BACKGROUND: Consumption of caffeinated beverages such as coffee and tea has been associated with a lower risk of type 2 diabetes (T2D). Paradoxically, short-term metabolic studies have shown that caffeine impairs postprandial glycemic control. OBJECTIVE: The objective was to prospectively examine the association of caffeinated compared with caffeine-free beverages, including coffee, tea, sugar-sweetened beverages (SSBs), and carbonated artificially sweetened beverages (ASBs), with T2D risk. DESIGN: We prospectively observed 74,749 women from the Nurses' Health Study (NHS, 1984-2008) and 39,059 men from the Health Professionals Follow-Up Study (HPFS, 1986-2008) who were free of diabetes, cardiovascular diseases, and cancer at baseline. RESULTS: We documented 7370 incident cases of T2D during 24 y of follow-up in the NHS and 2865 new cases during 22 y of follow-up in the HPFS. After major lifestyle and dietary risk factors were controlled for, caffeinated and caffeine-free SSB intake was significantly associated with a higher risk of T2D in the NHS (RR per serving: 13% for caffeinated SSB, 11% for caffeine-free SSB; P < 0.05) and in the HPFS (RR per serving: 16% for caffeinated SSB, 23% for caffeine-free SSB; P < 0.01). Only caffeine-free ASB intake in NHS participants was associated with a higher risk of T2D (RR: 6% per serving; P < 0.001). Conversely, the consumption of caffeinated and decaffeinated coffee was associated with a lower risk of T2D [RR per serving: 8% for both caffeinated and decaffeinated coffee in the NHS (P < 0.0001) and 4% for caffeinated and 7% for decaffeinated coffee in the HPFS (P < 0.01)]. Only caffeinated tea was associated with a lower T2D risk among NHS participants (RR per serving: 5%; P < 0.0001). CONCLUSION: Irrespective of the caffeine content, SSB intake was associated with a higher risk of T2D and coffee intake was associated with a lower risk of T2D.
"This could be due to the natural variability of plants and to differences in extraction procedures and analytical techniques. Epidemiological studies indicate that caffeine consumption is associated with a decreased risk of developing T2DM (Bhupathiraju et al., 2013; Biessels, 2010). Several studies suggest that long-term consumption of drinks with caffeine, such as tea or coffee, may facilitate the maintenance of normal glucose tolerance (Agardh et al., 2004; Salazar-Martinez et al., 2004; Van Dam et al., 2004; Yamaji et al., 2004). "
"(d) We identified three cohorts with multiple publications, from which we selected for this synthesis the one publication in which SSB was either the main study variable or the definition was the clearest. We identified two publications of the Health Professionals Follow-up study (HPFS); of these two publications, the one that assessed SSB as the primary study variable was selected for inclusion  and the other that presented analyses stratified by the main variable, caffeine consumption, was excluded . We selected one of the three publications from the Nurse’s Health Study (NHS). "
[Show abstract][Hide abstract] ABSTRACT: Background
Assessment of design heterogeneity conducted prior to meta-analysis is infrequently reported; it is often presented post hoc to explain statistical heterogeneity. However, design heterogeneity determines the mix of included studies and how they are analyzed in a meta-analysis, which in turn can importantly influence the results. The goal of this work is to introduce ways to improve the assessment and reporting of design heterogeneity prior to statistical summarization of epidemiologic studies.
In this paper, we use an assessment of sugar-sweetened beverages (SSB) and type 2 diabetes (T2D) as an example to show how a technique called ‘evidence mapping’ can be used to organize studies and evaluate design heterogeneity prior to meta-analysis.. Employing a systematic and reproducible approach, we evaluated the following elements across 11 selected cohort studies: variation in definitions of SSB, T2D, and co-variables, design features and population characteristics associated with specific definitions of SSB, and diversity in modeling strategies.
Evidence mapping strategies effectively organized complex data and clearly depicted design heterogeneity. For example, across 11 studies of SSB and T2D, 7 measured diet only once (with 7 to 16 years of disease follow-up), 5 included primarily low SSB consumers, and 3 defined the study variable (SSB) as consumption of either sugar or artificially-sweetened beverages. This exercise also identified diversity in analysis strategies, such as adjustment for 11 to 17 co-variables and a large degree of fluctuation in SSB-T2D risk estimates depending on variables selected for multivariable models (2 to 95% change in the risk estimate from the age-adjusted model).
Meta-analysis seeks to understand heterogeneity in addition to computing a summary risk estimate. This strategy effectively documents design heterogeneity, thus improving the practice of meta-analysis by aiding in: 1) protocol and analysis planning, 2) transparent reporting of differences in study designs, and 3) interpretation of pooled estimates. We recommend expanding the practice of meta-analysis reporting to include a table that summarizes design heterogeneity. This would provide readers with more evidence to interpret the summary risk estimates.
"Caffeine is found in many natural and processed products. Examples of these sources include green tea  , mate tea  , chocolate , and caffeinated beverages and energy drinks   . C. arabica  and Robusta coffee (C. "
[Show abstract][Hide abstract] ABSTRACT: Production of coffee beans is an important lifeline for the economy of several countries in Latin America, Africa, and Asia.
The brew from this well sought for cash crop is readily consumed due to its good sensory qualities owing to the presence of
many micronutrients. Some of these chemical compounds possess biological activities, including antiproliferative, antioxidant,
and antimicrobial effects. Four representative groups of these micronutrients, namely, caffeine, chlorogenic acid, diterpenes, and
trigonelline, play key roles in these bioactive effects of coffee. In order to guarantee the quality of coffee products and to protect
consumer interest and safeguard their well-being, it is extremely important to employ sensitive and accurate analytical methods in
the characterization and quantitative determination of these bioactive constituents. This review aims to present recent applications
in this regard.
Miriam Rabkin, Anthony Mutiti, Christine Chung, Yuan Zhang, Ying Wei, Wafaa M El-Sadr
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