Differences in growth and adiposity between UK Pakistani and White British children: the causes and consequences of smaller size and greater adiposity

Size at birth and growth in childhood are thought to be important stages of development in our lifespan and are known to be important to the risk of infant and childhood health and development problems. Over recent years these important phases of early development have also been linked to our risk of illness in later life, particularly diabetes and coronary heart disease. South Asian populations are known to be at particular risk of diabetes (2 - 4 fold higher) and coronary heart disease (50 - 80% higher) and this may be due to them having a tendency for more fat compared to lean mass. At birth, South Asian babies are generally smaller and lighter but recent studies show that like South Asian adults, they have more fat than White British individuals. This greater fatness for a given weight could be very important to the risk of diabetes and coronary heart disease but so far the reasons for it are not very clear. It is possible that being diabetic during pregnancy, which is more common in South Asian women, 'overfeeds' the infant leading to greater fatness at birth and possibly throughout life. If this is true then later generations would also overfeed their infants during pregnancy and a cycle of poor health and development could be set in motion. This continuation of risk could be made worse by the changes in environment and lifestyle experienced by South Asians who migrate to the UK such as the availability of high energy diets, a culture of less exercise and rising rates of obesity. How patterns of growth from birth to childhood differ in South Asian and White British children could also affect differences in health between these two groups in relation to childhood infections and other childhood health problems and could even affect how well children do in school. However research in this area has often used poorly designed studies with too few participants to give accurate results.

Using data and information from the Born in Bradford birth cohort study I will:
1.Look at whether how much a woman weighs at the start of pregnancy, how much weight she gains during pregnancy, her glucose (sugar) levels in pregnancy and whether she develops gestational diabetes, affect how much her child weighs and how fat they are at birth and also at age 4/5 years. I will look at whether the effect of any of these measurements is different depending on whether the mother and child are of Pakistani or White British origin.
2.Describe patterns of growth and differences in adiposity and blood pressure in UK born Pakistani origin children and UK born White British children
3.Look at whether different patterns of growth in UK born Pakistani origin and UK born White British children result in different rates of childhood infection and hospital admissions between these two groups. I will also look at whether different patterns of growth affect how well the children do in school.
4.Find out whether weight and fatness at birth and in childhood is different depending on whether parents and grandparents of Pakistani infants are born in the UK or South Asia.

To do this I will combine existing information from the BiB cohort with new information collected for the first time as part of this proposal. I will train and support school nurses in Bradford to collect skinfold measurements (used to estimate fatness) and blood pressure alongside the height and weight measurements recorded for all reception age children in the UK, including good coverage in Bradford. These measurements will be collected over 2 consecutive school years (2013/2014 and 2014/2015) and will involve approximately 8000 children. Cord blood
samples for the whole BiB cohort will be used to compare fat mass in Pakistani and White British infants at birth (approx 9000 samples). In addition I will merge information from routine health and education systems with the existing BiB data.

Aim
To describe differences in growth and adiposity between Pakistani and White British children from birth to age 4/5, to examine maternal causes of any differences and to explore the consequences for child health and development.
Objectives
1.To examine associations between maternal characteristics associated with developmental overnutrition and offspring size and adiposity at birth and age 4/5 years in Pakistani and White British children.
2.To develop growth trajectories from birth to age 4/5 and compare growth, adiposity and blood pressure between Pakistani and White British children
3.To examine whether size at birth and child growth are associated with health and educational outcomes in Pakistani and White British children.
4.To determine whether growth and fatness differ depending on whether the parents and grandparents of Pakistani infants were born in the UK or South Asia
Methods
This proposal will use new and existing data collected for the BiB study and will link with routine health information databases. New data collection will include skinfold and blood pressure measurements at age 4/5. Cord leptin assays will be completed on the whole BiB cohort and child health, hospital admission and education information will be extracted from routine health and education systems. Existing data will include maternal measures of hyperglycaemia and offspring size measurements. Statistical analysis will include multivariable linear regression models and tests for statistical interaction. Growth trajectories will be estimated using linear spline mixed effects models for Pakistani and White British children.
Scientifc and medical opportunities
Recent studies draw attention to differences in adiposity between South Asian and White British infants and children. Understanding more about the causes and consequences of these differences is crucial for planning public health interventions to tackle ethnic inequalities in diabetes and cardiovascular disease.

Understanding more about the causes and consequences of the thin-fat insulin resistant phenotype in South Asian populations is crucial for planning public health interventions to tackle the current ethnic inequalities in diabetes and cardiovascular disease, particularly as there is the potential for cross-generational cycles of increased risk. It is also important that additional measures of size (beyond height and weight) that can provide estimates of body fat are collected in childhood to contribute to our understanding of patterns of adiposity and their potential relationship with future cardiometabolic risk. The collection of blood pressure measurements at age 4/5 will also add importantly to this knowledge. The ethnic specific growth trajectories that will be developed through this fellowship will be useful for identifying important periods of child growth for UK born South Asian and White British children in, to my knowledge, the most detailed dataset currently available. Thus, the main beneficiaries of knowledge arising from this proposal are expected to be public health practitioners and clinicians who will be able to use the findings to inform public health policy (for example being able to identify at risk pregnancies and important patterns and periods of growth for the targeting of future interventions) and clinical practice (for example child obesity prevention strategies). Whilst my findings will not have an immediate impact and will not have all the answers, they will make an important contribution to the body of knowledge in this field that will, in time, underpin future public health interventions. Further, if patterns of child growth are also shown to be important to educational attainment, they have the potential to contribute to future social and education policy.

More specific beneficiaries include school nurses who will be trained to measure skinfold thicknesses. They will receive regular updates and feedback of results and will have the opportunity for greater involvement in this research and the Born in Bradford project from the outset. Their participation will give them access to current research that has particular relevance to their practice and the children they care for. Further, it will enhance their clinical skills and add importantly to their professional development. This will tie in closely with the NIHR CLAHRC for Leeds, York and Bradford which promotes stronger links between biomedical and applied research and in particular, is exploring how better measurement and feedback of data can translate into practice.

Ultimately, the output from this proposal will provide detailed information about the causes and consequences of the thin-fat phenotype seen in South Asian populations and will contribute to the development of interventions to lessen the inequalities in health and opportunity that they are currently exposed to.