How Much Coffee Should We Drink Each Day?

In 2019 alone, over 2,600 articles on “coffee” or “caffeine” have been published, according to MEDLINE, the most comprehensive database on life sciences and biomedical research. That means on every single day, we can find 5-10 published research articles on coffee or caffeine.  Often these studies reported results that contradict with each other.  More than 150 million of Americans drink coffee on a daily basis.  The truth is, no matter what we read, many of us can’t live without coffee and we won’t stop anytime soon.  We may as well understand it better and adjust our coffee routines according to the evidence.

How much caffeine are we taking in?

Caffeine is present in 60 plants. Coffee and tea are the most common source of caffeine, but there are many more 1.  The table below summarized the amount of caffeine in some common drinks and food.  The caffeine content in coffee varies depending on source of beans, roast method and brewing method. 

Table I. Caffeine content in some common drinks and food 1.

Espresso is my favorite coffee drink.  Its dark appearance and strong taste make people think it is stronger than a regular coffee.  However, the high-pressure steam during brewing process extracts more aromas and less caffeine.  Thus one serving of espresso has much less caffeine than a cup of drip coffee, given that they are made from same amount of coffee beans.

The popular K-cup yields 75-150 mg caffeine in an 8-oz cup, according to the official Keurig website).

How much coffee a day is safe?

Studies have shown that the effects of caffeine on our body are dose-dependent.  Many unwanted effects are related to consumption of large amount of coffee, say, more than 6 cups a day.

Daily consumption of 400 mg of caffeine is considered safe, as this amount is less likely to be associated with adverse effects 2.  That is about 3 cups of home brewed coffee in an 8 oz cup, or 1 Tall cup of coffee at Starbucks, or 10 shots of espresso.  Today an average American adult drinks two cups of coffee each day.

Our body processes caffeine differently.  Caffeine is primarily metabolized in liver by the enzyme cytochrome P450 1A2 (CYP1A2).  DNA variation in this enzyme contributes different rate of metabolism of caffeine and a wide range of half-life of caffeine in our body, which varies around 2-12 hours 3.

Health benefits of coffee

In the short term, coffee improves our alertness, cognitive function and learning ability.  Moreover, long-term drinking of coffee leads to protective effect against several diseases and better and longer living, as have been well supported by research.

Type 2 diabetes  People who drink coffee daily has reduced risk for diabetes.  Interestingly, decaffeinated coffee has similar protective effect against diabetes 4,5.

Parkinson Disease  Parkinson is a progressive neurodegenerative disease that affects 0.3% of population of 40 years or older 6.  Multiple large-cohort studies showed that coffee or caffeine intake is associated with lower risk of Parkinson disease 7,8.

Gout  Elevated serum uric acid leads to gout.  Increasing intake of either regular or decaffeinated coffee is associated with lower serum uric acid level and lower risk of gout 9,10.

Headache  Caffeine is used in combination with aspirin and tylenol for treating tension headache and migraine, and the combined form is more effective than using aspirin and tylenol alone 11,12.

However, it is important to keep in mind that long-term use of large amount of coffee induces headache 13.  Headache is also the most common symptoms of coffee withdrawal, occurring to 50% of affected individuals 14.

Longevity  Studies have shown that long-term coffee drinking is associated with lower mortality 15,16.  It does not necessarily mean that drinking coffee makes us live longer.  Some argue that healthier people may simply drink more coffee than less healthy people.  On the other hand, it has also been shown that having more than 4 cups of coffee daily is associated with higher mortality, suggesting moderate consumption of coffee is key to its health benefits 17.

Athletic Performance  I love this one.  Each time when I am training for a marathon, I make sure to drink coffee before my training run. In this case, I believe the aromas and taste of coffee affect my mental fitness, as much as what caffeine does to my physical fitness.  However, there are increasing number of studies in recent years supporting caffeine not only improve endurance of runners, but also other aspects of performance in a wide range of sports 18,19.

Adverse Effects of Coffee

Several adverse effects of coffee have been well studied.  These effects appear to be dose dependent, being more prominent in people who drink more than 5 cups of coffee each day.

High blood pressure  Coffee drinking can increase blood pressure by up to 10 mmHg in people who do not normally drink coffee, but have a much smaller effect on people who regularly drink coffee 2,20.

Anxiety – People who have history of anxiety or insomnia may experience more severe symptoms after drinking coffee.  However, this is more likely due to temporary effects of coffee, and there is no evidence supporting long-term use of coffee induces psychiatric disorders 21.

Reduced bone density and osteoporosis – Coffee consumption is associated with reduced bone density and higher risk for osteoporosis, particularly in people with lower calcium intake 22,23.

Interference with other medicine  Coffee has been shown to inhibit absorbance of certain medicine if taken together.  Some examples include iron supplement for treating anemia, Alendronate for treating osteoporosis and Levothyroxine for treating hypothyroidism 24–26.

