Two-Thirds of All Cancers Are Caused by One Thing: Your DNA

Two years ago, scientists at Johns Hopkins Kimmel Cancer Center looked at causes of cancers across the United States. They put them in a big database and found most cancers weren't caused by smoking or UV exposure, or lifestyle factors at all, but by regular DNA replication.

Their paper says that while 40 percent of cancers can be prevented with healthy lifestyle choices, the remainder of cancer causes were just dumb luck. Just problems in cell replication.

Precise rates of these DNA replication errors aren't entirely known, because DNA replicates at about 50 base pairs per second, and according to University of Toronto biochem professor Larry Moran, we can expect one mutation for every 10 billion base pairs.

Knowing that, all this does kind of make sense. There are trillions of cells in the human body (estimates range from 15 to 70 trillion, it's hard to say for sure). Different cells replicate at different rates - a red blood cell lives about four months, a skin cell lives a few weeks, and cells in the colon only live a few days. By the time you're 50, you've gone through 4600 generations of colon cells! That's insane! By the time you're 70 you've almost had six and a half thousand colons... many millions of cells in the colon dividing six and a half thousand times with tiny errors popping up here and there... it's no wonder cells become abnormal.

But skeptical scientists were quick to jump on this original paper - because it was only done in the U.S.! That's not generalizable to everyone in the world, right? Right. Well, now they've done it again. It took them two years - but this time they included data from 69 countries and added more cancer types. They found the same thing. 66 percent of cancers just, happen. And the rest were environmental factors, lifestyle choices and genetics.

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