Pauling with one word.
And then there are still studies available which connect the intake of high doses of antioxidants with cancer as cells which would otherwise go into apoptosis due to excessive damage (DNA for example) survive and get the chance to develop into cancer cells.
I see people conflate dietary vitamin C – often in ranges between 100-400 mg per day – and the effect of giving bolus doses of 10 or more grams one or more times per week. Before we even consider whether dietary vitamin C is a marker for a broader pattern of more fruits and vegetables, it should be clear that these are two different things.
What about all research done by Finns – that it is not wise for a smoker to consume excess antioxidants?
But anyway, there is genetic component, so do you need to select as much relatives (i mean just from one family with no cancer patients) as possible or vice versa? Do you need to exclude people from families with cancer patients, even if cancers are different? (Because cancer syndromes).
And, of course, lifestyle – maybe it would be better to choose cancer that is not so much affected by lifestyle or choose patients with eliminated lifestyle risk factor (e.g. slender women for research of breast cancer)?
“new evidence has been published in the highly respected journal ‘Nature’”
Note that the meta-analysis is published in mega journal “Scientific Reports”.