By Jennifer Ng, MD
Peer Reviewed
Addiction, by definition, is a negative word. It implies the overindulging of something with a high or uncertain risk to benefit ratio, such as coffee. Yet recently, writer Markham Heid informed coffee addicts all over the world, “Drink Coffee, Lower Your Diabetes Risk” [1]. To add to that, it’s not just coffee; tea and decaf can do it too, or so his article proclaims. Skeptical? Let’s review the evidence and judge for ourselves.
It turns out that this same issue has preoccupied researchers for some time. The earliest articles in the Pubmed database on coffee and diabetes date back to the 1960s, including one published in The Lancet titled, “Effect of coffee on glucose intolerance and circulating insulin in men with maturity-onset diabetes” [2]. Another Pubmed search using tea and diabetes uncovers a letter in a German journal titled “Letter: The effectiveness of the bean-shell tea in diabetes,” which dates back to 1973 [3]. Since then, the associations between the consumption of coffee, and to a lesser extent, tea, with reduced risk of diabetes mellitus (DM) have been replicated in many observational studies [4,5].
Starting off with the evidence for coffee: a 2009 systematic review analyzed 20 cohort studies investigating this association [4]. Participants totaled 517,325 men and women from Singapore, Puerto Rico, the United Kingdom, Finland, the United States, Japan, the Netherlands, and Sweden. Results showed that with each additional cup of coffee consumed daily, there was a 7% reduction in the excess risk of DM (relative risk [RR] 0.93, 95% confidence interval [CI] 0.91-0.95, p < .001). In fact, in this study, the risk of developing DM was about 25% lower in the group that drank 3 to 4 cups daily, as compared to those who drank only 0 to 2 cups per day (RR 0.76, 95% CI 0.69-0.82). Similarly, the consumption of 3 to 4 cups of decaffeinated coffee daily was also associated with a much lower risk of DM than that of those who consumed none (RR 0.64, 95% CI 0.54-0.77).
Taking the investigation one step further, an observational study published in 2014 looked at the effect of changes in coffee intake on the risk of diabetes using three cohorts – the participants in the Nurses’ Health Study (NHS), the NHS II and the Health Professionals Follow-up Study (HPFS) [5]. A total of 95,974 women and 27,759 men were included. Moderate to large increases in coffee consumption (> 1 cup per day), compared to no change (which included any change of 1 cup or less per week), over a 4 year period were associated with an 11% lower risk of developing DM in the subsequent 4 years (hazard ratio HR 0.89, 95% CI 0.82-0.97), even after adjusting for potential confounders such as baseline BMI and concurrent weight change. Inversely, moderate to large decreases in coffee consumption, compared to no change, over a four year period correlated with a 17% higher risk of developing DM in the subsequent 4 years (HR 1.17, 95% CI 1.08-1.26). Of note, these associations were seen only in caffeinated coffee consumption in this study.
Compared to that of caffeinated coffee, the evidence for tea consumption in reducing the risk of diabetes is less clear cut. The same 2009 systematic review mentioned above included 7 studies (n = 286,701) that investigated this association and found that the consumption of more than 3 to 4 cups of tea daily correlated with an 18% reduction in risk of DM compared to that of no tea consumption (RR 0.82, 95% CI 0.73-0.94) [4]. Of note, these studies included all different types of tea – decaffeinated, caffeinated, black, green, etc. On the other hand, the aforementioned study from 2014 found no significant association between the changes in tea consumption and subsequent risk of diabetes [5]. The authors hypothesized that the relatively lesser number of tea consumers in this study, compared to that of coffee, and the lower numbers of participants who made changes in tea consumption might have led to these negative results. Also, keep in mind that teas constitute a much more heterogenous population of beverages than do coffee, and therefore, depending on which tea is studied, the effects may be more variable.
