Coffee Myths

by Brian Dunning
May 14, 2024

If you're like many Skeptoid listeners, there is a good chance you are in your car right now on your morning commute, perhaps sipping your favorite coffee from your very awesome insulated stainless steel tumbler that you got on the Skeptoid store. And if that's the case, you might be wondering how much truth there is to that thing some insufferable person told you about coffee the other day. For it turns out the world is full of coffee myths. Any popular product — and coffee certainly qualifies — is going to draw myths and misinformation like flies. Today we're going to do our best to separate the true beans from the fake beans.

Let's get right into it. We'll start with:

1. The caffeine in coffee gets you going in the morning.

That nice shot of caffeine is what snaps you out of your doze mode and gets you energized for your day, right? Well, the truth is your coffee probably has very little effect. Caffeine is one of the psychoactive compounds that are easiest for people to develop a tolerance to. For most people, anywhere between two days and two weeks is all it takes for your body to develop that tolerance. If you've been drinking a daily coffee longer than that, you are almost certainly getting little or no actual psychoactive boost from that morning joe.

However, human brains are complicated, and it can still seem like you get that boost. The caffeine will still always give you some actual psychoactive effect, though it quickly becomes very mild. You get a nice placebo effect from the perception that you're getting your morning wakeup. You get the familiar physical ritual and sensory experience which your mind associates with the grab-and-go start of another day. Even if the caffeine itself isn't doing much, your coffee can still give you a morning jumpstart.

2. Coffee sobers you up.

I grew up thinking coffee could make a drunk person sober, just because that's in so many movies. But, as you can imagine, coffee has no effect at all on how intoxicated you are. It can't remove alcohol from the blood, or speed up its metabolization.

The one thing coffee can help with in such a situation is your level of wakefulness. If being drunk has made you sleepy, the caffeine in coffee or other drinks can make you more alert. Just don't mistake it for being able to drive or anything like that.

3. Coffee impairs digestion.

Some people point to the fact that coffee, which is acidic, can exacerbate symptoms for people with reflux. It's also a mild laxative, causing things to move through without as much time for normal digestion. For some people, these can result in discomfort.

But for most people, these same effects are generally good. The increased motility combats constipation, and the stimulated production of stomach acids and digestive enzymes helps break down fats and makes some nutrients more available. So for most people, it's mostly beneficial.

4. You should store coffee in the refrigerator.

Some say that storing your unused coffee beans or grounds in the refrigerator makes them last longer, as it slows down the oxidation process and thus preserves the flavors for longer. For whatever truth there may be to that, it has definite harmful effects as well.

First, there's a lot of humidity in refrigerators, and opening and closing the door causes temperature fluctuations which, along with that humidity, is likely going to make the coffee spoil or even mold, sooner than it would if stored at a constant room temperature. Furthermore, refrigerators have lots of food odors inside, and coffee is porous and great at absorbing odors. And that's definitely suboptimal for anyone who takes a special interest in their coffee's taste.

5. Coffee is dehydrating.

It's true that caffeine has a diuretic effect: it stimulates blood flow to the kidneys and makes you have more urine. It also has a few other minor effects that contribute to urine production. Some sources claim that this increased urine production results in overall dehydration.

However, this idea is forgetting one very important point: coffee is still about 98-99% water. It is extremely hydrating. The hydration you get from drinking your coffee far exceeds any dehydration from the diuretic effects. Coffee will not dehydrate you.

6. Pregnant women shouldn't drink coffee.

Pregnant women shouldn't do or not do anything they hear on any podcast, including this one. Do exactly what your doctor tells you.

With that said, the data show that consuming a lot of caffeine can lead to horrible effects like miscarriage, low birth weight, premature birth, and poor fetal development. While these effects are real, nearly all studies say that intake limited to 200-300mg of caffeine per day is not correlated with any of these negative effects. Caffeine per serving varies a lot, but 1-2 cups of coffee should keep you within that range.

And with that said, don't ever take any medical advice from any podcast, especially when the health of your soon-to-be bouncing baby is involved. Take it from your doctor only.

7. Coffee is bad for the bones.

There is plausible theory behind the effect caffeine can have on bones. Caffeine may cause more calcium to be excreted in the urine. Caffeine consumption may be correlated with reduced bone density in certain populations. And caffeine may also interfere with Vitamin D receptors, and Vitamin D also impacts bone health. So taken altogether, caffeine would seem to be bad for your bones.

However, this ignores your overall diet. Nearly everyone who eats anything remotely close to a full balanced diet gets more than enough of everything they need to completely erase these small nutritional impacts that caffeine takes away. For nearly everyone who eats meals, the amount of coffee you drink isn't nearly enough to produce an overall negative effect in your bones.

8. Coffee helps you lose weight.

A common belief about the caffeine in coffee is also a pretty glib one: it makes your metabolism and heart rate speed up, therefore it makes you burn more fat and get skinny.

Would that weight loss were as magically easy as enjoying your morning coffee; but sadly, life does not offer a whole lot of magically easy solutions to complicated problems. While caffeine can stimulate a mild, temporary boost to your metabolism, regular drinkers with a tolerance to caffeine get no meaningful such boost. And even so, the effect would be extremely remote at best, certainly not enough to play any significant role in weight loss.

9. Coffee consumption has been correlated with heart disease.

This same effect on increased metabolism that some regarded as a boon to weight loss was regarded as a health threat by others, who noted that increased metabolism also results in increased blood pressure.

But large scale studies have failed to confirm this fear. In fact, there's more scientific evidence that coffee is good for cardiovascular health. There's a correlation between modest coffee consumption and reduced risk of some kinds of heart disease, and also with improved function of the vessel walls. The antioxidants in coffee, like those you get from the rest of a normal diet, do play a role in the body's natural reduction of inflammation. So although these factors are generally small and are different for everyone, it's more likely that coffee is on the side of your body's good guys than of its bad guys.

10. Espresso has more caffeine than regular coffee.

We've all learned to be careful of that little tiny shot of espresso, because it packs a caffeine wallop that would wake up a frozen Siberian wooly mammoth. This is usually false. All brews and cups differ, but the average espresso has a bit more caffeine than the average coffee per unit of measure; yet the serving size is a lot smaller. It's smaller enough that a cup of coffee usually has significantly more caffeine than an espresso shot.

11. Coffee stunts your growth.

There's never been any evidence that coffee stunts your growth. This probably got started as a yarn parents told their kids to scare them away from consuming caffeine. They may have even thrown in a mention of the potential impacts to bone health. But really, it was probably just to get them to fall asleep at night and be able to concentrate on their homework.

12. Coffee is carcinogenic.

So for a long time, the WHO's subagency, the IARC (International Agency for Research on Cancer) had coffee in Group 2B. Group 2B is defined as stuff for which there is no evidence yet of carcinogenicity, but for which there is cause to study further. Wi-Fi, carpentry, listening to the radio, pickled vegetables, and the Earth's magnetic field are also in Group 2B. Yet the classification caused wooists worldwide to recoil in horror that coffee causes cancer. It is worth noting that the IARC has a pretty poor reputation among cancer researchers, and its classifications are often at odds with those of every other major cancer body in the world.

Then, back in 2016, the IARC did something it had never done before: it removed coffee from that classification, meaning that in their opinion, there is no cause to study it further. There is now no major scientific body on Earth that considers coffee to be a cancer risk.

13. Coffee is addictive.

This is not quite right, and it also depends a bit on how different people define addiction. This usually involves an inability to stop partaking in a substance or activity. Coffee doesn't really have that effect. It can (pretty easily) create a dependence, which means you get uncomfortable effects like headache and lethargy when you don't drink it; so you need a cup to stave those off. But it doesn't trigger your brain's reward centers the way that addictive drugs like opioids do. Dependence lacks the element of compulsion, which is central to an addiction.

14. Dark roast has more caffeine than light roast.

A lot of people think this, but it's false — sort of. Dark roasts are roasted longer than light roast, and roasting doesn't affect the amount of caffeine in the beans. So your dark roast bean has exactly the same caffeine content as your light roast bean. They're still the same kind of bean.

Here's the "sort of" part. Roasting a bean longer does slightly reduce its mass; and so, measured by weight, a certain amount of dark roast beans will usually have slightly more caffeine than that same weight of light roast beans. So call this one a myth or not, I'll let the pedants among you decide.

15. There are no coffee mugs in the Skeptoid store.

This crazy old myth needs to be put to bed once and for all. Yes, of course there are Skeptoid coffee mugs in the Skeptoid store. I can even offer empirical proof. Come to skeptoid.com/store and see for yourself. It's right there on your screen. But if that's not solid enough evidence for you, click the button to order one. When it shows up at your home, all nice and heavy and solid and laser engraved, fill it with your favorite coffee and then perform all the scientific measurements you want. You'll find that its dense ceramic composition has excellent low thermal inertia — and you can verify this with your thermal camera — which keeps your coffee warmer significantly longer than the cheaper mugs, like those from that other podcast. What's that, you want the web address again? It's skeptoid.com/store.

And there we have it, 15 myths about coffee, thoroughly debunked. Especially that last, worst myth intended to disparage the Skeptoid online store. Until next time, keep the pot warm, and whenever anyone tells you anything about your coffee, be skeptical.

By Brian Dunning
Follow @BrianDunning