Medical Studies About Coffee

A list of useful articles regarding Coffee and its affects on human organism.

Also see:

While surfing on PubMed (a service of the U.S. National Library of Medicine that includes over 17 million citations from MEDLINE and other life science journals) I came across many articles regarding coffee and its many affects on human organism.
This is a small list from those papers. I'll try to expand its contents regularly and maybe rewrite some stuff to make them more understandable for ppl without medical background.

Coffee Consumption and the Reduced Risk of Type 2 Diabetes:

Title: Metabolic and hormonal effects of caffeine: randomized, double-blind, placebo-controlled crossover trial.
Authors: Mackenzie T, Comi R, Sluss P, Keisari R, Manwar S, Kim J, Larson R, Baron JA.
Source: Metabolism, 2007 Dec;56(12):1694-8.
Abstract: In short-term studies, caffeine has been shown to increase insulin levels, reduce insulin sensitivity, and increase cortisol levels. However, epidemiological studies have indicated that long-term consumption of beverages containing caffeine such as coffee and green tea is associated with a reduced risk of type 2 diabetes mellitus. There is a paucity of randomized studies addressing the metabolic and hormonal effects of consuming caffeine over periods of more than 1 day. We evaluated the effect of oral intake of 200 mg of caffeine taken twice a day for 7 days on glucose metabolism, as well as on serum cortisol, dehydroepiandrosterone (DHEA), and androstenedione, and on nighttime salivary melatonin. A double-blind, randomized, placebo-controlled crossover study with periods of 7 days and washouts of 5 days comparing caffeine with placebo capsules was conducted. Participants were 16 healthy adults aged 18 to 22 years with a history of caffeine consumption. Blood samples from each subject were assayed for glucose, insulin, serum cortisol, DHEA, and androstenedione on the eighth day of each period after an overnight fast. Nighttime salivary melatonin was also measured. Insulin levels were significantly higher (by 1.80 μU/mL; 95% confidence interval, 0.33-3.28) after caffeine intake than after placebo. The homeostasis model assessment index of insulin sensitivity was reduced by 35% (95% confidence interval, 7%-62%) by caffeine. There were no differences in glucose, DHEA, androstenedione, and melatonin between treatment periods. This study provides evidence that daily caffeine intake reduces insulin sensitivity; the effect persists for at least a week and is evident up to 12 hours after administration.

Title: Pharmacological Bases of Coffee Nutrients for Diabetes Prevention
Author: Kitaro OKA
Source: YAKUGAKU ZASSHI, Vol. 127, 1825-1836 (2007).
Abstract: With an increasing number of studies describing the negative correlation of coffee consumption and the risk for type 2 diabetes mellitus, we were compelled to elucidate the nutrients which bring pharmacological effects on risk reduction for diabetes. In this review, the author's interest is focused on chlorogenic and caffeic acids derived from lightly roasted coffee beans, as well as nicotinic acid, volatile Maillard reaction products (vMRPs), and another structurally unknown compound contained in heavily roasted beans. Caffeine is a common compound in both lightly and heavily roasted beans and its anti-inflammatory effects on degenerative diseases such as diabetes mellitus has been reevaluated recently. The prophylactic effects of coffee on diabetes involve pleiotropy of plural components in accordance to the degree of the roasting. A new concept of nutritional blended coffee may be important to optimize the prophylactic effects of coffee on lowering the risk factors of diabetes and delaying the progress of diabetes complications as well.

