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Influences on childhood height: comparing two generations in the 1958 British birth cohort.

BACKGROUND
Genetics and early environment are known to influence height, but evidence is sparse on changes in these influences over time.


METHODS
The 1958 British birth cohort study includes all children born between March 3, 1958 and March 9, 1958, who were followed to age 41 yr, and one-third of their offspring in 1991. Childhood height in each generation (measured at 7 yr for cohort members and 4-18 yr for offspring) was converted to a standard deviation score based on the 1990 British growth reference. We used multilevel models to analyse influences on height in order to allow for the hierarchical within-family data structure.


RESULTS
Childhood height increased by 1 cm between 1958 cohort members and their offspring. Several influences on childhood height in the older generation (maternal smoking, breastfeeding, maternal age, social class, maternal education, and parental divorce) did not affect childhood height in the younger generation. Parental height was most strongly associated with childhood height and effects did not diminish between generations [adjusted increase approximately 2 cm for 1 maternal or paternal height standard deviation score (SDS)]. Third- or later-borns and those with three or more siblings had deficits of 1-2 cm (adjusted estimates) in both generations. Other factors, particularly indicators of socioeconomic position, showed weaker effects in the younger generation. For example, the growth deficit of 1.1 cm (adjusted estimate) among cohort members from households with >1.5 persons/room had disappeared in the offspring.


CONCLUSIONS
Within Great Britain, the adverse effects of environmental factors on childhood height have lessened between recent generations.