There is a thoughtful and thorough review about the effects of melatonin
in a recent issue of Cell -- I believe it was published either in late
December or early January. The author is David Weaver.
It's not good news. Weaver, one of the pre-eminent researchers of
melatonin biochemistry, points out serious flaws in the studies of
Pierpaoli and co-workers. For example, the mouse used in the pineal
transplant studies were of a strain which is defective in melatonin
production -- so any life extension seen in those studies could not have
been due to melatonin. Additionally, the drinking-water supplementation
experiment only observed life extension in one mouse strain; in another,
increased mortality due to reproductive tract cancer was observed in the
experimental group.
With all the hype on melatonin in the media, I think it's important to
know where the facts stand. The review is short, well-argued, and
accessible to the lay person. I recommend reading it.