Caffeine and diuresis during rest and exercise: A meta-analysis

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.

Causal associations between 45 dietary intake habits and urolithiasis: insights from genetic studies

Background

Different dietary habits can have varying effects on human health and metabolism, and these can be intervened and regulated. Kidney stones, as a disease caused by multiple factors, are largely attributed to diet and metabolism, but the potential causal relationship with dietary intake habits remains unclear. Therefore, this study aims to link the predicted dietary intake based on 45 genetic factors with urolithiasis and explore the potential causal relationship.

Methods

We extracted complete genome-wide association studies (GWASs) data on 45 dietary intake traits from the UK Biobank study. Data on kidney stones were obtained from the FinnGen database. In both univariable and multivariable Mendelian randomization analyses, we used inverse variance weighted (IVW) as the primary method to calculate P values, odds ratios (ORs), and 95% confidence intervals (CIs). We examined result heterogeneity using Cochran's Q test. We also carefully investigated potential sources of horizontal pleiotropy using the Mendelian randomization (MR)-PRESSO and MR-Egger methods, and conducted linkage disequilibrium score regression (LDSC) analysis on the corrected P values.

Results

Through univariable analysis, we identified 11 dietary habits that potentially causally associate with kidney stones among the 45 examined traits, including 9 protective factors and 2 risk factors. Based on the corrected results with false discovery rate (FDR) and sensitivity analysis, we found one relatively robust evidence. We controlled for common stone risk factors, such as body mass index and smoking, as confounders in multivariable analysis, and no significant results were observed after controlling for these confounders. Based on the LDSC analysis, most of the evidence supports significant genetic correlations with urolithiasis among the 11 traits with potential causal associations.

Conclusions

This study confirms the impact of certain dietary factors on the development of kidney stones. Our findings contribute to providing evidence for dietary adjustments in daily life or dietary guidance specifically targeting kidney stone patients.

Compositional Aspects of Beverages Designed to Promote Hydration Before, During, and After Exercise: Concepts Revisited

Hypohydration can impair aerobic performance and deteriorate cognitive function during exercise. To minimize hypohydration, athletes are recommended to commence exercise at least euhydrated, ingest fluids containing sodium during long-duration and/or high-intensity exercise to prevent body mass loss over 2% and maintain elevated plasma osmolality, and rapidly restore and retain fluid and electrolyte homeostasis before a second exercise session. To achieve these goals, the compositions of the fluids consumed are key; however, it remains unclear what can be considered an optimal formulation for a hydration beverage in different settings. While carbohydrate-electrolyte solutions such as sports drinks have been extensively explored as a source of carbohydrates to meet fuel demands during intense and long-duration exercise, these formulas might not be ideal in situations where fluid and electrolyte balance is impaired, such as practicing exercise in the heat. Alternately, hypotonic compositions consisting of moderate to high levels of electrolytes (i.e., ≥45 mmol/L), mainly sodium, combined with low amounts of carbohydrates (i.e., <6%) might be useful to accelerate intestinal water absorption, maintain plasma volume and osmolality during exercise, and improve fluid retention during recovery. Future studies should compare hypotonic formulas and sports drinks in different exercise settings, evaluating different levels of sodium and/or other electrolytes, blends of carbohydrates, and novel ingredients for addressing hydration and rehydration before, during, and after exercise.

International society of sports nutrition position stand: coffee and sports performance

Based on review and critical analysis of the literature regarding the contents and physiological effects of coffee related to physical and cognitive performance conducted by experts in the field and selected members of the International Society of Sports Nutrition (ISSN), the following conclusions represent the official Position of the Society:(1) Coffee is a complex matrix of hundreds of compounds. These are consumed with broad variability based upon serving size, bean type (e.g. common Arabica vs. Robusta), and brew method (water temperature, roasting method, grind size, time, and equipment).(2) Coffee's constituents, including but not limited to caffeine, have neuromuscular, antioxidant, endocrine, cognitive, and metabolic (e.g. glucose disposal and vasodilation) effects that impact exercise performance and recovery.(3) Coffee's physiologic effects are influenced by dose, timing, habituation to a small degree (to coffee or caffeine), nutrigenetics, and potentially by gut microbiota differences, sex, and training status.(4) Coffee and/or its components improve performance across a temporal range of activities from reaction time, through brief power exercises, and into the aerobic time frame in most but not all studies. These broad and varied effects have been demonstrated in men (mostly) and in women, with effects that can differ from caffeine ingestion, per se. More research is needed.(5) Optimal dosing and timing are approximately two to four cups (approximately 473-946 ml or 16-32 oz.) of typical hot-brewed or reconstituted instant coffee (depending on individual sensitivity and body size), providing a caffeine equivalent of 3-6 mg/kg (among other components such as chlorogenic acids at approximately 100-400 mg per cup) 60 min prior to exercise.(6) Coffee has a history of controversy regarding side effects but is generally considered safe and beneficial for healthy, exercising individuals in the dose range above.(7) Coffee can serve as a vehicle for other dietary supplements, and it can interact with nutrients in other foods.(8) A dearth of literature exists examining coffee-specific ergogenic and recovery effects, as well as variability in the operational definition of "coffee," making conclusions more challenging than when examining caffeine in its many other forms of delivery (capsules, energy drinks, "pre-workout" powders, gum, etc.).

TFOS lifestyle: Impact of societal challenges on the ocular surface

Societal factors associated with ocular surface diseases were mapped using a framework to characterize the relationship between the individual, their health and environment. The impact of the COVID-19 pandemic and mitigating factors on ocular surface diseases were considered in a systematic review. Age and sex effects were generally well-characterized for inflammatory, infectious, autoimmune and trauma-related conditions. Sex and gender, through biological, socio-economic, and cultural factors impact the prevalence and severity of disease, access to, and use of, care. Genetic factors, race, smoking and co-morbidities are generally well characterized, with interdependencies with geographical, employment and socioeconomic factors. Living and working conditions include employment, education, water and sanitation, poverty and socioeconomic class. Employment type and hobbies are associated with eye trauma and burns. Regional, global socio-economic, cultural and environmental conditions, include remoteness, geography, seasonality, availability of and access to services. Violence associated with war, acid attacks and domestic violence are associated with traumatic injuries. The impacts of conflict, pandemic and climate are exacerbated by decreased food security, access to health services and workers. Digital technology can impact diseases through physical and mental health effects and access to health information and services. The COVID-19 pandemic and related mitigating strategies are mostly associated with an increased risk of developing new or worsening existing ocular surface diseases. Societal factors impact the type and severity of ocular surface diseases, although there is considerable interdependence between factors. The overlay of the digital environment, natural disasters, conflict and the pandemic have modified access to services in some regions.

Water intake, hydration status and 2-year changes in cognitive performance: a prospective cohort study

BACKGROUND

Water intake and hydration status have been suggested to impact cognition; however, longitudinal evidence is limited and often inconsistent. This study aimed to longitudinally assess the association between hydration status and water intake based on current recommendations, with changes in cognition in an older Spanish population at high cardiovascular disease risk.

