Association of Human Milk Fatty Acid Composition with Maternal Cardiometabolic Diseases: An Exploratory Prospective Cohort Study *

Abstract

Background:

Human milk fatty acids derive from maternal diet, body stores, and mammary synthesis and may reflect women’s underlying cardiometabolic health. We explored whether human milk fatty acid composition was associated with maternal cardiometabolic disease (CMD) during pregnancy and up to 5 years postpartum.

Materials and Methods:

We analyzed data from the prospective CHILD Cohort Study on 1,018 women with no preexisting CMD who provided breast milk samples at 3–4 months postpartum. Milk fatty acid composition was measured using gas-liquid chromatography. Maternal CMD (diabetes or hypertension) was classified using questionnaires and birth records as no CMD (reference outcome group; 81.1%), perinatal CMD (developed and resolved during the perinatal period; 14.9%), persistent CMD (developed during, and persisted beyond, the perinatal period; 2.9%), and incident CMD (developed after the perinatal period; 1.1%). Multinomial logistic regression was used to model associations between milk fatty acid composition (individual, summary, ratios, and patterns identified using principal component analysis) and maternal CMD, adjusting for pre-pregnancy anthropometry and race/ethnicity.

Results:

Medium-chain saturated fatty acids (MC-SFA), lauric (C12:0; odds ratio [OR] = 0.73, 95% confidence interval [CI] = 0.60–0.89) and myristic acid (C14:0; OR = 0.80, 95% CI = 0.66–0.97), and the high MC-SFA principal component pattern (OR = 0.86, 95% CI = 0.76–0.96) were inversely associated with perinatal CMD. Long-chain polyunsaturated fatty acids adrenic acid (C22:4n-6) was positively associated with perinatal (OR = 1.21, 95% CI = 1.01–1.44) and persistent CMD (OR = 1.56, 95% CI = 1.08–2.25). The arachidonic (C20:4n-6)-to-docosahexaenoic acid (C22:6n-3) ratio was inversely associated with incident CMD (OR = 0.52, 95% CI = 0.28–0.96).

Conclusions:

These exploratory findings highlight a potential novel utility of breast milk for understanding women’s cardiometabolic health.

Introduction

Human breast milk is a dynamic biological fluid containing thousands of nutritional and bioactive molecules.¹ Fatty acids are among the most variable macronutrients in breast milk, derived from a combination of maternal dietary intake, maternal body stores (e.g., adipose tissue), or endogenous synthesis in the mammary gland, liver, or other tissues.² Fatty acid composition of human milk thus likely reflects maternal underlying health and metabolic capacity.³ For example, research has shown that human milk composition in obese mothers has significantly higher concentrations of saturated fatty acids (SFA) and lower concentrations of n-3 polyunsaturated fatty acids (PUFA) compared with normal-weight mothers.^4–7 However, limited research has explored human milk fatty acid compositional differences in relation to maternal diseases.

Cardiometabolic diseases (CMD), defined here as diabetes and hypertension, are leading contributors to morbidity among women and major risk factors for cardiovascular disease.⁸ Shared pathophysiology among CMD includes low-grade inflammation and insulin resistance, which can result in widespread perturbations to metabolic function.⁹ In women of childbearing age, CMD can manifest in several clinically distinct ways. CMD are common complications of pregnancy; the prevalences of gestational diabetes and hypertensive disorders in pregnancy (including gestational hypertension and preeclampsia) are approximately 7% and 10%, respectively.^10,11 Nearly 20% of these cases persist and develop into chronic forms of the diseases by 5 years postpartum.^10,12 CMD can also develop outside of pregnancy as a de novo chronic disease, with the incidence increasing as women age.¹³ Emerging metabolomic research using maternal blood plasma has documented subtle nuances in maternal metabolic and physiologic markers between perinatal (before and after birth), persistent, and incident CMD,^14,15 suggesting important subclinical differences in various phenotypes of these diseases.

The extent to which CMD affect human milk fatty acid composition remains unclear. Prior studies have focused on preexisting^16–20 or gestational^5,21 diabetes and preeclampsia^22,23 and reported discordant results, of which many were published in the 1990s on small samples (<15 women) or lacked control for the potential confounding effect of maternal body mass index (BMI). Importantly, existing studies have not separated and simultaneously compared perinatal, persistent, and incident CMD to determine whether fatty acid composition reflects subclinical distinctions between disease phenotypes. Such evidence would help to elucidate the complex interplay between human milk and maternal cardiometabolic health and generate insights on the potential value of milk composition as a risk biomarker for CMD. Therefore, we sought to explore whether human milk fatty acid composition was associated with maternal CMD phenotypes during pregnancy and up to 5 years postpartum.

