How can two biological variables have opposing secular trends, yet be positively related? A demonstration using timing of puberty and adult height

Timing of puberty and adult height have opposing secular trends yet are positively associated in individuals. We demonstrate this using data from a single sample and discuss possible statistical and epidemiological reasons behind it. The sample comprised 365 females from Fels Longitudinal Study born 1929-1992. We used Super-Imposition by Translation and Rotation (SITAR) to estimate individual age at peak height velocity (PHV) and PHV from serial height data (8149 observations between 5-24 years). General linear regression was used to investigate the association between height and age at PHV, and secular trends in height, age at PHV and PHV. Although adult height increased 0.42 (95%CI 0.08, 0.77) cm per decade, and age at PHV decreased 1.14 (-3.74, 1.45) weeks per decade, adult height increased by 2.44 (1.78, 3.10) cm per year higher age at PHV. We found tentative evidence the positive association between age at PHV and adult height strengthened 0.25 (-0.09, 0.59) cm each decade. Secular trends in related variables may differ if the between-individual and between cohort associations are different. To understand if a secular trend in one variable has contributed to a trend in another, each needs to be modelled over time, together with the changing association between them.</div

Delayed skeletal maturation is a major contributor to child height deficits in a low-income setting

Background: Studying the extent to which delayed skeletal maturation may contribute to childhood height deficits is important for assessing potential for recovery in heights. Aim: To investigate the discrepancy in height-for-age Z-scores (HAZ) based on chronological age (HAZ-19 CA) compared to bone age (HAZ-BA) and estimate proportion of HAZ deficits attributable to delayed maturation in both sexes.Subjects and methods: Using the WHO Growth References, HAZ-CA and HAZ-BA were calculated for Guatemala City children aged 6-8.99 years participating in the Universidad del Valle de Guatemala Longitudinal Study and attending a low or a very low SEP study school. A mixed effects model was developed to describe 1638 HAZ observations (Level 1) in 1107 children (Level 2) by HAZ-type, with interaction terms for HAZ-type by age, sex, school, and birth year. Results: On average, skeletal age was delayed by 1.1 (SD 1.0) years. Mean HAZ-CA was -1.7 (0.9) and HAZ-BA -0.6 (0.9). Greater proportions of the total height deficit were attributable to delayed skeletal maturation in males (60-87%) versus females (49-63%), and at low- (58-87%) versus very low-SES school (49-71%).Conclusion: Delayed maturation contributes to height deficits, supporting the idea that opportunity for catch-up growth continues past early childhood in both sexes.</p

Supplementary information files for Inequalities in adiposity trends between 1979 and 1999 in Guatemalan children

© the authors, CC-BY 4.0Supplementary files for article Inequalities in adiposity trends between 1979 and 1999 in Guatemalan childrenBackground: Guatemala suffered from civil war and high levels of inequality and childhood stunting in the second half of the 20th century, but little is known about inequalities in secular trends in adiposity.Objectives: To investigate differences in childhood body mass index (BMI) and skinfold thickness trajectories from 1979 to 1999 between three groups of children: High socioeconomic position (SEP) Ladino, Low SEP Ladino, and Low SEP Indigenous Maya.Methods: The sample comprised 19 346 children aged 7–17 years with 54 638 observations. The outcomes were height, BMI, triceps skinfold thickness (TST), and subscapular skinfold thickness (SST) Z-scores according to the Centers for Disease Control and Prevention (CDC) references. Sex-specific multilevel models were used to estimate and compare mean trajectories from 1979 to 1999 between the three groups.Results: Mean Z-scores were always highest for High SEP Ladino children and lowest for Low SEP Maya children. Despite their very short stature, the Low SEP groups had SST trajectories that were above the 50th centile. The BMI trajectories were relatively flat and within one major centile band of the CDC median, with differences between the three groups that were small (0.2–0.3 Z-scores) and did not attenuate over time. Conversely, the TST Z-score trajectories demonstrated larger positive secular trends (e.g., from −1.25 in 1979 to −0.06 in 1999 for Low SEP Maya boys), with differences between the three groups that were large (0.5–1.2 Z-scores) and did attenuate over time (in boys). Secular trends and between-group difference in the SST Z-score trajectories were less pronounced, but again we found stronger evidence in boys that the estimated inequalities attenuated over time.Conclusions: Secular trends and inequalities in skinfolds differ from those for BMI in Guatemalan children. Differences between groups in skinfolds attenuated over time, at least in boys, but whether this is good news is questionable given the very short stature yet relatively large subscapular skinfolds of the Low SEP groups.</p

