The following may have been discussed already with reference to vasospasm.
I was on no mail for a few days.  Ros Escott wrote a letter (JHL 10:6, 1994)
raising the question, do hormones play a role in nipple vasospasm for some
women?  I responded with my theory regarding mineral imbalance, in a letter
(JHL 10:3, 1994).  Clinically I had seen a number of women who even without
a mechanical reason for the vasospasm such as incorrect suck or anatomical
variation, experienced this blanching.  Pieces of my theory came from
raising two litters of dalmations. The litter born in the heat of July
caused a mineral depletion to the mother.  The vet had to come out and give
her calcium shots to stablize her.  Human birth can depleat mineral levels
affecting the release of homrmones and interfere with homeostatis.  I back
tracked to see what interacts with muscle contractions in nipple tissue.
Unfortunately I didn't set up ground work for a reliable study but in a very
small informal sample size,  the use of calcium and magnesium as dietary
supplements helped within a week's time.  Even the women who experienced
vasospasm due to mechanical reasons felt relief.  It was as if their nipples
were not as sensitive.  I wish that someone would do a formal study on this
issue!!!!
Joanne Burke Snyder MA, IBCLC
Latch-On Services, a Private Practice in Indianola, Iowa