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Study Title and Description

Thermoregulatory responses to exercise in the heat: chronic caffeine intake has no effect.



Key Questions Addressed
1 For [population], is caffeine intake above [exposure dose], compared to intakes [exposure dose] or less, associated with adverse effects on cardiovascular outcomes?
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Primary Publication Information
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TitleData
Title Thermoregulatory responses to exercise in the heat: chronic caffeine intake has no effect.
Author MW Roti,DJ Casa,AC Pumerantz,G Watson,DA Judelson,JC Dias,K Ruffin,LE Armstrong,
Country
Year 2006
Numbers

Secondary Publication Information
There are currently no secondary publications defined for this study.


Extraction Form: Cardiovascular Design
Design Details
Question... Follow Up Answer Follow-up Answer
What outcome is being evaluated in this paper? Cardiovascular
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What is the objective of the study (as reported by the authors)? The purpose of this study was to assess the effects of controlled chronic and acute caffeine ingestion on fluid-electrolyte, physiological and thermoregulatory responses during an exercise heat tolerance test (EHT).
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Provide a general description of the methods as reported by the authors. Information should be extracted based on relevance to the SR (i.e., caffeine related methods) Subjects There were 60 college-aged males who volunteered as subjects for this study, although one subject withdrew prior to the exercise trial due to personal reasons (n = 59). All subjects recalled their exercise practices during the 30 d before beginning this investigation. Included subjects were active but not highly trained, therefore subjects who were sedentary (exercised less than twice per week), or those who participated in prolonged or intense exercise (such as varsity athletes), were not selected for participation in this investigation. Subjects completed a medical history questionnaire to rule out any contraindications to participation; these included a history of cardiovascular, metabolic or respiratory disease or a history of heat illness. A dietary caffeine questionnaire also was completed and individuals with excessive caffeine habits (> 600 mg/day) and those truly caffeine naıve were not selected for participation. Subject diet and exercise levels were controlled throughout the duration of the investigation. Subjects recorded their physical activity history (1 mo) and were instructed to maintain those activity levels. No consumption of caffeine or drugs and only limited consumption (</= 2 servings per day) of alcohol were permitted during the 2 d prior to study onset and during the entire study duration. Subjects recorded their diet for the 2 d prior and during the 12 d of the study. Experimental Design The experimental design involved three randomized dosing groups of test subjects (n = 20 per group). The three groups were stratified for age, body weight (BW) and percent body fat (%BF). To account for differences in caffeine tolerance, each group standardized caffeine intake at 3 mg/kg-day during a 6-d dietary equilibrium period. On day 7, each group began consuming a unique treatment level of caffeine for 6 d: either 0 mg/kg-day (n = 20, G0), 3 mg/kg-day (n = 20, G3), or 6 mg/kg-day (n = 19, G6). Caffeine was taken in capsule form in two equal doses, following a double-blind design. The morning caffeine dose was ingested between 07:00 and 09:00 and was observed by an investigator. The afternoon caffeine ingestion occurred between 12:00 and 14:00 and was confirmed by phone. Serum caffeine levels were verified on day 6 1-h post afternoon ingestion. All subjects were found to be in compliance. On day 12 each subject performed a standardized 90 min exercise heat tolerance test (EHT) in a heated environmental chamber (Minus Eleven Inc., Model 200, Malden, MA). The EHT was a classic protocol (continuous treadmill walking; 1.56 m/sec; 5% grade). On the day of the EHT, subjects reported at 07:00 to receive their morning dose as usual, but then they returned between 12:00 and 14:00 to receive their second daily dose, 1 h post-prandial. Subjects relaxed for 30 min and were permitted to drink water ad libitum, after which no fluid was provided until after the EHT. Subjects then changed into exercise clothes (shorts, socks, and sneakers), and entered the environmental chamber. A heart rate monitor transmitter was positioned on the chest (Polar Electro, Kempele, Finland). After 20 min of standing equilibration, and immediately pre-exercise, min 0 measure of heart rate (HR) was recorded. Subjects walked at 1.56 m/sec at a 5% grade on a motorized treadmill (Lifestride 9100, Franklin Park, IL). Heart rate was measured every 15 min. Subjects stopped exercise at subjective exhaustion, minute 90 or when rectal temperature reached 39.5°C. All final measures were then recorded. Statistical Analyses Matching of volunteers was verified by analysis of variance (ANOVA) for measures of height, weight, age, body composition (percent body fat) and weekly activity score. A mixed design using one-way, two-way and repeated measures analyses of variance (ANOVA) evaluated significance. In all statistical tests, significance was considered to be obtained when p < 0.05. Post hoc paired-sample t -tests were applied where appropriate and evaluated with a Bonferroni adjustment. All statistics were computed using SPSS Base 10.0 Software (SPSS Inc., Chicago, IL) and data were reported as mean +/- standard error (SE).
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How many outcome-specific endpoints are evaluated? 1
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What is the (or one of the) endpoint(s) evaluated? (Each endpoint listed separately) Heart rate
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List additional health endpoints (separately). 2
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List additional health endpoints (separately).3
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List additional health endpoints (separately).4
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List additional health endpoints (separately).5
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List additional health endpoints (separately).6
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Clinical, physiological, other Physiological
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What is the study design? Controlled Trial
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Randomized or Non-Randomized? RCT
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What were the diagnostics or methods used to measure the outcome? Objective
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Optional: Name of Method or short description A heart rate monitor transmitter was positioned on the chest (Polar Electro, Kempele, Finland).
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Caffeine (general) Caffeine (general)
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Coffee, Chocolate, energy drink, gum, medicine/supplement, soda, tea, other?
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Measured or self reported? Measured
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Children, adolescents, adults, or pregnant included? Adults
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What was the reference, comparison, or control group(s)? (e.g. high vs low consumption, number of cups, etc.) 3 or 6 mg/kg-day vs. 0 mg/kg-day
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What were the listed confounders or modifying factors as stated by the authors? (e.g. multi-variable components of models.  Copy from methods) None
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What conflicts of interest were reported? No information provided
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Refid 16491580
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What were the sources of funding? This research was funded by a grant from the International Life Sciences Institute of North America, Washington, DC.
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Results & Comparisons

No Results found.