Structure of the dioxin polychlorinated dibenzo-p-dioxins

PCDD general structure by Edgar181 - Own work. Licensed under Public Domain via Wikimedia Commons

It’s not news that our environment – from the air we breathe to the food we eat – impacts on our health, including our risk of cancer.

But while some of the links between our environment and cancer are proven, evidence on other possible risks isn’t as convincing. When it comes to chemicals and cancer there seems no end to the media debate. But what does the evidence show?

Dioxins have been debated extensively by the media. And a new study, published in the journal Breast Cancer Research, looks at dioxins in our diet and breast cancer risk. So what does this latest study add to the mix?

First a little background.

What are dioxins?

Dioxins are mainly released from certain industrial processes, and from burning waste – especially some types of plastic, like PVC. But because we now know that these processes release dioxins, they’re largely regulated and the World Health Organisation (WHO) estimates that dioxin levels today are about 10 per cent of what they were in the 1970’s.

Never far from the headlines

Studies have shown that very high levels of certain dioxins can be harmful to health and the International Agency for Research on Cancer (IARC) classified one dioxin, TCDD, as carcinogenic to humans. But over recent decades the amount of TCDD produced has fallen rapidly.

But studies looking at dioxins and cancer aren’t perfect. Some of them have looked at animals given very high doses of dioxins, well above anything the general public would be exposed to. Other research has looked at groups of people whose jobs expose them to very high levels of dioxins. But these jobs often expose people to other chemicals which can increase the risk of cancer too. So teasing apart the role of individual chemicals is hard.

What these studies do tell us is that in principal, certain dioxins can cause cancer – but principal and practice can differ. And the levels of dioxins that most people would be exposed to are far smaller than the levels used in this type of research.

Looking at people

For most people, the main source of exposure to dioxins is through food and drink. So looking at diet, dioxin intake and whether a person goes on to develop cancer helps us understand what’s going on.

And the latest study has done just that, studying over 63,000 French women.

The team analysed the women’s diets, estimating their dioxin intake and following them for 15 years on average to look for differences in the amount of dietary dioxins in those who developed breast cancer.

Overall 97 per cent of women were well within the safety limits for dioxin exposure set by the WHO and the European Food Safety Authority (EFSA). And even in women whose diets had the highest levels of exposure, there wasn’t an increased risk of breast cancer.

This is the first study of its kind to look at breast cancer risk and dioxin intake from food in people. As with any scientific research, replication of a result gives us more confidence in it. This study gives us a good idea of how dioxin exposure might impact the health of the population, but needs to be replicated.

And no study is perfect. For this latest analysis, information on diet was only collected once in 1993. Although the questionnaire used to collect information aimed to look back comprehensively over the past 12 months, we can’t be sure that a diet reported at the beginning of the study stayed the same throughout follow up.

So this study gives us a snap-shot in time of diet, but means we can’t be sure that diets of the women studied didn’t change, which could have impacted on their dietary dioxin exposure.

The questionnaire was used to estimate the levels of dioxins in the women from this study – so any change in diet, body weight or levels of dioxins in food mean that the estimate could be less accurate.

But fortunately the levels of dioxins worldwide have decreased, and are now a fraction of their levels in previous decades.

So how does the latest study fit into the bigger picture on dioxins and cancer?

Water everywhere but not a drop to drink…

One of the most persistent myths surrounding dioxins is that they leach from plastic water bottles, causing cancer and other health issues.

There is something which may seem logical in the argument that plastics give off chemicals that are detrimental to our health. The arguments are also often put forward using very emotive language, and are falsely attributed to credible sources like Johns Hopkins University in the US – all of which seem to add to its credibility.

But in fact, Johns Hopkins have refuted the claims saying that there’s no good evidence that dioxins are even present in the plastic used in water bottles, and there’s no convincing scientific evidence to back up a link between using them and developing cancer.

How much is too much?

Because high concentrations of dioxins can impact health, they are carefully controlled and regulated. Safe levels for Europe have been set by the EFSA, taking into account studies looking at dioxins in cells, animals and people to set a maximum limit for dioxin exposure. This limit also has a safety margin factored in to account for any areas where research isn’t clear cut.

And even with this stringent safety limit, the overwhelming majority of people fall well within it in terms of their exposure. And this is far below the levels that have been shown to have any sort of impact on health in people and in animal studies.

Food in the European Union is also monitored carefully for the presence of many different substances, including dioxins. This monitoring is there as a back-up – making sure that our food meets the quality criteria set in Europe by the EFSA’s scientific panel.

Stable evidence

Lifestyle factors we can control, like diet, can have a big impact on our health, including our chances of developing cancer. But there are many things we can do to help stack the odds in our favour.

More than 4 in 10 cancers in the UK can be prevented through lifestyle changes like quitting smoking, reducing alcohol intake, being physically active, eating a healthy balanced diet and staying safe in the sun.

While this latest study isn’t perfect, it reassuringly doesn’t show a link between exposure to dioxins and breast cancer risk.

It can often appear from media headlines and internet hype that the picture is changing very rapidly when it comes to the environment and our health – especially in the volatile world of chemicals and cancer. Actually, the evidence is much more stable.

A version of this post also appeared on the Cancer Research UK Science blog.