Timing Matters: Time of Day Impacts the Ergogenic Effects of Caffeine-A Narrative Review.

Caffeine has attracted significant attention from researchers in the sports field due to its well-documented ergogenic effects across various athletic disciplines. As research on caffeine continues to progress, there has been a growing emphasis on evaluating caffeine dosage and administration methods. However, investigations into the optimal timing of caffeine intake remain limited. Therefore, this narrative review aimed to assess the ergogenic effects of caffeine administration at different times during the morning (06:00 to 10:00) and evening (16:00 to 21:00). The review findings suggest that circadian rhythms play a substantial role in influencing sports performance, potentially contributing to a decline in morning performance. Caffeine administration has demonstrated effectiveness in mitigating this phenomenon, resulting in ergogenic effects and performance enhancement, even comparable to nighttime levels. While the specific mechanisms by which caffeine regulates circadian rhythms and influences sports performance remain unclear, this review also explores the mechanisms underlying caffeine's ergogenic effects, including the adenosine receptor blockade, increased muscle calcium release, and modulation of catecholamines. Additionally, the narrative review underscores caffeine's indirect impact on circadian rhythms by enhancing responsiveness to light-induced phase shifts. Although the precise mechanisms through which caffeine improves morning performance declines via circadian rhythm regulation necessitate further investigations, it is noteworthy that the timing of caffeine administration significantly affects its ergogenic effects during exercise. This emphasizes the importance of considering caffeine intake timing in future research endeavors to optimize its ergogenic potential and elucidate its mechanisms.

A longitudinal study of factors associated with cognitive frailty in middle-aged and elderly population based on the health ecology model.

BACKGROUND: Cognitive frailty (CF) is an important geriatric syndrome and is reversible. It is crucial to develop preventive interventions for CF. We aimed to explore the associations between CF and its associated factors in Chinese aged 45 years and above. METHODS: Based on the available data of 3 waves in China Health and Retirement Longitudinal Study from 2011 to 2015, 16,071 individuals aged 45 years and above from 3 waves were included. Based on the health ecology model, the associated factors were classified as downstream, midstream and upstream factors. Generalized hierarchical linear model including time level, individual level, and province level was applied to analyze the associations between factors and CF. RESULTS: Multilevel factors have different effects on physical and cognitive function. In the downstream, old age, female, underweight, chronic diseases, and depression were risk factors of reversible CF and potentially reversible CF, and overweight was their protective factor. In the midstream, short or long night sleep duration was their risk factor, and > 30 and ≤ 60 min afternoon naps, alcohol drinking, and participation in social activities were their protective factors. In the upstream, living in rural areas was their risk factor, and high educational level, household consumption and GDP per capita were their protective factors. CONCLUSIONS: Physical function and cognitive function are affected differently by multiple factors. The occurrence and development of physical frailty and cognitive impairment may have some common mechanisms. CF can be influenced by multilevel factors, and multilevel and comprehensive management of CF should be achieved. KEY POINTS: Cognitive frailty was correlated with multilevel factors, including downstream, midstream, and upstream factors. It is crucial to focus on individual interventions such as physiological factors, psychological factors and health behaviors, especially the elderly, women and those with depression. Socioeconomic status was associated with the lower prevalence of cognitive frailty.