If you’re a tea or coffee drinker, you probably rely on your morning mug to give you a good jolt of caffeine. But even if hot beverages aren’t your thing, chances are you consume caffeine in some form during your day.
Caffeine shows up in a variety of products, including soda, chocolate, some ice creams, sports nutrition supplements, pain relievers, and headache medications, says Julie Upton, M.S., R.D., co-founder of nutrition website Appetite for Health. But despite its prevalence in foods and drinks, you’ve probably heard mixed reviews about whether or not it’s good for you. What’s a java-lover (or preworkout junkie) to think?
First, the basics: Caffeine is a stimulant that increases your heart rate and opens up your blood vessels, which boosts delivery of oxygen throughout your bod, making you feel alert. “On the flipside, caffeine may contribute to anxiety and sleep troubles,” says Sonya Angelone, R.D., a spokeswoman for the Academy of Nutrition and Dietetics. “Plus, since caffeine is addictive, stopping suddenly can cause withdrawal symptoms, such as headaches, irritability, and drowsiness.”
According to the Mayo Clinic, it appears to be safe for most healthy adults to consume up to 400 milligrams of caffeine a day (that’s about four cups of coffee). However, consuming more than 400 milligrams of caffeine a day can lead to insomnia, nervousness, restlessness, irritability, an upset stomach, a fast heartbeat, and muscle tremors, the clinic says.
For all of its potentially uncomfortable side effects, caffeine has many scientifically-proven perks. “Caffeine is a proven performance-enhancer,” Upton says. For example, one study published in the British Journal of Sports Science discovered that people who drank coffee before running 1,500 meters (which is just shy of a mile) on a treadmill finished their runs 4.2 seconds faster than those who didn’t drink coffee beforehand.
Related: Can Green Tea Really Help You Lose Weight?
There’s also some evidence to show that caffeine may even have a connection to your—woah—longevity. Research from Harvard University published in the journal Circulation found that higher consumption of coffee (both regular and decaf) was associated with a lower risk of mortality, including that due to heart disease, neurological diseases, type 2 diabetes, and suicide.
The connection between coffee and a lower risk of heart disease and Type 2 diabetes isn’t new: An analysis of several studies published in Circulation found a link between drinking three to five cups of coffee a day and a low risk of developing heart disease. Meanwhile, research published in the journal Diabetes Care found that moderate consumption (two or more cups per day) of decaf or regular coffee may lower the risk of developing Type 2 diabetes in younger and middle-aged women.
However, there may be a danger of too much of a good thing. A study published in the European Journal of Epidemiology discovered that people who consumed eight or more cups of coffee daily had a 58 percent greater risk of suicide than those who had less caffeine each daily. (It’s worth noting here that eight or more cups of coffee a day is a lot.)
Certain age groups and populations should consume caffeine with extra caution. The Mayo Clinic points out that children and teens are encouraged to have no more than 100 milligrams of caffeine a day, while people with heart conditions are typically advised to limit their caffeine intake, according to Upton. Pregnant women are also advised to limit the amount of caffeine they have daily since the stimulant can travel through the blood stream to the placenta and affect the developing baby, Angelone says. (The American Congress of Obstetricians and Gynecologists recommends that pregnant women have no more than 200 milligrams of caffeine a day.)
Bottom line: You know how caffeine makes you feel. If you find that you get jittery or just feel off after having a certain amount, scale back or try to eliminate it from your diet. But, if you don’t have any issues with caffeine and you don’t have a health condition that may be problematic with it, have at that java, tea, or supplement—just strive to stay within the 400 milligrams-a-day recommendation for max health benefits.
Related: Check out The Vitamin Shoppe’s new coffee category.