Article | Published:

Epidemiology and Population Health

Opposite associations of household income with adolescent body mass index according to migrant status: Hong Kong’s “Children of 1997” birth cohort

International Journal of Obesityvolume 42pages12211229 (2018) | Download Citation

Abstract

Background/objectives:

In economically developed settings, household income is usually inversely associated with child and adolescent adiposity, but this association may not extend to migrants. Hong Kong is a unique developed setting to study how household income and adolescent adiposity vary by migrant status given many Hong Kong-born Chinese children were born to parents who migrated from neighboring provinces of Mainland China.

Subjects/methods:

We examined differences between the associations of absolute household income vs. relative household income on adolescent body mass index (BMI) z-score or overweight (including obesity) status using a linear or logistic model in a Chinese birth cohort (n = 5613, 68% follow-up). We focused on whether the associations differed by mother’s or father’s migrant status (birthplace).

Results:

No association was found between absolute household income and BMI z-score among adolescents with either native or migrant mothers. However, the association of relative household income with BMI z-score varied by mother’s migrant status (P-values for interaction <0.0005). In adolescents of native born mothers, greater relative household income deprivation was associated with higher BMI z-score (0.03 z-score per USD 128 difference in Yitzhaki index, 95% confidence interval (CI) 0.01 to 0.05). However, in adolescents of migrant mothers, greater relative household income deprivation was associated with lower BMI z-score (−0.05, 95% CI −0.09 to −0.01). Similar association of relative household income with overweight (including obesity) status was found in adolescents of native born mothers but not in adolescents of migrant mothers.

Conclusions:

Relative income (mediated by social comparisons with others in society) appears to be relevant to adolescent adiposity, but the association depends on the interplay between individual characteristics (migrant background) and societal context.

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Acknowledgements

The authors thank colleagues at the Student Health Service and Family Health Service of the Department of Health for their assistance and collaboration. They thank Dr. Connie Hui for her assistance with the record linkage and the late Dr. Connie. for coordinating the project and all the fieldwork for the initial study in 1997–1998. M.K.K. thanks the Takemi Program in International Health at the Harvard T.H. Chan School of Public Health for her fellowship during which this manuscript was prepared.

Funding:

This work is a sub-study of the “Children of 1997” birth cohort which was initially supported by the Health Care and Promotion Fund, Health and Welfare Bureau, Government of the Hong Kong SAR [HCPF Grant #216106] and re-established in 2005 funded by the Health and Health Services Research Fund [HHSRF Grant #03040771]. This sub-study was funded by the Research Fund for the Control of Infectious Diseases [RFCID Grant #04050172] and the Health and Health Services Research Fund [HHSRF Grants #07080751 and #08090761], Government of the Hong Kong SAR.

Author information

Affiliations

  1. School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China

    • Man Ki Kwok
    • , C. Mary Schooling
    •  & Gabriel M. Leung
  2. City University of New York, Graduate School of Public Health and Health Policy, New York, NY, USA

    • C. Mary Schooling
  3. Department of Social and Behavioral Sciences, Harvard T.H. Chan School of Public Health, Boston, MA, USA

    • S. V. Subramanian
    •  & Ichiro Kawachi

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Conflict of Interest

The authors declare that they have no conflict of interest.

Corresponding author

Correspondence to C. Mary Schooling.

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DOI

https://doi.org/10.1038/s41366-018-0118-x