Advanced Search

Study Preview



Study Title and Description

Caffeine tolerance is incomplete: persistent blood pressure responses in the ambulatory setting.



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?
  • Comments Comments (
    0
    ) |

Primary Publication Information
  • Comments Comments (
    0
    ) |
TitleData
Title Caffeine tolerance is incomplete: persistent blood pressure responses in the ambulatory setting.
Author NH Farag,AS Vincent,BH Sung,TL Whitsett,MF Wilson,WR Lovallo,
Country
Year 2005
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
  • Comments Comments (
    0
    ) |
What is the objective of the study (as reported by the authors)? In this paper, we examine tolerance effects on the BP response to caffeine across the day in the ambulatory setting.
  • Comments Comments (
    0
    ) |
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) Study Population A total of 132 subjects ages 21-35 years were recruited from the community and enrolled in the study. Twenty-one subjects withdrew voluntarily at various points in the protocol, 11were found to be noncompliant and dropped, 1 was excluded due to abnormal lab values, 2 reported side effects and were excused, and 12 had missing ambulatory data on one or more of the 4 testing weeks reducing the sample size to 85 (men = 47 and women = 38. All were nonobese (body mass index [BMI] < 30) and in good health by self-report and routine physical exam. They had BPs in the normotensive range (BPs < 135/85 mmHg) at screening, and used no medications having cardiovascular or metabolic effects. They regularly consumed 50-700 mg/day of caffeine by structured interview. Approximately 64% reported consumption greater than 200 mg/day (equivalent to 2 or more cups of coffee). Study Design, Caffeine Dosing, and Compliance The design was a four-week, placebo-controlled, double-blind, randomized crossover trial of caffeine tolerance effects on BP responses to fixed challenge doses. Subjects were instructed to eliminate all sources of caffeine from their diet (coffee, tea, soft drinks, and chocolates) during the four weeks of the study. Each study week consisted of 5 maintenance days with placebo (P) or caffeine (C) self-administration at home. Day 6 consisted of a 6-hour lab protocol and 18 hours of ambulatory BP monitoring accompanied by placebo or caffeine challenges. Day 7 was a crossover day, with successive caffeine doses of 100 mg, 0 mg, and 0 mg, to buffer sudden changes in intake at weekly crossovers. Weekly dose schedules are shown in Table 2. Home maintenance doses were supplied in bottles of identical gelatin capsules (College of Pharmacy, University of Oklahoma, Oklahoma City, OK) containing either lactose or lactose mixed with 100 mg or 200 mg of USP caffeine (Gallipot, St. Paul, MN). Subjects were instructed to take a capsule at 08.00, 13.00, and 18.00 hours each day. Test-day challenge doses were supplied in capsules containing either lactose or lactose mixed with 250 mg of caffeine administered at 09.00, 13.00, and 18.00 hours. Compliance was assessed by capsule counts, by caffeine assay of saliva specimens collected at home each day at 13.00 hours (Salivette®, Starstedt, Germany), and from a saliva specimen collected each morning upon entering the lab. Subjects found to be noncompliant by any of these criteria were dropped and replaced. Ambulatory Blood Pressure Monitoring (ABPM) The laboratory protocol ended at 14.00 hours. Before dismissal from the lab, subjects were outfitted with a Spacelabs Model 90205 ABPM unit (Spacelabs, Redmond, WA). The apparatus was programmed to obtain a BP measurement every 15 minutes until 22.00 hours and every 30 minutes from 22.00 to 07.00 hours. Subjects returned the monitor in the morning. The data were edited using standard artifact detection software provided by Spacelabs. Acceptable records included at least two recordings per hour during daytime and one per hour during sleep. Sleep was defined by diary entries indicating "bedtime" and "morning awakening" times. Statistical Analysis The high and low tolerance groups were formed previously using a median split of the averaged diastolic BP responses to the acute 9:00 am and 1:00 pm laboratory caffeine doses during the C600 week, when tolerance would be expected to be at its greatest, as previously described. The ABPM data were analyzed using multivariate, repeated measures analyses of variance (MANOVAs) that included 4 test weeks (placebo-placebo [P-P], placebo-caffeine [P-C], caffeine low [C300], and caffeine high [C600]) x 2 tolerance groups (high vs low). We first tested the effect of caffeine tolerance on the averaged afternoon and evening systolic and diastolic BPs (awake BP). The same analysis was conducted for BP averaged during sleep. For each set of ANOVAs, we tested specific contrasts between the P-P control week versus the P-C, C300, and C600 weeks. Significance was set at α < .05. Preliminary analyses found no BP differences by gender or site (Oklahoma City vs. Buffalo), thus subsequent analyses did not include these factors.
  • Comments Comments (
    0
    ) |
How many outcome-specific endpoints are evaluated? 1
  • Comments Comments (
    0
    ) |
What is the (or one of the) endpoint(s) evaluated? (Each endpoint listed separately) Blood pressure (SBP and DBP)
  • Comments Comments (
    0
    ) |
List additional health endpoints (separately). 2
  • Comments Comments (
    0
    ) |
List additional health endpoints (separately).3
  • Comments Comments (
    0
    ) |
List additional health endpoints (separately).4
  • Comments Comments (
    0
    ) |
List additional health endpoints (separately).5
  • Comments Comments (
    0
    ) |
List additional health endpoints (separately).6
  • Comments Comments (
    0
    ) |
Clinical, physiological, other Physiological
  • Comments Comments (
    0
    ) |
What is the study design? Controlled Trial
  • Comments Comments (
    0
    ) |
Randomized or Non-Randomized? RCT
  • Comments Comments (
    0
    ) |
What were the diagnostics or methods used to measure the outcome? Objective
  • Comments Comments (
    0
    ) |
Optional: Name of Method or short description Blood pressure measured with a Spacelabs Model 90205 ABPM unit
  • Comments Comments (
    0
    ) |
Caffeine (general) Caffeine (general)
  • Comments Comments (
    0
    ) |
Coffee, Chocolate, energy drink, gum, medicine/supplement, soda, tea, other?
  • Comments Comments (
    0
    ) |
Measured or self reported? Measured
  • Comments Comments (
    0
    ) |
Children, adolescents, adults, or pregnant included?
  • Comments Comments (
    0
    ) |
What was the reference, comparison, or control group(s)? (e.g. high vs low consumption, number of cups, etc.) Subjects served as their own controls (placebo)
  • Comments Comments (
    0
    ) |
What were the listed confounders or modifying factors as stated by the authors? (e.g. multi-variable components of models.  Copy from methods) None
  • Comments Comments (
    0
    ) |
What conflicts of interest were reported? No information provided
  • Comments Comments (
    0
    ) |
Refid 15882556
  • Comments Comments (
    0
    ) |
What were the sources of funding? This study was supported by the Medical Research Service of the Department of Veterans Affairs and by Grants HL 32050, HL 32050-S2, and HL 07640 from the National Heart, Lung, and Blood Institute and M01-RR14467 from the National Center for Research Resources, Bethesda, MD.
  • Comments Comments (
    0
    ) |




Results & Comparisons

No Results found.