Methods

Study design and data source

We conducted a prospective cohort study using data from the CHILD Cohort Study, a population-based birth cohort in Canada. Between 2008 and 2012,^24,25 women with singleton pregnancies were enrolled from four sites in Canada (Edmonton, Manitoba, Toronto, and Vancouver) and were retained for longitudinal follow-up if they delivered a healthy infant >35 weeks’ gestation. Comprehensive health and environmental data have been collected using standardized questionnaires, home visits, clinical assessments, medical record linkage, and biological sample collection. We used questionnaire data from the prenatal, 1-year postpartum, and 5-year postpartum time points, medical record data from the birth hospitalization, and biological data from breast milk samples collected at the 3–4 months postpartum home visit. This secondary analysis of the CHILD Cohort Study data was approved by the Health Research Ethics Board at the University of Manitoba (HS2022:062).

Sample

Of the 3,455 women enrolled in the CHILD Cohort Study, we included 1,200 women who had their breast milk samples previously analyzed for fatty acid content, selected on the basis of representing a diverse health and socioeconomic subset of the full cohort.²⁶ We excluded those who responded to neither postpartum questionnaire (n = 110), self-reported CMD preexisting at the time of pregnancy (n = 35), were missing data on pre-pregnancy BMI or race/ethnicity (n = 28), or provided their milk sample within 2 months of giving birth (n = 9). The resulting sample size was 1,018 women.

Fatty acids

Prior to the 3–4-month postpartum home visit, women were provided a sterile collection jar and instructed to collect at least 10 mL of breast milk over two or more feedings (both before and after the feeding) and to keep the jar and sample continuously refrigerated. Breast milk samples were analyzed for fatty acid composition by gas-liquid chromatography at the University of Alberta as previously described.^27,28 The 27 fatty acids, summary measures, and ratios analyzed in this study are outlined in Supplementary Table S1.

Cardiometabolic disease

The presence and timing of CMD, defined as diabetes and hypertension (including preeclampsia), were measured using self-reported questionnaires in late pregnancy, 1 year postpartum, and 5 years postpartum and on the hospital birth record, with both distinguishing between pregnancy-associated and chronic forms of CMD. Women were classified into one of four phenotypes: no CMD at any point; CMD that developed and resolved during the perinatal period (perinatal CMD); CMD that developed during, and persisted beyond, the perinatal period (persistent CMD); or CMD that developed only after the perinatal period and up to 5 years postpartum (incident CMD). We defined the perinatal period as the time of conception up to 1 year postpartum.

Potential covariates

Potential covariates that have been associated with both human milk fatty acid composition and maternal CMD included maternal age, post-secondary education, race/ethnicity (White; Black, Indigenous, or People of Color [BIPOC]), pre-pregnancy BMI (based on measured height and either self-reported pre-pregnancy weight or measured weight at 1 year after birth),²⁹ prenatal dietary fat and cholesterol intake³⁰ measured through questionnaires, and infant sex and parity (primiparous; multiparous) documented on the hospital birth record. The lactation stage in weeks postpartum was documented at the time of milk sample collection. Fish oil supplementation during pregnancy was reported by very few participants (<3%) and thus not included as a covariate.

Analysis

We used descriptive statistics to compare sample characteristics and fatty acid composition according to the four categories of maternal CMD. We compared frequencies and proportions for categorical data (e.g., maternal education) using chi-squared tests and compared means and standard deviation (SD) for continuous data (e.g., each fatty acid) using analysis of variance (Table 2). Given the exploratory nature of this study, we used both traditional (<0.05) and liberal (<0.2) p-value thresholds to comment on potentially meaningful unadjusted differences in fatty acid composition by the maternal CMD group. For all subsequent analyses, we converted fatty acid measurements from proportions into Z-scores to ensure all fatty acids were interpreted on a comparable scale (per SD increase).

We then used principal component analysis (PCA) with varimax rotation to transform the 27 correlated fatty acids into a smaller number of uncorrelated principal components representing fatty acid patterns.²⁶ We retained PCA components with an eigenvalue ≥2 and named the patterns according to fatty acids demonstrating high factor loadings >|0.20|. We then predicted each woman’s score on each of the patterns, where higher positive scores represent greater alignment between the woman’s actual fatty acid composition and that captured by the PCA pattern.

