The Global Burden of Disease project is a decades long international collaboration, based at the Institute for Health Metrics and Evaluation at the University of Washington, but involving researchers around the world. It was originally funded by the World Bank, and now receives its principal support from the Bill and Melinda Gates Foundation.
GBD (not to be confused with golden brown and delicious) essentially tries to quantify the prevalence of diseases, and injuries around the world; the prevalence of associated disability; causes of death; and risk factors. They use a lot of complicated methods. If you're really interested you can read about them on the GBD website. There is certainly room for controversy about the accuracy of some of their estimates -- data sources are not great in many places -- and also about the philosophical validity of some of their concepts. But for understanding the essential challenges for public health around the world, they're the best we've got.
One construct I do need to explain for this post is the Disability Adjusted Life Year, or DALY. It doesn't actually tell us very much to just enumerate the causes of death. Everybody dies, after all, so what matter is at what age and what state of health they are in before they shuffle off this mortal coil. You could quantify the former just by using a metric called Life Years Lost -- assume that people naturally will live to some arbitrary age, say current life expectancy at birth*, and for all the people who die younger add up all the years between Age X and their deaths. But for people who are in a coma, or with severe dementia in a nursing home, or in chronic pain or whatever other ill fate they suffer, that isn't really good enough either.
So DALY combines YLL with years spent in a condition of less than ideal health, various of which conditions are considered to represent fractions of a life year. For example, if you live for a year being blind, that might be worth six months off your life. (I don't know that for a fact, just making up an example.) There are various ways of getting to those fractions, the most straightforward of which is to survey a bunch of people, ask them how much life time they would give up not to have the condition, and average the responses. There's a lot wrong with that, but at least it's something.
Anyway, a new GBD analysis finds that in 2019, 44.4% of all cancer deaths, and 42% of DALYs attributable to cancer, resulted from preventable risk factors. The most important of these, for both sexes, is not a surprise, tobacco. Since the reason so many people around the world use tobacco is marketing by tobacco companies, these deaths may be considered homicides. Alcohol use and what the authors call "dietary risk" were number two and three for males. I think dietary risk refers to consumption of cured and charred meat products. For females, they call the second leading risk factor "unsafe sex," but this mostly means human papilloma virus, which is preventable by a vaccine. Body mass index came in third -- obesity is a risk factor for cancer. Air pollution comes in fifth.
So it's possible to cut the burden of cancer nearly in half, without any sort of medical intervention or high technology. But there's little political will to do so, anywhere in the world.
*Right now it's 92 years, which is the "frontier life expectancy in 2050," although I seriously doubt we'll get there.
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