Sausages and cancer: what’s in a warning?

Tobacco, glyphosates and sausages are all carcinogenic ... "probably". But what does that really mean? And what does it tell us about WHO's risk-communication strategy? By Florian Fisch

(From "Horizons" no. 108 March 2016)​​​

​​​It's long become a ritual. At regular intervals, the World Health Organization (WHO) classifies chemicals and foodstuffs as carcinogenic – most recently, it was the sausage. The headlines automatically follow. 'Beware of the sausage' was the comment of the Neue Zürcher Zeitung, the main German-Swiss daily. Then passers-by on the street are asked for their opinion. "I don't pay any attention to studies", one of them told the Swiss TV programme 'Puls'. And an irritated butcher asks: "I'd like to know just how much a study like that costs, and what the use of it is".

As expected, the meat industry didn't take much pleasure in the news. But it's an open question as to just how big an effect WHO warnings have on public health. What's certain is that they sow much confusion. After the sausage warning, the US monthly The Atlantic described WHO as 'confusogenic' and said, "they are terrible at communicating their findings". Michael Siegrist, Professor of Consumer Behaviour at ETH Zurich, is looking into how risks are communicated. He agrees with The Atlantic. "WHO isn't tasked with scaring people. It's supposed to inform them".

An unequivocally low risk

Informing people is also exactly what WHO would like to do. It runs a specialised cancer agency called the International Agency for Research on Cancer (IARC), whose goal is "to identify the causes of cancer so that preventive measures may be adopted and the burden of disease and associated suffering reduced". They have thus far investigated over 900 different suspect factors, the best-known examples being smoking and passive smoking.

A specialist group analyses all the studies published on factors that cause cancer, and classifies these factors according to five categories. The first is 'carcinogenic to humans' and includes tobacco, ultraviolet rays and asbestos. The most recent addition was processed meat products. 'Probably carcinogenic' is the category assigned to red meat and the herbicide glyphosate (see "Is glyphosate carcinogenic?", p. 8). Apart from many 'not classifiable' agents, most factors are placed in the 'possibly carcinogenic' category, which includes radio waves and aloe vera extract. The only substance classified as 'probably not carcinogenic' is caprolactam, a chemical used in the production of nylon.

So are sausages and tobacco equally dangerous? No, writes WHO in a list of frequently asked questions: "The IARC classifications describe the strength of the scientific evidence about an agent being a cause of cancer, rather than assessing the level of risk". However small the risk, if it's unequivocal, then it comes into the top category. In another of the FAQs, there is mention of the Global Burden of Disease Project, which attributes 34,000 cancer deaths worldwide to diets high in processed meat. This is almost insignificant in comparison with the millions of deaths from tobacco.

A lack of guidelines

"Assessing the credibility of an effect is the first step in assessing risks, and a very significant one too", explains Béatrice Lauby-Secretan, a scientist at the IARC. The important work on weighing up this effect is postponed by WHO until a later date. Then it works with national health authorities who know the local context. Lauby-Secretan believes that it would be irresponsible to wait for additional information before communicating the results, because individuals could already start to change their everyday lives by taking the results into consideration.

WHO thus leaves it up to journalists to interpret this information for the general public. Heinz Bonfadelli, a former professor at the Institute of Mass Communication and Media Research at the University of Zurich, thinks that this is unwise. "I find it problematical when WHO doesn't contextualise the information it gives to the media, but instead refrains from giving guidelines for action". He suspects that WHO avoids doing this so as not to come into conflict with different interest groups.

Bonfadelli does admit that "Risk communication is always a difficult business". All the same, there are methods that could create less confusion. For example, WHO ought to plan ahead when informing the media "and consider how its information might be distorted". If it completely outsourced its risk analysis, then the national authorities in question could be informed two weeks in advance, for example, and could prepare the information to be passed on to journalists.

The damage of relative risks

Siegrist isn't convinced that this would help. "It's not just the consumers. Even the authorities themselves in some cases are unable to deal with risks". He believes that the problem lies squarely in communicating relative risks. WHO wrote in its media release that eating 50 grams of sausage per day can increase the risk of bowel cancer by 18 percent. "This information is completely useless. As a consumer, I need absolute figures in order to be able to assess a risk". According to the Cancer League in Switzerland, some 4,100 people develop bowel can cer every year. If meat consumption were reduced across the country, this number could sink to less than 3,500.

Communicating relative risks has tangible side effects, says Siegrist. "It has an impact on perceptions and leads people to worry more. Even absolute figures can seem more threatening if they are accompanied by relative figures". People are probably becoming dulled to all these threats. Siegrist believes that a need for public attention drives organisations like WHO to insist on keeping relative figures in their media communication.

WHO itself doesn't know whether these cancer warnings really have any impact. According to Lauby-Secretan, it would be extremely complicated to try and carry out a global analysis of behavioural change or of cancer rates. "We do know that after our press release, sales of processed meat went down noticeably in several countries". But for Siegrist the consumer behaviour specialist, the situation is quite clear: "If WHO wants to communicate seriously with the general public, then it has to get to grips with the current literature on risk communication".

Florian Fisch is a science editor at the SNSF.

G. Gigerenzer et al.: Helping doctors and patients make sense of health statistics. Psychological Science in the Public Interest (2008)
V. Bouvard et al.: Carcinogenicity of consumption of red and processed meat. The Lancet Oncology (2015)