Diabetogenic elevated childhood total fat in South Asians and Black African/Caribbeans relates to adverse early life growth and low socioeconomic position compared to Whites in the UK

Aims/hypothesis

Excess type 2 diabetes mellitus in ethnic minority groups remains unexplained, though greater fat mass makes a strong contribution. We hypothesized that height and weight through infancy in South Asian and Black African/Caribbean ethnic subgroups is more adverse than Whites. These, allied to poor socioeconomic position determine greater fat mass at age 7.

Methods

A secondary analysis of 19244 families from the UK Millennium Cohort Study (MCS), including 12280 White, 358 Indian, 650 Pakistani, 268 Bangladeshi, 163 Black Caribbean and 277 Black African births between 2000-2002. Birthweight was reported, and heights and weights measured at ages 3, 5, 7, 11, 14, and 17 years. Bioimpedence captured fat mass at ages 7, 11, 14 and 17, which were indexed to weight. Standardised differences in body habitus, using Whites as the comparator, were calculated. Growth was related to ethnic differences in fat mass and fat free mass at age 7 years, stratified by sex. Confounders included maternal anthropometry, smoking, infant breastfeeding, education, and parental income and area level socioeconomic deprivation.

Results

All ethnic minority subgroups had lower birthweight and accelerated infant height and weight growth compared to Whites. By age 3, all ethnic minorities were taller than Whites. This height advantage was progressively lost, most rapidly in Bangladeshis. By age 17 in boys and girls, Indians were 1.8/2.5, Pakistanis 2.2/3.4, Bangladeshis 4.8/6.0, and Black Caribbeans 1.6/0.5 cm shorter than Whites. Heights were equivalent only in Black Africans. By age 17, all South Asian groups were lighter, and Black African/Caribbean groups heavier than Whites. The ethnic gradient in height and weight in children mirrored that in mothers. All ethnic minority girls experienced early puberty compared to Whites. At age 7, standardized fat mass index (kg/m ² ) in boys/girls was 0.17/0.01 standard deviations greater in Indians, 0.21/0.04 in Pakistanis, 0.18/0.16 in Bangladeshis, 0.48/0.35 in Black Caribbeans, and 0.37/0.75 in Black Africans, compared to Whites. These persisted to age 17. Weight gain to age 3, and in Black Africans/Caribbeans, adverse individual and neighbourhood socioeconomic position contributed to accounting for ethnic differences in fat mass.

Conclusions/Interpretation

Ethnic minority children in the UK have poorer early growth compared to Whites, achieving shorter height, greater fat mass and early female puberty. Mirroring of maternal and offspring ethnic subgroup gradient in height and weight indicates inter-generational transmission. Persistent adverse socioeconomic circumstances perpetuate ethnic adversity in early life accrual of body fat.

Research in context

What is already known about this subject?

• Ethnic minority groups have early and excess risks of type 2 diabetes compared to Whites

• Ethnic minorities are known to have lower birthweight, and experience accelerated infant growth.

• Adult fat mass is greater in ethnic minority groups

What is the key question?

• Can ethnic differences in early growth, maternal body size, child rearing practices and socioeconomic position account for ethnic differences in child fat mass and fat free mass?

What are the new findings?

• All ethnic minority subgroups experience low birthweight and accelerated infant growth, and all, bar Black African girls, are shorter by age 17 compared to Whites.

• The magnitude of difference in achieved height and weight varies markedly by ethnic subgroup and mirrors the ethnic gradient observed in mothers.

• Accelerated infant growth contributes to excess childhood fat mass in children of Indian, Pakistani, Bangladeshi, Black African and Black Caribbean descent. Adverse individual and neighbourhood socioeconomic status makes an additional contribution in Black African and Black Caribbean children.

How might this impact on clinical practice in the future?

• Resolving parental and childhood individual and area socioeconomic inequalities is critical to reducing adverse early growth and excess adiposity that predisposes to type 2 diabetes.