Philippa,
It is documented that hormonal surges are higher during simultaneous
stimulation of both nipples; so if a woman tends to get headaches when her
hormones are fluctuating, it will be more noticeable when she nurses two
babies at the same time.  Prolactin, oxytocin, and vasopressin have all
been accused, in the medical literature, of causing headaches, but the
jury is definitely still out; in other words: nobody knows for sure what
causes these breastfeeding-related headaches.  (Email me directly for
references.)
Ginna
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Ginna Wall, MN, RN, IBCLC                       Phone (206)548-6368
Lactation Services Coordinator                  Fax (206)548-4809
University of Washington Medical Center         Mailbox 356153
1959 NE Pacific Street, Seattle WA 98195
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