Almost half of all global cancer deaths in 2019 were linked to preventable risk factors, the most common being smoking, alcohol use, and a high body mass index (BMI), an observational study found.
Published in The Lancet, the study found that 4.45 million cancer deaths were associated with one of 34 preventable risk factors. That accounts for 44.4% of all cancer deaths globally.
Risky behaviors, such as alcohol and tobacco use, were still the leading cause of otherwise preventable cancers in 2019. But the amount of cancer deaths caused by various metabolic risk factors—such as high BMI and high fasting plasma glucose an indicator of a risk of diabetes)—had the sharpest increase between 2010 and 2019.
“These results, in combination with local knowledge, may be useful for policymakers in determining what modifiable risk factors to target in cancer control planning efforts,” Kelly Compton, project officer on IHME’s Global Burden of Disease Cancer Team at the University of Washington and second author on the study, told Health. in a statement. “There is potential for future deaths and ill health due to cancer to be averted by reducing population-level exposures to these risks.”
Here's what the study revealed about which cancers are connected to these preventable risk factors, why people are still dying from preventable cancers, and how nations around the world can help prevent these types of cancers in the future.
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Data Finds Common Themes Globally
The fact that this study, funded by the Bill and Melinda Gates Foundation, was able to draw conclusions about cancer risks across 204 countries and territories is quite impressive, explained Ajay Maker, MD, professor and chief of surgical oncology at the University of California, San Francisco School of Medicine.
The study isn’t the first to come to this conclusion, but the breadth of the study sets it apart.
"The authors need to be congratulated on undertaking basically a Herculean task of trying to estimate cancer risk and the associated potential modifiable risk factors," Dr. Maker told Health. "As a field, we know that there are risk factors for certain cancers that are modifiable, but to be able to quantify this across the entire world, and show differences based on cultural, geographic [factors]—it's really fascinating."
Estimates for the number of cancer deaths, cancer incidence, and disability-adjusted life years—which is a measure of years lost due to premature mortality and years with a disability—were taken from data found in “cancer registries, vital registration systems, and verbal autopsy studies,” Compton explained.
Looking at the links between 23 cancers and 34 different risk factors—which researchers put into either an environmental and occupational, behavioral, or metabolic category—researchers were able to come up with the cancer burden associated with each risk factor. Breaking down the data by year, age group, gender, cause, and location, allowed them to determine which activities were associated with the highest numbers of cancer deaths.
Compton emphasized that these numbers are still just estimates, as more rural locations may have not had the same level of accessible data as other places.
Despite the complexity of the study, many cancer deaths and years of poor health could be prevented with a reduction in the prevalence of risk factors like tobacco use, alcohol use, and high BMI specifically.
Sex, National Differences
In addition to the broad and sweeping conclusions of the study, researchers found a number of differences along gender and geographic lines as well.
For instance, T the incidence of cancer deaths in 2019 caused by these preventable risk factors was actually higher in men than in women, the study found. There were 2.88 million cancer deaths in men tied to preventable risks, which is roughly 50.6% of all male cancer deaths. For women, it was 1.58 million, or 36.3%.
Though the study didn't explain why this was the case, experts had a few guesses.
"Men and women can develop different types of cancer or may react to certain risk factors differently given differences in anatomy and biology," Compton said. "There may also be differences in access to timely diagnosis and effective treatment."
In addition to biology or treatment, cultural norms may also play a role, Colleen M. McBride, MD professor of behavioral sciences and health education at the Emory University Rollins School of Public Health explained. Historically, she said, men tend to smoke and drink more than women, and they tend to eat more meat. All of those things may put them at a greater risk for cancer.
The study also mentions that environmental risks played a smaller role in women's disability life years than in men's, which may be because, globally, men are more likely to hold jobs that expose them to carcinogens.
Another point of divergence in the study's findings was between higher and lower income nations. The top three risk factors—smoking, heavy alcohol use, and a high BMI—were consistent globally and among more affluent nations, but poorer nations saw unsafe sex as their second highest risk factor, and alcohol use was bumped to number three.
