Absolutely (though it may not be enough), but not just for the reasons you think: a life jacket will keep the back of your head out of the water - which will help prevent damage to the brain.

You don't want to know where this research comes from, believe me.

Maybe he doesn't want to know, but I'm curious.

P.S. I'm also curious about what kind of damage can occur to the brain and from what exactly?

I believe he's referring to this: http://en.wikipedia.org/wiki/Nazi_human_experimentation

Much of that has been confirmed more recently by somewhat more humane (and more than somewhat more voluntary) experimentation by folks like Gordon Geisbrecht (U of Manitoba) and the Canadian Defence and Civil Institute of Environmental Medicine (DCIEM).

wear a wetsuit