Roasted Coffee and the Battle Against Bacterias:

Title: Isolation, Identification, and Quantification of Roasted Coffee Antibacterial Compounds
Authors: Maria Daglia, Adele Papetti, Pietro Grisoli, Camilla Aceti, Valentina Spini, Cesare Dacarro, and Gabriella Gazzani.
Source: Journal of Agriculture and Food Chemistry, ASAP Article, 10.1021/jf0722607.
Abstract: Coffee brew is a widely consumed beverage with multiple biological activities due both to naturally occurring components and to the hundreds of chemicals that are formed during the roasting process. Roasted coffee extract possesses antibacterial activity against a wide range of microorganisms, including Staphylococcus aureus and Streptococcus mutans, whereas green coffee extract exhibits no such activity. The naturally occurring coffee compounds, such as chlorogenic acids and caffeine, cannot therefore be responsible for the significant antibacterial activity exerted by coffee beverages against both bacteria. The very low minimum inhibitory concentration (MIC) found for standard glyoxal, methylglyoxal, and diacetyl compounds formed during the roasting process points to these α-dicarbonyl compounds as the main agents responsible for the antibacterial activity of brewed coffee against Sa. aureus and St. mutans. However, their low concentrations determined in the beverage account for only 50% of its antibacterial activity. The addition of caffeine, which has weak intrinsic antibacterial activity, to a mixture of α-dicarbonyl compounds at the concentrations found in coffee demonstrated that caffeine synergistically enhances the antibacterial activity of α-dicarbonyl compounds and that glyoxal, methylglyoxal, and diacetyl in the presence of caffeine account for the whole antibacterial activity of roasted coffee.

Mouth Hygiene and Coffee:

Title: Chlorogenic Acid in Coffee Can Prevent the Formation of Dinitrogen Trioxide by Scavenging Nitrogen Dioxide Generated in the Human Oral Cavity
Authors: Umeo Takahama, Kanako Ryu, and Sachiko Hirota.
Source: Journal of Agriculture and Food Chemistry, 55 (22), 9251–9258 10.1021/jf071700r.
Abstract: Coffee contains antioxidants like chlorogenic acid and its isomers. In this report, effects of coffee on the nitrite-induced N2O3 formation were studied using whole saliva and bacterial fraction prepared from the saliva. The formation of N2O3 was measured by fluorescence increase due to the transformation of 4,5-diaminofluorescein to triazolfluorescein. Coffee inhibited the nitrite-induced fluorescence increase, and 50% inhibition was observed at several µg of coffee/mL in bacterial fraction of saliva as well as whole saliva. During the inhibition of the fluorescence increase, concentration of chlorogenic acid and its isomers decreased. It is discussed that the reduction of NO2 by chlorogenic acid and its isomers contributed to the coffee-dependent inhibition of the fluorescence increase as N2O3 is formed from NO and NO2. When coffee was added to whole saliva, chlorogenic acid and its isomers bound to cells in the saliva. The rate of the fluorescence increase in bacterial fraction, which was prepared at defined periods after the ingestion of coffee, was increased to the rate before the ingestion of coffee with a half-time of about 1 h. This result suggests that chlorogenic acid and its isomers remained in the oral cavity for a few hours after ingestion of coffee. The significance of coffee drinking and rinsing of the mouth with coffee for the health of the oral cavity is proposed.

Coffee and Cholesterol:

Title: Coffee drinking induces incorporation of phenolic acids into LDL and increases the resistance of LDL to ex vivo oxidation in humans
Authors: Fausta Natella, Mirella Nardini, Federica Belelli and Cristina Scaccini.
Source: American Journal of Clinical Nutrition, Vol. 86, No. 3, 604-609, September 2007.
Abstract: Background: Epidemiologic and intervention studies indicate that both diet as a whole and single dietary components are involved in the risk of atherosclerosis. The resistance of LDL to oxidative modification is an ex vivo indicator of risk, which is modulated by dietary components. Coffee contains phenolic compounds with antioxidant activity. These molecules are found in plasma after the consumption of coffee, and it has been shown that, in vitro, they are able to decrease the susceptibility of LDL to oxidation.

Objective: The aim of this study was to evaluate the effect of coffee consumption on the redox status of LDL as modulated by the possible incorporation of phenolic acids into LDL.

Design: Ten healthy volunteers, after an overnight fast, drank 200 mL filtered coffee. Blood was drawn before and 30 and 60 min after drinking. Changes in LDL redox status were evaluated by the measure of LDL resistance to oxidative modification and the concentration of LDL(–), a mildly modified, electronegative LDL subfraction. Chlorogenic and phenolic acids concentration in LDL were measured by electrochemical HPLC.

