How burnt toast and roast potatoes became linked to cancer

In October 1997, something troubling was happened around the Hallandsås ridge in southwestern Sweden. Farmers had found cows paralysed or dead in their fields, lifeless fish were spotted floating in a local river and workers at a construction site began suffering from nausea and prickling sensations in their fingers.

Suspicion fell on a major construction project to drill a railway tunnel through the ridge. The project had been plagued by leaks and the construction company had resorted to injecting 1,400 tons of a sealant called Rhoca-Gil into tunnel walls. Tests confirmed that the sealant had leaked high levels of a toxic chemical into surrounding ground and surface water. The chemical was acrylamide.

What began as an environmental scandal soon morphed into a public health scare. Professor Margareta Törnqvist, an environmental chemist at Stockholm University, was enlisted to carry out tests on the construction workers, which revealed high levels of acrylamide in their bloodstream. Unexpectedly though, significant levels of the chemical were also present in a control group.

“We realised that if this background signal really was acrylamide it meant that ordinary people are always exposed to acrylamide,” said Törnqvist.

Since the compound is not found in wild animals, processed food was identified as the likely culprit. After discounting beef burgers as the source, Törnqvist and colleagues had discovered that acrylamide is found in highest concentrations in starchy food, like bread and potatoes, when it is cooked at high temperatures.

By 2000, the team had published a study involving rats being fed fried food that concluded that acrylamide consumption “is associated with a considerable cancer risk”.

The resultant public health advice became embroiled in controversy, however (“For me as a scientist it was a bit of a tough period,” Törnqvist recalls). And nearly a decade on, there is a lingering question, never satisfactorily resolved, over whether we should be worried about acrylamide in our diet.

This week, the UK’s Food Standard Agency became the latest regulator to draw consumers’ attention to the issue with its Go for Gold campaign that urges the public to avoid singeing their toast or leaving roast potatoes to char in the oven.

“As a general rule of thumb, aim for a golden yellow colour or lighter when frying, baking, toasting or roasting starchy foods like potatoes, root vegetables and bread,” the FSA recommends. At the same time, it acknowledges: “there is more to know about the true extent of the acrylamide risk.”

Critics of the advice were quick to point out that animal studies linking acrylamide to cancer have used doses so far above the average daily consumption in humans that extrapolating the results is questionable – even assuming the effect is comparable across species.

A person would need to eat 75kg (165lbs) of chips every day for two years, for instance, to be getting the cumulative dose of acrylamide (200 mg/kg daily) used in one rat study that showed the compound could cause DNA damage when it latched on to haemoglobin in the blood.

Törnqvist counters this argument with the observation that, although some chemicals have a minimum threshold concentration below which they are not dangerous at all, this is not the case for DNA-damaging chemicals, known as carcinogens.

“With chemicals that damage DNA it’s a linear dose response, so even the smallest dose contributes to the risk,” she said. “There is no threshold dose for the effect.”

It is partly the lack of any technical lower bound for toxicity, though, that has led to literally hundreds of every day chemicals being classed as carcinogens. The American Cancer Society describes acrylamide as a “probable carcinogen” in a list that also includes hot beverages, working as a hairdresser and insecticides. Short of retreating into a bunker (solar radiation also features), many items do not lend themselves to practical measures to reduce exposure. With acrylamide, at least, agencies can point to the simple step of not burning your toast.

Attempting to establish the existence of the link between a ubiquitous chemical and an incremental cancer risk is a daunting challenge, but there has been no shortage of attempts to do this.

A recent meta-analysis found no evidence of a risk for cancers of the oesophagus, stomach, pancreas, breast, lung and prostate. Again, this does not rule out the existence of a risk, but it does put a very low upper bound on the problem.

David Spiegelhalter, professor for the public understanding of risk at the University of Cambridge, said: “Nobody can put any numbers on acrylamide, but it can’t be that bad. We’d know about it if it was.”

By contrast, Cancer Research UK highlights that around 18,000 cases of cancer each year in the UK are caused by being overweight or obese, and it predicts that alcohol will cause around 135,000 cancer deaths over the next 20 years.

