A dangerous buildup of plaque inside the arteries may begin far earlier than many adults realize. New research found silent atherosclerosis in some people younger than 30, even though they had no known cardiovascular disease.

About one in 13 adults ages 18 to 29 already had evidence of atherosclerosis, which is the hardening of arteries caused by plaque. Across the full study population, more than half of the adults showed signs of plaque somewhere in their arteries.

Researchers from Denmark and Spain used advanced imaging to examine more than 16,800 adults. Participants ranged from 18 to 70 years old, and none had known cardiovascular disease when they entered the study.

Plaque was detected in 57.1% of participants, according to findings published in The New England Journal of Medicine in August. Its prevalence rose steadily with age, climbing from about one in 13 adults younger than 30 to roughly nine in 10 adults ages 60 to 70.

Atherosclerosis develops when cholesterol, fatty deposits and other substances accumulate inside arteries. The condition can progress silently for years before leading to a heart attack or stroke, making its presence in adults without diagnosed cardiovascular disease especially concerning.

“For decades, we have estimated cardiovascular risk using factors such as age, blood pressure and cholesterol,” Dr. Borja Ibáñez, a cardiologist and scientific director of Spain's National Center for Cardiovascular Research, said in a statement. He said the findings reveal another way to identify potential danger.

“This study shows that we can now go one step further and detect the disease directly before it causes a heart attack or stroke,” Ibáñez said. The research shifts attention from estimating risk factors alone to detecting whether artery disease is already present.

The findings come from the first phase of the ongoing international REACT study. Researchers are using the project to map how commonly silent artery plaque appears throughout adulthood.

During the study’s next phase, researchers plan to test whether detecting plaque earlier can improve the prevention of heart disease. The current findings do not establish that broad screening will directly prevent heart attacks or strokes.

“Until now, preventive decisions have been based on an estimate of risk, but we did not know whether the disease was already present,” said Henning Bundgaard, professor of cardiology at Rigshospitalet in Copenhagen. He described REACT as a detailed look at the progression of atherosclerosis.

“REACT shows that atherosclerosis can be detected decades before clinical manifestations appear and provides the most comprehensive atlas of the evolution of the disease across adult life,” Bundgaard said. The findings also revealed notable differences in when plaque developed among men and women.

Men tended to develop plaque five to 10 years earlier than women. Women experienced their sharpest increase in plaque prevalence between the ages of 40 and 60.

Common cardiovascular risk scores identified only a small share of participants who already had silent atherosclerosis. That result suggests traditional risk assessments alone may fail to detect some people whose arteries already contain plaque.

Researchers believe portable ultrasound could eventually help identify hidden plaque earlier, although they said more clinical trials are necessary. Experts also cautioned that the findings should motivate attention to heart health without causing panic.

“Finding plaque doesn't mean someone is about to have a heart attack, but finding it gives us an opportunity to address a patient's risk factors,” Dr. Sirisha Vadali, a cardiologist at HonorHealth Women’s Heart Health in Arizona, told Fox News Digital. Vadali was not involved in the research.

“We shouldn't wait for symptoms to start paying attention to heart health. Feeling healthy doesn't necessarily mean your arteries are free of plaque,” Vadali said.

She emphasized that the study does not mean every person younger than 30 should undergo artery screening. Decisions about additional testing should instead be based on each person’s individual risk factors.

Experts said people can help protect their cardiovascular health by avoiding tobacco, remaining active and eating a nutritious diet. Knowing blood pressure, cholesterol and other heart health risk factors can also help people address cardiovascular risk before symptoms appear.