METHODS

A prospective analysis was conducted of a cohort of 1957 adults (aged 55-75) with overweight/obesity (BMI between ≥ 27 and < 40 kg/m²) and metabolic syndrome from the PREDIMED-Plus study. Participants had completed bloodwork and validated, semiquantitative beverage and food frequency questionnaires at baseline, as well as an extensive neuropsychological battery of 8 validated tests at baseline and 2 years of follow-up. Hydration status was determined by serum osmolarity calculation and categorized as < 295 mmol/L (hydrated), 295-299.9 mmol/L (impending dehydration), and ≥ 300 mmol/L (dehydrated). Water intake was assessed as total drinking water intake and total water intake from food and beverages and according to EFSA recommendations. Global cognitive function was determined as a composite z-score summarizing individual participant results from all neuropsychological tests. Multivariable linear regression models were fitted to assess the associations between baseline hydration status and fluid intake, continuously and categorically, with 2-year changes in cognitive performance.

RESULTS

The mean baseline daily total water intake was 2871 ± 676 mL/day (2889 ± 677 mL/day in men; 2854 ± 674 mL/day in women), and 80.2% of participants met the ESFA reference values for an adequate intake. Serum osmolarity (mean 298 ± 24 mmol/L, range 263 to 347 mmol/L) indicated that 56% of participants were physiologically dehydrated. Lower physiological hydration status (i.e., greater serum osmolarity) was associated with a greater decline in global cognitive function z-score over a 2-year period (β: - 0.010; 95% CI - 0.017 to - 0.004, p-value = 0.002). No significant associations were observed between water intake from beverages and/or foods with 2-year changes in global cognitive function.

CONCLUSIONS

Reduced physiological hydration status was associated with greater reductions in global cognitive function over a 2-year period in older adults with metabolic syndrome and overweight or obesity. Future research assessing the impact of hydration on cognitive performance over a longer duration is needed.

TRIAL REGISTRATION

International Standard Randomized Controlled Trial Registry, ISRCTN89898870. Retrospectively registered on 24 July 2014.

The association between caffeine intake and risk of kidney stones: A population-based study

Background

Although many studies have proven the beneficial effects of caffeine on human health, the association between caffeine intake and the risk of kidney stones is limited in large epidemiologic studies.

Objectives

We aimed to investigate the association between caffeine intake and the risk of kidney stones.

Methods

A total of 30,716 participants (with weight numbers of 204, 189, and 886) with a history of kidney stone were included in this analysis. All data were survey-weighted, and corresponding logistic regression models were performed to examine the associations between caffeine intake and the risk of kidney stones.

Results

In a fully adjusted model, a per-quartile increase in caffeine intake was associated with a 5.32% decreased risk of kidney stones. In the subgroup analysis, the multivariate-adjusted odds ratios (95% confidence intervals) of the risk of kidney stones for per-quartile increments in caffeine intake were 0.9650 (0.9643, 0.9656) for men, 0.9320 (0.9313, 0.9327) for women, 0.9384 (0.9378, 0.9389) for white race individuals, 1.0281 (1.0270, 1.0292) for nonwhite race individuals, 0.9460 (0.9455, 0.9465) for overweight/obese individuals, and 0.9314 (0.9303, 0.9324) for non-overweight individuals, 0.9100 (0.9094, 0.9105) for caffeine from coffee, and 1.0021 (1.0013, 1.0029) for caffeine from non-coffee sources.

Conclusion

Caffeine intake was negatively associated with the risk of kidney stones. In subgroup analyses, the negative association of caffeine with kidney stone risk was only found in white individuals. In addition, the decreased risk was found higher in women and non-overweight individuals. Especially for women, white individuals and non-overweight individuals. The protective effect of caffeine intake from coffee on stone formation was more significant than that of caffeine from non-coffee sources.

Subjective Effects of Modafinil in Military Fighter Pilots During Deployment

INTRODUCTION: Fatigue has negative effects on flight safety, especially in military aviation, where missions are often performed under challenging conditions. Modafinil is a relatively new pharmaceutical able to counter the symptoms of fatigue, but efficacy has not yet been studied in operational military aviation. This study aims to establish effectiveness and safety of modafinil in military operations. METHODS: This field study was conducted during deployment in the Middle East by the Royal Netherlands Air Force fighter pilots. Prior to use operationally, pilots had to complete a 24-h ground test in which modafinil was administered during a nonflying period using a questionnaire to screen for duty-relevant side effects. If no side effects were reported, operational usage was allowed. In addition to registration of modafinil's effects, relevant data prior to and after administration were recorded, including caffeine consumption and sleep afterwards. RESULTS: Of the 75 pilots who completed ground testing, only one experienced duty-relevant side effects. Modafinil was used in 192 operational flights, mostly during night-time. In 128 (67%) of the flights, modafinil was used preventively, in 64 (33%) because of fatigue. In 182 (95%) of the flights, positive effects of modafinil were reported, with a maximum effect 2-3 h after administration. There was no statistical correlation between modafinil's beneficial effects and prior administration of caffeine or sleep medication, nor was sleep afterwards negatively affected. DISCUSSION: This study indicates modafinil is a suitable pharmaceutical countermeasure to minimize the effects of fatigue during real-life fighter operations, without signs of negative impact on flight safety or sleep quality afterwards.Wingelaar-Jagt YQ, Wingelaar TT, Riedel WJ, Ramaekers JG. Subjective effects of modafinil in military fighter pilots during deployment. Aerosp Med Hum Perform. 2022; 93(10):739–745.

Diuretics: a contemporary pharmacological classification?

Diuretics are drugs that increase the flow of urine. They are commonly used to treat edema, hypertension, and heart failure. Typically, the pharmacological group consists of five classes: thiazide diuretics, loop diuretics, potassium-sparing diuretics, osmotic diuretics, and carbonic anhydrase inhibitors. This traditional classification and the nomenclature of diuretics have not changed over the last decades, which means that it was not adapted to current pharmacological research. Modern approaches in the field of pharmacological nomenclature suggest the introduction of mechanism-based drug class designations, which is not yet reflected in the group of diuretics. Moreover, included drug classes have lost their relevance as diuretic agents. Carbonic anhydrase inhibitors, for example, are mainly used in the treatment of glaucoma. Newer agents such as vasopressin-2 receptor antagonists or SGLT2 inhibitors possess diuretic properties but are not included in the pharmacological group. This review discusses the currentness of the pharmacological classification of diuretics. We elaborate changes in the field of nomenclature, the contemporary medical use of classical diuretics, and new diuretic agents.

The Inverted U-Shaped Association of Caffeine Intake with Serum Uric Acid in U.S. Adults

BACKGROUND AND AIMS

Caffeine is a worldwide popularly consumed constituent in foods that can exert physiological effects. However, previous researches about the relationship between caffeine intake and serum uric acid (SUA) were limited and controversial. Therefore, we sought to investigate that relationship in U.S. adults.

