I don’t know about you, but my day doesn’t really start until after my first cup of coffee in the morning. I might do a stretch or two, but to get my motor runnin’, I’m a little more than dependent on that first cup. And I’m certainly not alone. More than 90% of U.S. adults consume caffeine regularly, and 1.6 billion cups of coffee are consumed in the world every day. All this consumption makes caffeine the most commonly used drug worldwide.

Yet as common as caffeine use is, it’s also quite controversial. According to some studies, moderate caffeine intake of up to four cups a coffee a day has a number of health benefits. Other studies suggest that even one cup per day could do harm.

Of course, with a mixture of over 1,000 bioactive compounds, coffee is more than just a vehicle for caffeine. However, since coffee is by far the greatest contributor to overall caffeine intake, it makes sense to turn to it; after all, it is the world’s most popular beverage. And regardless of your delivery of choice (e.g., gourmet espresso drinks, energy drinks, candy, etc.), you have to consider what else is along for the ride.

So, what’s the deal? Is caffeine bad for you? Good for you? Or like everything else, is the answer, “it depends”?

Let’s check in with the research…

How Does Caffeine Work?

Caffeine is a natural stimulant that’s found in 60+ different plant sources. The highest caffeine content can be found in filtered coffee (~95 mg in 8 ounces) [Note that a standard cup of coffee, however, is actually about 5 ounces.], energy drinks (~80 mg in 8.5), and espresso (~60 mg in 2 ounces). It’s also found in tea, hot cocoa, and chocolate bars. You’ll even find a little in decaffeinated coffee (~6 mg per 8 ounces). And you’ll find it in yerba mate, guarana berries, and yaupon holly. Caffeine is added to sodas as well as energy drinks. And, it is an ingredient in a number of pharmaceuticals and over-the-counter analgesics (for pain relief), cold/flu remedies, and diet aids often as the synthetic powder caffeine anhydrous.

What’s more, the amount of caffeine in your coffee of choice can vary significantly depending on how strong it is, how big your mug is, which type of bean is used, and how the beans are roasted. For example, robusta coffee contains more caffeine than arabica.

Interestingly, at dry weight, tea actually contains more caffeine than coffee beans, but less tea is used to prepare a cup, resulting in less caffeine than found in a cup of coffee (for example, 25 mg in green tea compared to 95 mg in a similar-sized cup of coffee).

Within just 15 minutes after consumption, lasting up to 6 hours later, moderate caffeine consumption (up to 250 mg) crosses the blood-brain barrier and begins to stimulate the central nervous system. ¹ As a result, it’s well-known for helping combat fatigue, increase alertness, improve focus and concentration, and enhance mood and feelings of well-being.

The Health Benefits of Caffeine

In addition to caffeine’s powerful effects on attention, some of the powerful benefits of caffeine include:

• Increase energy levels. ²
• Boost long-term memory. ³
• Improve alertness, attention, and mood, ⁴ especially for those who don’t regularly consume caffeine. ⁵
• Support weight loss. ⁶, ²⁴
• Reduce the risk of type 2 diabetes—moderate consumption of coffee (caffeinated and decaffeinated), but not tea, has been associated with a decreased risk of developing type 2 diabetes. ⁷
• Support liver health and potentially reduce the risk of liver cancer—in one study, 2 cups of coffee a day were associated with a 43% reduction in risk. ⁸
• Reduce the risk of oral cancers: research suggests drinking coffee may also protect against oral cancers, decreasing the risk by up to 50. ⁹
• Decreased risk of basal cell skin cancer. ¹⁰
• Reduce the risk of Parkinson disease. ¹¹, ¹²
• Protect against Alzheimer’s disease. ¹³
• Decrease the risk for cataracts. ¹⁴
• Decrease the risk of suicide: 3 large cohort studies suggest an association between reduced risk of suicide and caffeine consumption. ¹⁵
• Modestly reduce risk of stroke. ¹⁶, ¹⁷
• Decrease the risk of multiple sclerosis—six cups of coffee a day were linked to a 31% lower risk in one study. ¹⁸

It’s important to point out that many of these health benefits of caffeine are tied to coffee consumption, not specifically caffeine, which, believe it or not, is actually an antioxidant. So, if you’re getting your caffeine from other less-healthy sources (e.g., energy drinks, candy, chocolate, etc.), you have to take into considerate what else is along for the ride (e.g., sugar, calories, artificial chemicals).

