Physical activity to the current recommended guidelines and sleep quality of adults with insomnia

Systematic reviews have consistently found that moderate intensity physical activity levels at or above a threshold value of 150 minutes per week reliably deliver cardiovascular, metabolic and musculo-skeletal health benefits. As a result, this threshold value has been widely adopted as an aspirational, public health goal throughout the world. However, while epidemiological and laboratory studies have established clear links between physical activity and sleep outcomes, the evidence base does not yet provide guidelines on minimum levels of exercise likely to reduce insomnia symptoms and improve sleep quality. Such a guideline, if evidence based, could greatly clarify advice, and accelerate the use of physical activity goals to improve sleep outcomes in behavioural sleep medicine and public health. This thesis examined the current public-health recommendation of 150 minutes of moderate intensity activity per week in relation to sleep outcomes. To commence, it established a population-level pattern of the relationship between levels of physical activity and sleep quality by reviewing relevant epidemiological evidence. Exploratory analyses were then conducted using data from an ongoing longitudinal study of physical activity and health outcomes among older people (aged 65 years and above) in which respondents were classified as walking at or above, or below the recommended threshold of 150 minutes per week. In regression models controlling for health and demographic factors, these analyses showed that higher levels of walking were significantly and independently associated with a lower likelihood of either reporting insomnia symptoms (OR = 0.67 (95% CI = 0.45 0.91) p=0.04), or experiencing poor sleep efficiency (OR = 0.70 (95% CI = 0.52 0.94 p=0.02). Using the same data, the predictive validity of this activity threshold was then confirmed in a 27-year survival analysis which showed a significantly decreased all-cause mortality risk associated with the higher level of walking (HR = 0.75 (95% CI = 0.65 - 0.86) p<0.01). These findings offered proof of concept that physical activity-sleep relationships operated on a continuum, with sleep benefits possible even at relatively low levels of activity. Experimental evidence on the acute and sustained effects of physical activity on sleep quality was then analysed and discussed. Outcomes from this review, together with the preliminary analyses described above, were then used to inform the design of a randomised controlled trial to investigate the effects on sleep quality of increasing physical activity to currently recommended levels among sedentary people with insomnia. A total of 41 sedentary adults meeting DSM-IV criteria for insomnia (30 female; mean age 59.8±9.5) were randomised to a physical activity group (≥150 minutes moderate intensity activity/week) or a waiting list control group. The principal outcome was Insomnia Severity Index (ISI) change 6 months post baseline; secondary outcomes were anxiety (using the State Trait Anxiety Inventory) and depression (Beck Depression Inventory II). Physical activity was assessed using Actigraph GTX3+ accelerometers. Outcomes were assessed in univariate general linear models, adjusted for baseline confounders. Activity and sleep assessments did not differ at baseline. At 6 months post baseline the intervention group engaged in 213 min/week of moderate intensity PA, compared to the control group (82 min/week). Compared to the control group, the intervention group showed significant improvement in the ISI score at 6 months F(1,28) = 5.16, p=0.03), adjusted means difference = 3.37, with an adjusted Cohen's d =.78 (95% CI 0.10 1.45). There was a significant improvement in trait anxiety, and depression outcomes post-intervention, F(6,28)=4.41, p=0.05, and F(6,28)=5.61, p=0.02, respectively. The results showed that increasing activity in line with current guidelines could deliver clinically significant improvements in sleep quality and mood outcomes among inactive adults with insomnia. While the effect sizes are modest, the pattern of results reported here allow for two conclusions with clear implications for public health: 1) measures to increase levels of physical activity above the currently recommended threshold of 150 minutes per week could usefully be added to other approaches to insomnia management; and 2) the likelihood of improved sleep quality should be routinely added to those evidence-based cardiovascular and metabolic benefits most frequently associated with increased physical activity in behaviour change initiatives.