10 myths about coffee that just won't go away

Where the research really stands on the relationship between coffee and health

Photo by Thought Catalog on Unsplash

There is no beverage I enjoy more than coffee. It pairs perfectly with morning, which is my favorite time of day.

I hear a lot of conflicting evidence about coffee in the midlife space. That women should not drink it if they have hot flashes or sleep issues. Or that it needs to be consumed at the right time or else it will mess with cortisol levels.

As I dug into the research (or lack thereof) and compiled a list of myths, I found that according to a 2019 survey published in Nutrients, 66% of consumers have beliefs about coffee (and caffeine) that aren’t in line with what we know.

So, let’s dig into these myths one by one.

1. Coffee is mainly a stimulant

The 2019 survey found that:

Consumers see coffee mostly as a stimulant and are not informed about beneficial components and suggested health benefits.

While it is true that caffeine in coffee acts as a stimulant, there are benefits to consider. Caffeine, in doses up to approximately 300 mg, boosts various cognitive functions including alertness, attention, learning, and mood.

Coffee is also a key contributor to daily antioxidants, more so than fruits, tea and vegetables! It has over 1000 bioactive compounds linked to anti-inflammatory, antifibrotic and anticancer effects. Some of these compounds include chlorogenic acids, diterpenes, and cafetol.

Of course, the biochemical composition of coffee depends on the degree of roasting and the type of bean used. Yet research to date shows that drinking coffee can have health benefits which I’ll review in myth #8.

But the fact remains that coffee is more than just a stimulant.

2. Coffee causes hot flashes

I often see women advised to stay away from coffee if they have hot flashes. Yet the research is not even close to conclusive.

Two studies indicate a connection between caffeine and hot flashes, but they don’t establish cause and effect.

Not only that, but a 2020 study also showed chlorogenic acid (CGAs) found in coffee, reduces hot flashes. Eighty-two women were assigned to review CGAs (270mg) or placebo for 4 weeks.

After 4 weeks, the number and severity of hot flashes decreased in the CGAs group, starting at 2 weeks.

Of course, this is one study but interesting. Perhaps if you already have hot flashes, too much caffeine may exacerbate them.

“Anything that sort of makes you flush anyway,” Melanie Marin, MD, director of the menopause program in the Raquel and Jaime Gilinski Department of Obstetrics, Gynecology and Reproductive Science told SELF magazine, “can trigger hot flashes and night sweats.”

Could it be possible that regular coffee consumption helps prevent hot flashes? We need more research to know for sure, but as of now there’s no data showing coffee causes hot flashes.

3. Coffee messes with natural cortisol production

The theory that coffee messes with cortisol has been a hot topic in recent years. Cortisol levels typically reach their peak in the morning, usually around 8:30am. This theory suggests that consuming coffee before or during this time can disrupt cortisol production, resulting in an early rise and subsequent crash.

This has led to the advice that the best time to consume coffee is after the cortisol peak: 9:30-11. Yet, according to a 2024 review on the subject:

There is no evidence that caffeine ingestion upon waking is somehow responsible for an afternoon “crash” or that delaying consumption would somehow prevent this if it did occur.

The individual studies I found were mixed.

In a double-blind crossover trial, young men and women were given caffeine. Each week, they abstained from dietary caffeine intake for 5 days. Then, the researchers administered capsules containing a total of 0mg, 300mg, and 600mg/day of caffeine in divided doses (9am, 1pm, and 6pm) and monitored cortisol levels.

After 5 days of no caffeine, those who got caffeine showed a robust effect on cortisol earlier in the day, but this effect lessened with each caffeine consumption. The cortisol response at 9am was eliminated after 5 days of caffeine intake at doses of 300 mg and 600 mg, but levels increased at doses taken at 1pm and 7pm.

Lovallo et al, Psychosom Med. 2005; 67(5): 734–739....

The researchers found that tolerance to caffeine had a decreased impact on cortisol, particularly in the morning.

Another study with young women found that Arabic coffee had a cortisol reducing effect!

So, the evidence to date does not show that we need to consume coffee at a certain time. But we probably benefit from drinking it earlier in the day versus the afternoon.

4. Coffee dehydrates you

A 2024 review on coffee concluded that moderate intake (about 250-300mg caffeine) does not increase urine volume, resulting in net loss of fluids.

In one study, habitual male coffee drinkers were given 200 ml of coffee four times a day (containing 308 mg of caffeine) compared to water.

When looking at total body water, there was no difference in urine volume and 24-hour and urine osmolality.

However, high doses of 500mg or more may increase urine output somewhat over the short term. But saying that coffee is dehydrating is simply not true.

5. Coffee messes with sleep

This one is a half-truth. It’s true that when consumed closer to bedtime, coffee decreases sleep duration.

In a review of 24 studies, caffeine consumption was found to reduce total sleep time by 45 minutes and sleep efficiency by 7%.

But this did not occur when it was consumed at least 8.8 hours before bedtime or a pre-workout aid, 13.2 hours before bed. So, if you go to bed at 10, your last caffeine dose should be by 1pm, or pre-workout at 8am.

