High consumption of coffee could put your heart at risk, study finds

NEW YORK, Aug. 17 (UPI) -- Growing interest in caffeine's harmful effects on blood pressure and heart rate piqued Nency Kagathara's curiosity to explore the damage it can cause to cardiovascular health.

The Indian medical student then found in a study she led that drinking more than 400 milligrams of caffeine daily on most days of the week could raise otherwise healthy people's risk for cardiovascular disease.

"There is a gradual increase in noncommunicable disease burden like hypertension," or high blood pressure, Kagathara, a second-year student at Zydus Medical College and Hospital in Dahod, Gujarat, India, told UPI via email.

In explaining why she undertook this research project, Kagathara said, "Some of the risk factors of hypertension are known, whereas caffeine consumption is not yet acknowledged."

Some of those known risk factors are older age, genetics, obesity and high-sodium diet.

She is to present the study's findings Saturday at the American College of Cardiology Asia 2024 conference in Delhi, India.

"With chronic consumption of caffeine and caffeinated drinks, the autonomous nervous system becomes sensitized to caffeine's effects, resulting in a sustained elevation of heart rate and blood pressure over time," Kagathara and her collaborators wrote in the abstract of their presentation.

"This prolonged modulation can contribute to cardiovascular issues such as hypertension and increased risk of cardiovascular events."

High blood pressure is associated with an increased risk of coronary artery disease, heart failure, chronic kidney disease and dementia.

Researchers defined chronic caffeine consumption as the intake of any caffeinated beverages five days per week for more than one year. Their investigation concentrated on tea, coffee and aerated drinks such as Coca-Cola, Pepsi, Red Bull, Sting and Monster.

"This study adds to previously published studies that have demonstrated similar findings," said Dr. Eugene Yang, co-chair of the conference.

However, "the jury is out regarding the long-term effects of high caffeine intake and cardiovascular events," said Yang, a clinical professor of medicine in the cardiology division at the University of Washington School of Medicine in Seattle.

For this study, researchers recruited 100 healthy individuals ages 18 to 45 through random sampling. They measured participants' blood pressure and pulse and collected data on sociodemographics and daily caffeine intake.

Subsequently, participants took a three-minute step test, followed by blood pressure and heart rate measurements at one minute and five minutes after the test.

A total of 92 participants completed the study; the majority were male (62%), older than 30 (60%) and living in urban areas (79.3%).

Among the participants, 19.6% were identified as consuming more than 400 mg. of caffeine daily -- the equivalent of four to five cups of coffee.

Women, people working in business and management roles, and those residing in urban areas showed significant associations with higher daily caffeine intake.

There are between 95 and 200 mg. of caffeine in an 8-ounce cup of coffee, 35 to 45 mg. in a 12-ounce can of cola, 70 to 150 in an 8-ounce energy drink and 14 to 60 in an 8-ounce cup of tea, Kagathara estimated.

The U.S. Food and Drug Administration advises healthy adults to consume no more than 400 mg. of caffeine daily.

In the study, daily consumption of more than 600 mg. of caffeine correlated strongly with elevated heart rate (100 beats per minute) and blood pressure (greater than 140/90 mm Hg) after five minutes of rest following a three-minute step test.

This test is designed to measure aerobic fitness based on how swiftly heart rate recovers from exertion. "The more aerobically fit you are, the quicker your heart rate will return to normal after exercise," Kagathara said.

Frequent intake of more than 600 mg. of caffeine per day may result in long-term consequences, such as increased anxiety, insomnia, bone weakening and fractures, and acidity in the stomach, she noted, adding that sweating and palpitations also may occur.

In addition, Kagathara noted that people in older age groups may have cardiovascular conditions that impact their heart rate and blood pressure during a step test.

"Certainly, if an individual has an underlying cardiovascular condition -- hypertension requiring medication, prior heart attack or stroke -- or is sensitive to the effects of caffeine, then it is advisable to consume small amounts or to abstain," said Dr. Usman Baber, cardiovascular section chief at OU Health in Oklahoma City. He was not involved in the study.

"Overall, this study shows that caffeine consumption above a certain threshold does increase heart rate and blood pressure, which is not unexpected given that caffeine is a stimulant," Baber said.

He cautioned, though, that the number of participants was too small to draw firm conclusions.

Other factors besides caffeine quantity may have influenced the study's results, such as whether the participants who consumed more of it were less physically fit, said Dr. Gregory Marcus, chair-elect of the American Heart Association's committee on drugs, alcohol and tobacco.

"The amount of caffeine will affect different people differently," he said. "Each of us have a number of genes that determine how fast or slow we inherently break down caffeine," said Marcus, who also is a cardiologist and professor of medicine at the University of California-San Francisco.

He added: "While some may have an aggravation of high blood pressure, others may actually experience a decrease in their blood pressure due to the diuretic effect."

Dr. Jacqueline Hollywood, a cardiologist at Hackensack University Medical Center in Hackensack, N.J., said people often feel the stimulant impact of caffeine within minutes, but it can last for many hours.

"While moderate caffeine consumption is generally safe for healthy adults, excessive intake can have adverse effects on heart rate and blood pressure," Hollywood said.

To reduce potential risks, she said she recommends that people with pre-existing cardiovascular conditions monitor their heart rate and blood pressure regularly, especially after ingesting caffeine.

"Individuals with concerns about caffeine consumption or its effects on heart health should consult a health care professional for personalized advice," Hollywood said.