Faculty Peer Reviewed
At some point during my medical training, drinking coffee went from being an enjoyable, even indulgent, activity to being my primary weapon against fatigue and its associated decline in cognitive function. Although realizing this made me critically, and somewhat resentfully, evaluate my own consumption of coffee, it also made me think more generally about the role of coffee in today’s world. In the hospital, where many of us spend most of our time, coffee is ubiquitous. However, such avid consumption of coffee is not unique to the healthcare setting. Worldwide, coffee is the most common beverage after water, with approximately 500 billion cups consumed annually, and this number continues to increase . With such widespread consumption, it becomes important to think about the effects coffee may have on our health.
The neuropsychiatric effects of coffee are perhaps the most well known. The caffeine within coffee stimulates excitatory neurotransmitters by antagonizing adenosine receptors throughout the nervous system . This leads to improved reasoning, attention, memory, energy, and concentration . Caffeine also has the interesting ability to both generate and alleviate headaches. A meta-analysis of randomized controlled trials studying the use of coffee to treat migraine and tension headaches found analgesic effects with caffeine doses of at least 65 mg, or approximately 1 cup of coffee . In contrast, another study showed that daily coffee drinkers were more likely to have chronic migraines and analgesic rebound headaches compared to those who do not regularly drink coffee . Caffeine intake has even been associated with the development of acute psychiatric symptoms such as anxiety, insomnia, irritability, and panic attacks .
There are other neuropsychiatric effects of coffee that are important to consider. Although the DSM-IV does not officially recognize caffeine dependence and abuse, several studies have suggested that high caffeine intake can lead to dependence and abuse in ways similar to other psychoactive substances . Studies have also demonstrated an increase in other addictive behaviors in heavy coffee drinkers. Lopez-Garcia and colleagues found alcohol use to be 50-100% higher among women who drank over 6 cups of coffee each day when compared to those who drink 1 cup or less . Another important consequence of prolonged heavy coffee consumption is withdrawal, which can cause headache, fatigue, decreased energy and concentration, depression, and irritability. These symptoms can occur after abstaining from daily doses of caffeine as low as 100 mg per day, although symptom incidence and severity increases with higher doses . Withdrawal begins within 12-24 hours after the last cup, peaks at 1-2 days, and usually resolves by 8-9 days . Interestingly, re-administration of caffeine can reverse symptoms within 30-60 minutes, a fact that many of us have probably already empirically figured out .
Coffee has also been shown to have important implications for more complicated neurological problems. One important meta-analysis conducted in 2002 found evidence of a dose-response relationship between coffee intake and decreased risk of Parkinson disease . Although the mechanism for this relationship remains unclear, it seems that the rich supply of anti-oxidants in coffee promotes the expression of enzymes that mitigate the neurodegenerative effects of free radicals . Coffee has also been found to activate certain pathways, such as the Nrf2-ARE pathway, that strengthen endogenous neuroprotective mechanisms to help control the development of Parkinson’s . Studies have also shown that moderate daily caffeine intake may decrease the risk of Alzheimer’s disease . This is thought to occur because caffeine may reduce the expression of genes such as presenilin-1, which is important in the formation of the amyloid plaques that characterize this disease .
The effects of coffee on the development of malignancy remain controversial. Both positive and negative associations between coffee consumption and cancer risk have been described for most types of cancer . However, results that support these various associations remain contentious, as studies reporting conflicting results continue to emerge. This inconsistency is thought to be due at least in part to the complicated interactions between environmental and genetic factors in the development of malignancy, as well as to imperfect study design. At this point, it seems that coffee consumption may indeed be associated with decreased risk of hepatocellular, colorectal, prostate, and renal cancers [11,23]. In addition, a recent meta-analysis suggests that coffee is weakly associated with breast cancer risk in postmenopausal women . However, much further investigation is needed before clear conclusions can be drawn.
A great deal of research has also been done to examine how coffee affects cardiovascular health. Caffeine has been shown to increase inotropy by inhibiting the negative inotropic effects of adenosine and by increasing both intracellular calcium and myocardial sensitivity to calcium [13-15]. Other studies looking at the arrhythmogenic potential of coffee have found that this only occurs at doses much higher than those typically consumed, although patients with underlying cardiac disease appear to be at increased risk [16,17]. Still other studies have found that by increasing sympathetic activity coffee can acutely increase blood pressure by up to 10 mmHg, but only in non-habitual coffee drinkers . Despite these findings, several studies found that drinking up to 6 cups of coffee daily was not associated with an increased risk of chronic hypertension . Another study using the same data found that coffee did not affect plasma lipid levels and cardiovascular disease risk, even with consuming more than 6 cups of coffee each day . Follow-up studies have shown that coffee was not associated with increased all-cause or cardiovascular mortality, and that in women it may actually be cardioprotective [20,21].
As evidenced by the studies described above, examining the health effects of coffee has become an exciting area of research. Although most of this work focuses on associations with neuropsychiatric, cardiovascular, and malignant disease, newer studies are branching out even further to study, for instance, the effects of coffee on the risk of developing type 2 diabetes or osteoporosis, or its effects on the gut microbiome. While at this point it seems that there may be a slight overall benefit from drinking coffee, it is important to realize that most of the existing literature recommends consumption in moderation, or no more than 2-3 cups per day. Regardless, further research needs to be done in order to more clearly understand the exact health risks and benefits of drinking coffee.
Dr. Anish Parikh is a 1st year resident at NYU Langone Medical Center
Peer reviewed by Brian Greet, MD, Associate Editor, Clinical Correlations
Image courtesy of Wikimedia Commons
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