Background Elevated Resting Heart Rate (RHR) is an established cardiovascular risk factor and higher RHR even in childhood has been associated with higher adult mortality rates. We are the first to describe trajectories of age-related changes in RHR in the same individuals followed from childhood to later life. We hypothesised that indicators of better health, development and socioeconomic advantage in early childhood would be reflected in lower RHR trajectories, independent of smoking status.
Methods Data were from the Medical Research Council National Survey of Health and Development (maximum n=4779) followed from birth in 1946. RHR was measured on eight occasions between 6–69 years (three in childhood and five in adulthood). Information on early life factors was ascertained prospectively. Multilevel models were used to estimate life course mean RHR trajectory by sex, and to investigate associations with childhood socioeconomic position (SEP), birth weight (BW), growth from 2–6 years (conditional change in Body Mass Index (BMI) and height), duration of breast feeding (BF), and markers of neurodevelopment (age at first walking independently and cognitive ability at eight years).
Results Mean estimated RHR decreased with increasing age and plateaued from early adulthood tending to remain higher in women. In sex-adjusted analyses higher BW and conditional BMI change were associated with lower RHR at 6 years and across the life course (−0.57bpm (95% confidence interval: −0.95;−0.18) per 1 kg higher BW and −0.23bpm (−0.42;−0.05) per 1kg/m2 greater change in BMI); however neither influenced the rate of change with age in RHR. Neither SEP nor BF duration was associated with childhood RHR but associations with RHR trajectory emerged in adulthood such that by 60 years RHR was 1.28bpm (0.10;2.16) higher in participants from a disadvantaged versus advantaged SEP and −1.13bpm (−2.01;−0.24) lower for BF>=8 months versus never. A later age at walking independently was associated with a higher RHR at 6 years (1.33bpm (0.22;2.44) for>=18 months versus <12 months) but lower RHR in adulthood (−1.09bpm (−2.48;0.30) at 60 years). Childhood cognitive ability was not associated with RHR. In a model including all early life factors, estimates were typically only slightly attenuated from sex-adjusted models except that adjustment for conditional growth substantially reduced the effect of BW. Associations were independent of life course smoking status.
Conclusion Early life is a key period in determining future RHR trajectories with effects of potentially modifiable factors persisting into the seventh decade of life.
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