I always feel valued and trusted whenever I receive requests from people asking for my opinions about certain nutrition and health topics that they would like to know.  This time, a friend asked me about the health benefits/concerns related to coffee since coffee drinking is trendy in China. There are a lot of published research reports on coffee which would be hard to read all in a short time while someone is waiting for an answer. This blog is a summary mainly based on a recent review paper (1) plus my thoughts.
 

    Coffee and the Brain: One legend about coffee's discovery can trace its heritage back centuries to the ancient coffee forests on the Ethiopian plateau. Legend says the goat herder Kaldi first discovered the potential of these beloved beans after he noticed that after eating the berries from a certain tree, his goats became so energetic that they did not want to sleep at night.
 

    This is a vivid description of the effects of coffee: feeling energetic and not wanting to sleep. Coffee is consumed for its stimulatory effects owing to one of its main components caffeine. Coffee is the richest source of caffeine and two teaspoons of instant coffee contain approximately 100 mg of caffeine.

    In the brain adenosine is an inhibitory neurotransmitter. In normal conditions, it promotes sleep and suppresses arousal. Adenosine binds to adenosine receptors in the brain. This binding causes drowsiness by slowing down nerve cell activity. It also causes blood vessels to dilate, most likely to let more oxygen into the organ during sleep.

    Caffeine can also bind to adenosine receptors. When that happens, the nerve cell can no longer bind with adenosine because caffeine is taking up all the receptors that adenosine would normally bind to. Caffeine doesn't slow down the nerve cell's activity as adenosine would. Instead of slowing down because of the adenosine's effect, the nerve cells stay in the wakeful state. Caffeine also causes the brain's blood vessels to constrict, because it blocks adenosine's ability to open them up.

    Coffee and Its Important Constituents:  In addition to caffeine, some other components in coffee also play a role in its known benefits, i.e., chlorogenic acid and caffeic acid. These components are potent antioxidants and have several health benefits, such as protecting the body from the hazardous effects of free radicals.

    The health benefits of decaffeinated coffee are often attributed to chlorogenic acid. Likewise, its lignans and some mineral components also possess therapeutic potential. These antioxidants protect against DNA damage and improve the antioxidant status of the body.

    Caffeine is metabolized by the liver producing metabolites such as dimethylxanthines, paraxanthine, theobromine, and theophylline. These metabolites also have various health benefits, such as described in one of the earlier blogs about theobromine.

    Coffee and Diabetes Mellitus: Coffee drinking is inversely related to the risk of metabolic syndromes and diabetes mellitus. Caffeine exerts beneficial effects on glucose metabolism through increased uncoupling protein expression and lipid oxidation. The hypoglycemic effect of coffee may not be by caffeine alone, it may be the cumulative effect of various constitutes, including chlorogenic acid (1).

    When caffeine binds with adenosine receptors in the brain, it stimulates the uncoupling protein production and its related energy release, which is why you would feel energetic after drinking coffee. Glucose is the primary energy source used by the brain since the nerve cells would use more glucose to stay in the alert state. Since glucose is actively taken up and used by the brain, glucose in the blood would decrease.

    Coffee and Cardiovascular Disease: Coffee has some positive effects on heart health, but at the same time, coffee consumption may also cause cardiovascular disorders. Cardiovascular disease is one of the main causes of mortality in patients diagnosed with diabetes mellitus. Coffee consumption is inversely related to cardiovascular heart disease in diabetes mellitus. The presence of the antioxidants in coffee slows down the process of inflammation, protects from the hazardous effect of free radicals and against endothelial damage, thereby reducing the risk of cardiovascular disease.

    However, other mechanisms of action exist for coffee regarding its impact on the cardiovascular system. Caffeine consumption can affect blood pressure as it constricts blood vessels, increases arterial stiffness resulting in increased blood pressure. Some components present in unfiltered coffee like cafestol and kahweol raise serum lipids and increase the risk of cardiovascular disorders. Coffee drinking may also trigger coronary events and increase infarct size in patient groups. Excessive coffee drinking can aggravate cardiac arrhythmias (1).

    Coffee and Parkinson's Disease: Parkinson's disease is a brain disorder involving the inactivation of motor neurons. The cause of Parkinson's disease is multidimensional, aging, heavy metal toxicity such as from lead, and other chronic diseases such as diabetes mellitus can be some main risk factors. Many dietary components such as the use of coffee/caffeine and tea can result in lowering the risk of Parkinson's disease. Epidemiological studies have consistently demonstrated an inverse association between coffee consumption and Parkinson's disease.