METHODS

In this cross-sectional study, the total sample of 7888 selected participants (3838 males and 4050 females) were identified from the National Health and Nutritional Examination Surveys (NHANES) 2015-2018. All subjects were tested for serum uric acid levels (μmmol/L), and their daily caffeine intakes (mg/d) were obtained by an average of two 24-hour dietary recalls. Multivariate linear regression models were used to evaluate the association between two variables in total subjects and subgroup analyses. Generalized additive models with smooth curve fittings were also performed.

RESULTS

Multivariate regression analyses showed caffeine intake was negatively correlated with SUA after adjustment of other confounders. The subgroup analyses stratified by gender showed the negative correlation of caffeine intake with SUA was statistically significant in males but not in females. Furthermore, we observed a nonlinear inverse association of caffeine intake with SUA (P nonlinear <0.001) in the generalized additive model, followed by an inverted U-shaped curve (inflection point: 60.5mg/d) for all participants. This inverted U-shaped relationship between them could also be found in both genders, individuals aged below 60 years old, overweight (BMI of 25 to 30), and Non-Hispanic White individuals.

CONCLUSIONS

This study indicated that caffeine intake exhibited an inverse correlation with SUA, especially in males. In addition, this inverse relationship was nonlinear, which followed an inverted U-shaped curve.

Water Security and Nutrition: Current Knowledge and Research Opportunities

Water is an essential nutrient that has primarily been considered in terms of its physiological necessity. But reliable access to water in sufficient quantities and quality is also critical for many nutrition-related behaviors and activities, including growing and cooking diverse foods. Given growing challenges to water availability and safety, including climate change, pollution, and infrastructure degradation, a broader conceptualization of water and its diverse uses is needed to sustainably achieve global nutrition targets. Therefore, we review empirical and qualitative evidence describing the linkages between water security (the reliable availability, accessibility, and quality of water for all household uses) and nutrition. Primary linkages include water security for drinking, food production and preparation, infant and young child feeding, and limiting exposure to pathogens and environmental toxins. We then identify knowledge gaps within each linkage and propose a research agenda for studying water security and nutrition going forward, including the concurrent quantification of both food and water availability, accessibility, use, and stability. By making explicit the connections between water security and nutritional well-being, we aim to promote greater collaboration between the nutrition and water, sanitation, and hygiene sectors. Interdisciplinary policies and programs that holistically address the water-nutrition nexus, versus those that focus on water and nutrition independently, are likely to significantly advance our ability to ensure equitable access to healthy foods and safe water for all.

Effects of Caffeine and Caffeinated Beverages in Children, Adolescents and Young Adults: Short Review

The prevalence of ED consumption has increased over the past 10–15 years. Studies describing the effects of caffeine and caffeinated beverages show confusing results, so it seems important to regularly summarize the available facts, and in more detail. By a thorough analysis of more than 156 scientific papers, the authors describe the molecular background of absorption, as well as the positive and negative effects of different dosages of caffeine, just like its effects in physical activity and performance. ED and EDwA consumption is a regular habit of not only adults, but nowadays even of children and adolescents. There are no safe dosages described of caffeine or ED consumption for children. There are no positive short- or long-term effects of these compounds/products concerning developing brain functions, psycho-motor functions, or social development. Instead, there are many unpleasant side effects, and symptoms of regular or higher-dose ED consumption, especially at younger ages. This mini review describes many details of these unpleasant side effects, their severity, and motivations for consuming these compounds/products. In a quantitative research in Hungary (10–26 years, mean age: 15.6 ± 3.8 y, 1459 subjects, randomly chosen population), a survey based on a questionnaire asking people about their ED consumption habits was conducted. According to the data, 81.8% of the participants consumed EDs at least once, and 63.3% tried several products of the kind. A positive correlation was found between age and consumption (p < 0.001). The results show that a high proportion of this group often consumed EDwA, in many cases leading to harmful side-effects of caffeine overdose. In a sample of Hungarian high school and college students (17–26 years), ED consumption matched the international data, and only 19.7% of respondents did not use EDs at all (had never tasted an ED in their life).

Portuguese Football Federation consensus statement 2020: nutrition and performance in football

Nutrition is an undeniable part of promoting health and performance among football (soccer) players. Nevertheless, nutritional strategies adopted in elite football can vary significantly depending on culture, habit and practical constraints and might not always be supported by scientific evidence. Therefore, a group of 28 Portuguese experts on sports nutrition, sports science and sports medicine sought to discuss current practices in the elite football landscape and review the existing evidence on nutritional strategies to be applied when supporting football players. Starting from understanding football's physical and physiological demands, five different moments were identified: preparing to play, match-day, recovery after matches, between matches and during injury or rehabilitation periods. When applicable, specificities of nutritional support to young athletes and female players were also addressed. The result is a set of practical recommendations that gathered consensus among involved experts, highlighting carbohydrates periodisation, hydration and conscious use of dietary supplements.

Coffee Brews: Are They a Source of Macroelements in Human Nutrition?

Coffee brews, made by pouring water on coffee grounds or brewing in an espresso machine, are among the most popular beverages. The aim of this study was to summarize data on the content of macroelements (sodium, potassium, calcium, magnesium, and phosphorus) in coffee brews prepared with different methods, as well as to review the factors influencing the content of the elements. Studies from 2000 to 2020, published in the PubMed and Google Scholar databases, were reviewed. Taking into account the results presented by the authors, we calculated that one portion of coffee brew can cover 7.5% or 6.4% (for women and men) and 6.6% of the daily requirement for magnesium and potassium, respectively. Coffee provides slightly lower amounts of phosphorus (up to 2.2%), sodium (up to 2.2%), and calcium (up to 0.7% of the daily requirement for women and 0.6% for men). If coffee is drunk in the quantity of three to four cups, it can be an important source of magnesium, considering the risk of magnesium deficiency in modern societies.

The influence of coffee consumption on bioelectrical impedance parameters: a randomized, double-blind, cross-over trial

BACKGROUND

Bioelectrical impedance analysis (BIA) is a widely used method for estimating body composition. Avoiding foods/beverages containing caffeine is a frequently enforced pre-test protocol to ensure reliability of BIA measurements. However, few studies have evaluated whether this is necessary, with conflicting results. We aimed to determine whether the coffee consumption differing in caffeine content influences BIA parameters in healthy adults.

METHODS

Twenty-five healthy adults were enrolled in a randomized, double-blind cross-over trial. Three amounts of caffeine were given with 200 mL of coffee: 0 mg (11 g of decaffeinated), 200 mg (5.5 g of caffeinated plus 5.5 g of decaffeinated), and 400 mg of caffeine (11 g of caffeinated). BIA measurements were conducted at 6 different times, and coefficient variations (CV) explored.

