Hi!

It is my understanding that postpartum hair loss is due to
pregnancy, not breastfeeding.  I did a medline lit search and
only came up with one article "Changes in women's physical
health during the first postpartum year" Arch Family med 1993
Mar;2(3):2770-83.  Also I seem to remember this being
discussed in Williams Obstetrics but my copy is at home...

Anecdotally, I have lost tons of hair with all three of my
pregnancies.  My second baby died a few hours after birth and
 consequently I didn't have anyone to feed, but my hair loss
was still just as prevelant that time as with the other two;
both of whom were (and my 4 1/2 month old still is ) totally
breastfed.

Wendy Funk, MCH Epidemiology