More sleep, more milk

Abstract

Breastfeeding is the best feeding method for infants, but this task is particularly challenging for mothers. Sleep time and quality are undeniably reduced in the postpartum period. No study has demonstrated the relationship between slow-wave sleep and lactation. Here, we discuss a unique experimental case during which the mother self-reported her sleep with a SUUNTO 9 watch and quantified her milk volume, blind to sleep parameters. This case report highlights an interesting strong correlation between stage N3 (slow-wave) sleep duration and milk production. It also demonstrates that this production is linked positively to self-reported sleepiness in the morning and breast tension and negatively to the number of awakenings. These results emphasize the need for preserving sleep, especially N3 sleep, during breastfeeding. Splitting nighttime infant care between parents, preserving the mother’s sleep as much as possible during the first part of the night, could help improve lactation.

Citation:

Aerts C, Janaqi S, Cochen de Cock V. More sleep, more milk. J Clin Sleep Med. 2023;19(8):1563–1565.

INTRODUCTION

Breastfeeding is a natural physiological function of motherhood. It is recommended by the World Health Organization during the first 2 years of life because it is recognized as the best feeding method for infants. Maternal benefits include decreased risk of postpartum depression, breast and ovarian cancer, hypertension, cardiovascular disease, and type 2 diabetes mellitus. Benefits for the infant include decreased risk of atopic dermatitis, gastroenteritis, and unexpected infant death syndrome and a higher intelligence quotient. Nevertheless, breastfeeding is one of the most challenging aspects of the postpartum period. Mothers endorse the responsibility of giving qualitatively and quantitatively sufficient milk to their infants. Breastfeeding rates are lower than recommended, and more than 70% of mothers experience breastfeeding difficulties. Perception of an insufficient amount of milk and fatigue represent major risk factors for early breastfeeding cessation.¹ Main determinants such as the mother’s mood, hydration, and sleep are vulnerable during the early postpartum period. The aim of our case report was to measure the correlation between milk volume and the different factors suspected to influence lactation, especially sleep duration and quality.

REPORT OF CASE

C.A. gave birth by vaginal delivery, without complications, on April 26, 2022, at 41 weeks and 4 days of amenorrhea to a 3.03-kg, 48-cm girl who was exclusively breastfed. Every night, while the baby remained with her father the mother slept alone until the first breastfeeding, after which she kept the baby (room-sharing) for the rest of the night. From June 30 until July 22, each morning the volume of milk from the right breast was measured systematically during the 30 minutes after the mother awakened. A Medela Symphony breast pump (Medela AG, Lättichstrasse, Baar, Switzerland) was used, following the same 10-minute routine consisting of 2 minutes of stimulation and 8 minutes of expression. During the day, breastfeeding lasted 5 to 10 minutes and was alternate. During the night the baby was fed from the left breast only.

The number of feedings per 24 hours, the number of awakenings per night, the presence of the coparent, and the way of sleeping (bed-sharing/room-sharing) were reported in a diary. A Karolinska questionnaire, thirst sensation, and breast tension were reported right after morning awakening, blind to the milk volume. Mood was monitored by the Edinburgh Postnatal Depression Scale.

A SUUNTO 9 watch (SUUNTO, Vantaa, Finland) was worn on the left wrist (except for reload time, around 2 hours weekly) to measure total sleep time, sleep efficiency, latency to sleep onset, deep sleep duration, wakefulness duration, and daily caloric expenditure. The SUUNTO 9 technology’s sensitivity and specificity to evaluate sleep have been previously validated.² The slow-wave sleep duration quantified by the SUUNTO 9 watch was validated on C.A., during the breastfeeding period, with a 1-night gold standard blind polysomnography evaluation (Compumedics; D & DJ Burton Holdings, Melbourne, Victoria, Australia). The concordance between the 2 methods was 91%. The milk volume was measured blind to the sleep data.

This experimental case report was self-designed and carried out by C.A.

No naps were registered. No mood disorder was reported (Edinburgh Postnatal Depression Scale = 0) either at the beginning or at the end of the month. Thirst sensation was present 9 times out of the 20 mornings. Breast tension was reported as absent 1 time, mild 2 times, moderate 10 times, intense 6 times, and very intense only 1 time. The father was absent only 4 times. After nighttime breast feeding the baby was always room-sharing and was bed-sharing 18 out of the 20 nights. All other clinical data are reported in Table 1.

Table 1.

Correlations between collected morning milk volume, sleep, and caloric expenditure.