    Excessive daytime sleepiness can be used to predict the future pathogenesis of Parkinson's disease. Caffeine can keep the neurons stay active. Diabetes mellitus increases the chances of getting Parkinson's disease due to the increased neurodegeneration. Coffee drinking may be beneficial for reducing the risk and slowing down the progression of Parkinson's disease via its glucose-lowering potential to reduce the risk of diabetes mellitus (1).

    Coffee and Alzheimer's Disease: Alzheimer's disease is also a form of brain disorder. Increasing age, neurodegeneration, and some genetic factors are significant risk factors for the pathogenesis of Alzheimer's disease. Brain disorders are often from tissue damage/neurodegeneration, characterized by the loss of neurons in brain tissues. The antioxidants present in coffee can improve the overall antioxidant capacity of the body and thus could reduce oxidative stress and inflammation (the causes for neuron damage). Trigonelline, a constituent of coffee beans, demonstrated the regeneration of neuron dendrites and axons, in addition to memory improvement. Moderate coffee consumption is associated with a reduced risk of Alzheimer's disease (1).

    Coffee and Athletic Performance: Caffeine in coffee can improve athletic performance by keeping the brain in an alert state and boosted energy levels. This effect had prompted some athletes to dose up caffeine for a competitive edge. The World Anti-Doping Agency (WADA) banned high concentrations of caffeine from all Olympic events from 1984 to 2004. Even though it is no longer on the prohibited list, caffeine is still one of the stimulants on the WADA watch list, and athletes' caffeine levels are still actively monitored for patterns of use. The legal limit under previous restrictions was 12 mcg/ml in urine, roughly equivalent to drinking 8 servings of espressos over a few hours.

    Debate persists as to whether coffee is beneficial or troublesome for human health. When consumed in moderation, coffee can be good for your brain. In the short term, it may improve vigilance, learning, and reaction time. If you need coffee to stay awake to study overnight for your exams, it can work. Long-term moderate consumption may protect against brain- degenerative diseases like Alzheimer's and Parkinson's, and diabetes.

    For healthy adults, the U.S. Food and Drug Administration (FDA) has cited 400 mg caffeine a day, which is about 4 or 5 cups of coffee as an amount not generally associated with dangerous, negative effects. Caffeine can cause insomnia, nervousness, restlessness, stomach upset, nausea and vomiting, increased heart and breathing rate, and other side effects.

    Pregnant women and postmenopausal women should avoid excessive consumption of coffee. More than 300 mg of caffeine (about 2 to 3 cups of coffee) in a day may result in miscarriages and low-birth-weight babies. Caffeine can interact with some drugs, especially in women who take hormones to treat postmenopausal problems.

    Coffee can also cause high blood pressure or make high blood pressure worse. Risks for rheumatoid arthritis and osteoporosis also increase with increased regular coffee consumption (1). If you are anxious, drinking coffee can make it worse. The effect of coffee on people with cardiovascular disease is rather complex. I would suggest not drinking coffee if you have any cardiovascular disorders such as hypertension.

    The time it takes for the caffeine level to drop by half is an average of 5 hours. After 10 to 15 hours, there is no longer enough left to have an impact. My personal experience is that if I drink coffee later than mid-morning, I would have a problem sleeping at night. For the sake of a good night's sleep, I have changed drinking coffee to drinking tea altogether. For any of you who have insomnia, which is about 1/3 of the general population, coffee drinking may be one of the reasons why some people have difficulty falling into sleep. If you currently have sleep problems, I would caution you to think twice about whether you should drink coffee or not. Even if you have to drink coffee to stay awake during the daytime, I would suggest considering how much and when you may drink some.

    My personal view is that you can drink coffee just as you wish for any drink. Sometimes it may be necessary, such as when you visit France, you need to sip their dark coffee and eat a freshly baked croissant for breakfast at a corner bakery to embrace the experience. Whether you want to drink coffee every day in your life, especially if you cannot sleep at night, is very much a personal decision.

    Reference:

1. Butt, M. S., & Sultan, M. T. (2011). Coffee and its Consumption: Benefits and Risks. Critical Reviews in Food Science and Nutrition, 51(4), 363–373.