Inconclusive Evidence

Many studies on coffee and caffeine reported mixed effects on health, both benefits and harms.  Many factors may contribute to the complexity of this topic.  For instance, genetic variation in metabolism and response to caffeine may cause inconsistent outcomes in different studies.  Future studies are needed to address these remaining questions.

Cancers – Some studies have shown that coffee or caffeine is associated with reduced risk for certain cancers.  However, the evidence has been inconclusive and vary among different cancer types. 

Cardiovascular diseases – Caffeine can possibly affect function of heart and blood vessels through several different mechanisms.  However, studies have shown that caffeine from moderate coffee consumption does not add extra burden to cardiovascular system.  Moreover, some studies suggest that moderate coffee drinking is associated with lower risk of heart attack and stroke, and lower mortality 27,28.

Some patients with arrhythmias (irregular heart rhythm), may feel heart racing after drinking coffee due to the stimulant effect of caffeine. No evidence suggests that moderate coffee drinking triggers irregular heart rhythm 29.

Alzheimer Disease – Alzheimer disease affects older adults and is the most common cause of dementia.  Although some researchers found protective effects of coffee against Alzheimer disease in both human and animal model, some other studies do not support this notion 28,30,31.

GERD – Many patients and their physicians empirically associate coffee drinking with heartburn or gastroesophageal reflux disease (GERD).  However, evidence for such connection has been inconsistent 32,33.

Conclusion

For those of us who drink coffee daily, there is no scientific evidence suggesting that we should stop now.  Instead, coffee brings multiple health benefits and protects us from several diseases.  Moderation seems to be the key for striking the balance between benefits and adverse effects.  If we adhere to moderate coffee assumption (i.e., no more than 2 cups a day), we may be on our way to better fitness and a longer life.

Over 500 chemicals have been characterized from roasted coffee and their concentration in brewed coffee varies drastically.  Many studies have shown how these non-caffeine chemicals, such as antioxidants, benefit our health 34,35.  Hopefully future studies will offer us more reasons to enjoy our favorite coffee drinks.

The coffee sleeve from Sweetwaters

References

1.         Nieber K. The Impact of Coffee on Health. Planta Medica 2017;83(16):1256–63.

2.         Wikoff D, Welsh BT, Henderson R, et al. Systematic review of the potential adverse effects of caffeine consumption in healthy adults, pregnant women, adolescents, and children. Food Chem Toxicol 2017;109(Pt 1):585–648.

3.         Cornelis MC, El-Sohemy A, Kabagambe EK, Campos H. Coffee, CYP1A2 genotype, and risk of myocardial infarction. JAMA 2006;295(10):1135–41.

4.         van Dam RM, Willett WC, Manson JE, Hu FB. Coffee, caffeine, and risk of type 2 diabetes: a prospective cohort study in younger and middle-aged U.S. women. Diabetes Care 2006;29(2):398–403.

5.         van Dam RM, Hu FB. Coffee consumption and risk of type 2 diabetes: a systematic review. JAMA 2005;294(1):97–104.

6.         Pringsheim T, Jette N, Frolkis A, Steeves TDL. The prevalence of Parkinson’s disease: a systematic review and meta-analysis. Mov Disord 2014;29(13):1583–90.

7.         Costa J, Lunet N, Santos C, Santos J, Vaz-Carneiro A. Caffeine exposure and the risk of Parkinson’s disease: a systematic review and meta-analysis of observational studies. J Alzheimers Dis 2010;20 Suppl 1:S221-238.

8.         Noyce AJ, Bestwick JP, Silveira-Moriyama L, et al. Meta-analysis of early nonmotor features and risk factors for Parkinson disease. Ann Neurol 2012;72(6):893–901.

9.         Choi HK, Willett W, Curhan G. Coffee consumption and risk of incident gout in men: a prospective study. Arthritis Rheum 2007;56(6):2049–55.

10.       Choi HK, Curhan G. Coffee, tea, and caffeine consumption and serum uric acid level: the third national health and nutrition examination survey. Arthritis Rheum 2007;57(5):816–21.

11.       Goldstein J, Silberstein SD, Saper JR, Ryan RE, Lipton RB. Acetaminophen, aspirin, and caffeine in combination versus ibuprofen for acute migraine: results from a multicenter, double-blind, randomized, parallel-group, single-dose, placebo-controlled study. Headache 2006;46(3):444–53.

12.       Diener H-C, Gold M, Hagen M. Use of a fixed combination of acetylsalicylic acid, acetaminophen and caffeine compared with acetaminophen alone in episodic tension-type headache: meta-analysis of four randomized, double-blind, placebo-controlled, crossover studies. J Headache Pain 2014;15:76.

13.       Bigal ME, Sheftell FD, Rapoport AM, Tepper SJ, Lipton RB. Chronic daily headache: identification of factors associated with induction and transformation. Headache 2002;42(7):575–81.

14.       Juliano LM, Griffiths RR. A critical review of caffeine withdrawal: empirical validation of symptoms and signs, incidence, severity, and associated features. Psychopharmacology (Berl) 2004;176(1):1–29.

