Rowan Jacobsen

So that's why it can cause skin cancer.

So it was basically that learning that one fact back in like the 40s and 50s that made scientists start to say, uh-oh.

Light skin cancer, maybe we should think about how much sun we're getting.

Yeah, that was an important part.

And it's a big part of the story, I think, because that was really back in the 20s that we figured that out.

And then even a little earlier, we realized that sunlight could prevent rickets.

Rickets?

Yeah.

So rickets is like soft bone disease.

Like if you don't get enough calcium in your bones when you're a kid, when you're a baby, you get soft bones, you get rickets.

Really bad disease.

And in the Industrial Revolution, kids started getting rickets.

Farm kids never got rickets.

Then suddenly kids are working in factories.

They're living in cities that are choked with coal smog.

They're living in tenement buildings.

They're never seeing the sun, and they all start getting rickets, late 1800s.

Vitamin D. It was all vitamin D. At first, they thought maybe it was vitamin A. But it turned out that was how vitamin D was discovered, was some doctors figured out that it could solve rickets in kids.

And then they figured out that if sun hit skin, that's how we made vitamin D.

Then they figured out... How did they figure that out?