br week and moderate high PA participation in br
week and moderate/high PA participation in
PA ≥two times per week. On the right side
PA ≤three times per week and moderate/high
PA participation in PA ≥ four times per week.
The specific objectives of the present study were to assess whether aerobic PA is associated with diurnal and reactive LY3009120 patterns, and whether the association between aerobic PA and cortisol patterns dif-fered between women with and without a history of BC. In regards to our first objective, our hypothesis that women who engaged in aerobic PA more frequently (moderate/high PA group) would exhibit sig-nificantly less abnormalities in their cortisol patterns than those who engaged in aerobic PA less frequently or not at all (no/low PA group) was not supported as diurnal and reactive cortisol patterns did not diﬀer statistically across aerobic PA groups. In regards to our second objective, a marginally significant (p = .05) cancer experience by aerobic PA interaction was observed when analyzing diurnal cortisol data suggesting that women without a history of BC who engaged in aerobic PA more frequently (moderate/high PA group) had a lower cortisol level at awakening and 30 min after awakening than women with a history of BC. Moreover, the association between aerobic PA and reactive cortisol patterns appeared to diﬀer statistically based on wo-men’s cancer experience (i.e., history vs. no history of BC) when using the PA1 cutoﬀ, whereby women without a history of BC had a sig-nificantly higher overall cortisol reactivity to an acute stressor (both in terms of AUCi and time point fluctuations) than women with a history of BC.
Others have also failed to detect a significant association between PA and cortisol patterns, regardless of history of cancer.25,50 For ex-ample, similar to our findings, Payne et al.25 did not find diﬀerences in diurnal cortisol levels between women in an exercise group comprised of home-based walking compared to women in a usual care group during hormonal treatment for BC. Yet, the authors did observe a downward trend for women in the exercise group compared to the usual care group, suggesting that women exposed to the exercise in-tervention (n = 10) had lower overall cortisol levels than women in the
usual care group (n = 10). Nevertheless, the current evidence does not allow for conclusive inferences in favor of an association between PA and cortisol among women with a history of BC. It is possible that other factors or comorbid conditions may confound the association between PA and cortisol. First, cancer is often comorbid with several medication conditions that may impair cortisol regulation,32–34 thus decreasing the eﬀect of PA on cortisol regulation especially in those who experience severe medical conditions. Second, recent findings suggest that poor sleep may have powerful eﬀects on the immune function and that it is a risk factor for impaired cortisol regulation.51,52 Accordingly, as in-somnia is common among women with a history of BC,53,54 in-flammatory responses to sleep deprivation may represent one me-chanism aﬀecting the association between PA and cortisol. Third, the biological mechanisms underlying the observed association between PA and cortisol in the general population are unclear.40,41 It may be that alterations in hormonal responses caused by BC treatment compromise the beneficial eﬀect of PA on cortisol among women with a history of BC. Thus, further research should include the simultaneous inclusion of a number of covariates known to be related to both PA and cortisol regulation.
It is important to note that our study, similar to others,40 falls short of measuring PA parameters that may be implicated in the PA-cortisol association. Indeed, our PA measure was intended to provide an index of the total frequency of cardiovascular activities that raises a person’s heart rate, but it lacks sensitivity to test whether intensity (e.g., light, moderate, vs. vigorous), duration (e.g., shorter long and continuous vs. short intervals), type (e.g., aerobic vs. anaerobic), context (e.g., indoors vs. outdoors or individual vs. group-based), and/or time of day mod-erates the association between PA and cortisol among women. For in-stance, many studies have suggested that increases in circulating cor-tisol levels are relatively proportional to PA intensity whereby a minimum intensity (i.e., threshold) is required in order to provoke a HPA response.55–57 As the PA variable in our study was self-reported,
M. Lambert et al.
we had no way to precisely measure whether PA intensity went above thresholds required to influence inflammatory responses. Moreover, other behavioural variables such sleep, sedentary time, fitness status, and food/beverage intake that may alter cortisol responses to PA58–61 were also not considered (either due to limitations in sample size or because data were not collected). Future studies with direct assessments of PA (e.g., actigraphy) and more detailed PA questionnaires are needed, as well as better control for PA parameters and behavioural factors that could influence the association between PA and cortisol before firm conclusions can be made. Nevertheless, the eﬀect sizes (based on the partial eta2 values) in this study suggest that there is an association between aerobic PA frequency and cortisol patterns among women, which is critical as cortisol dysregulation is central to the etiology of several chronic conditions23,30,31 and it would be valuable to determine which specific aspects of PA can be promoted to prevent this dysregulation. Over the years, researchers and statisticians have high-lighted the importance of the use of eﬀect sizes and explained why reporting p-values alone might not be enough in order to truly under-stand the results of a study.62–66 Unlike p-values, eﬀect sizes are not impacted by sample size and oﬀer readers a quantitative index of the magnitude of the diﬀerence between groups. In the context of this study, consideration of the eﬀect sizes in tandem with p-values give primordial interpretive information about the results that are not con-founded with sample size. For that reason, we cannot discount the possibility that PA may still represent a protective factor for cortisol regulation and with a larger sample size, significant results might have emerged.67