Finally, we used multivariable multinomial logistic regression to model the association between human milk fatty acid composition (individual, summary, ratios, and patterns) and maternal CMD, yielding odds ratios (OR) and 95% confidence intervals (CI). We modeled fatty acid composition as the exposure (independent variable) and CMD as the outcome (dependent variable) to align with the temporal ordering of these data. That is, although CMD may have been present before or at the time of milk sample collection, the specific phenotype of CMD could only be classified into one of the four groups after follow-up until 5 years postpartum. First, we constructed a set of models with no CMD as the reference outcome group, with comparisons to (1) perinatal CMD, (2) persistent CMD, and (3) incident CMD, to examine how fatty acid composition differed based on the absence versus the presence of any CMD (current or future). Next, we constructed a set of models with perinatal CMD as the reference outcome group, with comparisons to (1) persistent CMD and (2) incident CMD, to examine how fatty acid composition differed for acute perinatal CMD versus CMD that continued or presented beyond the postpartum period. To avoid overadjustment due to small cell counts in the persistent and incident CMD groups, models were adjusted only for pre-pregnancy BMI and race/ethnicity, given the strong associations between these maternal factors and CMD in this sample. We modeled BMI using a restricted cubic spline with 3 knots at the recommended percentiles of the sample to allow for a flexible, nonlinear, confounding effect.³¹ Statistical significance was defined as a 95% CI that did not enclose the null value. Results were not adjusted for multiple testing and should be interpreted as exploratory. Data were analyzed in Stata MP version 17, and figures were generated in R version 4.1.0.

Results

Participant characteristics

Sample characteristics are shown in Table 1. There were 826 women with no CMD (81.1%), 152 women with perinatal CMD (14.9%), 29 women with persistent CMD (2.9%), and 11 women with incident CMD (1.1%). Diabetes was slightly more common in the perinatal CMD phenotype, whereas hypertension was more common in the persistent and incident CMD phenotypes. Compared with women with no CMD, women with all phenotypes of CMD were slightly more likely to be aged 35 years and older and significantly more likely to be overweight or obese or to self-identify as BIPOC. Prenatal dietary intakes of fat and cholesterol were not significantly different between CMD groups.

Table 1.

Sample Characteristics According to Maternal Cardiometabolic Disease (n = 1,018)

Characteristic	No CMD(N = 826)	PerinatalCMD (N = 152)	PersistentCMD (N = 29)	IncidentCMD (N = 11)	p-value
	n (%)
Cardiometabolic Disease					—
Hypertensive disorders	—	75 (49.3)	21 (72.4)	9 (81.8)
Diabetes mellitus	—	80 (52.6)	17 (58.6)	2 (18.2)
Maternal Age					0.65
<35 years	512 (62.0)	91 (59.9)	15 (51.7)	6 (54.5)
≥35 years	314 (38.0)	61 (40.1)	14 (48.3)	5 (45.5)
Maternal BMI Category					<0.01*
Normal weight (<25 kg/m²)	578 (70.0)	76 (50.0)	11 (37.9)	4 (36.4)
Overweight (25–29.9 kg/m²)	175 (21.2)	43 (28.3)	6 (20.7)	5 (45.5)
Obese (≥30 kg/m²)	73 (8.8)	33 (21.7)	12 (41.4)	2 (18.2)
Maternal Race/Ethnicity					0.01*
White	620 (75.1)	95 (62.5)	19 (65.5)	8 (72.7)
BIPOC	206 (24.9)	57 (37.5)	10 (34.5)	3 (27.3)
Infant Sex					0.71
Female	368 (44.6)	75 (49.3)	12 (41.4)	5 (45.5)
Male	458 (55.4)	77 (50.7)	17 (58.6)	6 (54.5)
Parity					0.89
Primiparous	445 (54.6)	86 (57.7)	15 (51.7)	6 (54.5)
Multiparous	370 (45.4)	63 (42.3)	14 (48.3)	5 (45.5)
Lactation Stage					0.47
2–3 months postpartum	575 (69.6)	113 (74.3)	24 (82.8)	8 (72.7)
4–5 months postpartum	209 (25.3)	34 (22.4)	3 (10.3)	3 (27.3)
≥6 months postpartum	42 (5.1)	5 (3.3)	2 (6.9)	0 (0.0)

	Mean ± SD
Prenatal Dietary Intake
Fat (grams/day)	71.6 ± 28.5	77.1 ± 29.7	75.1 ± 31.9	67.9 ± 25.4	0.18
Cholesterol (milligrams/day)	264.5 ± 162.9	295.8 ± 146.1	278.9 ± 147.1	296.5 ± 145.8	0.17

Cardiometabolic diseases (diabetes and hypertension) were not mutually exclusive; women could experience more than one. Eleven women were missing the mode of delivery data, and 14 women were missing parity data.

*Statistically significant difference (p < 0.05) based on chi-squared test for proportions or analysis of variance for means.

BIPOC, White, Black, Indigenous, or People of Color; BMI, body mass index; CMD, cardiometabolic disease; SD, standard deviation.