Even if the risk is small – undetectable in a population, even – Törnqvist argues that it is worth acting on.

“Why should [food agencies] bother about a lot of other things with much smaller risk if they don’t bother about acrylamide,” she said. “Shouldn’t we try to protect people from that the best we can?”

There are indications that, on advice from the FSA and other agencies, the food industry has taken the message on board. Between 2007 and 2015, there was an an average 30% reduction in acrylamide across all products in the UK, according to FSA figures.

However, Spiegelhalter argues that, while there may be a good case for issuing industry guidelines, there must be a higher bar for issuing public health warnings. The ultimate outcome of continual vague fear-mongering, he said, is not a society that examines its diet with meticulous and scientific rigour. Instead, other, more pressing health messages are simply diluted.

“People are fed up with continually being given public health advice about what appear to be rather minor issues,” he said. “I don’t believe exercises like this increase people’s trust in science. It just gives people an excuse to ignore what they don’t want to hear.”

How burnt toast and roast potatoes became linked to cancer

I"ve worked as a GP receptionist under a year and I"m already burnt out

It’s only 8.15am and the appointments for the day are already fully booked despite our appointment booking line opening at 8am. Less than a year ago this was an anomaly, now it’s the norm, as are queues out the door when we open. I spend the rest of the morning bearing the brunt of patient irritation, which is mostly aimed at our lack of appointments. I share their frustration because the service is substandard and it only seems to be getting worse.

The calls keep flooding in, the phone rings all day and I often finish work with a headache from the sound. The calls can be incredibly stressful one moment – talking to someone who is struggling to breathe – to mundane the next with patients who are convinced that their three-day cough constitutes an emergency. Patient anger often unfortunately comes back on to the receptionists, I wish they could see the wider picture and direct their anger at the government that is responsible for cutting their services.

Much of my job involves reducing doctors’ workloads so they can spend more time with patients. The administration aspect of the NHS is what keeps the service running. However, the demands of the job and the ever rising number of patients relative to staff make it impossible to do the job well. I think back to my early enthusiasm and my wish to help patients. Now I just feel the steady erosion of my capacity to help. I can’t offer people appointments that aren’t there. I can’t give any patient any real time and attention because there are just so many.

The stressful demands of the job mean that there are high levels of staff sickness; this makes staff morale low and turnover high. I’ve been in the role for less than a year and I’m already burnt out. I’m exhausted all the time and the stress from the job has affected my personal life, making it difficult to sleep and giving me a constant sense of worry. I’ve even been referred to counselling by my doctor because of the stress and anxiety my job causes me, ironically further burdening the NHS.

I work in a deprived area in the midlands and I’ve seen firsthand the long-lasting and far-reaching effects of poverty. The lack of investment and funding in the NHS means that we are having to do more with a decreasing level of resources and a lot of cuts mean people are getting put back on to their frontline GP service.

We have numerous patients with complex mental health issues who we are called about every day, usually by social workers or concerned relatives, because the support they need has been cut elsewhere. There’s the heroin addict who goes in and out of prison and mental health units – every time he is released he goes missing for days until we are informed that he has been sent back to another institution.

There was also a patient who was terminally ill with chronic obstructive pulmonary disease, but also suffered from severe anxiety and schizophrenia, who called us or the emergency service in a frantic state every day for months until he died. He would often be having panic attacks on the phone or hearing voices – this was incredibly distressing as I felt underprepared to deal with such complex issues. One woman was so distressed after cutbacks on the time she received from carers that she attempted suicide just weeks later. She now remains on an A&E ward.

Some people’s lives are so chaotic and their support networks so poor that it seems that the NHS is the only consistent factor in their lives. How will they cope when services they rely on continually suffer from cutbacks? Without drastic improvements in funding and a greater number of staff, these issues will only get worse. I worry about the future of our practice, our patients and the NHS at large. But for now I’m overstretched and exhausted, I’m certain that neither I nor the NHS can keep this up for much longer.

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I"ve worked as a GP receptionist under a year and I"m already burnt out