15.       Woodward M, Tunstall-Pedoe H. Coffee and tea consumption in the Scottish Heart Health Study follow up: conflicting relations with coronary risk factors, coronary disease, and all cause mortality. J Epidemiol Community Health 1999;53(8):481–7.

16.       Poole R, Kennedy OJ, Roderick P, Fallowfield JA, Hayes PC, Parkes J. Coffee consumption and health: umbrella review of meta-analyses of multiple health outcomes. BMJ 2017;359:j5024.

17.       Liu J, Sui X, Lavie CJ, et al. Association of coffee consumption with all-cause and cardiovascular disease mortality. Mayo Clin Proc 2013;88(10):1066–74.

18.       Higgins S, Straight CR, Lewis RD. The Effects of Preexercise Caffeinated Coffee Ingestion on Endurance Performance: An Evidence-Based Review. Int J Sport Nutr Exerc Metab 2016;26(3):221–39.

19.       Burke LM. Caffeine and sports performance. Appl Physiol Nutr Metab 2008;33(6):1319–34.

20.       Corti R, Binggeli C, Sudano I, et al. Coffee acutely increases sympathetic nerve activity and blood pressure independently of caffeine content: role of habitual versus nonhabitual drinking. Circulation 2002;106(23):2935–40.

21.       Kendler KS, Myers J, O Gardner C. Caffeine intake, toxicity and dependence and lifetime risk for psychiatric and substance use disorders: an epidemiologic and co-twin control analysis. Psychol Med 2006;36(12):1717–25.

22.       Harris SS, Dawson-Hughes B. Caffeine and bone loss in healthy postmenopausal women. Am J Clin Nutr 1994;60(4):573–8.

23.       Rapuri PB, Gallagher JC, Kinyamu HK, Ryschon KL. Caffeine intake increases the rate of bone loss in elderly women and interacts with vitamin D receptor genotypes. Am J Clin Nutr 2001;74(5):694–700.

24.       Gertz BJ, Holland SD, Kline WF, et al. Studies of the oral bioavailability of alendronate. Clin Pharmacol Ther 1995;58(3):288–98.

25.       Hurrell RF, Reddy M, Cook JD. Inhibition of non-haem iron absorption in man by polyphenolic-containing beverages. Br J Nutr 1999;81(4):289–95.

26.       Benvenga S, Bartolone L, Pappalardo MA, et al. Altered intestinal absorption of L-thyroxine caused by coffee. Thyroid 2008;18(3):293–301.

27.       Ding M, Bhupathiraju SN, Satija A, van Dam RM, Hu FB. Long-term coffee consumption and risk of cardiovascular disease: a systematic review and a dose-response meta-analysis of prospective cohort studies. Circulation 2014;129(6):643–59.

28.       Larsson SC, Orsini N. Coffee Consumption and Risk of Dementia and Alzheimer’s Disease: A Dose-Response Meta-Analysis of Prospective Studies. Nutrients 2018;10(10).

29.       Klatsky AL, Hasan AS, Armstrong MA, Udaltsova N, Morton C. Coffee, caffeine, and risk of hospitalization for arrhythmias. Perm J 2011;15(3):19–25.

30.       Arendash GW, Schleif W, Rezai-Zadeh K, et al. Caffeine protects Alzheimer’s mice against cognitive impairment and reduces brain beta-amyloid production. Neuroscience 2006;142(4):941–52.

31.       Barranco Quintana JL, Allam MF, Serrano Del Castillo A, Fernández-Crehuet Navajas R. Alzheimer’s disease and coffee: a quantitative review. Neurol Res 2007;29(1):91–5.

32.       Kim J, Oh S-W, Myung S-K, et al. Association between coffee intake and gastroesophageal reflux disease: a meta-analysis. Dis Esophagus 2014;27(4):311–7.

33.       Surdea-Blaga T, Negrutiu DE, Palage M, Dumitrascu DL. Food and Gastroesophageal Reflux Disease. Curr Med Chem 2019;26(19):3497–511.

34.       Richelle M, Tavazzi I, Offord E. Comparison of the antioxidant activity of commonly consumed polyphenolic beverages (coffee, cocoa, and tea) prepared per cup serving. J Agric Food Chem 2001;49(7):3438–42.

35.       Yen W-J, Wang B-S, Chang L-W, Duh P-D. Antioxidant properties of roasted coffee residues. J Agric Food Chem 2005;53(7):2658–63.

About the Author Isabel Wang, MD/PhD

I received my MD from PUMC in Beijing China and my Ph.D. in Biochemistry from Stony Brook University on Long Island. Over the years, I have worked in the fields of genetic research and clinical medicine in different parts of the US, including PA, MO, CT, FL, NY and MI. My research has been published in multiple scientific journals. Currently I live in Ann Arbor, MI with my husband and our children and Mango the orange tabby. I love hiking, running, baking, cooking and biking.

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