Coffee Conundrum
Where does the gavel come down on coffee? Should we be avoiding it or worrying less about using it to fuel us through the day? As a former barista and a lover of coffee in any form, no one is more eager for the scales to be tipped in the “benefit outweighs risk” direction than myself. Allow me to shed some light on where the science leaves us.
CONSTITUENTS
Throughout its lifecycle, from plant to cup, the coffee bean undergoes a transformation that impacts, not only its flavor, but also its physiological effects, due to changes in its chemical profile. Prior to roasting, green coffee beans are comprised of a myriad of chemical constituents including carbohydrates, lipids, proteins, chlorogenic acids (CGA), minerals, aliphatic acids, caffeine, trigonelline and free amino acids1. Through the roasting process, the content of certain constituents like carbohydrates, proteins, chlorogenic acids and free amino acids are reduced1, whereas levels of certain alkaloids (e.g. caffeine), minerals, oils, and aliphatic (open carbon chain) acids are increased1. New compounds, such as acrylamide, also arise via the roasting process2, and changes continue to occur as the beans are ground and processed through water at extremely high temperatures3. These processing methods and many of the constituents that are affected have been correlated to specific effects on multiple organ systems when consumed. I will go through the major organ systems that appear to receive the most impact here.
LONGEVITY
The literature is in abundant agreement that coffee consumption reduces risk of death from any cause1,3,4,5,6,7,8,9,10,11. This is great news considering it is one of the most prevalently consumed beverages worldwide12. In the largest analysis of evidence to date, 3-4 cups per day was found to be associated with the greatest benefit9. Other analyses had more broad conclusions of 2-5 cups per day (16-40 oz or up to 400 mg caffeine) being linked with the strongest beneficial health outcomes3. Exactly by how much coffee increases longevity is unclear.
CARDIOVASCULAR BENEFITS
One of the most discussed topics in the literature with regard to coffee’s effect on health seems to be heart disease, perhaps due to heart disease claiming more American lives than any other cause of death13. Coffee appears to offer protection against coronary artery disease, congestive heart failure, hypertension and stroke3,4,5,6,7,8,14. Up to 4 cups per day decreases risk for heart failure in a dose-dependent manner14. In the short term, it raises the stress hormone cortisol thereby increasing blood pressure, but consumption overtime seems to lower blood pressure levels14. This may be due to the antioxidant activity of chlorogenic acid and the beneficial effect that antioxidants have on the endothelium, or lining, of our blood vessels14. Coffee also contains nicotinic acid, a form of the B-vitamin niacin, which is used therapeutically to reduce cholesterol levels1. It also may exhibit mild estrogenic activity, which is protective against heart disease1. Despite existing correlations between coffee and heart palpitations (a noticeably rapid, strong, or irregular heartbeat15), consumption does not appear to change the frequency, inducibility, or severity of actual ventricular arrhythmia or atrial fibrillation, conditions in which the heart beats irregularly16,17,18,19.
NEUROPROTECTION
Due to the several constituents that act on estrogen receptors1, in addition to the antioxidant activity of CGA14 and a small but significant serotonin content1, coffee has been shown to offer many benefits for brain health. The estrogen-mimicking effects of the constituent octyl gallate serve to reduce production of amyloid beta proteins, proteins that accumulate in neurodegenerative diseases like Alzheimer’s Disease; B-sitosterol prevents oxidative stress; and other estrogen-mimicking constituents protect against the loss of dopaminergic neurons, which contributes to Parkinson’s Disease1,20,21. The stimulating effects of caffeine and the mood enhancing effects of serotonin also offer protection against Parkinson’s Disease and depressive disorders1. Shockingly, 3 cups of caffeinated coffee per day was shown to reduce the risk of Parkinson’s Disease development by a staggering 25%22. Four cups per day reduced suicide risk in both men and women by an even more impressive 50% in one study23. Reduction in risk for multiple sclerosis, which causes degeneration of the neuronal myelin sheath, has also been seen24.
METABOLIC EFFECTS
In discussing metabolism, it should be noted that single nucleotide polymorphisms (SNPs) have been identified in the gene coding for the enzyme responsible for caffeine metabolism, which helps to explain why some may be more sensitive to its effects (i.e. slow metabolizers) than others (i.e. rapid metabolizers)3.
