How Did Scientists Discover Smoking Causes Cancer?

Eat lots of fruits and vegetables, take regular exercise, and don’t smoke – probably the three most common health messages we all hear. The fact that smoking tobacco is a major risk factor for lung cancer – as well as numerous other diseases – is so well accepted now that it’s hard to imagine a time when doctors actually recommended smoking to their patients. But how did the tide start to turn?

As recounted in a 2013 article to commemorate its 50th anniversary, then US Surgeon General Luther L. Terry released a seminal report in 1964 stating that cigarette smoking caused lung and laryngeal cancer. Terry went even further, noting the growing evidence of an association between tobacco use and other conditions, including emphysema, heart disease, and other cancer types.

Back then, over half of American men and over a third of American women were active smokers. Most of us can’t remember or imagine a time when lighting up in a busy office or on an airplane was totally normal. But even centuries before, some had started to wonder whether smoking might be doing unseen harm to our health.

Early evidence of the dangers of smoking

One of the earliest publications making the connection between tobacco and ill health came all the way back in 1602. According to Cancer Council New South Wales, the anonymous English author of the essay suggested that tobacco smoke could have similar effects to the soot that chimney sweeps were exposed to, and which caused well-documented occupational illnesses.

Over the coming centuries, there were a handful of others who tried to alert people to the possible dangers of pipes, cigars, and eventually cigarettes, but few gained any traction with the wider public. It was only in the 20th century that lung cancer cases started to notably increase, and the number of medical reports pointing the finger at tobacco started to become harder to ignore – but that’s not for want of trying.

Fearful of attracting the ire of Big Tobacco and losing a whole lot of ad revenue to boot, newspaper editors were a bit twitchy about publishing anti-smoking articles during the early and mid-20th century. Debate raged within the medical community, too, with many finding it hard to accept the growing body of evidence and struggling to understand why not everyone who smoked heavily seemed to be seeing health issues.

As such, even as more and more reports were being released in the 1940s and 50s, anti-smoking efforts in the US were largely being led by health nonprofits rather than legislators, and many in the general public remained uninformed about the dangers.

The scientific case

Human studies

Let’s rewind slightly to the 1920s and 30s, and this increase in lung cancer cases that people were beginning to observe. It’s only thanks to the burgeoning field of epidemiology that the trend was noted at all – and in turn, research into lung cancer helped solidify some of the epidemiological techniques that are still in use today.

In 1939, German researcher Franz Hermann Müller performed an important case-control study. A mainstay of health research today, these studies compare two cohorts of people: the cases, who all have a particular disease or condition, and the controls, who are as similar to the cases as possible but, crucially, don’t have the disease.

While not a perfect piece of research, the paper was undoubtedly significant, and concluded that smokers were more likely to develop lung cancer than nonsmokers. Subsequent similar research found the same thing, but one important thing to note about these kinds of studies is that they can’t show causation – there was no reason to assume that the smokers weren’t getting lung cancer more often due to a simple coincidence, or some other unknown factor.

As we entered the 1950s, however, more data was adding further weight to the idea that smoking was bad news for health. Crucially, cohort studies were also being launched. These studies follow a group of people over a period of time, tracking their habits and health outcomes to look for trends. Evidence was mounting that smokers had poorer health outcomes than their non-smoking counterparts. 

Animal studies

As detailed by science historian Dr Robert Proctor in a 2011 paper, animal data also played a key part in the accumulation of evidence to link smoking to cancer. Pioneering Argentine cancer researcher Ángel H. Roffo demonstrated that tobacco smoke was carcinogenic when applied to the skin of rabbits. Similar experiments were repeated later with mice, and were widely covered in the media, with the public reaction spurring the tobacco companies to ever greater efforts to change the narrative.

And honestly, it worked, at least for a time. The mouse study came out in the 1950s, and smoking didn’t peak in the US until the mid-70s.

Other research

In addition to the human and animal evidence, other damning scientific data were beginning to stack up.

As Proctor explains, observations of lung cells in the lab had shown how cigarette smoke could damage the cilia, tiny hair-like structures that line the airways and move mucus and trapped particles – such as the nasty components of cigarette smoke that you really don’t want to be hanging around in there.

And in what might be considered one of the final nails in the coffin, remember those chimney sweeps? Well, in the 1930s, people figured out that it was a class of chemicals called polycyclic aromatic hydrocarbons, present in tar, that was the major source of their problems. It wasn’t long afterward that others, Roffo included, noted that the same chemicals were present in tobacco smoke, giving us a plausible mechanism by which smoking might cause cancer.

Where are we now?

By the 1960s, things were reaching a tipping point. Health associations across the US lobbied President Kennedy to open a Presidential Commission to look into the tobacco problem, which eventually led to the 1964 Surgeon General’s report where we began this whistle-stop tour through some of the history of smoking science.

The World Health Organization says that tobacco kills over 8 million people around the world every year, both directly and via secondhand smoke. Today, global smoking trends are a mixed picture, with some places moving to ban tobacco, while still others scrap similar plans. But the fact that smoking increases the risk of cancer is no longer contested, and continues to inform campaigns that seek to raise awareness of the danger and encourage people to quit for good.

This post was originally published on here