RESULTS

No differences were observed for group × time interaction on impedance, resistance, or reactance (p > 0.05). Values of BIA parameters increased after 30-min of coffee consumption, independently of the caffeine dosage (all p < 0.001). Body fat percentage followed the same pattern and increased after 45-min (p < 0.05). Median CV for consecutive impedance, resistance, and reactance measurements were >95%CI of expected device measurement error over 70-min, without difference between groups. Urine output volume was not different between groups (decaffeinated: 440.45 ± 197.57 mL; 200 mg: 471.80 ± 171.88 mL; 400 mg: 489.30 ± 204.10 mL, p > 0.05).

CONCLUSION

Coffee consumption influenced BIA-derived results after 70-min but was not related to caffeine content, likely due to water intake.

High-fat diet and caffeine interact to modulate bone microstructure and biomechanics in mice

AIMS

Although excessive fat and caffeine intake are independent risk factors for bone microstructural and functional disturbances, their association remains overlooked. Thus, we investigated the impact of high-fat diet (HFD) and caffeine alone and combined on serum lipid profile, bone microstructure, micromineral distribution and biomechanical properties.

METHODS

Forty female C57BL/6 mice were randomized into 4 groups daily treated for seventeen weeks with standard diet (SD) or HFD (cafeteria diet) alone or combined with 50 mg/kg caffeine.

KEY FINDINGS

The association between HFD and caffeine reduced the weight gain compared to animals receiving HFD alone. Caffeine alone or combined with HFD increases total and HDL cholesterol circulating levels. HFD also reduced calcium, phosphorus and magnesium bone levels compared to the groups receiving SD, and this reduction was aggravated by caffeine coadministration. From biomechanical assays, HFD combined with caffeine increased bending strength and stiffness of tibia, a finding aligned with the marked microstructural remodeling of the cortical and cancellous bone in animals receiving this combination.

SIGNIFICANCE

Our findings indicated that HFD and caffeine interact to induce metabolic changes and bone microstructural remodeling, which are potentially related to bone biomechanical adaptations in response to HFD and caffeine coadministration.

The Effects of Caffeine on Voice: A Systematic Review

BACKGROUND

Caffeine is considered a dehydrating agent due to its diuretic effects and influences the body's fluid balance. The relationship between voice and hydration has been widely investigated and it is accepted that inadequate hydration has detrimental effects on phonation. Since dehydration negatively affects the vocal folds and caffeine is considered a dehydrating agent, it can be hypothesized that voice might be negatively affected by caffeine intake. This systematic review aims to summarize and appraise the available evidence regarding the effects of caffeine on voice.

METHODS

Randomized and non-randomized experimental studies of healthy participants were retrieved following an electronic searching of six databases in June 2020. No publication, language or date restrictions were applied. Data extraction of relevant data and risk of bias assessment was conducted independently by two reviewers.

RESULTS

Five non-randomized experimental studies were deemed eligible for inclusion. The format of the administered interventions in the included studies was either liquid (coffee) or solid (caffeine tablets). Reported outcome measures used to examine the effects of caffeine on phonation consisted of acoustic, aerodynamic and (auditory & self-) perceptual. No measures were adversely affected by caffeine consumption.

CONCLUSION

Clinicians commonly advise patients to refrain from caffeine, as caffeine intake increases diuresis with subsequent effects on fluid balance. Such imbalances can potentially induce dehydration which can be detrimental to phonation. This notion cannot be supported empirically, as the evidence is deemed unreliable and no firm conclusions can be elicited to guide clinical practice. The results of this review demonstrate the lack of research in the field and the necessity for future investigations in order to inform evidence-based practice through reliable and valid outcomes.

Acute caffeine supplementation improves jumping, sprinting, and change-of-direction performance in basketball players when ingested in the morning but not evening

This study compared the effects of acute caffeine supplementation (3 mg/kg) administered in the morning and evening on performance-related variables in basketball players. Eleven, national-level, adolescent male basketball players underwent field-based fitness testing on four occasions: morning (10:00) with caffeine ingestion (AM_CAFF), morning (10:00) with placebo ingestion (AM_PLAC), evening (21:00) with caffeine ingestion (PM_CAFF), and evening (21:00) with placebo ingestion (PM_PLAC). Fitness testing included of a countermovement jump without arm swing (CMJ), CMJ with arm swing (CMJAS), squat jump (SJ), Lane Agility Drill (LAD), 20-m linear sprint, and Suicide Run with (SRD) and without dribbling (SR). Data were analysed using two-way repeated measures analyses of variance and paired t-tests, with effect sizes (ES) also determined for all pairwise comparisons. Follow-up t-test comparisons revealed that AM_CAFF produced small-moderate, significant (p<0.001), improvements in CMJ (ES = 0.51), CMJAS (ES = 0.40), SJ (ES = 0.51), and SR (ES = -0.45) compared to AM_PLAC. AM_CAFF also produced a moderate, significantly (p<0.001) faster LAD (ES = -0.61) compared to PM_CAFF. PM_PLAC demonstrated small-moderate, significant (p<0.05) improvements in CMJ (ES = 0.43), CMJAS (ES = 0.48), and 20-m sprint (ES = -0.63) compared to AM_PLAC. In contrast, AM_PLAC resulted in large, significantly (p<0.001), faster SRD (ES = -1.46) and SR (ES = -1.59) compared to PM_PLAC. Given the ergogenic effects of caffeine during basketball-specific fitness tests appear to be influenced by time of ingestion, basketball practitioners should consider administering caffeine only to players in the morning to improve vertical jump, sprinting, and change-of-direction performance, with no beneficial effects observed with caffeine ingestion in the evening.Highlights The effect of caffeine supplementation on basketball-specific performance related variables were mediated by ingestion time in elite, adolescent basketball players.AMCAFF produced small-moderate improvements in vertical jump, change-of-direction, 20-m linear sprint, and repeated-sprint performance compared to AMPLAC while PMCAFF produced trivial differences in each performance-related variable compared to PMPLAC.Comparisons between ingestion times in the placebo condition revealed vertical jump height and 20-m sprint speed were impaired in the morning compared to the evening, but these time-dependent differences were eliminated when caffeine was consumed in the morning.Basketball practitioners should consider administering caffeine only to players in the morning to improve vertical jump, sprinting, and change-of-direction performance, with no beneficial effects observed with caffeine ingestion in the evening.