A comparison of mean and SD fatty acid measures (individual, summary, and ratios) across maternal CMD groups is shown in Table 2. At a traditional p-value threshold (<0.05), there were significant differences for lauric acid and adrenic acid only. At a more liberal p-value threshold (<0.2), there were additional differences identified for myristic acid, pentadecylic acid, nervonic acid, vaccenic acid, and arachidonic acid (ARA).

Table 2.

Differences in Human Milk Fatty Acid Composition According to Maternal Cardiometabolic Disease

	Mean ± SD
	No CMD	Perinatal CMD	Persistent CMD	Incident CMD
Fatty acids	N = 771	N = 120	N = 18	N = 11	p-value
Fatty acids	SFA				p-value
Capric Acid (10:0)	0.72 ± 0.31	0.67 ± 0.33	0.64 ± 0.31	0.69 ± 0.34	0.23
Lauric Acid (12:0)	4.84 ± 1.67	4.50 ± 1.39	5.28 ± 1.8	4.67 ± 1.22	0.04^*
Myristic Acid (14:0)	5.96 ± 1.81	5.74 ± 1.82	6.59 ± 2.09	6.18 ± 1.18	0.12
Pentadecylic Acid (15:0)	0.31 ± 0.10	0.30 ± 0.10	0.26 ± 0.07	0.30 ± 0.13	0.08
Palmitic Acid (16:0)	20.85 ± 2.85	21.21 ± 2.98	20.74 ± 2.30	21.56 ± 2.88	0.44
Margaric Acid (17:0)	0.31 ± 0.08	0.32 ± 0.08	0.30 ± 0.08	0.31 ± 0.08	0.68
Stearic Acid (18:0)	6.59 ± 1.41	6.44 ± 1.23	6.61 ± 1.45	6.29 ± 0.95	0.56
Arachidic Acid (20:0)	0.16 ± 0.06	0.17 ± 0.06	0.16 ± 0.06	0.14 ± 0.06	0.21
Lignoceric Acid (24:0)	0.05 ± 0.03	0.05 ± 0.03	0.06 ± 0.03	0.05 ± 0.03	0.46
MUFA
Physeteric Acid (14:1n9)	0.21 ± 0.09	0.21 ± 0.09	0.19 ± 0.06	0.21 ± 0.10	0.60
Palmitoleic Acid (16:1n7)	2.69 ± 0.68	2.67 ± 0.67	2.76 ± 0.66	2.75 ± 0.75	0.93
Oleic Acid (18:1n9)	36.89 ± 3.74	37.0 ± 3.91	36.51 ± 3.63	36.55 ± 2.83	0.92
Nervonic Acid (24:1n9)	0.05 ± 0.02	0.05 ± 0.02	0.05 ± 0.02	0.04 ± 0.01	0.09
Vaccenic Acid (18:1t/c11)	3.09 ± 1.28	3.12 ± 1.25	3.61 ± 1.18	2.50 ± 0.83	0.06
N-3 PUFA
ALA (18:3n3)	1.92 ± 0.67	1.99 ± 0.67	2.01 ± 0.74	2.01 ± 0.49	0.62
Eicosatetraenoic Acid (20:4n3)	0.08 ± 0.04	0.08 ± 0.04	0.08 ± 0.04	0.08 ± 0.02	0.99
EPA (20:5n3)	0.09 ± 0.08	0.08 ± 0.08	0.08 ± 0.09	0.10 ± 0.07	0.57
DPA (22:5n3)	0.13 ± 0.06	0.13 ± 0.07	0.13 ± 0.07	0.14 ± 0.05	0.99
DHA (22:6n3)	0.20 ± 0.16	0.19 ± 0.16	0.18 ± 0.16	0.21 ± 0.09	0.83
N-6 PUFA
LA (18:2n6)	13.67 ± 3.06	13.85 ± 3.48	12.62 ± 2.45	13.99 ± 2.67	0.27
CLA (18:2c9, t11)	0.02 ± 0.01	0.02 ± 0.01	0.02 ± 0.01	0.02 ± 0.01	0.27
GLA (18:3n6)	0.10 ± 0.05	0.10 ± 0.06	0.09 ± 0.05	0.12 ± 0.05	0.52
Eicosadienoic Acid (20:2n6)	0.20 ± 0.06	0.21 ± 0.06	0.20 ± 0.05	0.22 ± 0.05	0.25
DGLA (20:3n6)	0.34 ± 0.11	0.35 ± 0.11	0.32 ± 0.10	0.34 ± 0.12	0.44
ARA (20:4n6)	0.38 ± 0.09	0.37 ± 0.10	0.34 ± 0.08	0.36 ± 0.08	0.17
Adrenic Acid (22:4n6)	0.04 ± 0.03	0.05 ± 0.03	0.06 ± 0.03	0.05 ± 0.03	<0.01^*
Osbond Acid (22:5n6)	0.03 ± 0.01	0.03 ± 0.01	0.02 ± 0.01	0.03 ± 0.01	0.25
Total
SFA	39.80 ± 5.13	39.42 ± 5.74	40.64 ± 4.69	40.20 ± 3.36	0.66
MUFA	42.93 ± 3.70	43.05 ± 3.91	43.13 ± 3.48	42.05 ± 2.55	0.84
PUFA-3	2.43 ± 0.81	2.48 ± 0.81	2.48 ± 0.95	2.55 ± 0.54	0.86
PUFA-6	14.78 ± 3.15	14.99 ± 3.54	13.68 ± 2.48	15.13 ± 2.69	0.24
Ratios
PUFA-6:PUFA-3	6.49 ± 1.85	6.43 ± 1.84	6.06 ± 1.89	6.14 ± 1.54	0.59
ARA:DHA	2.67 ± 1.60	2.54 ± 1.10	2.81 ± 1.25	1.96 ± 0.70	0.32

