Over 150 billion hours of heart rate data. From tens of millions of users all over the world, it allows interesting insights as sex, activity levels, age etc. are known, too. Check out the findings, mostly about resting heart rate, in this article. I hope this is made available to universities, hospitals etc. - the general public, instead of only selling it to pharma or insurance companies...
Resting heart rate insights
And some more about the 6 billion nights of sleep data: