Antioxidants in Coffee
Coffee is full of compounds that act as antioxidants in the lab, and because so many people drink so much of it, it is often the biggest source of them in their diet. Whether that does anything for your health is a separate, harder question, and the honest answer is that we do not know for sure.
This page covers what the antioxidants in coffee actually are, how roasting changes them, how much of our intake they account for, and what the research on health does and does not show. Where a claim comes from a study, the study is named at the bottom.
It is not medical advice. If you have a condition affected by caffeine, ask your doctor.
What the antioxidants are
Chlorogenic acids. The main group of polyphenols in coffee, abundant in green coffee beans. They are esters of caffeic and quinic acids, and they behave as antioxidants in laboratory tests. They also contribute to coffee's bitterness and acidity.
Melanoidins. Large brown compounds formed during roasting by the Maillard reaction, the same reaction that browns bread crust. They give roasted coffee its colour and some of its body, and they also show antioxidant activity in laboratory tests.
Others. Caffeine itself, trigonelline, and smaller amounts of other compounds all play a part. Coffee also contains the diterpenes cafestol and kahweol, which are relevant for a different reason, covered below.
What roasting does
Roasting destroys a large share of the chlorogenic acids in green coffee, and the darker the roast, the more is lost. At the same time it creates melanoidins, which are not present in green coffee at all. So a light roast keeps more chlorogenic acid, and a dark roast has more melanoidins. Measured antioxidant capacity in the lab does not fall in a straight line as roasting gets darker, because one group of compounds is partly replacing the other.
This is also why green coffee extract is sold as a supplement: it is a concentrated source of chlorogenic acids. Evidence for health effects of those supplements is weak and they are not the same as drinking coffee.
How much coffee contributes
In a Norwegian dietary study published in 2004, coffee was the single largest contributor to measured antioxidant intake among the people studied, ahead of fruit, vegetables, tea and wine. A later Norwegian study of women, published in 2014, found that coffee explained more of the variation in antioxidant intake between people than any other food.
That does not mean coffee is richer in antioxidants than fruit and vegetables gram for gram. It means people drink a great deal of it, every day, and it is a concentrated source. It is a statement about diets as much as about coffee.
What the health evidence shows
The most comprehensive summary is an umbrella review of meta-analyses published in the BMJ in 2017. It found that drinking coffee was more often associated with benefit than harm across a wide range of outcomes. The largest reduction in risk for death from all causes and from cardiovascular disease was seen at around three to four cups a day, compared with none. Associations with lower risk of some liver diseases were among the strongest and most consistent. Lower risk of type 2 diabetes, Parkinson's disease and some cancers was also reported.
The same review was careful about what that means. Most of the evidence is observational, rated low or very low quality, and cannot show cause and effect. People who drink coffee may differ from people who do not in many ways, and smoking in particular can distort the results. Studies using genetic methods to test causation did not find a causal link for type 2 diabetes or for mortality.
Antioxidants are one possible explanation for the associations, among several. Compounds that act as antioxidants in a test tube are absorbed, transformed and excreted by the body in ways that make their effects inside us much harder to measure. It is accurate to say coffee contains antioxidants and that moderate coffee drinking is associated with good health outcomes. It is not established that the first causes the second.
Who should be careful
Pregnancy. The 2017 review found high coffee intake in pregnancy associated with low birth weight, preterm birth and pregnancy loss. Many health bodies advise limiting caffeine in pregnancy. See caffeine by drink.
Unfiltered coffee and cholesterol. Cafestol and kahweol, which paper filters remove but French press, Turkish and boiled coffee do not, can raise LDL cholesterol in people who drink a lot of unfiltered coffee.
Fracture risk in women. The same review reported a possible association between high intake and fracture risk in women, which the authors described as uncertain.
Questions
Does coffee have antioxidants?
Yes. Mainly chlorogenic acids, which are reduced by roasting, and melanoidins, which are created by it.
Does light or dark roast have more antioxidants?
Light roasts keep more chlorogenic acids. Dark roasts have more melanoidins. Overall antioxidant capacity does not simply fall as roast gets darker.
Is coffee good for you?
For most healthy adults, moderate coffee drinking, around three to four cups a day, is associated with good health outcomes in large reviews. Most of that evidence is observational and cannot prove cause and effect.
Does adding milk cancel the antioxidants?
Some studies have found milk proteins bind certain polyphenols, but it is not clear that this matters for health. Drink coffee the way you enjoy it.
Sources
- Svilaas et al., Intakes of antioxidants in coffee, wine, and vegetables are correlated with plasma carotenoids in humans, Journal of Nutrition 2004 Coffee as the largest single contributor to measured antioxidant intake.
- Qureshi et al., Food items contributing most to variation in antioxidant intake, BMC Public Health 2014 Coffee explained 54 percent of the variation in antioxidant intake among Norwegian women.
- Ludwig et al., Coffee: biochemistry and potential impact on health, Food & Function 2014 Chlorogenic acids, melanoidins and the effects of roasting.
- Poole et al., Coffee consumption and health: umbrella review of meta-analyses of multiple health outcomes, BMJ 2017 Associations with health outcomes, the quality of the evidence, and cautions on pregnancy, fracture and unfiltered coffee.