"[In] affluent countries, [there's] overeating and access to alcohol, and not getting exercise, ," Dr. McBride told Health, "It's increasing your [metabolic] risk."
In countries with less resources, people are more likely to be exposed to human papillomavirus (HPV), and are less likely to have adequate access to needed cervical cancer treatment and screening, explained Lisa Force, MD, global burden of disease cancer team lead at IHME, and the study’s co-senior author.
But even though it wasn't in the top three risk factors, low socio-demographic countries saw the biggest increase in cancer deaths related to metabolic risk factors over the last decade.
“It’s not just obesity,” Dr. Maker said. “They defined metabolic risk factors as hypercholesterolemia, high blood pressure, high blood sugar, and increased BMI. So we know all of these things are increasing in our society, and I think what’s concerning is also seeing an increase in parts of the world where traditionally this was not an issue.”
But overall, cancer deaths from preventable risk factors were much higher in more affluent countries. Specifically, the five regions with the leading death rates from risk-attributable cancer were central Europe, east Asia, high-income North America, southern Latin America, and western Europe, the study found.
"27% of all risk-attributable cancer deaths occurred in countries with a high level of socio-demographic development despite only accounting for 13% of the global population," Dr. Force told Health.
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Cancers Most Commonly Tied to Preventable Risk Factors
Engaging with or having exposure to any of these risk factors could lead to a variety of different cancers, the study found.
Globally, for both men and women, tracheal, bronchus, and lung cancers were the most common. Also high on the list were colon and rectal cancers, and esophageal and stomach cancer for men, and breast and cervical cancer for women.
Many of us have been taught about the connection between smoking and lung cancer, with federally-funded ads encouraging people to stop smoking. But it’s important to screen and look for these other cancers as well. Lung cancer is just one of 18 cancers that the study links to smoking, Compton said.
"Alcohol has classically been linked to liver cancer and behavioral risk factors including obesity have been linked to multiple cancers, in addition to the ones already mentioned," Dr. Maker added. More robust messaging and increased public health efforts to make people aware of these other risks is a good place to start, he said.
Cancer Prevention Means Finding Ways of Living Healthier Lives
In addition to information about how many people died of preventable cancers and the risk factors to blame, the study found that the number of these deaths is going up. Risk attributable cancer deaths increased, globally, by 20.4% from 2010 to 2019.
The reasons for this aren't entirely clear yet, experts said. An increasingly globalized world where unhealthy products have a greater reach or our sedentary lifestyles could be at fault, Dr. McBride said.
And though the increase is cause for concern, it's not necessarily because individuals have become more lax in caring about their health or cancer prevention over the last decade.
"It is important to note that while the greatest individual risk factors contributing to cancer burden were categorized as 'behavioral,' these risk factors are often patterned by social determinants of health, such as poverty," Dr. Force said. "Individuals with cancer should not be blamed for their disease."
The answer instead lies in systemic change, Dr. McBride explains.
"44% of cancer could be prevented if we really got serious about taking on what we need to do to promote more healthful behaviors," Dr. McBride said. "Please do not go away thinking we just need to get people to do right, with this kind of moralistic [idea] of, 'You have to have willpower and all that.' This is a systemic problem, and that is going to require systemic wide interventions, and a long term commitment."
These system-wide changes could look very different across different regions, especially based on the highest cancer risk factors that are plaguing a population. But here in the U.S., Dr. McBride said, that means helping people live healthier lifestyles, with more access to and encouragement toward healthy food, and opportunities to walk and bike.
Even though the study's findings reveal that there's certainly much work to be done when it comes to reducing deaths from cancer—both risk-attributable and not—having access to this global data can help policymakers craft projects to reduce the behavioral, environmental, and metabolic cancer risks in their communities, Dr. Force explained. "A study like this highlights the progress that can be made when large groups of epidemiologists, behavioral scientists, physicians, and other scientists can all work together to gather this data," Dr. Maker said. "Nobody is immune from cancer. And I think what this study tells us is that there are common threads that bind us all together, regardless of our geographic location, socioeconomic status, or gender."
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