International society of sports nutrition position stand: caffeine and exercise performance

Following critical evaluation of the available literature to date, The International Society of Sports Nutrition (ISSN) position regarding caffeine intake is as follows: 1. Supplementation with caffeine has been shown to acutely enhance various aspects of exercise performance in many but not all studies. Small to moderate benefits of caffeine use include, but are not limited to: muscular endurance, movement velocity and muscular strength, sprinting, jumping, and throwing performance, as well as a wide range of aerobic and anaerobic sport-specific actions. 2. Aerobic endurance appears to be the form of exercise with the most consistent moderate-to-large benefits from caffeine use, although the magnitude of its effects differs between individuals. 3. Caffeine has consistently been shown to improve exercise performance when consumed in doses of 3-6 mg/kg body mass. Minimal effective doses of caffeine currently remain unclear but they may be as low as 2 mg/kg body mass. Very high doses of caffeine (e.g. 9 mg/kg) are associated with a high incidence of side-effects and do not seem to be required to elicit an ergogenic effect. 4. The most commonly used timing of caffeine supplementation is 60 min pre-exercise. Optimal timing of caffeine ingestion likely depends on the source of caffeine. For example, as compared to caffeine capsules, caffeine chewing gums may require a shorter waiting time from consumption to the start of the exercise session. 5. Caffeine appears to improve physical performance in both trained and untrained individuals. 6. Inter-individual differences in sport and exercise performance as well as adverse effects on sleep or feelings of anxiety following caffeine ingestion may be attributed to genetic variation associated with caffeine metabolism, and physical and psychological response. Other factors such as habitual caffeine intake also may play a role in between-individual response variation. 7. Caffeine has been shown to be ergogenic for cognitive function, including attention and vigilance, in most individuals. 8. Caffeine may improve cognitive and physical performance in some individuals under conditions of sleep deprivation. 9. The use of caffeine in conjunction with endurance exercise in the heat and at altitude is well supported when dosages range from 3 to 6 mg/kg and 4-6 mg/kg, respectively. 10. Alternative sources of caffeine such as caffeinated chewing gum, mouth rinses, energy gels and chews have been shown to improve performance, primarily in aerobic exercise. 11. Energy drinks and pre-workout supplements containing caffeine have been demonstrated to enhance both anaerobic and aerobic performance.

Padrões de consumo de bebidas energéticas e suplementos alimentares à base de cafeína por frequentadores de academias

Objetivo: Avaliar o nível de conhecimento, hábitos, e prevalência de consumo de energéticos e suplementos à base de cafeína por praticantes de exercícios físicos em academias. Métodos: Foi empregado um questionário autoaplicável de 27 perguntas no Google® Forms, divulgado em mídias sociais entre setembro e outubro de 2018. Resultados: Participaram 200 frequentadores de academias, 71% adultos jovens, 52% tendo mais de 2 anos de prática e frequência regular de 5 - 6 vezes por semana. A maioria da amostra era mulher (58,5%), praticante de musculação (61,6%) de MG (62,5%). O consumo sem orientação profissional foi de 81,6% nos energéticos e 53,9% para suplementos à base de cafeína. 73,3% dos consumidores de energéticos tinham objetivos relacionados com atividades sociais, preferindo a marca RedBul® (40,4%). Entre os consumidores de suplementos de cafeína houve preferência por termogênicos (32,7%) e cafeína pura (29,9%), com objetivo principal a melhora de performance (28,7%), apresentando respostas ergolíticas de taquicardia e palpitações como registrado nos energéticos. Não houve registro de efeitos adversos em 19,2% dos consumidores de cafeína e 40,8% de energéticos. As dosagens de consumo dos produtos estavam dentro da faixa de segurança (< 6 mg/kg). Conclusão: O consumo de ambos produtos foi feito sem orientação profissional, porém, com dosagens dentro da faixa de segurança. O consumo de bebidas energéticas esteve voltado para atividades sociais e melhora da performance esportiva. Foram registrados efeitos ergolíticos.

Energy-drink consumption is associated with asthma, allergic rhinitis, and atopic dermatitis in Korean adolescents

BACKGROUND/OBJECTIVES

Few studies have evaluated the effects of energy drinks on allergic diseases. The purpose of this investigation was to evaluate the association between energy drinks and various allergic diseases, including asthma, allergic rhinitis, and atopic dermatitis, in a large representative Korean adolescent population.

SUBJECTS/METHODS

This cross-sectional study used data from the Korea Youth Risk Behavior Web-based Survey collected from 2015 to 2016. A total of 129,809 participants (n = 67,056 for males; n = 62,753 for females) aged 12-18 years were included and were asked about their frequency of consumption of energy drinks such as Hot6^®, Redbull^®, and Bacchus^®. Their history of asthma, allergic rhinitis, and atopic dermatitis throughout life and in the last 12 months were obtained. The association between the frequency of energy-drink consumption and allergic diseases was analyzed using multiple logistic regression with adjustment for various covariates.

RESULTS

Age, sex, physical activity, obesity, region of residence, economic level, paternal and maternal educational level, smoking, and alcohol consumption differed significantly according to the frequency of energy-drink consumption (each P < 0.001). Frequent energy-drink consumption (≥7 times a week) was significantly associated with asthma throughout life (odds ratio [OR] = 1.30, 95% confidence interval (CI) = 1.03-1.64, P = 0.025), asthma within the last 12 months (OR = 1.65, 95% CI = 1.16-2.35, P = 0.006), allergic rhinitis within the last 12 months (OR = 1.21, 95% CI = 1.02-1.44, P = 0.030), and atopic dermatitis within the last 12 months (OR = 1.49, 95% CI = 1.17-1.90, P = 0.001) compared to no energy-drink consumption in the full-adjusted model.

CONCLUSIONS

Frequent energy-drink consumption is associated with allergic diseases, including asthma, allergic rhinitis, and atopic dermatitis, in Korean adolescents.

Up in the Air: Evidence of Dehydration Risk and Long-Haul Flight on Athletic Performance

The microclimate of an airline cabin consists of dry, recirculated, and cool air, which is maintained at lower pressure than that found at sea level. Being exposed to this distinctive, encapsulated environment for prolonged durations, together with the short-term chair-rest immobilization that occurs during long-haul flights, can trigger distinct and detrimental reactions to the human body. There is evidence that long-haul flights promote fluid shifts to the lower extremity and induce changes in blood viscosity which may accelerate dehydration, possibly compromising an athlete’s potential for success upon arrival at their destination. Surprisingly, and despite several recent systematic reviews investigating the effects of jet lag and transmeridian travel on human physiology, there has been no systematic effort to address to what extent hypohydration is a (health, performance) risk to travelers embarking on long journeys. This narrative review summarizes the rationale and evidence for why the combination of fluid balance and long-haul flight remains a critically overlooked issue for traveling persons, be it for health, leisure, business, or in a sporting context. Upon review, there are few studies which have been conducted on actual traveling athletes, and those that have provide no real evidence of how the incidence rate, magnitude, or duration of acute dehydration may affect the general health or performance of elite athletes.

Acute Caffeine Mouth Rinse Does Not Change the Hydration Status following a 10 km Run in Recreationally Trained Runners

Background and Aims

Caffeine mouth rinsing has emerged as an alternative to oral caffeine consumption for improving performance without provoking lower gastrointestinal distress. However, it remains unclear if hydration status and sweat rate are negatively affected by caffeine mouth rinsing. This study is aimed at evaluating the effects of 10 seconds of caffeine mouth rinsing (1.2% anhydrous caffeine solution) on hydration status and sweat rate following a 10 km run trial.

