Longitudinal study of thinness from birth to early childhood: the association with parental thinness

Aim Epidemiological research on thinness, particularly in early childhood, is limited. This study tracked thin children aged 5 years back to birth, compared them with normal‐weight children and investigated the relationship with parental thinness. Methods We enrolled 2678 children (50.5% boys) aged 5 years and attending kindergarten or nursery in the Nara Prefecture of Japan. The children's height and weight at birth, 1.5 years and 3.5 years, were obtained from mother–child health records. Child thinness was defined as having a body mass index (BMI) of less than the fifth percentile of the reference values for Japanese children, and parental thinness was defined as a BMI of