Coffee is one of life's rarest pleasures: a delicious drug that's also good for you.
When scientists study the long-term health effects of coffee drinking, they find that, on the whole, the apparent benefits (such as a reduced risk of cardiovascular disease and type 2 diabetes) outweigh the costs (like a heightened risk of certain cancers).
In fact, when the nation's top panel of nutrition experts came out with a new set of recommendations last week, they noted that 3 to 5 cups per day could actually be part of a healthy diet (a cup is 8 ounces of coffee). In many cases, it seems that caffeine is probably responsible for the benefits — although decaf coffee also brings some as well.
Here's a look at what those pros and cons actually are. Of course, there are some caveats. Most of the studies cited below are observational studies, which compare a large number of coffee drinkers and non-drinkers over time. Researchers try to statistically rule out any effects from unrelated differences between the groups (such as age, income, education, exercise, and diet) that might distort the results. And the reviews cited in this article are based off multiple studies (further reducing the risk of error). But ultimately, these studies find correlations, not causations. We don't know that coffee reduces the risk of diabetes — just that, on the whole, coffee drinkers get it less often.
Additionally, adding sugar to your coffee means increasing your risk of all sorts of chronic diseases, and cream and whole milk come with their own problems. For best results, drink it black.
Health benefits associated with drinking coffee
1) Lower rate of type 2 diabetes. A recent review of 28 studies found that coffee drinkers had lower rates of type 2 diabetes compared to non-coffee drinkers. What's more, people who drank more coffee had lower rates (one cup per day correlated with an 8 percent lower rate, while six cups per day correlated with a 33 percent lower rate). This association held true for drinkers of both normal coffee and decaf.
2) Lower rate of cardiovascular disease. A review of 36 studies that examined the correlation between coffee drinking and chronic cardiovascular problems found that people who drank anywhere between one and five cups of coffee per day had lower rates of heart disease, stroke, heart failure, and cardiovascular-related deaths than non-coffee drinkers. In this case, though, 3.5 cups per day appeared to be the sweet spot (15 percent reduction), followed by 1.5 cups per day (11 percent), then 5 cups per day (5 percent).
3) Lower rate of Alzheimer's, Parkinson's, and dementia. There hasn't been quite as much work done in this area, but a 2010 review of 11 studies found that coffee drinkers had a 16 percent reduced risk of developing Alzheimer's or other forms of dementia. Meanwhile, a 2014 review found that coffee drinkers had lower rates of Parkinson's disease, with people who drank three cups per day having the lowest rates. Drinkers of tea and other caffeinated beverages also saw reductions, though men had greater reductions than women.
4) Lower rates of some cancers. A 2011 review of 59 studies found that daily coffee drinkers had a lower chance of developing cancer overall, with each cup (up to six per day) correlating with a 3 percent reduced risk. Cancer-specific reviews have found reductions in the risk of prostate cancer, liver cancer, and colorectal cancer in particular.
5) Improved athletic performance — and perhaps memory. It's surprising, but experiments have consistently shown that caffeine ingestion can lead to a modest but measurable short-term improvement in athletic performance, in activities as varied as sprinting, cycling, weightlifting, and long-distance running. Meanwhile, other research has suggested that drinking a few cups of coffee after studying helped people remember the material the following day — though that work was preliminary, and more needs to be done to confirm the effect.
Negative health effects associated with drinking coffee
1) Higher rates of other cancers. Despite the benefits when it comes to certain cancers, coffee drinking is associated with heightened risks of other ones. Reviews have found that daily coffee drinkers develop laryngeal cancer, urinary tract cancer, and lung cancer at higher rates.
2) Higher cholesterol. Short-term controlled trials have found that daily coffee drinking increases cholesterol as well as low-density lipoprotein and triglycerides. Together, these factors generally increase the risk of cardiovascular disease and stroke. Obviously, this contradicts the broader finding that coffee drinking is associated with a reduced chance of cardiovascular disease, but people who are already concerned about their cholesterol levels should keep it in mind. (Using coffee made with a paper filter can also reduce levels of the chemical largely responsible for this effect.)
3) Anxiety and sleeplessness. For some people, caffeine consumption — especially at high levels — can cause anxiety, jitteriness, and trouble sleeping. This can often be solved by cutting back on coffee or by making sure to stop drinking it by mid-afternoon (it takes around three to five hours to leave the system), but some have to cut it out entirely.
4) Addiction. On the whole, a coffee habit seems to be more positive than negative. But caffeine is a drug, and one that you become chemically addicted to if you drink it every day. Trying to quit it usually leads to some withdrawal symptoms (like headaches, fatigue, and mental fogginess) for a week or two, until your brain adjusts to going without caffeine.
Neutral effects of coffee drinking
There are also a number of areas where coffee was long thought to cause particular health problems, but subsequent work has revealed that there's pretty much no effect:
1) Coffee doesn't significantly affect blood pressure long-term. Drinking caffeine causes a short-term spike in blood pressure, but controlled trials have found that drinking it daily doesn't lead to chronic high blood pressure. That may be because of other substances in coffee that drive down blood pressure, but we still don't know for sure.
2) There's no evidence that coffee cause ulcers. It was previously believed that coffee and other acidic substances led to the development of stomach ulcers, but scientists now believe they're caused mainly by bacterial infections or habitual use of aspirin or ibuprofen.
3) There isn't evidence that coffee causes chronic heartburn. Similarly, it was traditionally thought that drinking coffee and other caffeinated beverages could cause chronic heartburn (as part of gastroesophageal reflux disease, or GERD), because of the idea that caffeine relaxes the sphincter that normally prevents stomach acid from traveling up the esophagus. But there isn't evidence that coffee drinkers experience chronic heartburn at greater rates than non-drinkers.
4) Coffee doesn't dehydrate. Because coffee's a diuretic (i.e., it makes you urinate), it's widely assumed that it dehydrates you. But experiments show that, among habitual coffee drinkers, the beverage actually hydrates just as effectively as water — likely because drinking it every day allows your body to build up a tolerance to its diuretic effects.