Methods

Ten recreationally trained runners (30.1 ± 6.4 y) volunteered to participate in this double-blind, placebo-controlled, and crossover research study. Participants completed two 10 km run trials separated by approximately one week. Immediately prior to running, participants completed a 10-second mouth rinse protocol with either 300 mg of caffeine or microcrystalline cellulose (placebo) diluted in 25 mL of water. The effects of caffeine mouth rinsing on hydration status and sweat rate were assessed following a 10 km run trial.

Results

Sweat rate (placebo: 15.34 ± 9.71 vs. caffeine: 11.91 ± 6.98 mL · min⁻¹; p = 0.39), dehydration (placebo: 1.20 ± 0.57 vs. caffeine: 1.49 ± 0.29%; p = 0.15), and hydration (placebo: 15.32 ± 9.71 vs. caffeine: 11.89 ± 6.99 mL · min⁻¹; p = 0.37) measures were not significantly different between trials.

Conclusion

Caffeine mouth rinse does not appear to alter the hydration status or sweat rate following a 10 km run.

Caffeine and heat have additive but not interactive effects on physiologic strain: A factorial experiment

This study tested the interactive effects of heat and caffeine on exercise-induced physiological strain by using a 2x2 within-subjects factorial design. Thirty-five physically fit Caucasians underwent a bout of exercise under four conditions wherein ambient conditions (heat vs no heat) and caffeine (placebo vs caffeine; double-blinded) were manipulated. Exercise consisted of a 60-min walk and 5-min step/squat test while wearing weighted backpack. Primary outcomes include measures of physiologic strain (Core temperature [T_r] and heart rate [HR]). Secondary measures included blood pressure, markers of sweat loss, and creatine kinase (CK). Repeated measures models were created to evaluate the individual and combined effects of heat and caffeine. Key results indicated that heat and caffeine significantly increased T_r and HR after walking and stair-stepping. No significant heat by caffeine interactions were detected, and caffeine's main effects were relatively low (≤0.17 °C for T_r and ≤6.6 bpm for HR). Of note, heat and caffeine exhibited opposite effects on blood pressure: caffeine increased both systolic and diastolic blood pressure (by 6-7 mmHg) and heat decreased them (by 4-6 mm Hg; ps < 0.05). In summary, heat and caffeine affected physiologic strain during exercise but exhibited no synergistic effects. In contrast, neither factor affected muscle damage. Clinical implications for heat illness risk in the military are discussed.

Nonalcoholic Beverages as Sources of Nutrients in the Average Polish Diet

The aim of the study was to analyze the sources of energy, carbohydrates, 10 minerals, and 9 vitamins from nonalcoholic beverages in the average Polish diet. For the analysis, we used data from the 2016 Household Budget Survey conducted on the representative sample of the Polish population (36,886 households, n = 99,230). According to the source of data, we included four subgroups in analyzed food category: fruit juices, vegetable juices and mixed, mineral and spring waters, and other nonalcoholic beverages. We used the cluster analysis to assess the impact of sociodemographic and economic characteristics of the households on the structure of supplying energy and nutrients from each subgroup of the nonalcoholic beverages. Our analyses have shown that nonalcoholic beverages are primarily important in providing several nutrients: vitamin C (15.9% of the total vitamin C supply), vitamin B6 (8.9% of vitamin B supply), folates (8.5% of folate supply), carbohydrates (6.8% of carbohydrate supply), calcium (5.9% of calcium supply), and magnesium (5.5% of magnesium supply). The analysis of the consumption structure of this category of food showed that the subgroup of other nonalcoholic beverages brings more than three-fourth of carbohydrates (77%), vitamin B6 and folates (76% each), and 43% of vitamin C supplied by nonalcoholic beverages. More than half (51%) of vitamin C provided by nonalcoholic beverages comes from fruit juices and the remaining 6% comes from other juices (vegetable and mixed). In the case of minerals, mineral and spring waters consumption is important as it accounts for 65% of the calcium supply and 55% of the magnesium in nonalcoholic beverages category. The share of individual subgroups of beverages in the supply of ingredients in the diet is significantly differentiated by four socioeconomic characteristics of households: family life phase, age, socioeconomic type of household, and number of people in the household. This is particularly evident in the case of other nonalcoholic beverages, that the share of this subgroup in the energy and carbohydrates supply in the households of young people, employees (both blue-collar and white-collar workers), and families with children increases to 10%. Our results show that in order to reduce the intake of free sugars and increase the intake of deficient minerals, which is crucial in preventing noncommunicable diseases (NCDs), it is necessary to encourage consumers to replace sugar-sweetened beverages (SSBs) with water and eat fruits instead of drinking juice.

The effect of coffee consumption on insulin sensitivity and other biological risk factors for type 2 diabetes: a randomized placebo-controlled trial

BACKGROUND

In observational studies, coffee consumption has been consistently associated with a lower risk of type 2 diabetes mellitus. Trials examining the effect of coffee consumption on glucose metabolism have been limited by the use of surrogate insulin sensitivity indices, small sample sizes, lack of blinding, and short follow-up duration.

OBJECTIVES

We aimed to overcome limitations of previously conducted coffee trials in a randomized placebo-controlled trial of the effect of coffee consumption on insulin sensitivity.

METHODS

We conducted a 24-wk randomized placebo-controlled trial in 126 overweight, non-insulin sensitive (HOMA-IR ≥1.30), Chinese, Malay, and Asian-Indian males and females aged 35-69 y. Participants were randomly assigned to receive 4 cups of instant regular coffee (n = 62) or 4 cups of a coffee-like placebo beverage (n = 64) per day. The primary outcome was the amount of glucose metabolized per kilogram of body weight per minute (Mbw) assessed during steady-state conditions with a hyperinsulinemic euglycemic clamp. Secondary outcomes included other clamp-based insulin sensitivity measures, biological mediators of insulin sensitivity, and measures of fasting glucose metabolism.

RESULTS

Coffee consumption did not significantly change insulin sensitivity compared with placebo (percentage mean difference in Mbw = 4.0%; 95% CI: -8.3, 18.0%; P = 0.53). Furthermore, no significant differences in fasting plasma glucose (2.9%; 95% CI: -0.4, 6.3%; P = 0.09) or biological mediators of insulin resistance, such as plasma adiponectin (2.3%; 95% CI: -1.4, 6.2%; P = 0.22), were observed between coffee and placebo groups over 24 wk of intervention. Participants in the coffee arm experienced a loss of fat mass (FM) (-3.7%; 95% CI: -6.3, -1.1%; P = 0.006) and reduction in urinary creatinine concentrations (-21.2%; 95% CI: -31.4, -9.5%; P = 0.001) compared with participants in the placebo arm over 24 wk of intervention.

CONCLUSIONS

Consuming 4 cups/d of caffeinated coffee for 24 wk had no significant effect on insulin sensitivity or biological mediators of insulin resistance but was associated with a modest loss of FM and reduction in urinary creatinine concentrations.This trial was registered at clinicaltrials.gov as NCT01738399. Registered on November 28, 2012. Trial sponsor: Nestlé Research, Lausanne, Switzerland. Trial site: National University of Singapore.

