Abstract
People age at different rates. We have proposed that rates of aging can be quantified by the rate at which individuals accumulate health deficits. Earlier estimates, using cross-sectional analyses suggested that deficits accumulated exponentially, at an annual rate of 3.5 %. Here, we estimate the rate of deficit accumulation using longitudinal data from the Canadian National Population Health Survey. By analyzing age-specific trajectories of deficit accumulation in people aged 20 years and over (n = 13,668) followed biannually for 16 years, we found that the longitudinal average annual rate of deficit accumulation was 4.5 % (±0.75 %). This estimate was notably stable during the adult life span. The corresponding average doubling time in the number of deficits was 15.4 (95 % CI 14.82–16.03) years, roughly 30 % less than we had reported from the cross-sectional analysis. Earlier work also established that the average number of deficits accumulated by individuals (N), equals the product of the intensity of environmental stresses (λ) causing damage to the organism, by the average recovery time (W). At the individual level, changes in deficit accumulation can be attributed to both changes in environmental stresses and changes in recovery time. By contrast, at the population level, changes in the number of deficits are proportional to the changes in recovery time. In consequence, we propose here that the average recovery time, W doubles approximately every 15.4 years, independently of age. Such changes quantify the increase of vulnerability to stressors as people age that gives rise to increasing risk of frailty, disability and death. That deficit accumulation will, on average, double twice between ages 50 and 80 highlights the importance of health in middle age on late life outcomes.
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Acknowledgments
This project was sponsored by an operating grant from the Canadian Institutes of Health Research, No. MOP24388. The National Population Health Study was carried out by Statistics Canada. The authors obtained access to the data through an agreement with the Atlantic Research Data Centre of Statistics Canada, which obliged them to operate, for these purposes only, as “deemed employees” of Statistics Canada. Statistics Canada officials reviewed the analyses to ensure that confidentiality had not been breached and that the data were weighted properly to produce uniform estimates across reports. In no other way did any sponsor have influence over the data analyses. The authors also thank Dr. X Song for her for assistance in data preparation.
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Mitnitski, A., Rockwood, K. The rate of aging: the rate of deficit accumulation does not change over the adult life span. Biogerontology 17, 199–204 (2016). https://doi.org/10.1007/s10522-015-9583-y
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DOI: https://doi.org/10.1007/s10522-015-9583-y