Lifestyle more likely to affect a child’s BMI than the weight of their mother

Researchers from the University of Bristol and Imperial College London have found that a high Body Mass Index (BMI) of a mother before and during pregnancy is not a major cause of high BMI in their offspring – indicating that childhood and teen obesity is more likely to be a result of lifestyle factors.

The study was published today (1^st February 2022) in BMC Medicine used data from two longitudinal studies – Children of the 90s (also known as the Avon Longitudinal Study of Parents and Children) based at the University of Bristol, and Born in Bradford based in Bradford Teaching Hospitals NHS Foundation Trust.

It is known that greater maternal BMI before or during pregnancy is associated with a higher BMI in children, however the extent to which the mother’s weight causes obesity in childhood, or whether this is caused by environmental and lifestyle factors post conception and birth is unclear.

The research team from the University of Bristol used a method called Mendelian randomisation, which measures variation in genes to determine the effect of an exposure on an outcome. They looked at birthweight and BMI at age 1 and 4 years in both Children of the 90s and Born in Bradford participants, and then also BMI at age 10 and 15 years in just the Children of the 90s participants. They found that there was a moderate causal effect between maternal BMI and the birth weight of children, however in most older age groups they did not find a strong causal effect.

Lead author Dr Tom Bond, Senior Research Associate at the University of Bristol explained: “We found that if women are heavier at the start of pregnancy this isn’t a strong cause of their children being heavier as teenagers. This is important to know. Supporting women and men at all ages to keep a healthy weight will be needed to prevent obesity. It isn’t enough to just focus on women entering pregnancy. Despite this, there is good evidence that maternal obesity causes other health problems for mothers and babies (aside from offspring obesity). So prospective mothers should still be encouraged and supported to maintain a healthy weight. It will be important to broaden this work to investigate other characteristics of mothers and fathers during pregnancy and a child’s early life that might affect children’s weight, and also to look at the offspring when they are in adulthood and are old enough to begin showing early signs of heart disease risk.”

Paper:  Exploring the causal effect of maternal pregnancy adiposity on offspring adiposity: Mendelian randomization using polygenic risk scores. https://doi.org/10.1186/s12916-021-02216-w

About Children of the 90s

Based at the University of Bristol, Children of the 90s, also known as the Avon Longitudinal Study of Parents and Children (ALSPAC), is a long-term health-research project that enrolled more than 14,000 pregnant women in 1991 and 1992. It has been following the health and development of the parents and their children in detail ever since and is currently recruiting the children and the siblings of the original children into the study. It receives core funding from the Medical Research Council, the Wellcome Trust and the University of Bristol. Find out more at www.childrenofthe90s.ac.uk.

Born in Bradford

Born in Bradford is an internationally-recognised research programme which aims to find out what keeps families healthy and happy. We use this information to work with the local authority, health, education and voluntary sector providers across Bradford district to develop, implement and evaluate ambitious programmes to improve population health. We have a vast ‘city of research’ infrastructure which includes detailed health and wellbeing information on Bradfordians enrolled in our three birth cohort studies and a connected routine dataset of health, social care and education data for over 700,000 citizens living in Bradford and Airedale. We host a range of initiatives to improve health working with the local authority, health, education, cultural and voluntary sector providers. You can find out more about our research programme at www.borninbradford.nhs.uk.