Youth isn't enough to protect your heart.Last year, researchers examining a cohort of young adults in the US made an "ominous" observation.When they imaged and measured the carotid arteries of more than a thousand young participants, they noticed signs of subclinical injury.Some markers of arterial thickness were what would be expected in a 33-year-old.The average age of the participants was 23.Now, a follow-up study on that same cohort may explain why these potential injuries are occurring in adults under 30.Magnetic resonance angiography of cerebral artery and common carotid artery. (Paul Biris/Moment/Getty Images)The research, published in Circulation: Population Health and Outcomes, found that out of 1,283 young adults, as many as 80 percent of participants were classified as having cardiovascular-kidney-metabolic (CKM) Syndrome.The more advanced their stage of CKM, the more likely participants were to show signs of injury to the carotid arteries, which carry oxygenated blood to the brain.The finding is concerning, and may explain why cases of cardiovascular, metabolic, and kidney disorders are on the rise in younger cohorts.But these particular participants are not representative of all young people in the United States. The study focused on urban populations, and many participants came from disadvantaged backgrounds."Diet and physical activity scores were especially poor," the study authors noted.This puts participants at a higher risk of CKM.If you've never heard of this syndrome before, you're not alone. Last year, a US national survey found that 90 percent of respondents hadn't heard of CKM, either.