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Study Title and Description

Blood pressure response to chronic intake of coffee and caffeine: a meta-analysis of randomized controlled trials.



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 Blood pressure response to chronic intake of coffee and caffeine: a meta-analysis of randomized controlled trials.
Author M Noordzij,CS Uiterwaal,LR Arends,FJ Kok,DE Grobbee,JM Geleijnse,
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
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What is the objective of the study (as reported by the authors)? The objective of this meta-analysis was to quantify the chronic effect (> 7 days) of regular coffee and caffeine intake on BP, using data from randomized controlled trials.
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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) Selection of Studies We performed a systematic search for publications between January 1966 and January 2003 using the literature databases of Medline, Embase, Lilacs and Current Contents. A search was performed for the text words ‘coffee or caffeine’, ‘blood pressure or hypertension’ and ‘trial or intervention or random* or study’ in studies that were published in English-language journals. The Medline search was restricted to studies classified as randomized controlled trials. An additional manual search was conducted using reference lists from original research papers, former meta-analyses and review articles. Studies that met the following criteria were eligible for meta-analysis: (1) conducted in humans; and (2) random allocation of study participants to intervention and control groups. A total of 91 out of 156 reports that were identified fulfilled these criteria. Reasons for the exclusion of studies were: (1) duration of intervention of less than 7 days (n = 50); (2) duplicate publication of the same study (n = 3); (3) co-intervention (e.g. caffeine combined with ephedrine, nicotine or stress) from which the effect of coffee or caffeine could not be separated (n =21); (4) lack of concurrent control group or balanced crossover comparison period (n = 2); and (5) lack of data to calculate the net changes in BP (n = 1). Sixteen trials [6–21] comprising 25 relevant strata proved to be eligible for meta-analysis. Trials were published between 1984 and 2000 and varied in sample size from 10 to 123 participants (median: 45). The analysis included 1010 subjects in total. All trials were performed in adult populations, with mean ages between 23 and 77 years. Data Extraction Two authors (M.N., J.M.G.) independently abstracted data from original reports using standard forms. In case of disagreement, consensus was reached. Data collection included: (1) sample size; (2) characteristics of the study population, i.e. age, gender distribution (% males), baseline BP, baseline heart rate (HR), habitual coffee consumption and caffeine intake, use of antihypertensive medication; (3) study design (parallel or crossover), blinding procedures, duration of intervention, type of intervention and control treatment; and (4) BP and HR changes and associated measures of variance. For parallel trials the net BP effect of coffee or caffeine intake was calculated as BP change from baseline in the intervention group minus BP change from baseline in the control group. For crossover trials, BP level at the end of the control period was subtracted from BP at the end of the intervention period. Net effects of coffee or caffeine on HR were obtained similarly. In addition, the standard error (SE) for the net BP effect was obtained. If not reported, SEs were derived from 95% confidence intervals (95% CI), t -statistics or the individual variances for intervention and control groups (parallel trials) or intervention and control periods (crossover trials). Variances during the trial were assumed to be equal, and a correlation of 0.50 was assumed between baseline and final BP values, according to Follmann et al. Studies in which the active treatment consisted of caffeine tablets, either as the sole treatment or combined with decaffeinated coffee, were classified as caffeine trials. Caffeine intake at baseline was derived from the paper or, if not reported, estimated from pre-treatment coffee consumption, assuming that 150 ml of coffee contains 90 mg of caffeine. Cup size was considered equal to 150 ml if the actual size was not reported. In one trial among 36 subjects with a mean age of 23 years, caffeine doses were reported in mg/kg per day and we estimated the actual dose assuming an average body weight of 78 kg in men and 64 kg in women. Four reports of crossover studies did not provide baseline BP data, and we used mean BP in the control period as the pre-treatment BP level. Data on BP and HR could not be obtained from text or tables for one trial and we abstracted this information from graphs. Data on net changes in HR were missing in four trials. Statistical Analysis Statistical analyses were performed using SAS, version 8 (SAS Institute Inc., Cary, North Carolina, USA). Heterogeneity in BP response was examined by performing stratified meta-analyses. Predefined subgroups were created on the basis of a number of factors, including caffeine dose during intervention (< 410 mg/day versus >/- 410 mg/day). Analyses in subgroups for caffeine dose were based on the median of the frequency distributions of these variables. Stratified analyses were repeated using a multivariate model with adjustment for the following variables (except when used as a stratification factor): age (years), gender (% males), baseline BP (mmHg), type of intervention (coffee or caffeine), baseline caffeine intake (mg/day) and caffeine dose during intervention (mg/day).
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How many outcome-specific endpoints are evaluated? 2
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What is the (or one of the) endpoint(s) evaluated? (Each endpoint listed separately) Blood pressure (SBP and DBP)
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List additional health endpoints (separately). 2 Heart rate
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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? Meta-analysis
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Randomized or Non-Randomized?
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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 Methods would have been specified in individual studies
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Caffeine (general) Caffeine (general)
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Coffee, Chocolate, energy drink, gum, medicine/supplement, soda, tea, other? Coffee
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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.) >/= 410 mg/day vs. < 410 mg/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) age, gender, baseline BP, type of intervention, and baseline caffeine intake
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What conflicts of interest were reported? No information provided
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Refid 15834273
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What were the sources of funding? No information provided
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Results & Comparisons

No Results found.