Q: I like to have one small cup of coffee in the morning and, rarely, a second cup in the afternoon. Is this OK while nursing my 5-month-old daughter?
A: Most experts recommend caffeine in moderation--that is, one to two cups of coffee daily--while breastfeeding. Since the servings you're having are not the "grande" size, you and your baby should be just fine. (This is one aspect of breastfeeding where cup size does matter!)
Why the limit? According to Medications and Mothers' Milk by Thomas Hale, Ph.D. (Hale Publishing L.P., 2006), the "half-life" of caffeine is extremely long in newborns but much shorter in older infants. (A drug's half-life is the length of time it takes for half a dose to be cleared from the body.) The substance stays in a newborn's bloodstream for close to 100 hours; the half-life drops to 14 hours by the age of 3 to 5 months and then to about 2.6 hours in babies 6 months and older. It's about five hours in adults.
If, on the other hand, you were to drink four or five cups of coffee every day and your baby was on the young side, two things might happen: Your milk could have a lower iron content, and your baby (and you) could become jittery and irritable.