Tuesday 6 May 2014

Organic Food and Cancer Risk

There is a theory popular in certain alternative and complementary medicine circles that cancer is caused by environmental toxins, radiation, microwaves, mobile phones and just about every modern convenience in the household. While there's little evidence for any of this, the idea that there are 'chemicals' lurking in the environment has become common-place, particularly when it comes to food. Hence one of the most common questions from newly diagnosed cancer patients: should I switch to an organic diet? There are enough people out there pushing the idea that 'organic' food is healthier than conventionally grown food, so it should be no surprise that people naturally feel that food grown 'without chemicals' will help them in the fight against cancer. After all conventional crops depend on 'chemicals' and organic food doesn't. And we all know that chemicals, in this case mainly pesticides, are bad for you. Therefore organic food should be healthier, and the strong growth in organic food sales in the last ten or fifteen years shows how popular opinion has accepted this assertion. 

However, the results of a new UK study that looked at cancer risk and the consumption of organic food seems to suggest that popular opinion is pretty much wrong in this case (http://www.nature.com/bjc/journal/v110/n9/full/bjc2014148a.html). While organic food and alternative medicine advocates have pushed organics as a way of reducing cancer risk, the study shows that it makes little difference one way or another. The study in question appears in the British Journal of Cancer and is by Oxford University cancer epidemiologist Dr Kathryn Bradbury and co-workers. Part of the Million Women Study funded by Cancer Research UK and the Medical Research Council, this particular bit of research tracked 623 080 middle-aged British women for almost ten years and looked at their pattern of organic food consumption and the incidence of sixteen different cancer types, as well as overall cancer incidence.

Based on their reported eating habits the women were put into three groups: never, sometimes, or usually/always eating organic food. The headline result showed that eating organic was not associated with overall cancer incidence one way or another (in fact there was a tiny increased overall risk of about 3%, but it’s the sort of noisy result one can ignore). The results for the different types of cancer are mixed, with some showing increased or decreased risks, but no overall pattern or anything too dramatic. These results, in contrast to the myths of wholesome organic, have upset some people, especially the British Soil Association, the guardian of all things organic in the UK (including being the premier organic certification body in the country). 

According to Peter Melchett, Policy Director at the Soil Association, the study is flawed because certain confounders weren’t addressed, because the authors don’t understand what pesticides are found in food or how they get into food. However, he was quick to pick out one of the results for particular attention – the numbers show that there is an apparent 21% decrease in non-Hodgkins lymphoma risk among the women who reported usually or always eating organic food. However, there were other numbers that were not picked out by the Soil Association, the most alarming of which was the apparent 9% increase in the risk of breast cancer. This was a result that the study authors subjected to a series of additional statistical tests which didn't make the result disappear. More alarming still was the 37% increase in the risk of developing a soft tissue sarcoma, a form of cancer which is rare and hard to treat. Why no mention of those figures at the Soil Association?

Of course the fact is that all of these figures are dealing with relative risk, which is standard practice in epidemiological studies. To get some perspective, the chances of getting non-Hodgkins lymphoma is about 2.1%, so if the results of this study hold true, then sticking to an always organic diet will reduce that to 1.66%. The figures for breast cancer are around 12.3% life-time risk, and this will be increased to 13.4% if you go the all organic route. And if you really want to trade punches with the proponents of organic, you can point out that a high-organic diet in the population will lead to more cancers as the incidence of breast cancer is much higher than the incidence of non-Hodgkins.

However, it’s unlikely that this finding is going to do much to change the minds of those who've decided that organics=healthy. After all, this is not the first negative study when it comes to organics and health. A systematic review published in the Annals of Internal Medicine in 2012 found that ‘The published literature lacks strong evidence that organic foods are significantly more nutritious than conventional foods.’ There were differences reported to do with pesticide residues but nothing to cause alarm. In terms of nutrient content, there was one statistically significant nutrient where organics out-did conventional produce: phosphorous. Now, if you’re coming out of a famine and have the choice then eating organic is the better choice, but if you’re not then increased phosphorous is pretty much irrelevant as it’s abundant in the diet.

It’s concern about pesticide residues that ultimately drive the idea that organics are better for us. This ignores the fact that even organic food uses pesticides, for example rotenone and pyrethrin, some of which are considered carcinogenic or otherwise hazardous to health. And, just to throw in some numbers, a study by the United States Department of Agriculture in 2012 found that 4% of organic food samples had pesticide residues above the 5% EPA limit, which technically meant they would have failed the organic certification they carried.   

But leaving that aside, the chemophobia of much of the population is stoked by the use of in vitro studies which show that certain pesticides are carcinogenic. However, there is a huge difference between the inside of a petri dish and the inside of a human. Pesticides are amongst the most heavily regulated chemical agents in the world, and if there was a link to cancer incidence then we would expect to see it in studies such as this one, and in studies that looked at farm workers and others who have greater exposure to pesticides. One recently published paper looked at the incidence of cancer in agricultural workers in France during the period 2005 – 2009 (the AGRICAN study). It reported that overall agricultural workers were healthier than the general population, with reduced cancer incidence compared to the general population in the same areas.

There are, of course, problems with this new study in the UK. For one there was no stratification by type of organic diet – so, for example, we don’t know whether the lymphoma result was skewed by an excess of vegans or carnivores. And the categories of never, sometimes, or usually/always eating organic are by necessity coarse and difficult to quantify – for example how can you tell how much non-organic food the usually group has? But for all that, this is study with a large sample size and if there was a positive signal that eating organic protects against cancer you’d expect to see it.

So, what conclusion can we draw from this? It's the basic point really, that additional fruit and veg is healthier regardless of how it's grown. So if you want to save some money and are currently eating organic to reduce your risk of developing cancer, then switching to non-organics won't harm your health but will benefit your bank balance.

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