I had never heard that ahaha but it doesn't seem very plausible indeed that our bodies would regenerate themselves every 7 years. But it's very true about number 7 - 7 days of the week..Don't they say that in order to calculate a dog's life in human years, you should multiply its age by 7?
Or, that a marriage survives if you can make it until the 7th year?

Those are the only ones I can think of tight now...

Thanks for all the details about cell regeneration, interesting read!