Exploring a New Natural Treating Agent for Primary Hypertension: Recent Findings and Forthcoming Perspectives

Primary hypertension describes abnormally-high systolic/diastolic blood pressure in a resting condition caused by various genetic or environmental risk factors. Remarkably, severe complications, such as ischemic cardiovascular disease, stroke, and chronic renal disease have led to primary hypertension becoming a huge burden for almost one-third of the total population. Medication is the major regimen for treating primary hypertension; however, recent medications may have adverse effects that attenuate energy levels. Hence, the search for new hypotensive agents from folk or traditional medicine may be fruitful in the discovery and development of new drugs. This review assembles recent findings for natural antihypertensive agents, extracts, or decoctions published in PubMed, and provides insights into the search for new hypotensive compounds based on blood-pressure regulating mechanisms, including the renin-angiotensin-aldosterone system and the sympathetic/adrenergic receptor/calcium channel system.

Effects of Caffeine on Tennis Serve Accuracy

This study examined the effects of caffeine on tennis serve accuracy. Division II tennis athletes (n = 10) completed two serve trials (double-blind, counterbalanced) following ingestion of 6 mg/kg of caffeine or matched placebo an hour prior to data collection. During each tennis serve trial, participants completed 48 non-fault serves divided into 3 sets with 2 serves per 8 different targets. Following each 2 serves per target format, participants completed a shuttle run sprint. Separate 2 (trial) × 8 (targets) repeated measures analysis of variances (ANOVAs) were used for distances from the target center "delta", and necessary tries for each of the 3 sets. A 2 (treatment) × 3 (set) repeated measures ANOVA was used for shuttle run times. While results were not significant, the treatment main effect approached significance (p = 0.07) in set 2 for the delta of distances when comparing caffeine (96.2 cm ± 19.8) versus placebo (107.1 cm ± 16.3). While there was no significance in sprint times, each sprint was consistently faster following caffeine consumption. Post-trial surveys revealed subjective responses approached significance with greater feelings of stomach distress (p = 0.08) and nervousness (p = 0.13) following caffeine and elevated feeling of fatigue (p = 0.19) following placebo. Therefore, with no impairment in serve accuracy coupled with some evidence of reduced fatigue, results suggest caffeine may benefit tennis athletes. Extending the understanding of the effects of caffeine on tennis serve accuracy and performance could benefit overall match performance, with the potential of improving the match outcome in extended playtime.

Caffeine intake and the risk of recurrent kidney stones in adults, an analysis of 2007-2014 National Health and Nutrition Examination Surveys

PURPOSE

The association between caffeine intake and the risk of recurrent kidney stones is unknown. We examined the association between caffeine intake and the risk of recurrent kidney stones in adults.

METHODS

Individuals with history of passing at least one kidney stone were included from 2007 to 2014 National Health and Nutrition Examination Survey. Recurrent kidney stones were defined using a standard questionnaire and structured dietary recalls were used to determine caffeine intake. The weighted logistic regression was used to assess the association between caffeine intake and the risk of recurrent kidney stones, and the non-linear relationship was explored with restricted cubic splines. Caffeine and dietary confounders (minerals and vitamins) were adjusted for total energy intake with residual model.

RESULTS

The multivariate-adjusted odds ratios (95% confidence intervals) of recurrent kidney stones for per-quartile increment in caffeine intake were 1.15 (1.01-1.31) overall, 1.11 (0.96-1.29) for white race individuals, 1.33 (1.09-1.63) for non-white race individuals, 1.15 (0.97-1.36) for men, 1.24 (1.01-1.53) for women, 1.54 (1.08-2.19) for non-overweight individuals, 1.11 (0.97-1.28) for overweight/obese individuals, 1.13 (0.99-1.29) for caffeine from coffee, and 0.90 (0.79-1.03) for caffeine from non-coffee sources. A linear relationship was found between caffeine intake and the risk of recurrent kidney stones overall and in subgroup analyses.

CONCLUSION

Compared with those who reported passing only one kidney stone, caffeine intake was independently and linearly associated with a higher risk of recurrent kidney stones in adults, especially for women, individuals of non-white race and non-overweight subjects. The increased risk may arise from caffeine from coffee.

Wake up and smell the coffee: caffeine supplementation and exercise performance—an umbrella review of 21 published meta-analyses

Objective

To systematically review, summarise and appraise findings of published meta-analyses that examined the effects of caffeine on exercise performance.

Design

Umbrella review.

Data sources

Twelve databases.

Eligibility criteria for selecting studies

Meta-analyses that examined the effects of caffeine ingestion on exercise performance.

Results

Eleven reviews (with a total of 21 meta-analyses) were included, all being of moderate or high methodological quality (assessed using the Assessing the Methodological Quality of Systematic Reviews 2 checklist). In the meta-analyses, caffeine was ergogenic for aerobic endurance, muscle strength, muscle endurance, power, jumping performance and exercise speed. However, not all analyses provided a definite direction for the effect of caffeine when considering the 95% prediction interval. Using the Grading of Recommendations Assessment, Development and Evaluation criteria the quality of evidence was generally categorised as moderate (with some low to very low quality of evidence). Most individual studies included in the published meta-analyses were conducted among young men.

Summary/conclusion

Synthesis of the currently available meta-analyses suggest that caffeine ingestion improves exercise performance in a broad range of exercise tasks. Ergogenic effects of caffeine on muscle endurance, muscle strength, anaerobic power and aerobic endurance were substantiated by moderate quality of evidence coming from moderate-to-high quality systematic reviews. For other outcomes, we found moderate quality reviews that presented evidence of very low or low quality. It seems that the magnitude of the effect of caffeine is generally greater for aerobic as compared with anaerobic exercise. More primary studies should be conducted among women, middle-aged and older adults to improve the generalisability of these findings.

Soft drink consumption during and following exercise in the heat elevates biomarkers of acute kidney injury

The purpose of this study was to test the hypothesis that consuming a soft drink (i.e., a high-fructose, caffeinated beverage) during and following exercise in the heat elevates biomarkers of acute kidney injury (AKI) in humans. Twelve healthy adults drank 2 liters of an assigned beverage during 4 h of exercise in the heat [35.1 (0.1)°C, 61 (5)% relative humidity] in counterbalanced soft drink and water trials, and ≥1 liter of the same beverage after leaving the laboratory. Stage 1 AKI (i.e., increased serum creatinine ≥0.30 mg/dl) was detected at postexercise in 75% of participants in the Soft Drink trial compared with 8% in Water trial ( P = 0.02). Furthermore, urinary neutrophil gelatinase-associated lipocalin (NGAL), a biomarker of AKI, was higher during an overnight collection period after the Soft Drink trial compared with Water in both absolute concentration [6 (4) ng/dl vs. 5 (4) ng/dl, P < 0.04] and after correcting for urine flow rate [6 (7) (ng/dl)/(ml/min) vs. 4 (4) (ng/dl)/(ml/min), P = 0.03]. Changes in serum uric acid from preexercise were greater in the Soft Drink trial than the Water trial at postexercise ( P < 0.01) and 24 h ( P = 0.05). There were greater increases from preexercise in serum copeptin, a stable marker of vasopressin, at postexercise in the Soft Drink trial ( P < 0.02) than the Water trial. These findings indicate that consuming a soft drink during and following exercise in the heat induces AKI, likely via vasopressin-mediated mechanisms.