Inequalities in adiposity trends between 1979 and 1999 in Guatemalan children

Background: Guatemala suffered from civil war and high levels of inequality and childhood stunting in the second half of the 20th century, but little is known about inequalities in secular trends in adiposity.Objectives: To investigate differences in childhood body mass index (BMI) and skinfold thickness trajectories from 1979 to 1999 between three groups of children: High socioeconomic position (SEP) Ladino, Low SEP Ladino, and Low SEP Indigenous Maya.Methods: The sample comprised 19 346 children aged 7–17 years with 54 638 observations. The outcomes were height, BMI, triceps skinfold thickness (TST), and subscapular skinfold thickness (SST) Z-scores according to the Centers for Disease Control and Prevention (CDC) references. Sex-specific multilevel models were used to estimate and compare mean trajectories from 1979 to 1999 between the three groups.Results: Mean Z-scores were always highest for High SEP Ladino children and lowest for Low SEP Maya children. Despite their very short stature, the Low SEP groups had SST trajectories that were above the 50th centile. The BMI trajectories were relatively flat and within one major centile band of the CDC median, with differences between the three groups that were small (0.2–0.3 Z-scores) and did not attenuate over time. Conversely, the TST Z-score trajectories demonstrated larger positive secular trends (e.g., from −1.25 in 1979 to −0.06 in 1999 for Low SEP Maya boys), with differences between the three groups that were large (0.5–1.2 Z-scores) and did attenuate over time (in boys). Secular trends and between-group difference in the SST Z-score trajectories were less pronounced, but again we found stronger evidence in boys that the estimated inequalities attenuated over time.Conclusions: Secular trends and inequalities in skinfolds differ from those for BMI in Guatemalan children. Differences between groups in skinfolds attenuated over time, at least in boys, but whether this is good news is questionable given the very short stature yet relatively large subscapular skinfolds of the Low SEP groups.</p

Growth delay: an alternative measure of population health based on child height distributions

Indicators of child height, such as mean height-for-age Z-scores (HAZ), height-for-age difference (HAD) and stunting prevalence, do not account for differences in population-average bone developmental stage. Propose a measure of child height that conveys the dependency of linear growth on stage rather than chronological age. Using Demographic and Health Surveys (2000–2018; 64 countries), we generated: (1) predicted HAZ at specific ages (HAZ regressed on age); (2) height-age (age at which mean height matches the WHO Growth Standards median); (3) Growth delay (GD), the difference between chronological age and height-age; (4) HAD; and (5) stunting prevalence. Metrics were compared based on secular trends within countries and age-related trajectories within surveys. In the most recent surveys (N = 64), GDs ranged from 1.9 to 19.1 months at 60 months chronological age. Cross-sectionally, HAZ, HAD and GD were perfectly correlated, and showed similar secular trends. However, age-related trajectories differed across metrics. Accumulating GD with age demonstrated growth faltering as slower than expected growth for children of the same height-age. Resumption of growth at the median for height-age was rarely observed. GD is a population-level measure of child health that reflects the role of delayed skeletal development in linear growth faltering.</p

Inequalities in adiposity trends between 1979 and 1999 in Guatemalan children

Background: Guatemala suffered from civil war and high levels of inequality and childhood stunting in the second half of the 20th century, but little is known about inequalities in secular trends in adiposity.Objectives: To investigate differences in childhood body mass index (BMI) and skinfold thickness trajectories from 1979 to 1999 between three groups of children: High socioeconomic position (SEP) Ladino, Low SEP Ladino, and Low SEP Indigenous Maya.Methods: The sample comprised 19 346 children aged 7–17 years with 54 638 observations. The outcomes were height, BMI, triceps skinfold thickness (TST), and subscapular skinfold thickness (SST) Z-scores according to the Centers for Disease Control and Prevention (CDC) references. Sex-specific multilevel models were used to estimate and compare mean trajectories from 1979 to 1999 between the three groups.Results: Mean Z-scores were always highest for High SEP Ladino children and lowest for Low SEP Maya children. Despite their very short stature, the Low SEP groups had SST trajectories that were above the 50th centile. The BMI trajectories were relatively flat and within one major centile band of the CDC median, with differences between the three groups that were small (0.2–0.3 Z-scores) and did not attenuate over time. Conversely, the TST Z-score trajectories demonstrated larger positive secular trends (e.g., from −1.25 in 1979 to −0.06 in 1999 for Low SEP Maya boys), with differences between the three groups that were large (0.5–1.2 Z-scores) and did attenuate over time (in boys). Secular trends and between-group difference in the SST Z-score trajectories were less pronounced, but again we found stronger evidence in boys that the estimated inequalities attenuated over time.Conclusions: Secular trends and inequalities in skinfolds differ from those for BMI in Guatemalan children. Differences between groups in skinfolds attenuated over time, at least in boys, but whether this is good news is questionable given the very short stature yet relatively large subscapular skinfolds of the Low SEP groups.</p

Correlations of pre-adult IQ tests scores.

Correlations of pre-adult IQ tests scores.</p

Pre-adult IQ test scores by test used.

Box plot (median, quartiles, minimum, maximum) of IQ test scores by test used (Pinter Cunningham A (N = 22), Pinter Durost A(N = 29), Otis Intermedio (N = 35), Pinter General Intermedio (N = 28), and Otis Superior (N = 34).</p

Correlations of pre-adult IQ scores and later life test scores.

Correlations of pre-adult IQ scores and later life test scores.</p

Overview of the different rationales for choosing pre-adult test scores for their stability and predictive ability.

Overview of the different rationales for choosing pre-adult test scores for their stability and predictive ability.</p