Secular trends in body composition for children and young adults: The fels longitudinal study

Abstract

Objectives To determine secular trends by birth decade in body mass index (BMI), waist circumference/height (W/Ht), percent body fat (PBF), and fat free mass adjusted for height squared (FFM/Ht2) in children and adolescents aged 8–18 years. Methods Serial data were analyzed from 628 boys and 591girls aged 8 to 18 years who participated in the Fels Longitudinal Study. Subjects were stratified by birth decade from 1960 through 1999. Means and standard deviations were computed for all measurements by birth decade, age and sex. A repeated-measures analysis of variance was used data to ascertain secular trends separately for boys and girls. Results Boys and girls born in the 1990s had significantly higher mean BMI, W/Ht and PBF than did children born in previous decades. Mean FFM/Ht2 was significantly smaller in boys born in the 1990s than boys of the same age born in earlier decades. No secular trend was noted in FFM/ Ht2 in girls by decade of birth. Conclusion Our analysis of serial data collected over four decades confirms the secular trend in childhood BMI previously observed in successive cross-sectional studies. Our analysis discloses significant positive secular trends in W/Ht and PBF in both boys and girls and a significant negative secular trend in FFM/Ht2 in boys over the last four decades of the 20th century. The secular changes presage increases in the prevalence of conditions associated with childhood and adolescent obesity – such as hypertension, glucose intolerance, and dyslipidemia – that may appear as early as the second decade of life.

Age as a moderator of the secular trend for grip strength in Canada and the United States

“…There is very little evidence with respect to secular trends in fat-free mass. In children and adolescents, a study (Sun et al, 2012) conducted in the US found that fatfree mass (adjusted for height) was lower in boys born in the 1990s than in boys born in the 1960s, 1970s or 1980s, but there was no secular trend on this measure in girls. (According to Malina (2004), height in children in the US increased very slightly and only at the 5th and 10th percentiles, between 1963-1994; thus the adjustment for height should not have affected the across-time comparisons of fat-free mass in the study by Sun et al) For adults, the only data available are for US Army recruits (Sharp et al, 2002).…”

Peak Bone Mass and Patterns of Change in Total Bone Mineral Density and Bone Mineral Contents From Childhood Into Young Adulthood

“…Details of FLS participants and data collection process have been reported previously (16, 20). All FLS participants have been monitored since birth and have had serial measures of stature and weight taken at one, three, six, nine and 12 months, then semi-annually to 18 years, and biennially thereafter.…”

“…DXA was measured through Hologic ™ QDR 4500 Elite densitometer (Hologic, Waltham, MA) and a Lunar LPX machine. The calibration of the measurement and conversion between the Hologic and Lunar DXA machines were described in detail formerly (20). The number of DXA measurements and ages at which repeated DXA measurements were made vary and depend on the age of a participant when DXA measurements were introduced into FLS; age when the minimum weight was required for measurement of DXA; and whether annually scheduled examinations were missed.…”

Secular trends in the fat and fat-free components of body mass index in children aged 8–18 years born 1958–1995

“…A recent paper (Sun et al 2012) examined trends in body composition in children born between 1960–1999 in the Fels Longitudinal Study (Roche 1992). Differences in mean BMI, percentage body fat (%fat) and a fat-free mass index (FFMI = fat-free mass/height 2 ) between birth year decades were tested within yearly chronological age groups; a trend in increasing BMI and %fat was observed in the absence of a trend in increasing FFMI.…”

“…552). To ameliorate this issue, the recently published paper (Sun et al 2012) used conversion equations to adjust the hydrodensitometry values to obtain similar means to the DXA values, but these equations have not been validated in any publication. The concern over pooling data from two different methods which were implemented over different periods of the study is that assessment of secular trends may be biased by the known intra-method differences.…”