Full disclosure: I’m writing this while drinking my 3^rd coffee of the day. I’ve tried not to let this influence my judgment.

Caffeine has long been pigeonholed as a “sin,” alongside things like alcohol, fast food, and sugary desserts. Once in a while, someone will even try tell me how they’re “being good” by switching their regular espresso for a decaf mocha.

Not everyone agrees that caffeine is terrible for you, of course. In the opposite camp, there are those who maintain that coffee has many health benefits—especially when combined with grass fed butter and a helping of blueberries.

So, what’s the truth here? Will caffeine turn you into an adrenally fatigued zombie with cardiac problems, or is it the elixir of everlasting youth? As usual, it’s probably somewhere in the middle.

The difference between acute and chronic effects

Any time we talk about the effects of a particular drug or dietary intervention, we need to be a bit careful, as there are two different types of effects. There are immediate effects that you notice in the short term when you first take the drug, and then there are the long-term effects that are associated with taking it regularly. These may be totally different, or even opposite from each other. With that in mind, let’s take a quick tour of some of the main findings.   

The risks

Caffeine use has been talked about as a risk factor for a number of potential issues. Let’s look at several of these in turn, starting with the most serious outcomes first.

• Cardiovascular disease, arrhythmias, and palpitations

There is still some controversy over the question of whether caffeine use can trigger cardiac problems. One oft-quoted study seemed to suggest that drinking coffee can trigger heart attacks in some people. A more careful view of the literature, though, suggests that while caffeine use might be problematic for some people (such as those who already have cardiovascular problems such as high blood pressure or previous heart attacks), overall it doesn’t appear to be associated with an increased risk.

A review of the literature in 2013 found that there was actually a negative correlation between moderate coffee use and cardiovascular disease, with people who drank between three and five cups of coffee a day having the lowest risk. Even heavy coffee drinkers were not found to be at an increased risk.

• Insomnia

In contrast to the findings with cardiovascular disease, the link between caffeine consumption and insomnia appears relatively straightforward. There’s a good chance that drinking lots of coffee will reduce your amount and quality of sleep, and the bad news is that this effect is likely to get worse as you get older. Some people are much more sensitive to this than others, and there are suggestions that this may be partly due to genetic factors. If insomnia is a problem for you, then you may very well want to consider reducing your caffeine intake, especially later in the day.

• Fatigue

Aside from interfering with sleep, chronic caffeine use can also contribute to fatigue in other ways. If a person has become tolerant to regular coffee use, they might get withdrawal effects when they don’t take it. Regular coffee drinkers may feel more tired than normal or develop a headache if they don’t keep their caffeine levels topped up. It doesn’t, however, seem to cause “adrenal fatigue” as some people suggest – mainly because there’s no evidence supporting the existence of such a condition.

The possible benefits

Coffee intake has been associated with a wide range of positive health outcomes, such as a reduced risk of various types of cancer, Parkinson’s disease, type 2 diabetes, Alzheimer’s disease, and dementia. There are suggestions that short-term use may improve various kinds of mental and physical performance (although others have argued that the difference is in most cases caused by a reversal of caffeine withdrawal, rather than a true benefit of caffeine).

What we don’t know

There’s still a lot we don’t know here. The risks and benefits of caffeine use are likely to vary considerably from one person to another. While we can look at some statistical patterns, they don’t necessarily give us a good idea of the effect that your regular morning coffee is having on you as an individual. While one person may benefit from drinking several cups of coffee a day, another may develop problems when taking a much smaller dose. At the moment, there are some recommended limits, but these are really little better than guestimates. We have no accurate way to figure out your optimal caffeine dose.

There’s also likely to be a difference depending on how you drink your caffeine. The effects of drinking coffee are likely to be different from consuming the same amount of caffeine in energy drinks, for example, because of the other substances present in the different beverages.

Finally, it’s important to remember that, as with a lot of research about nutrition, many of the studies that these findings are based on are observational. That means that it’s hard to distinguish between an association and a causal effect. Does coffee really reduce your risk of getting Alzheimer’s disease, or is it just that people who drink more coffee are also more likely to do other things that reduce their risk? There’s still considerable uncertainty.

The verdict

This one is simultaneously true and false. Too much of anything is bad for you, by definition. And it’s certainly possible to drink too much caffeine. But the devil is in the dosage. The idea that substances can be divided easily into “good” and “bad” is popular, but it doesn’t fit well with reality. Caffeine has both positive and negative effects. Your optimal dose will vary depending on many different factors, but it seems likely that moderate caffeine consumption is entirely compatible with a healthy lifestyle. Some people may benefit from cutting down, especially those with cardiovascular problems, or those who struggle to sleep, for example. And if you drink so much coffee that you struggle to function without it, then you might wish to experiment with cutting back to see how it affects you. If you’re pregnant or trying to get pregnant, then restricting your caffeine intake is probably wise. But for most of us, there’s no need to reach for the decaf just yet.