Nonlinear components of age-related change in sleep initiation

Background: Although primary studies suggest that ability to initiate sleep declines as people age, no systematic literature review has addressed the age(s) at which adults experience the greatest change in their ability to i nitiate sleep. Objective: To explore whether there are any points in time across the adult life span when the rate of change in ability to initiate sleep increases o r decreases. Methods: Mathematical modeling was used to generate data points from inform ation about central tendency, variance, and correlations between age and ti me to sleep onset provided by seven research reports. The reports represent 258 subjects ages 17 to 91 years. Smoothing splines were used to identify inflection points suggestive of major changes in sleep initiation across th e life span. Results: Two mathematical models were generated. One model suggested that i nflection points may exist around ages 30 and 50 years, respectively. With this model, the amount of time until sleep onset increased until the age of 30 years, but was unchanged from ages 30 to 50 years. Ability to initiate sleep appeared to decline steadily after the age of 50 years. The second mo del, with a p value of 0.05, lacked adequate power to identify a significan t nonlinear trend. Conclusions: Decline in ability to initiate sleep may not occur at a steady rate over the adult life span. Further research is needed to pinpoint thre sholds of change and possible gender differences in thresholds.