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Study Title and Description

Association between caffeine intake and bone mass among young women: potential effect modification by depot medroxyprogesterone acetate use.



Key Questions Addressed
1 For [population], is caffeine intake above [exposure dose], compared to intakes [exposure dose] or less, associated with adverse effects on bone and calcium balance outcomes?
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Primary Publication Information
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TitleData
Title Association between caffeine intake and bone mass among young women: potential effect modification by depot medroxyprogesterone acetate use.
Author CM Wetmore,L Ichikawa,AZ LaCroix,SM Ott,D Scholes,
Country
Year 2008
Numbers

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


Extraction Form: Bone & Calcium Outcomes
Design Details
Question... Follow Up Answer Follow-up Answer
Refid 18004611
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What outcome is being evaluated in this paper? Bone and Calcium
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What is the objective of the study (as reported by the authors)? The purpose of the current population-based prospective study was, therefore, to determine whether habitual caffeine intake was associated with either bone mass or changes in bone mass in a large cohort of 625 women, aged 14 to 40.
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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) Study population 625 women, aged 14 to 40 years at baseline, who were enrollees of Group Health Cooperative; subjects were recruited to participate in either of two 3-year longitudinal studies examining the effects of use and discontinuation of depot medroxyprogesterone acetate (DMPA) injectable contraception on bone mineral density. Data collection Study subjects were asked to visit the clinic every six months throughout the 24- to 36-month follow-up period. At baseline and each follow-up visit, participants completed questionnaires. Height and weight were measured in the clinic and were used to compute body mass index (BMI). Exposure assessment Caffeine consumption was estimated based on quantities; self reported quantities of caffeinated beverage intake were converted to mg caffeine per day. Conversions of caffeine content of beverages were derived from the scientific literature and U.S. FDA reports.: 136 mg per 8 oz. coffee, 48 mg per 8 oz. tea, 36 mg per 12 oz. caffeinated soft drink, and 40 mg per 1 oz. shot of espresso. After computing the estimated caffeine intake based on cups or cans of caffeinated beverages consumed per day, as reported on the semi-annual questionnaires, women were classified into one of three caffeine exposure categories: none (0 mg/d), low (≤200 mg/d), and high (>200 mg/d). Outcome measurement: BMC and BMD of the total hip, the lumbar spine (L1-L4), and the whole body were measured in the clinic at baseline and each follow-up visit by dual-energy x-ray absorptiometry (DEXA) using Hologic bone densitometers (Hologic, Inc., Bedford, MA). Statistical analyses: Baseline categorical characteristics of study participants were compared using Pearson’s χ2 tests to assess the statistical significance of overall differences among caffeine intake groups. Cross-sectional and repeated measures data analysis methods were used to assess associations between caffeine intake and BMC and BMD, and change in BMC and BMD. Marginal generalized estimating equations (GEE) were used to examine crude and adjusted mean BMC and BMD by baseline caffeine exposure group. An independent working correlation matrix was utilized for the GEE analysis, since there were both time dependent covariates (i.e., age, BMI, physical activity score, dietary calcium and alcohol intake, smoking, DMPA use, and prior pregnancy) and fixed covariates (i.e., race/ ethnicity and family history of fracture at any point prior to or during follow-up) in the models, and robust standard errors were computed. For all models, individual Wald’s tests were used to evaluate between-group differences (using 0 mg/d as the referent group) and linear trends (using a grouped linear term for the categorized caffeine consumption variable). A priori rationale and results from preliminary bivariate analyses were used to select the covariates included in multivariable models.
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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) Bone mineral density
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Clinical, physiological, other Clinical, physiolgical
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What is the study design? Cohort
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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 dual-energy x-ray absorptiometry (DEXA)
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Caffeine (general) Caffeine (general)
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Coffee, Chocolate, energy drink, gum, medicine/supplement, soda, tea, other? coffee, soda, tea
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Measured or self reported? Self-report
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Children, adolescents, adults, or pregnant included? Adolescents, Adults
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What was the reference, comparison, or control group(s)? (e.g. high vs low consumption, number of cups, etc.) Series of analyses conducted on caffeine terciles: none (0 mg/d), low (≤200 mg/d), and high (>200 mg/d).
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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, BMI, physical activity score, dietary calcium and alcohol intake, smoking, DMPA use, and prior pregnancy, race/ ethnicity and family history of fracture at any point prior to or during follow-up
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What were the sources of funding? This study was supported by grant number 2R01 HD031165 from the National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD (Dr. Scholes
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What conflicts of interest were reported? Not addressed by authors
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Results & Comparisons

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