The Impact of Dietary Factors on the Sleep of Athletically Trained Populations: A Systematic Review

Common questions and misconceptions about caffeine supplementation: what does the scientific evidence really show?

Caffeine is a popular ergogenic aid that has a plethora of evidence highlighting its positive effects. A Google Scholar search using the keywords "caffeine" and "exercise" yields over 200,000 results, emphasizing the extensive research on this topic. However, despite the vast amount of available data, it is intriguing that uncertainties persist regarding the effectiveness and safety of caffeine. These include but are not limited to: 1. Does caffeine dehydrate you at rest? 2. Does caffeine dehydrate you during exercise? 3. Does caffeine promote the loss of body fat? 4. Does habitual caffeine consumption influence the performance response to acute caffeine supplementation? 5. Does caffeine affect upper vs. lower body performance/strength differently? 6. Is there a relationship between caffeine and depression? 7. Can too much caffeine kill you? 8. Are there sex differences regarding caffeine's effects? 9. Does caffeine work for everyone? 10. Does caffeine cause heart problems? 11. Does caffeine promote the loss of bone mineral? 12. Should pregnant women avoid caffeine? 13. Is caffeine addictive? 14. Does waiting 1.5-2.0 hours after waking to consume caffeine help you avoid the afternoon "crash?" To answer these questions, we performed an evidence-based scientific evaluation of the literature regarding caffeine supplementation.

Alpha-lactalbumin and sleep: A systematic review

Insufficient sleep is a growing global problem, with poor sleep associated with many negative health and performance outcomes. Previous reviews investigating the effect of diet on sleep have highlighted the amino acid tryptophan as a promising sleep-promoting nutrient, with the richest food source of tryptophan, ⍺-lactalbumin, requiring further investigation. Therefore, this systematic review aimed to review the existing evidence of association between ⍺-lactalbumin and sleep. Four electronic databases (CINAHL Complete, Embase, MEDLINE Complete, and SPORTDiscus with Full Text) were searched from database inception to March 2023, with primary research articles included if they contained α-lactalbumin as an independent variable, an outcome measure of sleep or sleepiness, and participants were ≥ 18 years old. Eight studies were reviewed, with four studies recruiting athletic populations (50%) and four recruiting healthy participants (50%). Sleep or sleepiness was measured objectively in six studies (75%), with two studies employing polysomnography and four utilizing actigraphy to assess sleep. Across the studies, 20-60 g of ⍺-lactalbumin was supplemented, with five studies (63%) observing a positive association between α-lactalbumin and sleep. Sleep-onset latency was the primary sleep metric improved following evening supplementation of α-lactalbumin (≤ 3.5 hr pre-sleep), with no studies observing any negative associations with sleep. Data from this review suggest that individuals that have difficulty initiating sleep may benefit most from pre-sleep α-lactalbumin supplementation. Further research is required to establish the effect that α-lactalbumin has on sleep architecture, through the use of more comprehensive sleep analysis tools such as portable electroencephalography or polysomnography, in combination with stringent dietary controls.

Sleep and circadian hygiene practices association with sleep quality among Brazilian adults

Objective

To investigate the association of sleep and circadian hygiene practices (sleep-promoting and sleep-disturbing behaviors) with sleep quality indicators.

Methods

Participants (n = 2050; 18-65 y) were part of virtual population-based research. Logistic regression models were fitted to assess differences in the OR (95% CI) of poor quality with sleep-promoting/disturbing practices (time-of-day of exercise, pre-bedtime routine, naps, electronic devices with illuminated screens, caffeine and alcohol consumption, and smoking). Linear regression analyses evaluated differences in sleep duration, latency, and awakenings associated with the same variables. Restricted cubic splines were used to study the shape of the association of screen time before bed with sleep duration, latency, and awakenings. Analyses were adjusted for age, sex, region, marital status, educational level, evening diet quality, and BMI.

Results

Evening use of electronic devices with illuminated screens showed a negative effect on all sleep parameters. Reporting dinner as the largest meal and evening caffeine consumption was associated with shorter sleep duration and longer sleep latency. Smokers had higher odds of longer latency. A protective effect of morning exercises was demonstrated on sleep quality, latency, and awakenings. Alcohol consumers presented lower odds of poor quality and lower frequency of awakenings. Pre-bedtime practices showed no or negative effect on sleep outcomes.

Conclusions

Recommendations to promote sleep quality and prevent sleep-related problems, with corresponding circadian health benefits, should include engaging in regular exercise, preferably in the morning, and avoiding naps, heavy meals close to bedtime, caffeine, smoking, and evening screen exposure.