In global health, we've long patted ourselves on the back with the comforting notion that each generation lives longer and healthier than the last. Life expectancy climbed, child mortality plummeted, and vaccine-preventable diseases were nearly wiped off the map. But since the turn of the century, that upward trajectory has stalled - and in some cases, we've slid backwards. Because nothing says "progress" like regressing.

Take cancer, once considered a disease of the elderly. While most cancers still strike older people, a new report reveals that a growing number of cancers are showing up in people under 50 - a phenomenon charmingly dubbed "early onset cancer." The report, from the World Cancer Research Fund, analyzed data on 12 different cancer types across England, the US, and the Netherlands over the past 20 years. Spoiler alert: the findings aren't pretty.

So what's behind this generational shift? Some change in our lifestyles or environments over a single generation has cranked up the risk. What exactly that change is remains a mystery - because apparently, we can put a man on the moon but can't figure out why our kids are getting colon cancer.

Prof Devi Sridhar is chair of global public health at the University of Edinburgh.