Sleep and Feeding Method
What is the relationship between sleep and the type of milk fed to babies?
Research has begun to demonstrate some significant differences between the sleep patterns of infants fed human milk versus those fed dairy-based formula, but the effects are complex. It is thought that differences may arise as a consequence of the difficulty involved in digesting cow’s milk formula, which causes longer and deeper periods of sleep earlier in life for formula-fed infants (or did with earlier formula products) (Cavkll 1981), and the need of breastfed infants to feed frequently day and night (Anuntaseree et al. 2007; Barnard 1999).
Although total number of awakenings differ, Quillian (1997) reported no difference in total infant sleep duration overall. Similarly, despite experiencing a greater number of awakenings, research suggests that breastfeeding mothers get the same amount of sleep (Gay et al. 2004, Montgomery-Downs et al. 2010) or more sleep (Doan et al. 2007, Doan et al 2014) overall compared to formula-feeding mothers. Galbally et al’s (2013) research also found that that breastfeeding at 6 months was associated with more frequent infant waking during the night and difficulties sleeping alone. However, breastfeeding was not associated with infants having problems falling asleep or having restless sleep. This may be influenced by the presence of melatonin in breastmilk. This hormone is secreted during the night by adults but not in infants and has a hypnotic effect as well as a relaxing effect on the smooth muscle of the gastrointestinal tract. Engler et al’s (2012) research compared formula fed and breastfed infants aged 2-4 months and found that exclusive breastfeeding was associated with improved sleep and a reduction in irritability/colic.
Formula is associated with reduced arousal
Formula-fed infants have been found to arouse less easily from sleep (Horne et al 2004). We also know that breastfeeding is protective against SIDS; the effect being stronger for exclusively breastfed infants (Vennemann et al. 2009, Hauck et al. 2011). Arousal from sleep is thought to be an important mechanism protecting infants from potentially fatal cardiac or respiratory episodes associated with SIDS (Hunt 1992, Mosko et al. 1996, Mosko et al. 1997, Horne et al. 2010).
One concern, therefore, is that when parents introduce formula to their infants’ diets in order to encourage ‘settling’ or ‘sleeping through’, this not only disrupts the physiological processes underlying successful lactation (due to loss of frequent night-time feeds when prolactin production is greatest), thus putting successful long term breastfeeding at risk, it may also increase the risk of SIDS in arousal-deficient infants. The introduction formula or solid foods is often encouraged or supported by commonly held views linking infant sleep to feeding practices. Recent research by Rudzik and Ball (2016) found that popular wisdom in the UK tightly links breastfeeding and inadequate night-time sleep. As a result, mothers are frequently advised by peers and family to introduce formula or solid foods to infants to promote longer sleep. However, the extent to which mothers acted upon this advice depended on what they considered to be ‘normal’ sleep. Mothers who breastfed were shown to be more likely to accept that fragmented infant sleep was normal for breastfed babies, and something they needed to learn to cope with, whilst mothers who were formula feeding felt that infant night waking was a problem that had to be fixed.
Another study by Brown and Harries (2015) questions the relationship between night waking and infant feeding method among older infants. This research, involving infants aged 6–12 months, found no difference in reports of night wakings or night feeds between mothers who were currently breastfeeding or formula feeding. Infants who received more milk or solid feeds during the day were less likely to feed at night but not less likely to wake. Increasing infant calories during the day may therefore reduce the likelihood of night feeding but will not reduce the need for parents to attend to the infant in the night. These findings support St James-Roberts et al.’s (2015) findings that ‘normal’ sleep in infants in the first year of life, regardless of feeding method, involves bouts of sleep alongside episodes of waking.
|Human milk||Dairy based formula milk|
|More fragmented sleep (Tikotzy et al 2009)||Longer periods of sleep, earlier in life (Horne et al 2004)|
|Shorter sleep bouts (Elias et al, 1986)||Deeper periods of sleep, earlier in life (Horne et al 2004)|
|Later sleep consolidation (Touchette et al. 2005)||Earlier sleep consolidation (Touchette et al. 2005)|
|Presence of melatonin (sleep hormone) in breastmilk (Engler et al 2011)||Absence of melatonin or other maternal hormones (Engler et al 2011)|