To the Editor:
International recommendations discourage feeding infants anything other than breast milk for the first 6 months of life1,2—in part, because of concern that supplementation would reduce a mother’s breast milk supply as a consequence of reduced suckling. Conversely, perceived “insufficient milk” is commonly reported by mothers throughout the world3–6 as a reason for early supplementary feeding or discontinuation of breastfeeding.
In a recent commentary in EPIDEMIOLOGY, Kramer and colleagues reflect on a “formidable obstacle to causal inference”3(p. 793) regarding infant feeding: do differences in infant feeding behaviors cause differences in infant growth or do growth patterns instead affect infant feeding choices (“reverse causality”3,7)?
Detailed prospective data with which to address these questions are rare. A study from Argentina provides some insights. Five hundred mothers who planned to breastfeed for 9 months, with no supplementary feeding for 4 months, were enrolled.8 Here, we consider the patterns of supplementation (milk or other foods) during the infants’ first 4 months of life (which was the duration of unsupplemented breastfeeding recommended at the time this study was conducted).
The Table presents infant weight gain in relation to timing of supplementation, using the notation in the directed acyclic graph depicted by Kramer et al3 (eFigure, http://links.lww.com/EDE/A763; Kramer’s Figure 4). One-third of mothers who were observed at 4 months had already begun supplementation. For each month, weight velocity during the period leading up to the follow-up visit (which occurred at time j + 1) was highest for infants who were not yet supplemented, somewhat lower for those who had begun supplementation before this interval (before time j), lower still for those who began supplementation during this interval (j to j + 1), and lowest for those who began supplementation at the time of this visit.
At time j + 1, mothers who had begun supplementing before time j reported the highest percentages of perceived decreased milk production—presumably because supplementary foods had been providing some of the infants’ nutritional needs for at least 1 month. Once supplementation began, the reported daily breastfeeding frequency and average duration per feeding both declined, suggesting that these mothers were producing less milk. Of concern is the observation that, more than a month after supplementation had begun, these infants continued to grow more slowly than unsupplemented infants.
Among mothers who began supplementing at time j + 1, maternal reports about decreased milk production expressed at that visit—as well as the slowest infant growth of the 4 groups—clearly preceded supplementation. (International recommendations1,2 instead encourage more frequent breastfeeding to stimulate the milk supply.)
For mothers who began supplementing during the interval j to j + 1, we cannot be sure which mechanism is at work. However, we do know that at the previous visit (time j) few of these mothers had reported decreased milk production, and infant weight velocity had been relatively high. These results suggest that, for at least some of these mothers, the decision to begin supplements between these two visits was not prompted by perceived decreased milk production or slow weight gain but rather led to these problems.
Among mothers who had not begun supplementation, very few reported that milk production was “unsatisfactory” (Table). These infants had the highest weight velocity.
One limitation of our study is the small sample sizes in the three supplementing groups, due in part to study attrition; thus, confidence intervals are broad and overlapping. Nonetheless, similar patterns in all 4 months lend credence to these results. Analyses of larger data sets are warranted to explore the longitudinal associations of mothers’ reports of insufficient milk, supplementary feeding of young infants, and infant weight gain.
Margaret F. McCann
Angel Victor Moggia
Department of Obstetrics
School of Medicine
Buenos Aires University
Buenos Aires, Argentina
3. Kramer MS, Moodie EE, Platt RW. Infant feeding and growth: can we answer the causal question? Epidemiology. 2012;23:790–794
4. Clayton HB, Li R, Perrine CG, Scanlon KS. Prevalence and reasons for introducing infants early to solid foods: variations by milk feeding type. Pediatrics. 2013;131:e1108–e1114
5. McCann MF, Bender DE. Perceived insufficient milk as a barrier to optimal infant feeding: examples from Bolivia. J Biosoc Sci. 2006;38:341–364
6. McCann MF, Baydar N, Williams RL. Breastfeeding attitudes and reported problems in a national sample of WIC participants. J Hum Lact. 2007;23:314–324
7. Schisterman E, Whitcomb B, Bowers K. Invited commentary: causation or “noitasuac”? Am J Epidemiol. 2011;173:984–987; reply 988
8. McCann MF, Moggia AV, Higgins JE, Potts M, Becker C. The effects of a progestin-only oral contraceptive (levonorgestrel 0.03 mg) on breast-feeding. Contraception. 1989;40:635–648