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How Mother's Milk Is Made

Linda J. Smith, BSE, FACCE, IBCLC
Dayton, Ohio, USA
From: LEAVEN, Vol. 37 No. 3, June-July 2001, p. 54-55

"Not enough milk" is the most common reason for supplementing or discontinuing breastfeeding. Sometimes this is real; other times it is imagined. The progress in understanding milk synthesis comes partly from dairy physiologists (who have a financial interest in knowing exactly how to have cows produce plenty of milk) and partly from those helping women breastfeed.

Before the 1940s, everyone thought most of the milk was made during the let-down reflex, because it flows faster during let-down. (This included dairy scientists as well as breastfeeding advocates.)

In 1944, Peterson showed that milk secretion was continuous but let-down was a different and separate process. Letdown (or MER-milk ejection reflex) squeezes out milk that is already made and stored in the alveolar lumen (small ducts into which milk from the alveoli is ejected). Milk isn't made any faster during MER. It just flows faster.

Since the 1990s, Peter Hartmann's research in Australia with breastfeeding women has found (actually "is finding" because this research is ongoing) that the rate of milk synthesis - how fast the secretory cells make milk - is related to the degree of emptiness (or fullness) of the breast. This is called autocrine (or local) control. As the alveolar lumen fills, compounds in the retained milk itself (Feedback Inhibitor of Lactation or FIL, peptides, fatty acids, and possibly other components) signal the secretary cells to slow down milk synthesis. The emptier the breast is, the faster it tries to refill - similar to an automatic icemaker. Hartmann says the rate of milk synthesis in women ranges from 11 to 58 ml/hour/breast, or about 1/3 of an ounce to 2 ounces per breast per hour. Emptier breasts make milk faster than fuller ones. When milk is regularly and thoroughly removed from the breast, milk synthesis is unrestricted.

Hartmann's research has documented what we in La Leche League have known for a long time--that milk supply is regulated by baby's needs. A baby rarely empties all of the available milk from his mother's breasts. In 1993, Hartmann found that babies remove an average of 76 percent of the available milk from their mother's breasts in a 24-hour period. This allows a baby to have short-term control of his mother's milk production.

I explain this using what I call the "80:20 concept." The 80 percent is the usual amount of milk taken by baby each day. The 20 percent is the residual amount of milk that remains in mother's breasts. If more than 80 percent of the milk is removed, supply increases to maintain the 80-20 ratio. If less than 80 percent is removed, supply decreases to maintain the 80-20 ratio. Even though this is an over-simplification of a very complex process, the core principle has held steady as new research emerges.

Research shows that the mother's diet, her fluid intake, and other factors have little influence on milk production. If the "milk removal" piece of the puzzle is in place, mothers make plenty of good milk regardless of dietary practices. If the "milk removal" part isn't there, nothing else can make up the difference.

The significant inhibiting (risk) factors to a full milk supply appear to be (1) breast surgery; (2) retained placenta; (3) Sheehan's syndrome or pituitary shock; (4) hormonal contraception; and (5) insufficient glandular tissue. If none of those are factors for a mother, it's exceedingly rare that she won't make plenty of milk. Rare situations do exist, however.

In my practice, there are two common reasons for "not enough milk": (1) the baby isn't at breast enough minutes per day, nursing sessions are ended before the baby lets go, or feeding intervals are stretched out too far between, or something else is given to the baby to "tide him over," or (2) the baby is not effectively transferring milk: either because of shallow attachment at the breast or a sucking problem.

The research shows that preventing and treating engorgement quickly is critical. Whenever possible, all feedings should be directly at the breast following baby's cues. Mothers should allow baby to finish the first breast first, watch for baby to signal when he is finished by self-detaching, and then offer the second breast. Babies need to breastfeed 8-12 times per day until the milk supply is established. Most babies will breastfeed a total of at least 140 minutes per day, averaging 10-30 minutes per nursing session. Mothers can be encouraged to use breastfeeding for both nourishment and nurture.

My plea to all: Look at the baby carefully. I don't hesitate to recommend pumps as tools because I see so many young babies with temporary poor suck responses. The poor suck leaves milk in the breast, which compromises milk supply, resulting in a hungry disorganized baby and no milk. With a good pumping routine, the mother has plenty of her own milk to work with while we figure out how to help the baby feed better at the breast. Supply is usually the easiest part to fix. Remember, it's still supply and demand, or "use it or lose it."

Linda J. Smith, BSE, FACCE, IBCLC is an internationally known author, teacher, lecturer, and proud grandmother. She has been an LLL Leader for almost 27 years in nine cities and two countries. Linda is a lactation consultant in private practice in Dayton, Ohio, USA. She is a founder of IBLCE, founder and past board member of ILCA, and currently sits on the United States Breastfeeding Committee representing the Coalition for Improving Maternity Services (CIMS). Linda and her husband, Dennis, own and operate the Bright Future Lactation Resource Center (


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