Statistically significant difference (p < 0.05) based on analysis of variance.

ALA, α-linoleic acid; ARA, arachidonic acid; CMD, cardiometabolic disease; DGLA, dihomo-γ-linoleic acid; DHA, docosahexaenoic acid; DPA, docosapentanoic acid; EPA, eicosapentaenoic acid; GLA, γ-linolenic acid; LA, linoleic acid; MUFA, monounsaturated fatty acids; PUFA, polyunsaturated fatty acids; SD, standard deviation; SFA, saturated fatty acids; CLA, conjugated linoleic acid.

Using PCA, we identified four components or “patterns” of human milk fatty acid composition that explained 54.6% of the variation in fatty acids: high long-chain SFA and monosaturated fatty acid (MUFA) (17.0%), high n-6 PUFA (14.2%), high n-3 PUFA (13.3%), and high medium-chain SFA (10.1%). The factor loadings, which describe how strongly each individual fatty acid contributes to the various patterns, are shown in Table 3.

Table 3.

Human Milk Fatty Acid Patterns from Principal Component Analysis and Fatty Acid Loadings After Varimax Rotation

Fatty acid	High Long-Chain SFA and MUFA	High n-6 PUFA	High n-3 PUFA	High Medium-Chain SFA
SFA
Capric Acid (10:0)	—	—	—	0.38
Lauric Acid (12:0)	—	—	—	0.59
Myristic Acid (14:0)	—	—	—	0.52
Pentadecylic Acid (15:0)	0.41	—	—	—
Palmitic Acid (16:0)	0.39	—	—	—
Margaric Acid (17:0)	0.38	—	—	—
Stearic Acid (18:0)	0.26	—	—	—
Arachidic Acid (20:0)	—	0.36	—	—
Lignoceric Acid (24:0)	—	0.42	—	—
MUFA
Physeteric Acid (14:1n9)	0.39	—	—	—
Palmitoleic Acid (16:1n7)	0.23	—	—	—
Oleic Acid (18:1n9)	—	—	—	−0.37
Nervonic Acid (24:1n9)	—	0.32	—	—
Vaccenic Acid (18:1t/c11)	—	—	—	—
N-3 PUFA
ALA (18:3n3)	−0.25	—	—	—
Eicosatetraenoic acid (20:4n3)	—	—	0.34	—
EPA (20:5n3)	—	—	0.48	—
DPA (22:5n3)	—	—	0.48	—
DHA (22:6n3)	—	—	0.47	—
N-6 PUFA
LA (18:2n6)	−0.33	—	—	—
CLA (18:2c9, t11)	—	0.31	—	—
GLA (18:3n6)	—	0.24	—	—
Eicosadienoic acid (20:2n6)	—	—	—	—
DGLA (20:3n6)	—	0.42	—	—
ARA (20:4n6)	—	—	0.23	—
Adrenic acid (22:4n6)	—	0.38	—	—
Osbond acid (22:5n6)	—	—	0.23	—
Explained variance, %	17.0	14.2	13.3	10.1

ALA, α-linoleic acid; ARA, arachidonic acid; DGLA, dihomo-γ-linoleic acid; DHA, docosahexaenoic acid; DPA, docosapentanoic acid; EPA, eicosapentaenoic acid; GLA, γ-linolenic acid; LA, linoleic acid; MUFA, monounsaturated fatty acids; PUFA, polyunsaturated fatty acids; SFA, saturated fatty acids; CLA, conjugated linoleic acid.

