Not sleeping with parents linked to baby's stress in bath: Dutch study

Biologist Carolina de Weerth analysed the data from 163 mothers and their children together with her colleague Marieke Tollenaar. All of the mothers kept a diary for the first 2 months following their child’s birth. Each day they recorded where and for how long the child had slept the night before. About one-quarter of the babies always slept in a room other than that of their parents and about forty percent nearly always slept in the parents' bedroom. The remainder sometimes slept in their own room and sometimes in their parents’ room. De Weerth: ‘We then measured the cortisol level in the saliva of each baby following two different stress moments, including being put in the bath.’ Cortisol is a hormone released during stress. We discovered that babies who slept separately from their parents experienced, on average, a stress level nearly 40% higher when put in the bath than babies who slept in their parents’ room.

This is the first study into the correlation between sleeping location and stress level in babies. One possible explanation is that parents function as an external stress regulator for the child. If the child sleeps in the parents’ room they are quickly available at night to relieve the child of restlessness or discomfort. The comfort and attention received reduce the baby’s stress. De Weerth: ‘Subtle signals of disquiet in the baby, like a certain sound, are noticed sooner if the child sleeps in the same room than when it sleeps in a different room. In the latter case the parents might only intervene in the event of ‘major signals’ such as crying because they miss the more subtle signals.’ Babies that sleep in a separate room are therefore less used to their parents being the persons who can moderate stress. According to the researcher this effect might persist during daytime activities such as being put in the bath.

The researcher emphasises the importance of a baby learning to experience stress. ‘It is quite normal if babies respond to their environment and their cortisol level goes up and down accordingly. It only becomes a problem if babies experience chronic stress and recover from this slowly. That is detrimental to their health and also for the adjustment of their stress system.’ The researchers will now investigate the longer term effect of sleeping separately on the stress system of the older child.

Provided by Netherlands Organisation for Scientific Research (NWO)