Height and intelligence in the Lothian Birth Cohort 1921: a longitudinal study

The relationship between height and intelligence has long been subject to investigation [1–5]. Life-long levels for both height and intelligence emerge during childhood development. Although both height and IQ are highly heritable with demonstrable genetic associations [6, 7], distinct environmental contributions are also evident [8, 9]. Early studies considered both height and IQ to be outcomes of social disadvantage in [10]; however, the relationship between height and IQ in childhood is not fully explained by shared effects of social class or putative in utero programming [11]. Height in middle age predicts cognitive performance in old age [12] when not controlled for the direct influence of childhood IQ on later life cognition [13]. Hitherto, relationships between height and intelligence have focussed on height as a developmental outcome. However, with the advent of mass population ageing, a new cause of changes in height becomes of increasing importance: changes occurring secondary to degenerative diseases of old age [14]. There is a paucity of evidence on factors influencing change in height in old age [15, 16], and relationships to intelligence fall under the emerging discipline of cognitive epidemiology [17, 18] including, as noted above, height in middle age [5].

Longitudinal studies are necessary to investigate the relationship between height and intelligence in older adults because age differences in height derived from cross-sectional studies can be the result of differential secular influences among cohorts [19–21]. Using such a longitudinal design across seven decades, we studied the associations of IQ, height and life-time IQ change in a sample first assessed for IQ at age 11.