Genetic and environmental factors affecting menarcheal age in Spanish women.

Genetic and environmental contributions to menarcheal age were studied in 267 Spanish girls and women born between 1948 and 1981, and their mothers born between 1922 and 1959 (n = 200). Recalled age at menarche, as well as family environment characteristics (family size, birth order, father's occupation and father's educational level) were obtained from each woman. Mean age at menarche in mothers (13.45 years; SD = 1.51) was significantly (p < 0.01) greater than in daughters (13.03 +/- 1.28 years). Year of birth and family size accounted for a significant amount of the variation in age at menarche in both mothers and daughters, whereas occupation of the father only appeared related to menarcheal age in the mothers subsample. Birth order and father's educational level did not contribute significantly to the age at menarche. The mother-daughter and sister-sister correlations (maximum likelihood estimates) for age at menarche were 0.30 and 0.35, respectively (both significant at p < 0.001). This supports the genetic and environmental contribution to the age at menarche, even though the influence of environmental variables may change over time.