Coffee contains the stimulant caffeine, which exerts an antagonistic effect on adenosine receptors and is responsible for its overall metabolism-enhancing effect5. Directly following coffee consumption, blood glucose and insulin levels temporarily increase due to increased cortisol levels as a result of this stimulant effect3. However, a variety of constituents in coffee offer long-term protection from insulin desensitization and type 2 diabetes mellitus (T2DM)3,5. Increases in adiponectin, an insulin-sensitizing cytokine, were seen with coffee consumption, which may be responsible, along with the beneficial antioxidant activity of CGA, for the reduction in T2DM risk25. Reduction in diabetes risk was seen with consumption of 4-6 cups per day, with every additional daily cup offering an added 7% risk reduction3.
An inverse association between coffee consumption (15 or more cups per week) and leptin levels has also been documented in both males and females26. Leptin is a hormone that signals satiety to the brain, and as levels increase, cells become more and more desensitized to its effects, which increases risk for obesity3. Coffee seems to be associated with lower leptin levels, which may explain why higher coffee consumption is associated with lower BMI, particularly among those genetically predisposed to obesity3. The effects observed on adiponectin/blood sugar levels and leptin/obesity demonstrate an overall positive effect on adipocyte (fat cell) function, which likely contributes to the beneficial metabolic effects of coffee consumption3.
CANCER PREVENTION
Coffee’s role in cancer has been controversial because of key compounds believed to be carcinogenic that are present in the roasted bean1,3,27. Acrylamide, for example, is not present in green coffee but is formed via the Maillard reaction when beans are roasted at high temperatures, and it may exhibit carcinogenic activity2. Trigonelline, a metabolic byproduct of niacin, is found in green and roasted beans and may possess mutagenic activity on estrogen-dependent breast cancers, particularly after roasting1. Furthermore, hot beverages consumed at 149F (65C), or above, are potentially carcinogenic in and of themselves, regardless of content3. The International Agency for Research on Cancer (IARC) thus recommends allowing your coffee beverage to cool before consuming, as coffee is typically served at 65C3.
Despite these unsettling facts, reassurance is offered by IARC’s recent conclusion that coffee is associated with a decreased risk for liver and endometrial cancer and is unlikely to cause breast cancer, prostate cancer or pancreatic cancer3. Several biochemical pathways that are promoted by various constituents in coffee reduce oxidative stress, promote apoptosis (regulated cell death) and autophagy (cellular “clean-up”), improve insulin sensitivity, and stimulate glucose uptake, all processes which reduce risk of cancer development1.
Breast cancer and coffee consumption is an area of particular contention, not only because coffee is linked with fibrocystic breast changes, which can obscure masses on routine screening mammograms, delaying diagnosis28, but also because of data on coffee consumption in existing breast cancer. One study specifically investigating coffee consumption in breast cancer patients found intake to be associated with greater mortality27. However, the authors noted that it was unclear whether more coffee consumption just pointed to underlying fatigue and worse disease status in this group with worse outcomes or if the outcomes were related to the coffee itself. Nonetheless, the data is unclear and thus breast cancer patients, particularly if estrogen-receptor positive due to the effects of trigonelline1, should be especially cautious with coffee consumption.
GASTROINTESTINAL HEALTH
People often report symptoms of heartburn or abdominal pain with coffee consumption29, which brings into question its effect on the GI tract. One study investigated mechanistic effects of coffee in the gut and found that it causes a temporary increase in gastrin, which stimulates stomach acid production29. However, the authors observed that increased gastrin following coffee consumption only correlated with GI symptoms on an individual basis, and therefore, symptoms may be more reflective of an individual’s sensitivity to caffeine. Other studies have failed to prove any association between coffee consumption and dyspepsia, gastroesophageal reflux disease, peptic ulcer disease, gastritis or stomach cancer5. There is even question as to whether coffee is unsafe in patients with inflammatory bowel disease, with some studies showing a possible protective effect of caffeine on ulcerative colitis and Crohn’s development5. To this same end, coffee has been shown to exhibit anti-inflammatory effects on the GI system as a whole, which appear to decrease risk for several diseases of the liver, including hepatic steatosis (fatty liver disease), fibrosis (hardening of the liver), cirrhosis (liver scarring due to inflammation)9, and liver cancer30.
RESPIRATORY BENEFITS
The effect that came most as a surprise as I sifted through the research was coffee’s benefits on lung health. One review article discussed coffee’s association with improved asthma control3 and another population-based cohort study demonstrated reduced risk of death from respiratory disease with greater coffee consumption11. Further research on this topic may help to elucidate mechanisms.
RISKS
Despite a plethora of health benefits uncovered in association with rather significant amounts of coffee ingestion, there are still risks to be taken seriously, the most common being short-term caffeine effects such as anxiety, heart palpitations, insomnia, and tremors3. These are experienced by a large percentage of coffee drinkers and can vary depending upon tolerance and timing of consumption in relation to meals and bed time3.