Relationship between caffeine intake and autosomal dominant polycystic kidney disease progression: a retrospective analysis using the CRISP cohort

Background

Caffeine has been proposed, based on in vitro cultured cell studies, to accelerate progression of autosomal dominant polycystic kidney disease (ADPKD) by increasing kidney size. Since ADPKD patients are advised to minimize caffeine intake, we investigated the effect of caffeine on disease progression in the Consortium for Radiologic Imaging Studies of Polycystic Kidney Disease (CRISP), a prospective, observational cohort study.

Methods

Our study included 239 patients (mean age = 32.3 ± 8.9 ys; 188 caffeine consumers) with a median follow-up time of 12.5 years. Caffeine intake reported at baseline was dichotomized (any vs. none). Linear mixed models, unadjusted and adjusted for age, race, sex, BMI, smoking, hypertension, genetics and time, were used to model height-adjusted total kidney volume (htTKV) and iothalamate clearance (mGFR). Cox proportional hazards models and Kaplan-Meier plots examined the effect of caffeine on time to ESRD or death.

Results

Caffeine-by-time was statistically significant when modeling ln(htTKV) in unadjusted and adjusted models (p <  0.01) indicating that caffeine consumers had slightly faster kidney growth (by 0.6% per year), but htTKV remained smaller from baseline throughout the study. Caffeine consumption was not associated with a difference in mGFR, or in the time to ESRD or death (p > 0.05). Moreover the results were similar when outcomes were modeled as a function of caffeine dose.

Conclusion

We conclude that caffeine does not have a significant detrimental effect on disease progression in ADPKD.

Electronic supplementary material

The online version of this article (10.1186/s12882-018-1182-0) contains supplementary material, which is available to authorized users.

Caffeine in Kidney Stone Disease: Risk or Benefit?

Kidney stone disease is a global health care problem, with a high recurrence rate after stone removal. It is thus crucial to develop effective strategies to prevent the formation of new or recurrent stones. Caffeine is one of the main components in caffeinated beverages worldwide (i.e., coffee, tea, soft drinks, and energy drinks). Previous retrospective and prospective studies have reported contradictory effects of caffeine on kidney stone risk. Although it has a diuretic effect on enhancing urinary output, it may slightly increase the stone risk index. However, 3 large cohorts have suggested a preventive role of caffeine in kidney stone disease. In addition, a recent in vitro study has addressed relevant mechanisms underlying the preventive role of caffeine against stone pathogenesis. This review summarizes the relevant data from previous evidence and discusses the association between caffeine consumption and kidney stone risk reduction.

Nutrition Influences Caffeine-Mediated Sleep Loss in Drosophila

Study objectives

Plant-derived caffeine is regarded as a defensive compound produced to prevent herbivory. Caffeine is generally repellent to insects and often used to study the neurological basis for aversive responses in the model insect, Drosophila melanogaster. Caffeine is also studied for its stimulatory properties where sleep or drowsiness is suppressed across a range of species. Since limiting access to food also inhibits fly sleep-an effect known as starvation-induced sleep suppression-we tested whether aversion to caffeinated food results in reduced nutrient intake and assessed how this might influence fly studies on the stimulatory effects of caffeine.

Methods

We measured sleep and total consumption during the first 24 hours of exposure to caffeinated diets containing a range of sucrose concentrations to determine the relative influence of caffeine and nutrient ingestion on sleep. Experiments were replicated using three fly strains.

Results

Caffeine reduced total consumption and nighttime sleep, but only at intermediate sucrose concentrations. Although sleep can be modeled by an exponential dose response to nutrient intake, caffeine-mediated sleep loss cannot be explained by absolute caffeine or sucrose ingestion alone. Instead, reduced sleep strongly correlates with changes in total consumption due to caffeine. Other bitter compounds phenocopy the effect of caffeine on sleep and food intake.

Conclusions

Our results suggest that a major effect of dietary caffeine is on fly feeding behavior. Changes in feeding behavior may drive caffeine-mediated sleep loss. Future studies using psychoactive compounds should consider the potential impact of nutrition when investigating effects on sleep.

Energy and sports drinks in children and adolescents

Sports drinks and caffeinated energy drinks (CEDs) are commonly consumed by youth. Both sports drinks and CEDs pose potential risks for the health of children and adolescents and may contribute to obesity. Sports drinks are generally unnecessary for children engaged in routine or play-based physical activity. CEDs may affect children and adolescents more than adults because they weigh less and thus experience greater exposure to stimulant ingredients per kilogram of body weight. Paediatricians need to recognize and educate patients and families on the differences between sport drinks and CEDs. Screening for the consumption of CEDs, especially when mixed with alcohol, should be done routinely. The combination of CEDs and alcohol may be a marker for higher risk of substance use or abuse and for other health-compromising behaviours.

Coffee with High but Not Low Caffeine Content Augments Fluid and Electrolyte Excretion at Rest

BACKGROUND

Low levels of caffeine ingestion do not induce dehydration at rest, while it is not clear if larger doses do have an acute diuretic effect. The aim of the present investigation was to examine the acute effect of low and high levels of caffeine, via coffee, on fluid balance in habitual coffee drinkers (at least one per day) at rest.

METHODS

Ten healthy adults (eight males and two females; age: 27 ± 5 years, weight: 89.5 ± 14.8 kg, height: 1.75 ± 0.08 m, and body mass index: 29.1 ± 4.4 kg m^-2) ingested 200 mL of water (W), coffee with low caffeine (3 mg kg^-1, LCAF), or coffee with high caffeine (6 mg kg^-1, HCAF) on three respective separate occasions. All sessions were performed at 09:00 in the morning in a counterbalanced, crossover manner, at least 5 days apart. Subjects remained in the laboratory while urine samples were collected every 60 min for 3 h post ingestion.

RESULTS

Absolute caffeine consumption was 269 ± 45 and 537 ± 89 mg for the LCAF and HCAF, respectively. Coffee ingestion at the HCAF trial induced greater diuresis during the 3-h period (613 ± 101 mL, P < 0.05), when compared to W (356 ± 53 mL) and LCAF (316 ± 38 mL). In addition, cumulative urinary osmotic excretion was significantly greater in the HCAF (425 ± 92 mmol, P < 0.05), as compared to the W (249 ± 36 mmol) and LCAF (177 ± 16 mmol) trials.

CONCLUSION

The data indicate that caffeine intake of 6 mg kg^-1 in the form of coffee can induce an acute diuretic effect, while 3 mg kg^-1 do not disturb fluid balance in healthy casual coffee drinking adults at rest.