Coffee: science based benefits and risks

In this Article (Index)

Coffee, a tasty beverage with promising health benefits.

• Coffee
• Chemical compositon of Coffee: Caffeine and phytochemicals
• Caffeine
• How much should you drink?
• Decaffeinated coffee
• Pytochemicals
• Chlorogenic acid (CGA)
• Health Benefits of Coffee
• Risks and Side Effects

Coffee

Coffee is one of the most popular hot (and cold) drinks in the world, with 40% of the world's population drinking it. In 2022, Americans drank 517 million cups of coffee per day; more than 1½ cups per capita. 66% of Americans reported drinking coffee in the past day. (6).

Yearly per capita consumption vary by country from Finland with 12.2 kg to 5.9 kg in Brazil, 4-5 kg in the U.S. and 0.8 kg in China.

Coffee is obtained from the seeds (or coffee beans) of two species of the coffea tribe of plants. There are 129 species of coffea but only two provide almost all the coffee consumed worldwide: Coffea arabica also known as Arabica accounts for roughly 70% of the global production, and Coffea canephora or "Robusta", which covers the remaining 30%.

Coffee shrubs and trees are native to Africa and Asia, and the two commercial varieties have been planted in most tropical and subtropical regions. The plant does not tolerate frost.

The demand for Arabica is boosted by its complex flavor and particular taste. Robusta contains more caffeine and is more intense and bitter. It is more resistant to diseases and easier to cultivate. (2)

Chemical compositon of Coffee: Caffeine and phytochemicals

Caffeine

1,3,7-trimethylxanthine (C₈H₁₀N₄O₂), also known as caffeine, is the most commonly used psychoactive drug in the world. It was first isolated from the coffee bean by German Chemist Ferdinand Runge in 1819.

Caffeine is also found in cocoa beans (and therefore in chocolate), tea leaves, guarana seeds, and kola nuts. It is also extracted and added to energy drinks and cola sodas.

Caffeine is alkaloid that exerts a stimulating effect on the central nervous system, promoting alertness, arousal, and mental performance. It reduces the feeling of tiredness and drowsiness. It also increases blood pressure slightly, but at higher doses it can cause increased heart rate, and palpitations (arrhythmias and tachycardia).

How much caffeine can you drink?

In some people it causes anxiety, insomnia, upset stomach, and headache.

The Food and Drug Administration (FDA) reports that a "normal" intake of caffeine that should not cause negative effects in adults is 400 milligrams per day. this is roughly equivalent 2 to 3 12-fl.oz. (350 ml) cups of coffee. Some people may be more sensitive, it depends on how each person metabolizes caffeine. Pregnant and nursing women should talk to their physician about reducing their caffeine intake. (6)

"Decaffeinated" coffee contains caffeine too

Caffeine is removed from coffee by passing a hot solvent through the beans before they are roasted. This solvent (supecritical CO₂, water, or organic solvents like methylene chloride or ethyl acetate) selectively dissolves the caffeine, extracting it. However, it does not remove 100% of the caffeine. In the U.S. manufacturers claim to have removed more than 97% of the original caffeine (leaving 3% in the coffee), in the UK and European countries, the maximum caffeine content for decaffeinated roasted coffees is set at 0.1%. (6)

Pytochemicals

Like all plant-based foods, coffee contains bioactive compounds known as phytochemicals (phyto = plant). These are bioactive compounds that will end up in your cup of coffee. The exact proportion depends on how the coffee has been stored, processed, and roasted and also, how it has been brewed.

The main component found in coffee are phenolic compounds like chlorogenic acid, as well as carbohydrates, protein, minerals, caffeine, trignelline, and fats. (2)

Chlorogenic acid (CGA)

Although most of the CGA is loste during roasting, coffee is the main dietary source of this potent polyphenol. CGA is also found in blueberries and sunflower seeds.
CGA is an antioxidant, anti-inflammatory, and has antiseptic properies againsg virus and bacteria. CGA lowers cholesterol, blood sugar and has heart, and cancer protective effects. (2)

Boiled or filtered?

Boiled or unfiltered coffee contains more diterpenes than filtered coffee. Diterpenes inhibit the synthesis of bile acid and this has a negative impact on blood lipids (cholesterol). Filtered coffee is a healthier option as it increases the "good" HDL cholesterol levels. (8)

Health Benefits of Coffee

Health promoting properties of Coffee

Coffee has a stimulatory effect on nervous system, which makes it the beverage of choice for many people; and it also has health benefits.
Several studies have reported that drinking coffee reduces the risk of Alzheimer's disease, Parkinson's disease, cardiovascular diseases, Type-2 diabetes, liver cirrhosis, and some types of cancer. (2)

Below we will look into these health promoting effects, but first we will describe its chemical composition.

