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Characterization of the infant BMI peak: Sex differences, birth year cohort effects, association with concurrent adiposity, and heritability

Authors

  • William Johnson,

    1. MRC Unit for Lifelong Health and Ageing, London
    2. Division of Epidemiology and Community Health, School of Public Health, University of Minnesota, Minneapolis, MN, USA
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  • Audrey C. Choh,

    1. Division of Epidemiology, Lifespan Health Research Center, Boonshoft School of Medicine, Wright State University, Dayton, OH, USA
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  • Miryoung Lee,

    1. Division of Epidemiology, Lifespan Health Research Center, Boonshoft School of Medicine, Wright State University, Dayton, OH, USA
    2. Department of Pediatrics, Boonshoft School of Medicine, Wright State University, Dayton, OH, USA
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  • Bradford Towne,

    1. Division of Epidemiology, Lifespan Health Research Center, Boonshoft School of Medicine, Wright State University, Dayton, OH, USA
    2. Department of Pediatrics, Boonshoft School of Medicine, Wright State University, Dayton, OH, USA
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  • Stefan A. Czerwinski,

    1. Division of Epidemiology, Lifespan Health Research Center, Boonshoft School of Medicine, Wright State University, Dayton, OH, USA
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  • Ellen W. Demerath

    Corresponding author
    1. Division of Epidemiology and Community Health, School of Public Health, University of Minnesota, Minneapolis, MN, USA
    • MRC Unit for Lifelong Health and Ageing, London
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Correspondence to: Ellen W Demerath, Ph.D., Division of Epidemiology and Community Health, University of Minnesota, 1300 South 2nd Street, Suite 300, Minneapolis, MN 55454, USA. E-mail: ewd@umn.edu

Abstract

Objectives

To characterize an early trait in the BMI-for-age curve, the infant BMI peak.

Methods

BMI-for-age curves were produced for 747 non-Hispanic, white Fels Longitudinal Study participants, from which individual age (AgePeak) and BMI (BMIPeak) at maximum infant BMI were estimated. Multivariable general linear regression was used to examine the effects of sex and birth year cohort (1929–1950, 1951–1970, and 1971–2010) on AgePeak and BMIPeak, with associations between BMIPeak and concurrent sum of four skinfold thicknesses assessed in a subsample (N = 155). Heritability (h2) of AgePeak and BMIPeak was estimated using maximum-likelihood variance components analysis.

Results

AgePeak occurred at 9 months of age in both sexes, but BMIPeak was 0.4 kg/m2 higher for boys than for girls (P-value < 0.001). Infants born between 1971 and 2010 experienced a 1.5 month earlier AgePeak and a 0.35 kg/m2 lower BMIPeak than infants born between 1929 and 1950 (P-values < 0.001). Skinfold thickness explained 37% of the variance in BMIPeak in boys and 20% of the variance in girls (p-values < 0.001). AgePeak and BMIPeak were significantly heritable (h2 = 0.54 and 0.75, respectively).

Conclusions

Both AgePeak and BMIPeak decreased over successive birth year cohorts in the Fels Longitudinal Study. Despite a positive association of BMIPeak with concurrent adiposity, AgePeak appears to occur later than does the well-documented peak in infant fat mass and BMIPeak does not capture known sex differences in infant adiposity. Strong heritability of these infant BMI traits suggests investigation of genetic control, and validation of their relationship to body composition is greatly needed. Am. J. Hum. Biol. 25:378–388, 2013. © 2013 Wiley Periodicals, Inc.

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