The association of human milk fatty acid composition and maternal CMD after adjustment for pre-pregnancy BMI and race/ethnicity and with no CMD as the reference outcome group is shown in Figure 1. Point estimates reflect the change in relative odds per SD increase in individual or total fatty acids or the change in relative odds per 1 unit increase in fatty acid ratios and patterns. Among the SFA, there were inverse associations between the proportions of medium-chain SFA lauric acid (adjusted OR = 0.73, 95% CI = 0.60–0.89) and myristic acid (adjusted OR = 0.80, 95% CI = 0.66–0.97) and perinatal CMD and between the proportion of long-chain SFA pentadecylic acid and persistent CMD (adjusted OR = 0.57, 95% CI = 0.36–0.91). There was a positive association between the proportion of long-chain SFA arachidic acid and perinatal CMD (adjusted OR = 1.19, 95% CI = 1.01–1.41). Among the MUFA, there was a borderline significant positive association between the proportion of vaccenic acid (adjusted OR = 1.37, 95% CI = 1.00–1.86) and persistent CMD. Among the PUFA-3 and PUFA-6, there were positive associations between the proportion of adrenic acid and perinatal CMD (adjusted OR = 1.21, 95% CI = 1.01–1.44) as well as persistent CMD (adjusted OR = 1.56, 95% CI = 1.08–2.25). Among total fatty acid measures, no associations were observed. Among fatty acid ratios, there was an inverse association between the ARA-to-docosahexaenoic acid (DHA) ratio and incident CMD (adjusted OR = 0.52, 95% CI = 0.28–0.96). Among fatty acid patterns, there was an inverse association between scores on the high medium-chain SFA pattern and perinatal CMD (adjusted OR = 0.86, 95% CI = 0.76–0.96).

FIG. 1.

Association of human milk fatty acid composition and maternal cardiometabolic disease with no cardiometabolic disease as the reference outcome group (n = 1,018). Models are adjusted for pre-pregnancy body mass index (kg/m²) and race/ethnicity. *Statistically significant result, wherein 95% confidence intervals do not contain the null value of 1. ALA, α-linoleic acid; ARA, arachidonic acid; CMD, cardiometabolic disease; DGLA, dihomo-γ-linoleic acid; DHA, docosahexaenoic acid; DPA, docosapentanoic acid; EPA, eicosapentaenoic acid; GLA, γ-linolenic acid; LA, linoleic acid; LC, long chain; MC, medium chain; MUFA, monounsaturated fatty acids; PCA, principal component analysis; PUFA, polyunsaturated fatty acids; SFA, saturated fatty acids.

The association of human milk fatty acid composition and maternal CMD after adjustment for pre-pregnancy BMI and race/ethnicity and with perinatal CMD as the reference outcome group, to examine how fatty acid composition differed for acute perinatal CMD versus CMD that continued or presented beyond the postpartum period, is shown in Figure 2. Among the SFA, there was a positive association between the proportions of medium-chain SFA lauric acid (adjusted OR = 1.62, 95% CI = 1.04–2.54) and myristic acid (adjusted OR = 1.46, 95% CI = 1.01–2.15) and persistent CMD and a borderline significant inverse association between the proportion of long-chain SFA pentadecylic acid and persistent CMD (adjusted OR = 0.61, 95% CI = 0.37–1.00). Among the MUFA, there was a positive association between the proportion of vaccenic acid and persistent CMD (adjusted OR = 1.52, 95% CI = 1.04–2.24). Among the PUFA-3 and PUFA-6, there was only one borderline significant inverse association between dihomo-γ-linoleic acid and persistent CMD (adjusted OR = 0.63, 95% CI = 0.40–1.00). Among total fatty acid measures, no associations were observed. Among fatty acid ratios, there was an inverse association between the ARA:DHA ratio and incident CMD (adjusted OR = 0.49, 95% CI = 0.25–0.97). Among fatty acid patterns, no associations were observed.

FIG. 2.

Association of human milk fatty acid composition and maternal cardiometabolic disease with perinatal cardiometabolic disease as the reference outcome group (n = 192). Models are adjusted for pre-pregnancy body mass index (kg/m²) and race/ethnicity. *Statistically significant result, wherein 95% confidence intervals do not contain the null value of 1. ALA, α-linoleic acid; ARA, arachidonic acid; CMD, cardiometabolic disease; DGLA, dihomo-γ-linoleic acid; DHA, docosahexaenoic acid; DPA, docosapentanoic acid; EPA, eicosapentaenoic acid; GLA, γ-linolenic acid; LA, linoleic acid; LC, long chain; MC, medium chain; MUFA, monounsaturated fatty acids; PCA, principal component analysis; PUFA, polyunsaturated fatty acids; SFA, saturated fatty acids; CLA, conjugated linoleic acid.

