In a recent study published in Clinical Nutrition, researchers investigated the influence of biological and psychological postpartum maternal stress on human milk fatty acid composition through a prospective cohort study in Amsterdam.
Maternal postpartum stress is known to affect the health of the infant, with exposure to stress during the developmental period potentially increasing the risk of a wide range of metabolic and mental health disorders in the child.
One of the suggested mechanisms of transmission of maternal stress to the newborn child is through compositional changes in human milk, specifically the levels of fatty acids. Studies have shown that fatty acids are essential for the healthy development of the infant, and insufficient levels of fatty acids in the diet increase the risk of diseases later in life.
Experiments with animal models have shown that exposure to stress during early development leads to low levels of polyunsaturated fatty acids in the plasma and brain. While various factors such as body mass index, genetics, and maternal diet can influence the fatty acid composition of human milk, emerging evidence suggests that the psychopathologies of postpartum stress can change the fatty acid composition of human milk. However, conclusive studies on how stress affects human milk fatty acid composition are lacking.
About the study
The present prospective cohort study called the Amsterdam mother’s milk study, recruited pregnant or new mothers aged 18 years or older who intended to breastfeed their infants at least for the first month. Mothers with gestational diabetes mellitus or on glucocorticoid or psychopharmaceutical medications were excluded, as were neonatal infants with major congenital disorders or diseases which reduced their life expectancy to below a month.
The study included two groups of new mothers to cover a wide range of stress levels. This high-stress group consisted of mothers whose infants had been hospitalized for at least two days and a control group consisting of mothers with healthy infants.
Psychological stress perceptions were assessed using a validated questionnaire to determine factors such as early-life stress due to abuse, neglect, or trauma, lifetime history of stress, and situational stress levels. The questionnaire also evaluated anxiety, postnatal depression, and food intake in the mothers.
Hair samples were collected once, before ten days from birth, to measure cortisol and cortisone levels, which were used as the last trimester baseline of stress. Two and three samples of saliva and milk samples, respectively, were collected on days 10, 17, and 24 after birth. Saliva swabs were collected to measure the cortisol awakening response. Milk samples were used to assess fatty acid and cortisol levels.
The results determined that maternal postpartum stress was correlated to lower concentrations of total fatty acids, monounsaturated fatty acids, saturated fatty acids, long-chain polyunsaturated fatty acids, and omega-6 (n6) polyunsaturated fatty acids in mature milk (collected on days 17 and 24), but not in transitional milk (collected on day 10).
The absolute concentrations of total fatty acids, polyunsaturated fatty acids, and omega-6 polyunsaturated fatty acids were lower in the high-risk group compared to the control group. The relative concentrations of fatty acids and cortisol levels did not differ between the high-risk and control groups.
Analysis of perceived psychological stress revealed that lifetime stress negatively affected the levels of omega-6 polyunsaturated fatty acids and linoleic acid and the omega-3 to omega-6 polyunsaturated fatty acids ratio. Recent depression, anxiety, and perceived stress did not affect human milk fatty acids. The authors noted that other lifestyle factors and dietary intake could also indirectly affect the concentrations of fatty acids in human milk.
Overall, the study showed that maternal postpartum stress resulted in lower concentrations of total, saturated, long-chain polyunsaturated, monounsaturated, and omega-6 polyunsaturated fatty acids in mature human milk. The authors believe that the low levels of fatty acids in human milk could transmit stress signals to the infant.
Furthermore, the study found that recent perceived stress, anxiety, and depression did not influence the fatty acid concentrations in human milk. Still, a history of stress exposure did negatively impact human milk composition. According to the authors, chronic stress levels could cause physiological and metabolic changes in the mother’s body that manifest noticeably during postpartum stress.