Establishing these associations (or lack thereof) between coffee, tea and the risk of diabetes, is just the tip of the iceberg. The more interesting question is how coffee or tea may lower the risk of diabetes. Caffeine is an obvious possible answer, as it is a commonality between these two beverages. It may modulate the risk of diabetes in several different ways. For one, caffeine intake is associated with significantly higher levels of adiponectin (an endogenous insulin sensitizer) in people who drink 4 or more cups per day, as compared to those who don’t drink coffee regularly [6]. Therefore, the more coffee (and caffeine) that is consumed, the higher the levels of adiponectin and the more sensitized the body’s tissues are to insulin, counteracting the effects of insulin resistance, which is a key feature of type 2 diabetes.
Another possible explanation, however, of caffeine’s effect on diabetes involves sex hormone-binding globulin (SHBG), the levels of which have been shown to be increased by caffeine consumption [7]. In a New England Journal of Medicine study, low levels of SHBG were shown to correlate with impaired glucose control whereas higher levels of SHBG were associated with a lower risk of diabetes in post-menopausal women (multivariable odds ratios 0.09, 95% CI 0.03-0.21, for the fourth (highest) quartile of plasma SHBG levels, p<0.001 for trend) [8]. Similar results were seen among men as well. Additionally, certain polymorphisms in the SHBG alleles, which increase the levels of SHBG, were also associated with a lower risk of DM. SHBG’s role in attenuating the risk of diabetes is likely due to its effects on sex hormones, as they are known to be involved in many different biologic actions.
Caffeine, with it effects on SHBG and adiponectin, certainly seems to be a plausible explanation for why caffeinated coffee is associated with reduced risk of diabetes, but it cannot be the only explanation, given that decaffeinated coffee and tea (a composite of caffeinated and decaffeinated varieties in the studies) also are intermittently associated with a lower risk of diabetes. Polyphenols, which are a group of compounds found in both coffee (i.e. chlorogenic acid and phytic acid) and tea (i.e. catechins), may be another contributing factor [9,10]. They are known to cause a variety of different effects including increased insulin sensitivity [11,12] and decreased glucose absorption and utilization [13,14]. Antioxidant activity is also part of the repertoire of polyphenol compounds [9] and interestingly, some researchers speculate that antioxidants may play a role in protecting pancreatic beta islet cells from oxidative stress and in helping sensitize peripheral tissues to insulin [10].
While both polyphenols and caffeine in coffee and tea may contribute to their separate beneficial associations with lowered future diabetes risk, do remember that caffeine, at least, may have other less than beneficial effects, such as its arrhythmogenic potential, as well as its effects on possibly increasing other addictive behaviors [15]. Intake of coffee or tea, like everything else, is best done in moderation. Still, the next time you choose to indulge in your caffeinated or decaffeinated beverage of choice, as long as it’s only an extra cup or two, don’t beat yourself up about it. After all, there is a chance that you could be saving yourself from diabetes, in the future.
Dr. Jennifer Ng is a 3rd year resident at NYU Langone Medical Center
Peer reviewed by Terry Seltzer, MD, Medicine, NYU Langone Medical Center
Image: “Coffee vs tea.” Cartoon. 2014. Yeshiva University Observer. Web. 07 May 2014. http://www.yuobserver.org/2014/02/the-ultimate-showdown-tea-vs-coffee/
References:
1. Heid, Markhan. Drink Coffee, Lower Your Diabetes Risk. Time web site. 1 May 2014. time.com/84722/drink-coffee-lower-your-diabetes-risk/
2. Jankelson, OM et al. Effect of coffee on glucose intolerance and circulating insulin in men with maturity-onset diabetes. Lancet 1967, 1(7489):527-9.
3. Petrides, P. Letter: The effectiveness of the bean-shell tea in diabetes. Munch Med Wochenschr 1973,115(42):1854.
4. Huxley, R et al. Coffee, decaffeinated coffee, and tea consumption in relation to incident type 2 diabetes mellitus: a systematic review with meta-analysis. Arch Intern Med 2009, 169:2053–2063.