Discussion

In this prospective cohort study, the fatty acid composition of mature breast milk differed modestly according to maternal CMD during pregnancy and up to 5 years postpartum after controlling for pre-pregnancy BMI and race/ethnicity. The proportion of medium-chain SFA lauric and myristic acid was associated with lower odds of perinatal CMD compared with no CMD or persistent CMD. This trend was also reflected in the inverse association between the high medium-chain SFA pattern derived from the PCA and perinatal CMD. The proportion of long-chain PUFA-6 adrenic acid was associated with greater odds of perinatal and persistent CMD compared with no CMD. In addition, the ARA:DHA ratio was associated with lower odds of incident CMD when compared with no CMD or to perinatal CMD. Though exploratory, results suggest that human milk fatty acid composition may, to some extent, reflect subclinical differences in maternal CMD phenotypes; in doing so, it could offer valuable prognostic information on women’s propensity for resolving pregnancy-associated CMD or developing new-onset CMD in the years following delivery.

Few studies have examined mature breast milk fatty acid composition in mothers with CMD,³² with regional, secular, and methodologic differences. One study by Jackson et al. in 1994 reported similar levels of medium-chain SFA but lower levels of n-6 PUFA in human milk measured up to 3 months postpartum from U.S. women with preexisting insulin-dependent diabetes compared with matched control women.²⁰ More recent work on pregnancy-associated CMD offers mixed findings. Wen et al. reported similar levels of SFA and PUFA but lower levels of MUFA in human milk measured during the first month of lactation from Chinese women with versus without gestational diabetes after controlling for maternal age, gestational age, and maternal BMI.²¹ Sarkadi et al. reported lower unadjusted levels of certain SFA (e.g., lauric acid) and higher levels of n-6 PUFA (e.g., linoleic acid) but similar levels of MUFA in human milk measured 10–12 weeks postpartum from Ukrainian obese women with gestational diabetes compared with obese and normal-weight women without gestational diabetes.⁵ Dangat et al. reported similar unadjusted levels of SFA, MUFA, and α-linoleic acid but higher levels of DHA in human milk from women with preeclampsia compared with normotensive women, when measured at 3 days, 1.5 months, and 3.5 months postpartum.^22,23

This study, set in a contemporary cohort of Canadian women, adds to the literature by detecting differences in human milk fatty acid composition across groups of women with clinically distinct phenotypes of CMD that may present during or after pregnancy. Our findings somewhat align with those of Simon et al. in identifying associations between selected SFA and n-6 PUFA and perinatal CMD. For SFA composition, our work more clearly pinpoints these differences to medium-chain SFA specifically among women whose CMD resolves postpartum. Lower proportions of medium-chain SFA, assuming the same total fat intake, may implicate metabolic perturbations in the mammary gland, where these fatty acids are synthesized endogenously from glucose,³³ that are distinct to acute perinatal CMD. Postpartum plasma glucose levels are generally lowest in women without CMD, elevated in women who experience pregnancy-associated CMD resolving shortly after birth, and highest in women whose pregnancy-associated CMD eventually progresses into a long-term form of the disease.^15,34 This suggests that the differences in the availability of glucose as a precursor molecule is, on its own, an insufficient explanation for lower medium-chain SFA in women with perinatal CMD. Variation in hormonal profiles across CMD phenotypes, which may, in turn, affect the regulation of mammary gland lipid synthesis, may be a more suitable hypothesis to explain the differences in medium-chain SFA that we observed. For example, animal model research has identified thyroid hormone responsive protein spot 14 as a potential key regulator and promoter of fatty acid synthesis in the mammary gland,³⁵ and human research has demonstrated markedly lower plasma thyroid hormone levels in women who experience pregnancy-associated CMD compared with those who do not.^36,37

For n-6 PUFA composition, our work highlighted positive associations between n-6 PUFA adrenic acid and both perinatal and persistent CMD compared with no CMD. N-6 PUFA are derived from linoleic acid, an essential fatty acid consumed through diet, through a desaturation and elongation pathway in the liver or peripheral tissues before getting transported from maternal blood plasma into the mammary gland.³⁸ Adrenic acid is a longer chain carbon (C22:4n6) that occurs later in this pathway.² There is some evidence to suggest that linoleic acid metabolism is impaired in women with pregnancy-associated CMD, resulting in lower plasma levels of longer carbon chain fatty acids,³⁹ which is somewhat contrary to our finding of a greater proportion of adrenic acid in the breast milk of these women. It is possible that the abnormal transport of n-6 PUFA from plasma into the mammary gland or the regulation of n-6 PUFA into breast milk in women with CMD more suitably explains our finding; the mechanics of these aspects of lactation are incompletely understood⁴⁰ but have been increasingly studied in relation to maternal metabolic health.⁴¹

