Association between low birthweight and high resting pulse in adult life: is the sympathetic nervous system involved in programming the insulin resistance syndrome?

To test the hypothesis that elevated sympathetic nervous system (SNS) activity could be determined in utero and be one of the processes mediating the link between size at birth and insulin resistance and raised blood pressure in adult life, we have studied the resting pulse rate of 449 men and women aged 46 to 54 (mean 50) years born in Preston, Lancashire, England whose birth size was recorded in detail. The subjects were visited at home by trained fieldworkers who measured resting pulse rate and blood pressure using an automated recorder. The resting pulse rate ranged from 44 to 108 (mean 73) beats min(-1). It rose with increasing body mass index (r = 0.14, p = 0.003) and waist to hip ratio (adjusted for sex r = 0.10, p = 0.003) and correlated significantly with systolic and diastolic blood pressures (p = 0.001), fasting glucose (p = 0.02), split proinsulin (p = 0.001), and triglyceride concentrations (p = 0.02). The pulse rate fell progressively from 76 beats min(-1) among subjects who weighed 5.5 lb (2.5 kg) or less at birth to 71 beats min(-1) among those who weighed 7.5 lb (3.3 kg) or more (decline in pulse rate per kg increase in birthweight = 2.7, 95 % CI 0.6 to 4.8 beats min(-1). The association was independent of current body mass index, waist to hip ratio and of potential confounding variables including smoking, alcohol consumption, and social class. Although the resting pulse rate is an imperfect index of SNS activity, these findings are consistent with the hypothesis that elevated SNS activity established in utero is one mechanism linking small size at birth with the insulin resistance syndrome in adult life.