Chronobiology of Exercise: Evaluating the Best Time to Exercise for Greater Cardiovascular and Metabolic Benefits.

Physiological function fluctuates across 24 h due to ongoing daily patterns of behaviors and environmental changes, including the sleep/wake, rest/activity, light/dark, and daily temperature cycles. The internal circadian system prepares the body for these anticipated behavioral and environmental changes, helping to orchestrate optimal cardiovascular and metabolic responses to these daily changes. In addition, circadian disruption, caused principally by exposure to artificial light at night (e.g., as occurs with night-shift work), increases the risk for both cardiovascular and metabolic morbidity and mortality. Regular exercise is a countermeasure against cardiovascular and metabolic risk, and recent findings suggest that the cardiovascular benefits on blood pressure and autonomic control are greater with evening exercise compared to morning exercise. Moreover, exercise can also reset the timing of the circadian system, which raises the possibility that appropriate timing of exercise could be used to counteract circadian disruption. This article introduces the overall functional relevance of the human circadian system and presents the evidence surrounding the concepts that the time of day that exercise is performed can modulate the cardiovascular and metabolic benefits. Further work is needed to establish exercise as a tool to appropriately reset the circadian system following circadian misalignment to preserve cardiovascular and metabolic health. © 2022 American Physiological Society. Compr Physiol 12:3621-3639, 2022.

Cardiac autonomic control during non-REM and REM sleep stages in paediatric patients with Prader-Willi syndrome.

Cardiac death is the second most prevalent cause in Prader-Willi syndrome (PWS). Paediatric patients with PWS often present cardiac autonomic dysfunction during wakefulness, obesity and sleep-disordered breathing. However, the extent of cardiac autonomic modulation during sleep in PWS has not been documented. The objective of this study was to assess alterations in cardiac autonomic modulation of paediatric patients with PWS during different sleep stages. Thirty-nine participants in three groups: 14 PWS, 13 sex and age-matched lean controls (LG) and 12 obese-matched controls (OB). All participants underwent overnight polysomnography, including continuous electrocardiogram recordings. Heart rate variability (HRV) was analysed during representative periods of each sleep stage through time and frequency domains calculated across 5-min periods. Between-within ANOVAs were employed (p < .05). The results show that total HRV was lower in PWS than OB and LG during slow-wave sleep (SWS) (standard deviation of all NN intervals [SDNN] ms, p = .006). Parasympathetic modulation assessed by time-domain analysis was lower during SWS in PWS compared to both OB and LG (square root of the mean of the sum of the squares of differences between adjacent NN intervals [RMSSD] ms, p = .004; SDSD, standard deviation of differences between adjacent NN intervals [SDSD] ms, p = .02; number of adjacent NN intervals differing by >50 ms [NN50] ms, p = .03; proportion of adjacent NN intervals differing by >50 ms [pNN50] ms, p = .01). Sympathovagal balance assessed by frequency-domain analysis was lower during both N2 and SWS than during the rapid eye movement (REM) sleep stage, but not different among groups. In conclusion, this group of paediatric patients with PWS had impaired cardiac autonomic balance due to reduced parasympathetic modulation during SWS. This result could imply an underlying increased cardiovascular risk in PWS even during early age and independent of obesity.

The prevalence and correlates of subclinical atherosclerosis among adults with low-density lipoprotein cholesterol <70 mg/dL: The Multi-Ethnic Study of Atherosclerosis (MESA) and Brazilian Longitudinal Study of Adult Health (ELSA-Brasil).

BACKGROUND AND AIMS: The prevalence and correlates of subclinical atherosclerosis when low-density lipoprotein cholesterol (LDL-C) levels are low remain unclear. Therefore, we examined the association of cardiovascular risk factors and subclinical atherosclerosis among individuals with untreated LDL-C <70 mg/dL. METHODS: We included participants from the Multi-Ethnic Study of Atherosclerosis (MESA) and the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) cohorts. To optimize accuracy, LDL-C was calculated by the validated Martin/Hopkins equation that uses an adjustable factor for the ratio of triglycerides to very low-density lipoprotein cholesterol. We defined subclinical atherosclerosis as a coronary artery calcium (CAC) score >0 in the combined cohort or common carotid intima media thickness (cIMT) in the 4th quartile, using cohort-specific cIMT distributions at baseline. Logistic regression models examined the cross-sectional associations of cardiovascular risk factors and subclinical atherosclerosis. RESULTS: Among 9411 participants not on lipid lowering therapy, 263 (3%) had LDL-C <70 mg/dL (MESA: 206, ELSA: 57). Mean age in this population was 58 (SD 12) years, with 43% men, and 41% Black. The prevalence of CAC >0 in those with untreated LDL-C<70 mg/dL was 30%, and 18% were in 4th quartile of cIMT. In demographically adjusted models, only ever smoking was significantly associated with both CAC and cIMT. Similar results were obtained in risk factor-adjusted models (smoking: OR, 2.29; 95% CI, 1.10-4.80 and OR, 3.44; 95% CI, 1.41-8.37 for CAC and cIMT, respectively). CONCLUSIONS: Among middle-aged to older individuals with untreated LDL-C <70 mg/dL, subclinical atherosclerosis remains moderately common and is associated with cigarette smoking.

Educational Inequalities in Cardiovascular Risk Factor and Blood Pressure Control in the Elderly: Comparison of MESA Cohort and Chilean NHS Survey Outcome Measures.

BACKGROUND: Social determinants differ between countries, which is not always considered when adapting health policies and interventions to face inequalities in noncommunicable diseases and their risk factors. OBJECTIVES: The study sought to analyze educational inequalities in controlled blood pressure (CBP), obesity, and smoking in study populations from Chile and the United States in 2 periods, both countries with large social inequalities. METHODS: The study used data from the first and fifth waves of the MESA (Multiethnic Study of Atherosclerosis) cohort, and the 2003 and 2009 to 2010 Chilean National Health Survey (CNHS) survey outcome measures. The study compared cardiovascular risk factors prevalence as well as relative index of inequality (RII) and slope index of inequality (SII) between the 2 samples. RESULTS: In the CNHS 67.9% and 52.6% of participants had below primary education in 2003 and 2009 to 2010, respectively, compared with 12.3% and 8.1% in the first and fifth waves of the MESA study, respectively. Smoking prevalence was higher and increased in the CNHS compared with the MESA study, concentrated in better-educated women in both years (RII: 0.34; 95% confidence interval [CI]: 0.17 to 0.68; and RII: 0.55; 95% CI: 0.34 to 0.89, respectively). In contrast, smoking decreased over time in the MESA study in all socioeconomic strata, although relative inequalities increased in both sexes (for women, RII: 2.32; 95% CI 1.36 to 3.97; for men, RII: 3.34; 95% CI 2.04 to 5.47). CBP prevalence in both periods was higher in the first and fifth waves of the MESA study (69.7% and 80.2%) compared with the 2003 and 2009 to 2010 CNHS samples (34.2% and 52.3%), but only for the MESA study RII, favoring the better educated, was it significant in both periods and sexes. Obesity inequalities for Chilean women decreased slightly between 2003 and 2009 as prevalence grew in the most educated (RII: 2.21 to 1.68; SII: 0.29 to 0.22, respectively); conversely, they increased for both sexes in the MESA study. CONCLUSIONS: The study findings confirm that patterns and trends in prevalence, and absolute and relative inequalities vary by country, suggesting that context and cultural issues matters.