Strengths of this study include the relatively large and diverse sample of postpartum women from whom milk samples were collected and the ability to evaluate and control for key potential confounders. However, there are limitations to consider. We lacked data and were thus unable to account for subsequent pregnancies when classifying women’s CMD status up to 5 years postpartum. Unmeasured confounding from a family history of CMD as well as CMD severity and treatment during the perinatal period is possible; for example, a preponderance of women with well-controlled CMD may have obfuscated differences in fatty acid composition.¹⁶ Our sample comprised of women who were still breastfeeding at 3 months postpartum in order to provide a breast milk sample at that time. This likely reduced our outcome rate, given that pregnancy-associated CMD is a risk factor for early breastfeeding cessation^42–44 and limits the generalizability of our findings to women who have established lactation. Finally, some estimates were imprecise due to small sample sizes in the persistent and incident CMD groups, and there is the possibility of type 1 error given the large number of comparisons conducted. Results should therefore be interpreted as exploratory and hypothesis-generating and would benefit from replicatory studies.

Our findings suggest that human milk fatty acid composition, and particularly proportions of SFA and n-6 PUFA, could be investigated further as a biomarker of pregnancy-associated CMD resolution or progression and thus expand the existing focus of metabolomic research on maternal CMD beyond blood plasma. Moreover, additional research on the links between CMD pathophysiology and lactation physiology would further our understanding of how differences in human milk composition reflect aspects of maternal metabolic capacity, broadening the scientific focus on human milk composition beyond its nutritive and health value for infants to include its informative value for women’s health.

Conclusion

In the CHILD Cohort Study, the composition of certain SFA, n-6 PUFA, and fatty acid ratios in mature breast milk were associated with maternal CMD phenotypes during pregnancy and up to 5 years postpartum. Proportions of medium-chain SFA lauric acid and myristic acid were inversely associated with perinatal CMD specifically, and proportions of long-chain PUFA-6 adrenic acid were positively associated with both perinatal and persistent CMD. These exploratory findings highlight a potential novel utility of human milk composition for understanding women’s subclinical cardiometabolic function as it relates to the resolution or progression of pregnancy-associated CMD.

Footnotes

Acknowledgments

We are grateful to all the families who took part in the CHILD Cohort Study and the entire CHILD team at McMaster University, University of Manitoba, University of Alberta, University of Toronto, and University of British Columbia. We thank Sue Goruk and Maria Giurgius (University of Alberta) for assisting with the analysis of human milk fatty acids.

Authors’ Contributions

N.V.S. and M.B.A. conceptualized the study. N.V.S., S.T., and M.B.A. developed the methodology. M.B.A. is the Deputy Director of the CHILD Cohort Study and facilitated access to the dataset. N.V.S. conducted the analysis and wrote the original article draft. S.T., K.M., E.S., T.J.M., C.J.F., S.E.T., P.S., P.J.M., and M.B.A. critically reviewed the article and interpreted the results. All authors approved the final version of the article.

Disclosure Statement

C.J.F. serves on the ByHeart advisory board. M.B.A. has consulted for DSM Nutritional Products and serves on the Malaika Vx and Tiny Health scientific advisory boards. She has received honoraria for speaking at symposia sponsored by Medela, Prolacta Biosciences, and the Institute for Advancement of Breastfeeding and Lactation Education and has contributed without remuneration to online courses on breast milk and the infant microbiome produced by Microbiome Courses. N.V.S., S.T., K.M., E.S., T.J.M., S.E.T., P.S., and P.J.M. report no conflicts of interest related to the study.

Funding Information

The CHILD Cohort Study has been funded through the core support from the Canadian Institutes of Health Research (CIHR) and the Allergy, Genes and Environment Network of Centers of Excellence. The analysis of human milk fatty acids was funded by the Manitoba Medical Services Foundation and CIHR. This secondary analysis project was funded by the International Society for Research on Human Milk and Lactation and Family Larsson-Rosenquist Foundation through a Trainee Expansion Program Travel Fund awarded to N.V.S.

At the time of this work, N.V.S. was supported by a CIHR Doctoral Award. M.B.A. is supported by a Tier 2 Canada Research Chair in the Developmental Origins of Health and Disease and is a fellow of the CIFAR Humans and Microbiome program. S.T. is supported by a CIHR Vanier Scholarship.

Supplementary Material

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