Hydration in pregnancy and breastfeeding - During lactation
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Figure 7.Average rates of milk production in exclusively breastfeeding women.
Adapted from Neville et al. 1988.
Breast milk contains, on average, 87% water (EFSA, 2010), water content varies depending on the time of day. During a single breastfeeding episode, foremilk (the milk obtained at the beginning of breastfeeding) has higher water content and keeps the infant hydrated, whereas hindmilk (milk released near the end of breastfeeding) contains two to three times more fat than foremilk (Riordan and Wambach, 2009).
Since breast milk is produced using maternal body water, a milk volume of 750 mL/d at 87% of water equals a significant extra water loss for the mother, compared to the daily normal losses. Maintaining water balance can therefore be challenging for lactating women.
Maternal water intake during lactation should be sufficient to compensate the water lost through milk. Thus, in theory, the water intake of lactating women should be at least equivalent to non-breastfeeding women, plus the quantity of water transfered into the maternal milk, estimated to be 600 to 700 mL/d (EFSA, 2010; IoM 2004) (Figure 8).
Figure 8.Water balance in breastfeeding women.
Data on actual fluid intake in breastfeeding women are scarce. Two studies, performed with a limited number of subjects, have shown that fluid intake of US lactating women is about 16% (300mL) higher than non-breastfeeding women (Ershow et al., 1991); this is not enough to meet theoretical requirements (Stumbo et al., 1985), but these results need to be confirmed with further research. From a physiological point of view, a powerful thirst sensation, reported during breastfeeding episode, could help increasing fluid intake (Bentley, 1998). However, the underlying mechanisms are unclear and the effect of this thirst sensation on women’s fluid intake is unknown.
The question has been raised whether fluid intake quantity can influence breast milk production. But scientific data have consistently shown that neither an increased nor a restricted fluid intake quantity affects the volume of milk produced (Dusdieker et al., 1985; Dusdieker et al., 1990; Horowitz et al., 1980; Prentice, 1984).
This is consistent with data demonstrating that overall maternal nutrition status has little influence on milk quantity and quality (IoM, 1991). Infants receive the nutrients and water they need, sometimes to the detriment of the mother, and milk quantity is driven by infant demand.
However, healthy diet and adequate hydration desirable to maintain maternal health (IoM, 1991) and are therefore often advised by health care professionals to breastfeeding mothers (Lawrence and Lawrence, 1999).
Take home messages
Breast milk production progressively increases across the lactating period, reaching 750 mL/d at 6 months postpartum.
Breast milk is mainly composed of water (on average, 87%).
The mother needs to compensate the production of milk by drinking sufficient water.
The quantity of milk produced meets infant needs, even if this means putting the mother at risk of dehydration