Variable	Measure	Pearson Correlation	95% CI	P
No. of feedings per 24 hours (both sides)	10.5 (1.64)	−0.0143	−0.454, 0.4309	.95
Maternal total sleep time (minutes)	446.50 (47.86)	0.22	−0.2435, 0.6058	.34
Sleep efficiency (%)	82.05 (10.24)	0.2118	−0.2546, 0.5982	.37
Latency to sleep onset (minutes)	6.75 (10.96)	0.06	−0.3924, 0.49	.80
Stage N3 sleep duration (minutes)	136.6 (46.69)	0.57	0.1744, 0.81	.0083
Wakefulness duration (minutes)	52.5 (32.61)	0.11	−0.3484, 0.5278	.64
Latency to first breastfeeding awakening (minutes)	147.45 (58.08)	0.26	−0.2208, 0.6207	.30
No. of awakenings	3.2 (1.24)	−0.08	−0.5042, 0.3763	.74
Measure of self-reported sleepiness at morning awakening (Karolinska)	4.3 (1.59)	0.36	−0.1026, 0.6899	.12
Caloric expenditure (kcal)	1,861 (189.48)	0.05	−0.4015, 0.4818	.83

Data are means (standard deviation). CI = confidence interval.

We looked for linear correlations using a Pearson test between collected morning milk volume and all other continuous measured variables (Table 1). Collected milk volume was strongly positively correlated to stage N3 sleep duration (Figure 1), whereas other measures did not correlate (Table 1).

Figure 1. Correlation between morning milk volume and stage N3 sleep duration.

Because all our variables were not independent, to predict milk volume we created a multivariate regression model, aggregating all the data (continuous data reported in Table 1 and discontinuous data described in the results). Data were z-scored and we calculated a multivariate model using the Lasso method to approximate milk volume with a minimal set of variables. The obtained model (error rate 16%, P = .000328) predicted milk volume with 4 variables out of 14.

The main influence of our predictive model of collected milk volume came from stage N3 duration (9.9), followed by self-reported sleepiness in the morning (8.4), number of awakenings (−7.63), and breast tension (5.64).

DISCUSSION

This case report demonstrated an interesting strong correlation between stage N3 duration and milk production in the morning. It also highlighted that this production is linked positively to self-reported sleepiness in the morning and breast tension and negatively to the number of awakenings.

Breastfeeding is a natural process that stimulates the secretion of prolactin during stage N3 sleep.³ The prolactin action lasts several hours and regulates the amount of milk produced. The release of oxytocin is much shorter, facilitating milk ejection,⁴ and is associated with better mood.⁵ Our case report shows evidence that increased stage N3 sleep may promote milk production. This is in line with the increased amount of stage N3 sleep measured in breastfeeding mothers.⁶ One study has demonstrated that the longer their sleep duration the more mothers tend to breastfeed.⁷

Sleep amount is frequently reduced in the postpartum period, but this reduction is probably less important for breastfeeding mothers.⁸ Preserving sufficient sleep quality, especially stage N3 sleep, seems critical to optimize lactation. Another study has highlighted that poor sleep quality reported on questionnaires was a significant predictor for lower milk volume estimated through infants’ measured weight.⁹ According to the literature and our results, we can propose the following virtuous circle model: Breastfeeding increases slow-wave sleep, during which prolactin is secreted to produce more milk, allowing breastfeeding.

Subjective sleepiness in the morning was associated with more milk. This might be indirectly linked to stage N3 sleep known to be associated with more sleep inertia.¹⁰ In the same way, the number of awakenings was associated with less milk, probably because it reduces stage N3 sleep duration. Finally, breast tension was associated with production of milk already stored in the breast at feeding time.

We did measure prolactin in this case, which could be a limitation. However, prolactin production is highly variable and does not represent a good marker for lactation.¹¹ All in all, our main limitation is the unique case report justifying further studies, but the constraints linked to the protocol may prevent larger explorations.

Breastfeeding is vulnerable, and here we demonstrate that stage N3 sleep preservation is a determinant of milk production. Stage N3 sleep duration is higher at the beginning of the night, which makes this period critical for good lactation. Room-sharing is recommended to prevent unexpected infant death syndrome; nevertheless, it can alter the quality of the mother’s sleep. Splitting nighttime infant care between parents, preserving the mother’s sleep as much as possible during the first part of the night, could help improve lactation.

DISCLOSURE STATEMENT

All the authors have seen and approved the manuscript. Work for this study was performed at the Department of Sleep and Neurology, Beau Soleil Clinic, Montpellier, France. The authors report no conflicts of interest.