Mental health disorders are more common in people born during the winter

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Levels of the stress hormone cortisol are higher in women who give birth in the autumn and winter than those who give birth in the spring or summer, finds a new study by researchers at Cardiff University.

The new findings could explain why mental health disorders are more common in people born during the winter.

Professor Ros John, from Cardiff University’s School of Biosciences, explained: “Although maternal cortisol levels naturally rise during pregnancy, our data shows that autumn and winter babies are exposed to particularly high levels just before they are born.

On average, women giving birth in the autumn/winter had 20% more salivary cortisol just before delivery than those giving birth in spring/summer.

“As higher levels of cortisol in pregnant women have previously been associated with a higher risk of children developing mental health disorders, the new findings could explain why these disorders are more common in people born during the winter months.

They don’t, however, explain the reason why women who give birth in winter or autumn have these higher levels of cortisol.”

Seasonal changes in mood and behaviour are commonly reported in the general population but considerably less is known about how the seasons can affect mood during pregnancy. Using data from the longitudinal Grown in Wales study, the Cardiff University researchers investigated the relationship between the seasons and salivary cortisol concentrations, depression and anxiety symptoms, custom birthweight centiles and placenta weight in pregnant women living in South Wales.

While the team found a link between season and concentrations of salivary cortisol at term, they didn’t find an association between season and maternally-reported mental health symptoms, birthweight or placental weight.

The study included 316 women. Data was gathered at the presurgical appointment prior to a booked ELCS and immediately after birth, through an extensive questionnaire and notes recorded by the research midwife.

Cortisol was derived from maternal saliva samples.

The paper ‘Seasonal variation in salivary cortisol but not symptoms of depression and trait anxiety in pregnant women undergoing an elective caesarean section’ was published in Psychoneuroendocrinology.


Intrauterine growth restriction and shortened duration of gestation are risk factors for neonatal morbidity and mortality [1] and are associated with child growth faltering in many low and middle income country (LMIC) settings [2].

An estimated 15 % of children are born low birth weight and 11 % are born preterm globally [3].

Complications from preterm birth are estimated to be responsible for 35 % of the world’s 3.1 million neonatal deaths [4] and a leading cause of under-5 mortality worldwide [5].

Risk factors for smaller size at birth or shortened duration of gestation include poor nutrition during pregnancy, infections, and maternal stress [68].

Interventions to improve birth outcomes in LMIC have had limited success at increasing size at birth or duration of gestation.

Maternal multiple micronutrient (MMN) supplements have been found to result in a small increase in birth weight of 22 g and an increase in the duration of gestation [910].

Other nutritional interventions, such as provision of calcium or zinc, have been found to result in a reduced risk of preeclampsia [11] and a modest increase in the duration of gestation [12].

Lipid-based nutrient supplements (LNS) provided during pregnancy have been evaluated for their effects on birth outcomes and early childhood growth in three studies to date, in Burkina Faso [13], Ghana [14], Malawi [15].

In impoverished communities, malnutrition is compounded by a variety of physical and psychosocial stressors that may further compromise pregnancy.

Acute or chronic psychosocial experiences [16] and the biologic measure of serum or salivary cortisol concentrations [17] have been associated with shortened duration of gestation and intrauterine growth restriction.

Cortisol is a regulatory hormone involved in the hypothalamic-pituitary-adrenal axis (HPA) response to stress as well as in the fetal-placental-maternal neuroendocrine system regulating the maintenance of pregnancy and the timing of parturition [18].

Cortisol and corticotropin-releasing hormone (CRH) concentrations rise exponentially over the course of pregnancy due to a positive feedback mechanism via the placenta [19]. They peak at the time of delivery and have been hypothesized to serve in regulating the ‘placental clock’, determining the timing of parturition [20].

CRH promotes fetal prostaglandin and estrogen synthesis, which lead to myometrial activation and contractility [19].

Cortisol also is involved in fetal growth and maturation. The late gestation rise in cortisol concentration is related to a shift from rapid fetal growth towards tissue maturation [21].

Elevated cortisol concentration is negatively associated with IGF-1 activity [22] and, importantly, is involved in fetal lung maturation through the production of surfactant to prepare the fetus for postnatal life [23].

Despite the physiologic explanations for a normal rise in cortisol during pregnancy, higher than expected increases in cortisol and CRH concentrations have important short- and long-term negative functional consequences on the health of the pregnancy and the offspring in later life [2425].

In the short term, elevated CRH is associated with placental dysfunction, including shallow trophoblast invasion and poor placental vascularization which can lead to intrauterine growth restriction and preeclampsia [26].

Elevations in perceived stress and cortisol concentrations have been related to higher concentrations of proinflammatory cytokines and lower concentrations of anti-inflammatory cytokines [2728].

In the longer-term, excess glucocorticoid exposure has been associated with the life-long function of the HPA axis in the offspring, and has been hypothesized to increase susceptibility to a variety of conditions including depression, hypertension, type 2 diabetes mellitus, and cognitive impairments [2529].

The fetus is somewhat buffered from the effects of high maternal cortisol concentrations through the activity of the 11-β-hydroxysteroid dehydrogenase (HSD)-2 enzyme in the placenta, which converts maternal cortisol to an inactive cortisone [30].

Yet this is not a perfect barrier and fetal and maternal cortisol concentrations are highly correlated suggesting that abnormally high maternal cortisol concentrations could affect the developing fetus [31].

The activity of the 11-β-HSD2 enzyme appears to be sensitive to maternal malnutrition [243233], which would result in greater fetal exposure to active cortisol, particularly during late gestation.

There is some evidence that cortisol concentrations may be elevated among undernourished individuals, including short term studies suggesting that cortisol concentration increases during energy restriction [3435] and that stunted children have elevated cortisol concentrations and a blunted cortisol response to stressors [3638].

One trial among Nepali pregnant women reported that late gestation cortisol concentrations were lower among women who received multiple micronutrient supplements compared to a control [39], so it is plausible that improvements in nutrition may alter cortisol concentrations.

Thus, the effects of malnutrition and elevated cortisol concentrations during pregnancy may interact deleteriously on the developing fetus, with both immediate and long-term results.

In the present study, we aimed to evaluate

1) whether maternal cortisol concentration would be affected by nutritional supplementation starting early in pregnancy and

2) whether maternal perceived stress and salivary cortisol concentration during pregnancy are associated with smaller newborn size and shorter duration of gestation.

These questions were examined within the context of a three-armed, randomized controlled trial of LNS, MMN, or iron-folic acid tablets (IFA) during pregnancy in rural Malawi. Our hypotheses were that 1) women who receive LNS during pregnancy would have lower salivary cortisol concentration at 28 wk and 36 wk gestation compared to the MMN and IFA groups and 2) both salivary cortisol and perceived stress during pregnancy would be associated with shorter duration of gestation and smaller size at birth.


More information: Samantha M. Garay et al. Seasonal variation in salivary cortisol but not symptoms of depression and trait anxiety in pregnant women undergoing an elective caesarean section, Psychoneuroendocrinology (2019).  DOI: 10.1016/j.psyneuen.2019.05.029

Journal information: Psychoneuroendocrinology
Provided by Cardiff University

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