5. Bhupathiraju, SN et al. Changes in coffee intake and subsequent risk of type 2 diabetes: three large cohorts of US men and women. Diabetologia. 2014 Apr 26. [Epub ahead of print] DOI 10.1007/s00125-014-3235-7 http://dx.doi.org/10.1007/s00125-014-3235-7
6. Williams, CJ et al. Coffee Consumption Is Associated With Higher Plasma Adiponectin Concentrations in Women With or Without Type 2 Diabetes: A prospective cohort study. Diabetes Care. March 2008; 31(3):504-507. doi: 10.2337/dc07-1952. http://care.diabetesjournals.org/content/31/3/504.long
7. Goto, A et al. Coffee and Caffeine Consumption in Relation to Sex Hormone–Binding Globulin and Risk of Type 2 Diabetes in Postmenopausal Women. Diabetes. January 2011; 60:1, 269-275; published ahead of print October 28, 2010, doi:10.2337/db10-1193 1939-327X http://diabetes.diabetesjournals.org/content/60/1/269.long
8. Ding, EL et al. Sex Hormone–Binding Globulin and Risk of Type 2 Diabetes in Women and Men. N Engl J Med 2009, 361(12):1152-1163. http://www.nejm.org/doi/pdf/10.1056/NEJMoa0804381
9. Ferruzzi, MG. The influence of beverage composition on delivery of phenolic compounds from coffee and tea. Physiol Behav. 2010 Apr 26;100(1):33-41. doi: 10.1016/j.physbeh.2010.01.035. Epub 2010 Feb 6. http://linkinghub.elsevier.com/retrieve/pii/S0031-9384(10)00058-2
10. Pereira, MA et al. Coffee consumption and risk of type 2 diabetes mellitus: An 11-Year Prospective Study of 28 812 Postmenopausal Women. Arch Intern Med. 2006;166(12):1311-1316. doi:10.1001/archinte.166.12.1311 http://archinte.jamanetwork.com/article.aspx?articleid=410548
11. Rodriguez de Sotillo, DV et al. Insulin receptor exon 11+/? is expressed in Zucker (fa/fa) rats, and chlorogenic acid modifies their plasma insulin and liver protein and DNA. J Nutr Biochem. 2006,17:63–71.
12. Venables, MC et al. Green tea extract ingestion, fat oxidation, and glucose tolerance in healthy humans. Am J Clin Nutr. 2008,87:778–784.
13. Johnston, KL et al. Coffee acutely modifies gastrointestinal hormone secretion and glucose tolerance in humans: glycemic effects of chlorogenic acid and caffeine. Am J Clin Nutr. 2003, 78: 728–733.
14. Shimizu, M et al. Regulation of intestinal glucose transport by tea catechins. Biofactors. 2000, 13: 61–65.
15. Parikh, Anish. The Health risks and benefits of drinking coffee. Clinical Correlations: The NYU Langone Online Journal of Medicine. Jul 17 2013. https://www.clinicalcorrelations.org/?p=6254
One comment on “Get Your Caffeine fix while lowering your diabetes risk – too good to be true?”
I enjoyed reading this thorough and interesting review on the potential role of coffee and caffeine on glucose metabolism. Caffeine’s principal pharmacologic action is to non-selectively block adenosine receptors. This action accounts for the arrhythmias and jitteriness resulting from over-caffeination and is responsible for the beneficial role of coffee and caffeine in graduate medical education (keeping sleep-deprived house staff and others awake). Work in our laboratory has highlighted the role of adenosine and adenosine receptors in the development of fatty liver, a common accompaniment of diabetes, and there is a significant literature on the potential utility of adenosine receptor (specifically the A2B receptor) blockade in the treatment of experimental diabetes in mice. Moreover, we have reported that another adenosine receptor, the A2A receptor, plays an important role in hepatic fibrosis/cirrhosis and a number of observational studies indicate that coffee drinking diminishes the risk of dying from liver disease in a dose-dependent fashion. It will be interesting to see whether studies of adenosine receptor antagonists will be useful for the treatment of diabetes and liver disease.
Comments are closed.