Caffeine may also be responsible for bone loss and increased fracture risk, particularly in women3. Thus, it may be important for women to ensure adequate dietary calcium intake if they frequently consume coffee26.
Although coffee’s beneficial effects on cardiovascular health are well-detailed above, associations have also been made between the diterpene content and increased serum cholesterol levels, particularly with boiled unfiltered coffee3. Luckily, a standard coffee filter effectively removes diterpenes and the resulting preparation has a neutral effect on cholesterol levels3.
Concerns regarding the presence of carcinogens in coffee were also addressed above. The consensus is that coffee does not lead to development of cancer and may even offer protection3. The one exception applies to individuals with existing breast cancer, especially estrogen-receptor positive breast cancer, who should exercise caution as it is unclear whether coffee is associated with worse outcomes1,27.
A category of risk not yet discussed is coffee in pregnancy or in youth. Coffee does appear to be linked to low birth weight and preterm birth when consumed by pregnant women and thus should be avoided in pregnancy1,3,9. Long-term data on the effects of coffee consumption in children is lacking, though one study reported negative effects in young people with consumption of more than 4 cups per day31.
Slow metabolizers are unfortunately at greater risk when it comes to the negative effects of coffee due to prolonged exposure following consumption3. This includes a greater risk of hypertension and heart attack, even though coffee has been shown to be protective against these conditions in the large majority of the population3.
Finally, the caffeine content of coffee lends itself to dependence, both physical and psychological. If consumed regularly, withdrawal effects of headache, fatigue and lethargy will likely develop in its absence3. Withdrawal symptoms reinforce coffee intake, but the silver lining is that these symptoms may actually prove advantageous given the many health benefits of coffee listed above.
CONCLUSION
The scientific community appears to be in large agreement that, in general, benefits conferred from coffee consumption outweigh its potential harm, and that maximum benefit is reached between 2 and 6 cups per day, depending on the study. Coffee is sadly the single richest source of antioxidants in the American diet3, and it is the one of the most commonly consumed beverages worldwide12, so it is a huge relief that it serves a largely beneficial role in our health.
Of course, positive data must be qualified. First, there are still potential harmful effects of coffee, and these vary on a person-to-person basis. If you notice that coffee tends to give you anxiety, tremors, or insomnia, then likely 6 cups per day is not realistic for you (and perhaps these symptoms are also serving as a clue that you are a slow metabolizer and thus more susceptible to the harmful effects of coffee). Second, there are still many limitations with the data that we have, primarily that we cannot presume direct causation of these positive health outcomes from coffee consumption simply because of a strong correlation. Unfortunately, it would be impossible to run a double-blinded placebo-controlled investigation of coffee because of the nature of the way in which we consume this substance. Additionally, most of the data we have comes from observational studies in which coffee consumption levels are self-reported and then aspects of the subjects’ health are measured over time. Observational evidence is generally considered weaker than that from interventional studies, whereby confounding variables would be well-controlled for to best isolate the effect of the substance in question. With observational studies, we risk confounding biases related to other healthy behaviors that coffee drinkers may be more likely to engage in. Nonetheless, the plethora of statistically significant associations between coffee consumption and positive health outcomes is undoubtedly convincing, particularly as the science begins to uncover more and more mechanisms by which these health effects are possible.
A NOTE ON THE FUTURE OF COFFEE RESEARCH
Due to the limitations of current research, in order to better isolate the impact of coffee on development of conditions like heart disease, cancer, diabetes and neurodegenerative disease, it would be great to see more prospective studies controlling for diet and lifestyle factors which may also contribute to a reduction in these conditions. This would require following large groups of people over many years and is admittedly a huge undertaking. In the interim, additional data on how variations in coffee origin, roasting method and brewing method affect the chemical composition32 and thus its physiological effect profile may help to elucidate further mechanisms by which coffee exerts potentially beneficial or deleterious effects on human health.
REFERENCES
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11. Park SY, Freedman ND, Haiman CA, Le Marchand L, Wilkens LR, Setiawan VW. Association of coffee consumption with total and cause-specific mortality among nonwhite populations. Ann Intern Med. 2017;167:228-235.
12. International Coffee Organization. The Current State of the Global Coffee Trade. CoffeeTradeStats. 2016.
13. Heart Disease Facts. Centers for Disease Control and Prevention. Updated 28 Nov 2017. Accessed 25 Nov 2019.
Created by: Jenna Hamza, ND
