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Updated: May 18, 2026
Assessment of Child Anthropometry in a Large Epidemiologic Study
Published on: February 2, 2017
Secular changes in BMI and the associations between risk factors and BMI in children born 29 years apart
S M Williams1, R W Taylor, B J Taylor
1Department of Preventive and Social Medicine, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand. sheila.williams@otago.ac.nz
Insights
Maternal factors like higher body mass index (BMI) and smoking during pregnancy significantly contribute to rising childhood obesity rates. Changes in these societal factors, not behavioral ones, are key drivers of childhood BMI increases over generations.
Area of Science:
- Pediatrics
- Public Health
- Epidemiology
Background:
- Childhood obesity is a growing concern with multifactorial causes.
- Previous research identified parental BMI, birth weight, and lifestyle factors as associated with children's BMI.
- Limited understanding exists regarding generational changes in these associations and their contribution to secular BMI trends.
Purpose of the Study:
- To examine changes in risk factors for childhood body mass index (BMI) over a 29-year period.
- To assess the association between these risk factors and BMI at ages 3 and 7 years.
- To quantify the contribution of identified risk factors to secular BMI changes in children at age 7.
Main Methods:
- Utilized two New Zealand birth cohorts (Dunedin Multidisciplinary Health and Development Study, 1972-73; Family Lifestyle, Activity, Movement and Eating Study, 2001-02).
- Collected data on birth weight, anthropometric measures (ages 3, 5, 7), maternal factors (age, education, smoking), and child lifestyle (TV time, sleep).
- Analyzed changes in risk factor associations and their contribution to BMI trends over 29 years.
Main Results:
- A significant increase in BMI was observed over the 29-year period (0.84 kg m⁻² at age 7).
- Increased maternal BMI was strongly associated with offspring BMI, accounting for approximately 20% of the rise in children's BMI.
- Maternal smoking during pregnancy, despite decreased prevalence, showed an increased association with BMI, contributing significantly to the observed increase.
Conclusions:
- Societal factors, particularly increased maternal BMI and smoking during pregnancy, are primary drivers of secular increases in childhood BMI.
- Changes in behavioral factors like sleep duration and television viewing had minimal impact on childhood BMI trends in this population.
- Public health interventions targeting maternal health and reducing smoking in pregnancy are crucial for addressing childhood obesity.
Unlabelled:
What is already known about this subject Factors associated with children's body mass index (BMI) include parents' BMIs, birth weight, maternal smoking, sleep duration and television watching. Few studies have attempted to quantify either changes in the association between risk factors and BMI or the contribution of changes in the risk factors to increases in BMI over a generation. What this study adds The magnitude of the association between most risk factors and children's BMIs has not changed over a 29-year period. Increases in the population level of mothers' body mass index (BMI) explains ~20% of the increase in children's BMI whereas the smaller increase in fathers' BMI contributes only 6%. Maternal smoking, despite the decrease in prevalence, contributes ~17%.
Objective:
Using two cohorts born 29 years apart in Dunedin, New Zealand we aim to examine changes in risk factors and their associations with body mass index (BMI) at ages 3 and 7 years, and estimate their contribution to the secular changes in BMI at age 7 years.
Methods:
Birth weight and anthropometric measures at ages 3, 5 and 7 years were obtained for 974 participants in the Dunedin Multidisciplinary Health and Development Study (DMHDS), born in 1972-1973, and 241 in the Family Lifestyle, Activity, Movement and Eating Study (FLAME), born in 2001-2002. Information about maternal age, education and smoking in pregnancy, as well as breastfeeding, children's television time and time in bed, was obtained by questionnaire.
Results:
The increase in BMI over the 29-year period was 0.84 (95% CI 0.61, 1.06) kg m(-2) at age 7. A 1-unit difference in the mother's BMI was associated with a 0.06 (0.03, 0.08) kg m(-2) difference in offspring in both studies; the 3.4 (2.8, 4.0) kg m(-2) increase in the mothers' BMIs accounts for a change of 0.19 kg m(-2) in the children's BMI. The much smaller generational increase in fathers' BMI (0.7 kg m(-2) ) correspondingly had a more limited effect on change in child BMI over time (0.06 kg m(-2) ). Although smoking in pregnancy decreased by 15% (8, 21) its association with BMI increased from 0.20 (-0.01, 0.42) in the DMHDS cohort to 1.24 (0.76, 1.71) kg m(-2) in the FLAME cohort, contributing 0.18 kg m(-2) to the increase in children's BMI.
Conclusions:
Societal factors such as higher maternal BMI and smoking in pregnancy contribute most to the secular increase in BMI, with changes in behavioural factors, including sleep and television viewing, having little effect in this setting.
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