http://www.livescience.com/33179-does-human-body-replace-cells-seven-years.html

It's a neat idea, and one that has caught the popular imagination. Here's how the story goes: Every seven years (or 10, depending on which story you hear) we become essentially new people, because in that time, every cell in your body has been replaced by a new cell. Don't you feel younger than you were seven years ago?

It is true that individual cells have a finite life span, and when they die off they are replaced with new cells. As The New York Public Library's Science Desk Reference (Stonesong Press, 1995) notes, "There are between 50 and 75 trillion cells in the body.... Each type of cell has its own life span, and when a human dies it may take hours or day before all the cells in the body die." (Forensic investigators take advantage of this vaguely morbid fact when determining the cause and time of death of homicide victims.)

Red blood cells live for about four months, while white blood cells live on average more than a year. Skin cells live about two or three weeks. Colon cells have it rough: They die off after about four days. Sperm cells have a life span of only about three days, while brain cells typically last an entire lifetime (neurons in the cerebral cortex, for example, are not replaced when they die).

There's nothing special or significant about a seven-year cycle, since cells are dying and being replaced all the time. It's not clear where this myth began; perhaps some well-meaning but innumerate person simply added up the all the lifespans of the body's various types of cells and (mistakenly) assumed that all the cells are renewed after seven years.

I've already seen a couple people perpetuate this myth on this forum before, so I thought I'd post this here.

For some, it might seem like a no-brainer (PUNS) that, when your neurons die, they never come back.
i mean, it was for me, but i never really put two and two together i suppose

Thoughts?

Actually when your neurons die, them not coming back is a myth.

Neurons actually do regenerate, but they do it very slowly. And I believe more recent studies have shown that learning, even in mature brains, stimulates neuron growth. New experiences open new pathways.

Actually when your neurons die, them not coming back is a myth.

Neurons actually do regenerate, but they do it very slowly. And I believe more recent studies have shown that learning, even in mature brains, stimulates neuron growth. New experiences open new pathways.

Neuron growth, sure, like filling a balloon with water--but not popping the balloon once filled, and expecting it to have itself repaired overnight, right?

As for brain cells regenerating, yeah, it seems you're right--but they still don't regenerate fast enough for your body to be "fully" replaced over a seven year period. Right? Either way, apparently they're trying to get stem cells to behave like brain cells as a means to cure paralysis. Pretty cool.

It came from here.

Had a quick run through of "Dr Frisen from Stockholm" and it turns out it's from a published journal in 2005. It's not just myth, it's real.

That said, there is nothing special about 7/10 years specifically. It's just that's the minimum age for everything in your body to have been regenerated at least once, e.g. In the time it takes your whole liver to have regenerated (3-500 days), cells in your colon would have done 100 regenerative cycles (a lifespan of a colon being ~4 days). By the time your bones (IIRC this has the longest cell "lifespan") has regenerated, the cells in your liver would have died and regenerated ~10 times.

Isn't that a nice word.

Regenerate

Just rolls off the tongue that one. Sounds so durable.

Holy shit I didn't realise I'd written that word so many times. Disregard, I dunno, 3 of them, but you get the drift.

I actually got to know the complete body regeneration rumor through a webcomic that mainly consits of Jaden Smith's twitter posts.

No kidding.