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Maternal factors explain much of social gradient in child obesity

Smoking and pre-pregnancy overweight account for 40% of UK social divide in child obesity

Louise Prime

Tuesday, 10 May 2016

Smoking during pregnancy and being overweight before getting pregnant account for about two-fifths of the differences in childhood obesity rates across the socioeconomic classes in the UK, researchers have reported* in Archives of Disease in Childhood. They have called for policies to help mothers to stay a healthy weight, breastfeed and quit smoking for their children’s as well as their own benefit, and to help tackle the increasing inequalities in childhood overweight.

A research team led from the University of Liverpool set out to investigate the various factors behind the known excess prevalence of overweight and obesity among children from socioeconomically disadvantaged backgrounds. They looked at nearly 12,000 children taking part in the Millennium Cohort Study (all born in the UK between September 2000 and January 2002), to see which early-life factors – according to data from detailed questionnaires completed by their mothers – were associated with differences in the children’s height and weight measured at 11 years old.

Each mother had provided information on whether she was overweight before this pregnancy; whether she smoked during pregnancy; the birthweight of the child; whether the child was born prematurely or by caesarean section; whether the child was breastfed; and how soon s/he was weaned onto solid foods. Full information was available for 9,424 children.

Overall, one in five children whose mothers were educated to at least degree level were overweight by the age of 11, compared with one in four of those whose mothers were less well educated. Once the researchers had taken into account confounding factors including the child’s sex and ethnicity, and maternal age of at least 30 when they were born, they found that several other factors were still significantly associated with an increased relative risk (RR) of the child being overweight by the time they were 11 years old. These were being female, their mother being overweight before this pregnancy or smoking during it, high birthweight, never having been breastfed, and being introduced to solid foods before 4 months. The more heavily a mother smoked during pregnancy, the greater her child’s risk of being overweight by 11, even after accounting for other risk factors.

The study authors reported: “Maternal pre-pregnancy overweight and maternal smoking during pregnancy attenuated the RR [of a child being overweight at 11 years] in the lowest maternal qualifications group by around 40% suggesting a considerable amount of the social inequalities in preadolescent overweight can be explained by these two variables.” They added that their results suggest that shorter duration of breastfeeding may make a small contribution to the increased risk of preadolescent overweight in more disadvantaged children.

They concluded: “Policies to support mothers to maintain a healthy weight, breastfeed and abstain from smoking during pregnancy are important to improve maternal and child health outcomes, and our study provides some evidence that they may also help to address the continuing rise in inequalities in childhood overweight.”

* Massion S, et al. Exploring the impact of early life factors on inequalities in risk of overweight in UK children: findings from the Millennium Cohort Study. Arch Dis Child 2016; 0: 1–7. doi:10.1136/archdischild-2015-309465.

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