The Science Behind Your Cup of Coffee

Let’s talk coffee.  ☕ Most of what you see online about caffeine isn’t exactly glowing. It could raise blood pressure, cause jitters, mess up your sleep, or [insert other downside here].

But here’s some (good) news out of New Orleans. A study just presented at the annual clinical meeting of the American Heart Association found that coffee drinkers with a history of atrial fibrillation (AFib) had a lower risk of AFib recurrence than those who abstained completely from drinking coffee.

• Zoom In: Researchers at UCSD studied 200 people in several countries and followed them for 6 months. While some may have expected those who drank coffee (at least 1 cup a day) to have had a HIGHER risk of AFib recurrence, the opposite result was found: the coffee drinkers were at 39% lower risk of having AFib than the group who abstained.

Rejoice! More good data about coffee! In the spirit of evidence-based celebration, let’s review how coffee affects your health.

Caffeine Can Benefit The Heart

The recent study, cutely called DECAF (although it used regular coffee), isn’t the first to look at how caffeine influences heart health:

• A 2022 meta-analysis reported that daily coffee consumption is not associated with an increased risk of atrial fibrillation; in fact, some studies suggest a LOWER risk among moderate coffee consumers.
• A 2025 analysis found that moderate coffee drinkers had a lower risk of hypertension, type 2 diabetes, heart failure, and overall mortality compared to non-drinkers.

Caffeine Can Boost Clarity & Physical Performance

Beyond helping us get up from bed? Caffeine can enhance our mental function and physical strength:  

• A 2020 study found that people on a low caffeine dose (about 1-2 cups of coffee) performed better on the Stroop test and showed greater prefrontal cortex activity.
• A meta-analysis found that women who consumed 1-3 cups of coffee before exercise showed greater muscular strength and endurance, especially in upper-body exercises.

How Long Does Caffeine Stay in Your System?

Caffeine has upsides. But how long does it actually stick around? Well, for most healthy adults, its half-life (the time it takes for your body to clear half of it) is 2.5 to 5 hours.  

But that window can stretch or shrink depending on dose, genetics, liver health, whether you smoke, are pregnant, are taking oral contraceptives or hormone replacement therapy (HRT), and more.  

• Zoom In: Women on oral contraceptives metabolize caffeine more slowly, about 10.7 hours vs. 6.2 hours in non-OC users. HRT may have a similar effect.  

Translation: if you’re drinking coffee later in the day and have any of these factors, the “buzz” might last longer.

How Much Caffeine is Too Much?

Caffeine and coffee aren't risk-free. Go beyond 400 mg of caffeine per day (about 3-4 cups of brewed coffee), and you might get side effects like anxiety, heart palpitations, or restless sleep.

For some, too much caffeine causes more than just jitters. It may raise blood pressure, increase stroke risk, or, in rare cases, trigger arrhythmias, especially if you have underlying heart conditions.

And because caffeine is a stimulant, it’s not always friendly to the nervous system. If you live with anxiety, insomnia, or bipolar disorder, the extra dose of adrenaline and cortisol can worsen your symptoms.

A Nutritionist’s Guide to Caffeine

1) Drink up to 2-3 cups of caffeinated coffee per day.

This is what appears to align with many of the cardiovascular and cognitive benefit data.

2) Go for caffeinated coffee instead of decaf (unless you are sensitive to the effects of caffeine).

It seems that caffeinated coffee is where much of the “heart benefit” signal is found. There’s not as much reliable data about decaf or other caffeinated beverages like teas.

3) Make sure it’s right for you.

If you have insomnia, anxiety disorders, arrhythmias, or are pregnant (pregnancy doubles caffeine half-life), you may need to cut back or drink it earlier in the day.

4) Don’t load up late in the day.

As you get older, your body metabolizes caffeine more slowly, so that afternoon cup can linger and keep you wired well into the night. I NEVER have coffee after 2:30 PM unless I plan to be awake all night. Protect your sleep!

Bottom Line

Keep your coffee habit, but make it work for you. And don’t listen to the wellness ‘noise’ out there that tries to convince you that coffee is bad for you! What IS bad for you is the mountain of whipped cream, syrup, and/or sugar that often accompanies the coffee at various popular coffee chains!

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