A prospective study of heart rate and externalising behaviours in young children.

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Low heart rate predicts externalising and delinquent behaviour in adults, adolescents and school-age children. In younger children the evidence is less clear. Moreover, the specificity of the relation between the autonomic nervous system and different forms of externalising behaviour is uncertain. We investigated the longitudinal relation between resting mean heart rate and different externalising behaviours. In 412 children of the Generation R Study, we measured resting mean heart rate at 14 months. At 3 years, child problem behaviour was assessed by the mother with the Child Behavior Checklist. In a gift delay task, we observed whether children were compliant and whether they lied about their noncompliance. The association of heart rate with behaviour was contrasted with the effect of harsh parenting. In our main analysis, we examined the association between heart rate and reported and observed child behaviour. For comparison, the association of heart rate with behaviour was contrasted with the effect of harsh parenting. Mean heart rate was positively associated with Anxious/Depressed scale scores (β = .1, 95% CI = 0.01; 0.2, p = .04), but not with Aggressive Behaviour (β = .02; 95% CI = −0.1; 0.1, p = .8) nor Attention Problem scale scores (β = .08, 95% CI = −0.3; 0.5, p = .8). We could not demonstrate an association between mean heart rate and noncompliance during the gift delay task (OR = 1.14, 95% CI = 0.9; 1.1, p = .2), but lower heart rate predicted higher odds of the child lying (OR = 0.56, 95% CI = 0.3; 0.9, p = .03). In contrast, harsh parenting was associated with mother-reported Aggressive Behaviour (β = .7, 95% CI = 0.4; 0.9, p < .001) and Attention Problems (β = .2, 95% CI = 0.1; 0.3, p < .001), but not with observed lying (OR = 1.03, 95% CI = 0.8; 1.4, p = .8). Lower resting mean heart rate at age 14 months predicts low anxiety symptoms and higher odds of lying at age 3 years. Low resting mean heart rate may be less an indicator of early childhood aggression than of fearless behaviour.