6. Coffee causes hypertension

The relationship between coffee intake and hypertension is controversial. A systematic review and meta-analysis, which looked at 25 studies (13 cross-sectional and 12 cohorts), revealed a link between coffee intake and a reduced risk of hypertension. Although the effect was small.

This could be because of various reasons, but one caught me by surprise. The caffeine in coffee is a vasodilator. Yep, it increases nitric oxide production, which is one theory why it makes a good ergogenic aid.

Learn more about the importance of nitric oxide here.

In a randomized double-blind crossover trial, the researchers administered caffeinated and decaf coffee to 18 subjects (average age 37), of which 60% were female. They both had caffeinated and decaffeinated coffee separated by a wash-out period of 7 days.

Although the caffeine coffee acutely increased blood pressure, it had a more pronounced effect on flow-mediated dilation, which is positively linked to nitric-oxide induced vasodilation.

Studies show that drinking coffee can cause a short-term increase in blood pressure, but in trials of greater than 2 weeks lessens this effect mostly likely because of tolerance.

One caveat is those with severe high blood pressure. A 2022 study in the Journal of American Heart Association found increased risk of cardiovascular mortality in this group who drank 2 or more cups a day. If you have high blood pressure, check with your healthcare provider.

7. Coffee is bad for your bones

Research shows that high caffeine intake can have a negative effect on calcium absorption and subsequent bone health. But like most things, the dose makes the poison.

According to the 2024 review, less than 4 cups of coffee (<400 mg caffeine) does not have this effect and anything over may cause issues.

Yet, more research is needed to draw firm conclusions.

8. There are no health benefits

The 2019 survey on coffee revealed that:

A relevant minority of consumers (25%) thought that drinking coffee could have positive effects on health.

According to a 2017 umbrella review of 201 meta-analyses of observational research and 67 outcomes and 17 meta-analyses of intervention studies, coffee intake was more often linked to benefit than harm.

The largest reductions in risk were at 3-4 cups a day, which was linked to reduced all-cause mortality (17%), cardiovascular mortality (19%), cardiovascular disease (15%) and cancer (18%).

Controlling for smoking nullified harmful effects, except in pregnancy, where coffee intake was linked to adverse outcomes such as low birth weight and fracture risk in women but not men.

Robust randomized controlled trials are needed to understand whether the observed associations are causal. Importantly, outside of pregnancy, existing evidence suggests that coffee could be tested as an intervention without significant risk of causing harm.

-Pool et al, BMJ. 2017; 359: j5024.

Some studies reveal a connection between coffee consumption and a lower risk of type 2 diabetes. Yet the Coffee for Metabolic Health (COMETH), a 24-week randomized placebo-controlled trial investigating the effect of coffee on insulin sensitivity, showed no effect.

The mechanism for potential health benefits could be coffee’s antioxidant activity, vasodilator effect, or ability to lower uric acid, as revealed in this review.

9. Coffee intake causes heartburn

Typical advice for those who have heartburn is to eliminate coffee. Yet research is lacking. According to 15 case-control studies, there was no significant association between GERD and coffee intake.

Yet another study found that 6 cups a day compared to those with low intake increased risk. And in a substitute analysis, replacing 2 servings of coffee or soda with water decreases the risk of GERD symptoms.

It’s likely that coffee intake doesn’t cause GERD, but drinking it may exacerbate symptoms. Interestingly, a pilot study with dewaxed coffee showed a reduction in GERD symptoms, but more studies are needed.

Dewaxed coffee undergoes a process that removes waxy lipids that naturally coat coffee beans, significantly reducing the caffeine and acidity.

If you enjoy coffee but find it aggravates your reflux or other digestive issues, consider cutting back—or trying dewaxed coffee — while looking for the root cause of the digestive issue.

10. Coffee has the same effect on everyone

As with most anything, we all react uniquely to the effects of coffee and caffeine. Studies that compare twins have found that caffeine use, tolerance, and potential withdrawal symptoms are highly heritable (35 to 77%).

Certain gene variants affect how quickly (or slowly) the body breaks down caffeine.

I know my husband can drink coffee after dinner and sleep like a baby, while I need to stop by noon or else I’ll toss and turn.

Others may find coffee drinking becomes problematic, because they can’t control how much they consume or have adverse side effects. The American Psychiatric Association has acknowledged Caffeine Use Disorder, but needs more research to recognize it in the DSM.

As I’ve gotten older, I cannot drink coffee right after a workout. I need to consume a full meal in me or else I feel shaky.  

Sensible coffee guidelines

Consuming <3-4 cups (up to 300-400mg caffeine–95mg per cup) is deemed safe and may offers certain health benefits. 

If coffee doesn’t agree with you or you don’t like it, there is no need to drink it as you can get any potential benefits in other ways.

Early day consumption (9 hours before bed) helps keep coffee from interrupting sleep. But don’t worry about waiting to drink it after 9:30, unless you find that works for you.

If you have reflux, other digestive issues, or hot flashes exacerbated by coffee, you should consider using a dewaxed coffee blend, half caff or decaf until the issue is resolved.

To maximize levels of chlorogenic acid, consider using green coffee beans. In one study, medium roasted, fine-ground green coffee beans had the highest levels of CGAs.

Well, that’s it for myths and the research.

Do you drink coffee? Has your tolerance changed in midlife? Let’s discuss in the comments.