New research has discovered a “crucial link” between sleep deprivation and the failure to lose weight gained during pregnancy, reported the Daily Mail . “Sleep – not diet – is the key to shedding pounds after childbirth”, the newspaper said. It goes on to say that just two hours extra a night can make the difference in weight, “those who were sleeping for five hours or less when their babies were six months old were three times more likely to be carrying an extra 11 pounds at their baby's first birthday than mothers who got seven hours”.
The news story is based on the findings of a study of 940 women looking at the amount of sleep they were getting six months after the birth of their babies. Although the researchers found a link suggesting that women who slept less were more likely to be carrying extra pounds when their baby was one year of age, sleep is not the only factor that should be considered when thinking about post-pregnancy weight, many factors other than sleep have been linked to weight retention after birth.
Where did the story come from?
This research was carried out by Dr Erica Gunderson of Kaiser Permanente Research Foundation, California, and colleagues of the Obesity Prevention Program and Department of Nutrition, Harvard, and Brigham and Women’s Hospital, Boston, US. Funding was provided by the US National Institutes of Health, Harvard Medical School, and Harvard Pilgrim Health Care Foundation. It was published in the peer-reviewed medical journal American Journal of Epidemiology.
What kind of scientific study was this?
This was a cohort study, which was designed to investigate whether length of sleep was linked to post-pregnancy weight retention. This follows previous research that linked lack of sleep to chronic diseases such as heart disease and diabetes.
The researchers followed a group of 940 women from the 2,128 participants of Project Viva: a cohort study that was examining the link between diet and lifestyle during pregnancy, the pregnancy outcome and the subsequent health of the baby. The women were recruited to Project Viva at their first clinic antenatal visit. For this study, the researchers excluded those women who had smoked during or after pregnancy, or who got pregnant again before the one-year follow-up, or any who had incomplete study data. The remaining 940 women were asked to complete questionnaires at interview at six months after birth, and were then contacted again by post when the baby was a year old.
The researchers obtained information on antenatal, behavioural and socio-demographic factors, breastfeeding, sleep patterns, pre-pregnancy weight, and weight at one year. The difference between pre-pregnancy weight and their weight when a baby was one year old was regarded “not substantial” if it was less than 11lb (5kg) and “substantial” if it was 5kg or greater. Most of the women (786) also had weight measurements available at six months. The women were grouped according to how much sleep they had over an average 24 hours. The researchers also looked at the changes in sleep pattern between six months and one year and their retention of weight. The results took into account other possible risk factors that are known to influence weight. These include the number of children, diet, pre-pregnancy weight and factors such as income, education, social class and address.
What were the results of the study?
The researchers found that 13% of their sample had substantial weight retention at one year. They found that there was increased risk of substantial weight retention in mothers who slept five or fewer hours a night at six months, compared with those who slept for seven hours.
Women whose hours of sleep decreased between six months and one year after birth, were also at increased risk of substantial weight retention compared with those whose sleep remained the same. The researchers also found that women who were younger than 25 years old, were educated to a level less than a postgraduate degree, had a lower income, were single parents, were overweight or obese prior to pregnancy, or who had excess weight gain during pregnancy, were significantly more likely to have substantial weight retention at one year.
What interpretations did the researchers draw from these results?
The researchers conclude that sleep deprivation at six months following delivery, and in the subsequent months up to one year, is associated with substantial weight retention at one year. This, they suggest, may be due to a lack of sleep causing an increased release of hormones that stimulate hunger and appetite. They say that “interventions to prevent postpartum obesity should consider strategies to attain optimal maternal sleep duration”.
What does the NHS Knowledge Service make of this study?
Although this study has demonstrated that sleep duration of five hours or less a night in the first year after birth may be linked to weight retention, the study has also shown that this is not the only factor affecting weight. There are limitations to the study that should be considered when interpreting its findings, several of which the authors acknowledge:
- The researchers have only looked at sleep duration from six months onwards, and not examined any relationship between weight gain and the period when sleep may be most affected: from birth to six months.
- There is no available information about sleep patterns prior to pregnancy and how this related to whether the woman was overweight or not.
- The researchers have to rely upon sleep patterns reported in answers to a series of questions that were asked only twice; sleep patterns may not have remained the same every night or over a number of weeks.
- Weight at one year after birth and pre-pregnancy weight were reported by the women in the study, and may be subject to reporting errors. The researchers, looked at the results of a few women where they had clinic weights available, and found that self-reported and clinic-measured weights differed by about 2.2lb (1kg).
- As the study was conducted in mostly white participants in urban and suburban areas of Massachusetts in the US, the results may not be generalisable to other ethnicities or population groups.
Some degree of weight gain during and following pregnancy is almost inevitable, and many new mothers find it a struggle to regain pre-pregnancy weight. Even if it were proved that women would find it easier to lose more weight if they slept seven or eight hours a night, with a new baby in the house finding a solution to broken nights and interrupted sleep is unlikely to be straightforward or achievable.
Sir Muir Gray adds...
The arrival of a baby changes everything; it is unlikely that a single factor can explain something as complex as getting back to pre pregnancy weight and shape, but sleep deprivation could be one of the factors.