• Lower Death Risk
• Diabetes
• Weight Loss
• Heart Health
• Cancer
• Neuroprotective against Alzheimer's, Parkinson's and Dementia
• Liver health
• Gout
• Joint diseases and being overweight: Mixed results
• Coffee modifies the gut microbiome

Lower Death Risk

Using data from 521,330 subjects of the EPIC (European Prospective Investigation into Cancer and Nutrition) study, followed up on average for almost 16½ years, a study (10) found that:

Coffee drinking was associated with reduced risk for death from various causes. Marc J. Gunter et al. (2017)(10)

Those who were among the highest 25% of coffee intake had "lower all-cause mortality" (12% risk reduction in men and 7% in women), and "digestive mortality" (risk reduction of 59% in men and 40% in women).

Women had a risk reduction in: vascular disease mortality (22%), cerebrovascular disease mortality (30%) but a higher risk of ovarian cancer mortality (+31%).

The benefits of coffed can be summarized as follows. These were noted by an analysis that used observational studies so these findings don't mean a cause-effect relationship:(1)

1. Coffee may contribute to the prevention of inflammatory and oxidative stress-related diseases, such as obesity, metabolic syndrome, and type 2 diabetes.
2. Coffee consumption seems to be associated with a lower incidence of several types of cancer and with a reduction in the risk of all-cause mortality.
3. The consumption of up to 400 mg/day (1–4 cups per day) of caffeine is safe. However, the time gap between coffee consumption and some drugs should be taken into account in order to avoid interaction.

Let's look into these health claims in detail.

Diabetes

Coffee's bioactive compounds have an effect on Type 2 diabetes (T2D): (2)

• Coffee may contribute to the prevention of oxidative stress and T2D-related illnesses such as cardiovascular disease, retinopathy, obesity, and metabolic syndrome
• Consuming up to 400 mg/day (1-4 cups per day) of coffee is associated with lower risks of T2D
• Caffeine consumed between 0.5 and 4 h before a meal may inhibit acute metabolic rate
• Both caffeinated and decaffeinated coffee are associated with reducing the risks of T2D.

Weight Loss

This study also found that "long-term consumption of coffee is associated with [a] decreased body weight. This has been attributed to the consumption of coffee with the abundance of bioactive chemicals."
The weight loss effect could be due to the effect of coffee's phytochemicals like the effect of caffeine that promotes burning more calories (thermogenic effect), or CGA that lowers glucose absorption in the gut, and blood sugar limiting the formation of fatty tissue. "Dietary caffeine consumption has been related to decreased long-term weight gain." (2)

However, some studies question this weight-lowering effect:

Joint diseases and being overweight: Mixed results

Bad for the joints and obesity

A Mendelain randomization (MR) study (learn more about MR trials) used data from 333,214 participants of the UK Biobank to evaluate the effects of drinking coffee on different diseases. It found "little evidence for notable harm or benefit with respect to higher habitual coffee consumption. The only evidence for harm was seen with respect to osteoarthrosis, other arthropathies and obesity." (3)

They found that coffee intake actually increased the risk of suffering from osteoarthrosis (+23%), other joint diseases (+22%) and being overweight (+28%).

Good for joint diseases and obesity

However, another more recent study from 2024 found the opposite effects of coffee intake: "long-term increases in circulating caffeine may reduce bodyweight and the risk of osteoarthrosis and osteoarthritis. We confirm prior genetic evidence of a protective effect of plasma caffeine on risk of overweight and obesity." (16)

The authors found a 3% risk reduction for obesity, osteoarthrosis and osteoarthritis and calculated that ⅓ of this effect was due to a lower bodyweight, and the remaining impact was due to coffee that improved blood lipid levels, sugar and protein metabolism and lowered chronic inflammation.

Moderate Coffee consumption is good for your heart

Several studies have found that drinking coffee regularly is linked to a lower risk of developing some types of cardiovascular disease (high blood pressure, heart failure, and atrial fibrillation. These studies show a "J" shaped association where a moderate consumption lowers the risk while higher intake increases it.

Moderate coffee consumption leads to a decrease in all-cause and cardiovascular-related mortality, hypertension, cholesterol, heart failure, and atrial fibrillation. However, no conclusive relationship between coffee and coronary heart disease risk has been consistently identified. Mendoza MF, Sulague RM, Posas-Mendoza T, Lavie CJ., (2020) (8)

Mixed results of Coffee on Cancer

Coffee Associated with a Reduced Risk of Cancer

Some metanalysis of published data and controled trials have reported that a higher coffee intake is associated with a lower cancer risk, below is a summary of these findings, with a reduced risk in the following cancers:

• Hepatocellular cancer. (12)
• Breast cancer among postmenopausal women, slight evidence. (12)
• Liver cancer; with a 15% risk reduction for increasing coffee intake by 1 cup/day. (11)
• Endometrial cancer; with an 8% risk reduction for increasing coffee intake by 1 cup/day. (11)
• "possible decreased risk" for oral/pharyngeal cancer. (11)
• Gastric cancer; 12 to 15% risk reduction. (13)
• Prostate cancer; 1.2% risk reduction for each additional coffee cup/day. Risk reduction was the following: localized (7%), advanced (12%), and fatal (16%). (14)

