CERTAINLY don't take any of this as gospel, but it's interesting anyway:
"ZMA™ is a special combination of zinc, magnesium, and vitamin B-6. The zinc in this outstanding product is specifically formulated as zinc aspartate and zinc mono L-methionine which makes it incredibly bioavailable because of the two forms of chelates. The magnesium is also found in a chelated form bound to aspartate which makes it very bioavailable as well. In fact, the magnesium and zinc are bound together to the aspartate which can also (chemically speaking) enhance absorption."
http://www.tsrf.com/supplements/supplements_zma.htm
"In ZMA the Magnesium and vitamin b-6 are bound to the zinc to keep it circulating in the body longer thus making it more effective than regular zinc."
http://www.ghrenewu.us/useghrenewu.htm
"the aspertate is a bigger molecule of zinc and magnesium, so the bioavailability is higher for both. REgular zinc and mag are made froma smaller molecule. All the studies of ZMA were done with the aspertate molecules so that would be the kind you would wnat."
http://www.nutritionalsupplements.co...918&highlight=