Some of these studies just show associations, and people are unique. So, we can’t conclusively state that caffeine does have all or even some of these effects for all people. But there is at least an association with these potential benefits that’s worth considering. Yet caffeine consumption isn’t for everyone. In fact, it also comes with some negative effects…

The Potential Negative Side Effects of Caffeine

With the good can come the bad. With caffeine consumption, modest use may have benefits, but excessive use (especially more than 500 to 600 mg per day) can lead to a number of negative side effects. ¹⁹ These include:

• Nervousness
• Irritability
• Restlessness
• Sleeplessness
• Migraine headaches
• Frequent urination
• Inability to control urination/incontinence ²²
• Stomach upset
• Rapid/racing heartrate
• Muscle tremors
• Decreased fertility by up to 27% ²⁰
• Low birth weight for babies (if the mother consumes more than 300 mg per day during pregnancy)
• Gout attacks ²¹

It may also make the symptoms of depression and anxiety worse. And higher intakes have actually been linked to increased weight, lower achievement in school, and a greater risk of severe depression, though it’s unclear if the increased consumption causes the depression or if depression causes increased caffeine consumption.

Caffeine consumption is also not recommended for children, pregnant women or those trying to become pregnant, and it should be limited (if not excluded) for adolescents and nursing mothers due to its potentially negative effects on sleep, which is key to learning and development. ²² It’s also not recommended for people who are sensitive to caffeine and those who may feel anxious. And how sensitive you are may be due to your genes.

Caffeine & Your Genes

For folks who are sensitive to caffeine, even a single cup of coffee or tea can lead to unwanted side effects like feeling restless, anxious, or difficulty falling asleep. Meanwhile, others seem to enjoy a quad espresso without batting an eyelash.

Believe it or not, this might be due to your genetics, which can determine how fast or slow you metabolize caffeine.

Those who metabolize caffeine slowly don’t just face discomfort when they consume caffeine (feeling jittery, anxious, and irritable), they can also increase their risks for adverse effects (like non-fatal heart attacks). Whereas those who metabolize caffeine more rapidly actually enjoy more of the positive effects mentioned above (including a reduced risk of heart attack). ²⁶

If you don’t trust your gut instincts, you can take a DNA test to determine if you carry a version of the gene (CYP1A2) that makes you a “slow” caffeine metabolizer. Researchers have discovered that those with a TT or CT Genotypes, for example, are likely to consume more coffee per day on average whereas those with a CC Genotype are likely to consume a typical amount. And those with an AA Genotype are likely to be fast metabolizers compared to AC and CC Genotypes, who more slowly metabolize caffeine. 25, ²⁶

In addition to genetic factors, how you respond to caffeine can depend on how often and how much you typically consume, your weight, age, health conditions, and if you are using any medications. What you put into your body can also affect how you metabolize caffeine. For example, smokers have been shown to metabolize caffeine twice as fast as those who don’t smoke.

Caffeine Addiction & Withdrawal Symptoms

If you think you might be addicted to caffeine, you’re probably right. Well, sort of. Caffeine has been shown to activate similar mechanisms as other “drugs of abuse.” It’s associated with subjective positive effects like increased well-being, feeling more social, and increased energy and alertness, and some people may become dependent. (Guilty!)

That being said, after a mere 20 to 48 hours of quitting, the withdrawal symptoms of even the heaviest user go away. And researchers have shown caffeine doesn’t activate the usual pathways that other addictive substances do. Thus, it’s not considered to be truly addictive.

Still, if you’ve decided that caffeine is no longer your cup of coffee, you may think it’s time to stop. If so, you’re better off gradually weening yourself off as giving it up cold turkey can often lead to some pretty uncomfortable withdrawal symptoms. These can include:

• Headaches
• Irritability
• Difficulty focusing
• Increased fatigue

Fortunately, the symptoms are typically fairly mild and you’ll get back to your “old self” within a few days.

Is Caffeine Bad For You — A Recap

Is caffeine bad for you? The answer is, of course, it depends. Some people are clearly more sensitive to its effects than others—and if you are sensitive, you’re probably better off without it or at least better off limiting the amount you consume.

Yet for many of us, there are some pretty impressive health benefits of caffeine consumption. Those benefits, however, evaporate if too much is consumed. So, ensure you consume no more than 200 – 400 mg a day, which corresponds with research showing that the largest benefits of coffee consumption comes with 15 – 25 ounces per day (180 – 300mg caffeine). But if your caffeinated vehicle of choice includes energy drinks, soda, chocolate, gourmet espresso and tea drinks, or certain supplements, don’t forget that adds up as well.

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