Results: The resistance of LDL to oxidative modification increased significantly after coffee drinking, but the LDL(–) concentration did not increase. The concentration into LDL of conjugated forms of caffeic, p-coumaric, and ferulic acids increased significantly after coffee drinking.

Conclusion: Drinking 200 mL (1 cup) coffee induces an increase in the resistance of LDL to oxidative modification, probably as a result of the incorporation of coffee's phenolic acids into LDL.

Roasting Time and How it Affects Coffee Nutrients:

Title: Effect of Roasting Conditions on the Polycyclic Aromatic Hydrocarbon Content in Ground Arabica Coffee and Coffee Brew
Authors: Justin Koffi Houessou, Saber Maloug, Anne-Sophie Leveque, Corine Delteil, Bertrand Heyd, and Valerie Camel.
Source: Journal of Agriculture and Food Chemistry, 55 (23), 9719–9726 10.1021/jf071745s
Abstract: Roasting is a critical process in coffee production as it enables the development of flavor and aroma. At the same time, roasting may lead to the formation of nondesirable compounds, such as polycyclic aromatic hydrocarbons (PAHs). In this study, Arabica green coffee beans from Cuba were roasted under controlled conditions to monitor PAH formation during the roasting process. Roasting was performed in a pilot spouted bed roaster, with the inlet air temperature varying from 180 to 260 °C, using both dark (20 min) and light (5 min) roasting conditions. Several PAHs were determined in both roasted coffee samples and green coffee samples. Also, coffee brews, obtained using an electric coffee maker, were analyzed for final estimation of PAH transfer coefficients to the infusion. Formation of phenanthrene, anthracene, and benzo[a]anthracene in coffee beans was observed at temperatures above 220 °C, whereas formation of pyrene and chrysene required 260 °C. Low levels of benzo[g,h,i]perylene were also noted for dark roasting under 260 °C, with simultaneous partial degradation of three-cycle PAHs, suggesting that transformation of low molecular PAHs to high molecular PAHs occurs as the roasting degree is increased. The PAH transfer to the infusion was quite moderate (<35%), with a slightly lower extractability for dark-roasted coffee as compared to light-roasted coffee.

Does Coffee Consumption has Side-effects?

Title: Association between coffee consumption and risk of hypertension
Authors: Paolo Palatini a; Francesca Dorigatti a; Massimo Santonastaso b; Susanna Cozzio c; Tiziano Biasion d; Guido Garavelli e; Achille C. Pessina a; Lucio Mos.
Source: Annals of Medicine, Volume 39, Issue 7 2007 , pages 545 - 553.
Abstract: Background: The longitudinal relationship between coffee use and hypertension is not well known.

Aim: We did a prospective study to investigate if there is a temporal relationship between coffee consumption and development of sustained hypertension.

Method: We assessed 1107 white subjects with elevated blood pressure who were followed up for 6.4 years. Coffee intake and other life-style factors were ascertained from regularly administered questionnaires. Incident physician-diagnosed hypertension was the outcome measure.

Results: During the follow-up, 561 subjects developed sustained hypertension, whereas 546 subjects did not meet the criteria for treatment. Coffee drinkers developed sustained hypertension more frequently than abstainers (53.1% versus 43.9%, P = 0.007). The incidence of hypertension did not differ between moderate and heavy coffee drinkers. Kaplan-Meier analysis confirmed that sustained hypertension was developed more frequently by coffee drinkers compared with nondrinkers (P<0.001). The adjusted relative risk of hypertension was greater in both categories of coffee drinking than in abstainers (hazard ratio, 95% confidence limit (CL) = 1.24, 1.06-1.44). The risk of hypertension associated with coffee drinking increased gradually with increasing level of alcohol use (adjusted P for interaction = 0.005).

Conclusions: In subjects screened for stage 1 hypertension a nonlinear association was found between coffee consumption and development of sustained hypertension.