Hormones and handedness

The Wessex Growth Study has monitored the growth and psychological development of short normal (SN) and average height control subjects since they entered school in 1985/1986. During psychometric testing, we found that 25% SN compared to 9% control subjects wrote with their left hand. The short group also attained significantly lower scores on measures of IQ and attainment and displayed less internalisation of control. Laterality, however, is thought to be influenced by the intrauterine environment and has been associated with pubertal delay. At recruitment, short children had a relatively low birth weight, delayed bone age and were more likely than controls to be short for family.

To determine if birth conditions were associated with lateral preference and whether laterality could account for the differences found during the psychometric assessment or predict pubertal timing of SN children.

Subjects were classified as right- (RH) or left-handed (LH) according to the writing hand and the data were investigated examining the effect of handedness and stature.

RH and LH SN children were no more likely to suffer birth complications than those of average height. Psychometric testing did not reveal any significant differences between RH and LH SN children and their patterns of growth appeared to be similar. However, both RH and LH SN children scored less well on tests of cognitive ability and analyses of covariance revealed significant gender/handedness effects for both the timing of puberty and final height.

The increase in left-handedness among SN children did not appear to be related to adverse birth conditions, but it may be that the hormones responsible for growth and development also play some part in brain laterality and cognitive development.