Drinking too much caffeine could be bad for your heart health, new study finds. Here's how to know if you're overdoing it.

You may wake up in the morning desperate for a cup of coffee (or four) to kickstart your day. However, a new study says that overdoing it on caffeine may have implications for your heart.

The new findings, from Zydus Medical College and Hospital in Dahod, India, says that regularly drinking more than 400 mg of caffeine per day could increase the likelihood that otherwise healthy individuals will develop heart disease. For reference, 400 mg is, per the Mayo Clinic, the equivalent of roughly four cups of brewed coffee, 10 cans of soda or two energy drinks.

The small study looked at 92 healthy individuals between the ages of 18 and 45, 19.6% of whom were considered chronic caffeine users. Researchers found that those consuming more than 400 mg of caffeine daily had elevated heart rates and blood pressure. This effect was even more pronounced in those consuming over 600 mg daily, which is equivalent to about six to seven cups of brewed coffee.

The study authors say that caffeine’s impact on the autonomic nervous system (which helps control things like your heart rate and blood pressure) could put undue stress on the heart, as well as other parts of the body. Hypertension, or high blood pressure, increases the risk of health issues such as heart attacks, strokes, heart failure, aneurysms and chronic kidney disease — and is often referred to as the “silent killer.”

What experts say

Caffeine is a stimulant. Dr. Jamie Alan, associate professor of pharmacology and toxicology at Michigan State University, previously told Yahoo Life that consuming caffeine “will increase heart rate, open up the lungs and increase wakefulness.” (That last effect is why so many people reach for a coffee in the morning.)

Caffeine may also raise blood pressure, albeit temporarily, according to the Mayo Clinic. Contrary to what this new study found, this effect is more commonly seen in people who don’t consume caffeine regularly and therefore have not developed a tolerance for the stimulant. While it’s unclear why some people experience this, some researchers believe it may have to do with caffeine causing the adrenal glands to release more adrenaline (raising blood pressure) or caffeine blocking a hormone that causes arteries to widen. Despite this effect, people with high blood pressure aren’t typically told to cut out caffeine entirely.

Dr. Gregory Marcus, a cardiologist and professor of medicine at the University of California, San Francisco, tells Yahoo Life that these findings remind us that commonly consumed substances like caffeine may have effects on our heart and blood vessels. However, he notes that it’s possible that the effects attributed to caffeine could have been caused by other factors, such as age or fitness level.

“It is important to remember that while blood pressure and heart rate are important determinants of health, the best way to determine health effects is to examine actual cardiovascular outcomes, such as rates of stroke, heart attack and heart rhythm disturbances,” Marcus says.

There have been studies that suggest coffee could be good for the heart. For example, one study from 2023 found that regular caffeinated coffee consumption is associated with a decreased risk of hypertension, heart failure and atrial fibrillation. Research from 2021 also found that caffeinated coffee may reduce the risk of heart failure.

What is considered too much caffeine?

Dr. Brynna Connor, a specialist in family medicine, tells Yahoo Life that the Food and Drug Administration recommends no more than 400 mg of caffeine per day. “Anything beyond that is considered too much, and people may start to experience symptoms such as headaches, irritability and jitters,” she says.

She adds, however, that the severity of these symptoms depends on each individual’s sensitivity to caffeine and how quickly it is metabolized. “While the average half-life of caffeine is between three and seven hours, people with a slower metabolism or liver problems may experience the effects of caffeine longer, and more acutely, as the stimulant would take longer to pass and subsequently stay in their bloodstream longer.”

Connor warns that caffeine in quantities of 1,200 mg, especially if consumed in a short time frame, can be “toxic and lead to severe side effects such as seizures.” That is the equivalent of 12 to 15 cups of coffee — or about three of Panera’s now discontinued Charged Lemonades.

Marcus says that it’s hard to say what amount of caffeine is universally applicable because caffeine tolerance varies greatly among individuals due to genetic variants that cause us break down caffeine at different speeds and to the amount of caffeine we regularly consume.

People who have caffeine on a regular basis become more tolerant of its effects because our bodies ramp up the systems that get rid of caffeine, Marcus explains. Someone who doesn’t drink much caffeine may feel ill after drinking just one espresso, he says, but someone who drinks caffeinated beverages on a regular basis may experience minimal effects after even several cups of coffee.

“Ultimately, individuals should listen to their body, and learn to recognize the amount of caffeine for them that results in uncomfortable sensations, such as feeling tremulous or shaky, nervous or experiencing a racing heart,” Marcus says.