We are fed a constant diet of medical scare stories that often seem to contradict each other. Which ones should we believe?

Our brains are constantly sweeping the environment for threats. Is that stranger friendly or a mugger? Might this cloud of dust poison me? Will I fall under a train if I stand here? Without even thinking about it, the survival instinct is for ever on, which is why, says Brunel University’s James Carney, a Wellcome Trust fellow in the medical humanities, we are suckers for scary headlines about health. You know the ones: “Processed meat gives you cancer” or “Toxic plant killer could give you Parkinson’s disease.”

“Bad news yanks at our attentional biases,” says Carney, “and it sucks us into its orbit like a cultural parasite on our tendency to look for bad things so we can avoid them.” It’s the same reason people rubberneck at car crash sites; we are hungry for details, to fully get the measure of this enemy. However, threat monitoring is an exhausting business and our brains jump on cognitive shortcuts – such as voices of scientific authority – at every opportunity. The trouble with scary health studies is that they are too numerous and complex for concerned, busy laypersons to keep up with, or attempt to fathom their true significance. Anxiety, guilt at inaction or fatalism ensue.

To compound the confusion, studies often contradict what has already been reported. “What can people believe?” ask Nicky Lidbetter, chief executive of Anxiety UK. “Our mindsets shift about things. For example, fat was seen as the evil of society, but now it’s sugar. People who are already anxious need to know which information they can trust and how applicable what they are reading is.”

Studies are, of course, published as part of an essential discourse between scientists. “One of the problems is that the media takes each of these things as if it comes from nowhere, in a vacuum,” says Aaron E Carroll, pediatrics professor at Indiana University School of Medicine. He regularly talks anxious readers down from alarmist health headlines in his writing for the New York Times, and in his new book tackling food demonisation, The Bad Food Bible: How and Why to Eat Sinfully. His mantra: “When you get scared, be sceptical.”

We are like moths to a flame in the face of stories about silent killers in everyday things, and other aspects of our normal, comforting routines, he believes. “And if it’s something we think about as a vice,” says Carroll, “then you’re getting all the Venn diagrams overlapping – it’s moralising, it’s scary, it causes disease – all wrapped up together so you can say: ‘That bad person who drinks the cocktail is the one who gets cancer. I’m going to be OK, or ‘I’m the one who needs to change my behaviour.’”

Carroll is a big fan of a 2013 study that picked 50 common ingredients out of a cookbook and then searched through all the literature to see which had been associated with cancer. Cancer risks or benefits had been found in most of the foods, and the evidence was overwhelmingly poor. “Everybody is full of fear,” says Carroll, “but you don’t need to be afraid of meat or the scare tactics on alcohol. A lot of the studies are positive. There are tonnes and tonnes of things you can eat and still be healthy and not live in constant terror all the time. The research and the evidence need to be looked at together and when you do that, the case against a lot of these things doesn’t hold up, and sometimes it actually points in the opposite direction.”

This month, it was reported that the American Society of Clinical Oncology had warned even light drinking could cause cancer. “Like, oh my God, they just announced alcohol causes cancer,” faux-gushes Carroll. “But that’s just not what happened. The studies they refer to have existed for years. Scaring people sells. People are afraid of cancer, and when they read the news, it’s as if we just figured it out what causes cancer, but it’s not true.”

The path to calmly digesting stories of the health bogeymen lies in acquiring basic scientific literacy. Understanding the hierarchy of study types and their relative quality is important, says Carroll. “Any study with tiny animals or that’s been done in the lab has to be taken with a pinch of salt. Studying eight genetically identical male mice doesn’t tell you much about the totality of human experience and nutrition.” Cohort studies are problematic, too, because they look at existing data on groups of people and spot associations, but any actual cause remains untested. “If associations are found in a cohort study, you then go: ‘OK, let’s confirm this now.’ But too often we just stop at the observational data and say this is definitive.”

The randomised control trial is the gold standard. With alcohol research, he says, “they’re often relying on big cohort studies, and it’s disappointing that they ignore the randomised control trials that have shown that light drinking could be protective of diabetes, might be protective of it in terms of heart disease”.

Carney points out that the No 1 killer of children in the US is cars, yet people still love cars. When it comes to assessing risk, we need to be less subjective and more statistically savvy.

Gerard Blair is assistant editor for news at the NHS and works on the Behind the Headlines section of the NHS Choices website, which gives impartial analysis of health stories in the media. “Increases in risk can sound scary,” he says, “but to understand the real-life effect of a rise, you first have to know what your baseline risk is. There can be a statistically significant increase in the risk of developing a condition, yet that might only equate to a tiny fraction of a rise in actual cases.” Which is why you are probably better off taking advice from medical bodies – Public Health England, National Institute for Health and Care Excellence (Nice) – whose panels of experts pore over all the research before compiling guidelines.

In reality, says Blair, “core public health advice has remained unchanged for many years: exercise regularly, achieve and maintain a healthy weight, eat a nutritious and balanced diet, avoid overexposure to sunlight, stick to the alcohol guidelines and quit smoking to maximise your chances of a long and healthy life”.

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