For other cancers there were mixed results but hints of a positive effect in colorectal cancer, and a confounding effect caused by smoking in bladder cancer. (11)

Mendelian randomization studies don't show a cancer protective effect

A Mendelian randomization (MR) study evaluated data from 46,155 cases and 270,342 controls to analyze the association between coffee intake and the overall risk of developing cancer, and dying from cancers in general, and also for specific types of cancer. It found that:

• "There was no observational association between coffee intake and overall cancer risk or cancer death."
• "There is no strong causal relationship between coffee and risk of breast, ovarian, lung or prostate cancer."

Concluding that coffee intake does not seem influence the chances of suffering from cancer or dying from it. (9)

Neuroprotective against Alzheimer's, Parkinson's and Dementia

Coffee may have a protective effect on the nervous system and reduce the risk of developing Alzheimer's disease, Parkinson's disease, and dementia. However, why it exerts this effect is still poorly understood, but apparently it is due to coffee's caffeine. Different studies have shown an association linking a higher intake of caffeine with a lower risk of neurodegenerative diseases. For instance, the Canadian Study of Health and Aging following 1,023 subects analyzing Alzheimer's disease found that "coffee consumption was associated with a reduced risk of Alzheimer’s disease [of] 31%." (7)

Liver health

A meta-analysis found that incrasing coffee intake by cup/day reduced the risk of liver cirrhosis by 15%, with a positive effect on liver enzymes.(11)
The EPIC study also showed that coffee drinkers also had lower serum levels of alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma-glutamyltransferase (GGT), liver enzymes associated with liver health. (10)

Gout

MR studies show that coffee intake is linked to lower uric acid levels and a reduced risk of gout. (4)

Coffee modifies the gut microbiome

Studies have shown that different varieties of gut bacteria increase in coffee drinkers (Bacteroides, Porphyromonas, Prevotella, Faecalibacterium, and Alistipes) due to the presence of caffeine.
A recent publication (17) found that a bacteria, Lawsonibacter asaccharolyticus, isolated in 2018 by Sakamoto M, Iino T, Yuki M, and Ohkuma M. is more prevalent among coffee drinkers and that it thrives on caffeine, quinic acid and trigonelline. It is also linked do decaffeinated coffee consumption. The L. asaccharolyticus produces acetate and butyrate in the colon, short chain fatty acids that have health promoting properties.

Those who drank more than 3 cups of coffee per day had up to 8 times higher levels of it, in comparison to those who drank fewer than 3 cups of coffee per month.

This is important because it shows that coffee exerts an effect on gut bacteria, which in turn are linked to the immune system and the gut-brain axis, with important effects on our overall health.

Comments on Health Benefits

As you have noticed, there are smoe discrepancies between the findings of observational studies and Mendelian randomized studies for joint health and obesity. There area more; Nordestgaard (15) compared the outcomes of observational studies and Mendelian randomization studies on the health effects of coffee consumption and concluded that there is a strong discrepancy between observational studies and MR studies.

Observational studies found significant risk reductions of in many diseases associated to a high coffee intake: cardiovascular mortality (10-15%), cardiometabolic diseases such as ischemic heart disease (10-15%), stroke (20%), type 2 diabetes (30%), also a reduced risk for obesity, endometrial cancer, melanoma (skin cancer) and lung cancer.

But Mendelian randomziation studies didn'd find any effect of coffee drinking and any of those conditions. Instead MR studiesfound a higher risk of colorectal cancer and a lower risk of gallstones (of around 5-45%). Concluding that there is "no evidence to support causality from Mendelian randomization studies for most diseases except gallstones."

Risks and side effects

We have already mentioned the side effects of excessive caffeine intake. Studies also suggest that a heavy coffee intake increases risk of heart disease.
Coffee is a diuretic, and the effect is caused by its caffeine content.

Maughan (2003) (18) sets the diuretic threshold at 250 - 300 mg of caffeine, which is "equivalent to the amount found in 2-3 cups of coffee or 5-8 cups of tea."

The U.S. Food and Drug Administration (FDA) (19) sets a level of 400 milligrams a day (about four or five cups of coffee) as one that is not dangerous or has negative effects for healthy adults; there is no level specified for children.

Regarding higher doses of caffeine, the FDA (20) describes its negative side effects as follows:

• 1,200 mg: Toxic effects such as tachycardia, ventricular arrhythmia, and seizures.
• 10,000 to 14,000 mg: life-threatening dose. But, lower doses can also be life-threatening in children or other sensitive populations.

An excessive intake of coffee can also interfere with sleep, and cause insomnia.