Written and edited by Abel B. Daartey, PharmD

Coffee is one of those everyday drinks that has been accused of almost everything: helping the liver, raising anxiety, protecting against diabetes, disturbing sleep, and maybe even affecting cancer risk. The truth is more interesting than a simple “good” or “bad.”

When researchers look across large population studies, coffee is more often linked with benefit than harm. But most of that evidence is observational, meaning it can show patterns but cannot prove that coffee itself caused the outcome. People who drink coffee may differ from people who do not in many other ways: smoking history, diet, sleep, income, alcohol use, exercise, and health conditions.

So the better question is not “Does coffee prevent cancer?” The better question is: where is the evidence strongest, where is it weak, and what should ordinary people do with it?

The Strongest Signals: Liver and Womb Cancer

The World Cancer Research Fund reports strong evidence that coffee reduces the risk of liver cancer and womb cancer, also called endometrial cancer [1]. For several other cancers, the evidence is less certain and should be treated as suggestive, not proven.

A large umbrella review in the BMJ found that coffee consumption was more often associated with health benefit than harm across many outcomes, including some cancer outcomes [2]. A more recent review in GeroScience also summarized evidence suggesting lower risks for hepatocellular carcinoma, endometrial cancer, and some other cancer types among regular coffee drinkers [3].

The liver story is probably the most convincing. Coffee is linked with lower liver enzyme levels, lower fibrosis risk, and lower risk of cirrhosis in many studies [2,3]. Since cirrhosis and chronic liver injury can increase the risk of hepatocellular carcinoma, it makes biological sense that coffee might show a protective pattern in liver cancer research.

What Is Inside Coffee?

Coffee is not just caffeine. It contains hundreds of chemical constituents, including chlorogenic acids, trigonelline, cafestol, kahweol, melanoidins, and many roasting-derived compounds [5]. The final mixture depends on the bean, roast level, brewing method, serving size, and whether the coffee is filtered.

Some of these compounds can affect biological pathways that matter in cancer prevention research:

• Oxidative stress: Coffee polyphenols can influence antioxidant defenses and may help reduce some forms of DNA damage in experimental settings [5].
• Inflammation: A short clinical trial found that filtered coffee consumption changed several inflammatory and metabolic markers over four weeks [6]. This does not prove cancer prevention, but it supports the idea that coffee is biologically active.
• Metabolism: Coffee drinking has been linked with lower risk of type 2 diabetes in multiple observational studies [7]. That matters because insulin resistance and poor metabolic health are also connected to risk for several cancers.
• Liver biology: Coffee may influence bile acid metabolism, liver enzymes, fibrosis pathways, and adenosine signaling in liver tissue [2,3].

Where the Risk Signals Appear

Not all coffee research points in a protective direction. Some studies have reported a higher lung cancer signal among coffee drinkers, but this is one of the hardest findings to interpret because coffee drinking and cigarette smoking have historically clustered together in many populations [3]. Residual confounding by smoking is a major concern.

The clearest IARC warning is not about coffee chemistry. It is about temperature. IARC classified drinking coffee as Group 3, meaning it could not be classified as carcinogenic to humans. But IARC classified very hot beverages, usually above about 65 degrees C, as probably carcinogenic to humans because repeated heat injury may damage the lining of the esophagus [4].

In plain language: coffee itself is not the problem in that warning. Burning-hot liquid is the problem. Letting very hot drinks cool a little is a simple, practical step.

Caffeine Is Personal

Caffeine affects people differently. Some people drink coffee at night and sleep well. Others drink one cup at noon and feel wired until bedtime. Genetics, liver enzymes such as CYP1A2, medications, pregnancy, anxiety, reflux, insomnia, and heart rhythm symptoms can all change how coffee feels in the body [8].

This is why “3 to 4 cups a day” should not be treated as a prescription. Some umbrella reviews find that moderate coffee intake, often around 3 to 4 cups daily, is associated with lower risk for several outcomes [2]. But that does not mean everyone should aim for that amount. A pregnant person, someone with severe anxiety, uncontrolled reflux, insomnia, or caffeine-triggered palpitations may need much less.

What This Means in Practice

For most healthy adults, moderate coffee intake appears compatible with cancer prevention advice, especially if the coffee is not consumed very hot and is not loaded with sugar or high-calorie additions. The evidence is most supportive for liver and endometrial cancer, and weaker for most other cancers.

Coffee should not be used as a substitute for the things with stronger evidence: avoiding tobacco, limiting alcohol, maintaining metabolic health, screening when eligible, treating hepatitis when present, vaccination against hepatitis B when indicated, and following medical advice for liver disease.

So yes, coffee has a better cancer story than many people think. But it is still just coffee. Useful maybe, biologically interesting for sure, but not a medicine.

This article is for science education only and is not medical advice. If you are pregnant, have heart rhythm symptoms, severe anxiety, reflux, insomnia, liver disease, or take medications affected by caffeine, discuss coffee intake with a qualified health professional.

References

1. World Cancer Research Fund. Coffee, tea and cancer. Available at: https://www.wcrf.org/preventing-cancer/topics/coffee-tea-and-cancer/.
2. Poole R et al. (2017) Coffee consumption and health: umbrella review of meta-analyses of multiple health outcomes. BMJ 359:j5024. doi:10.1136/bmj.j5024.
3. Kunutsor SK et al. (2024) Coffee consumption, cancer, and healthy aging: epidemiological evidence and underlying mechanisms. GeroScience 47:1517-1555. doi:10.1007/s11357-024-01332-8.
4. Loomis D et al. (2016) Carcinogenicity of drinking coffee, mate, and very hot beverages. Lancet Oncol 17:877-878. doi:10.1016/S1470-2045(16)30239-X. IARC Volume 116 summary: IARC evaluation.
5. Ludwig IA et al. (2014) Coffee: biochemistry and potential impact on health. Food Funct 5:1695-1717. doi:10.1039/C4FO00042K.
6. Kempf K et al. (2010) Effects of coffee consumption on subclinical inflammation and other risk factors for type 2 diabetes: a clinical trial. Am J Clin Nutr 91:950-957. doi:10.3945/ajcn.2009.28548.
7. van Dam RM and Hu FB (2005) Coffee consumption and risk of type 2 diabetes: a systematic review. JAMA 294:97-104. doi:10.1001/jama.294.1.97.
8. Cornelis MC et al. (2006) Coffee, CYP1A2 genotype, and risk of myocardial infarction. JAMA 295:1135-1141. doi:10.1001/jama.295.10.1135.

Featured image created using Google Gemini AI.