Sometimes health can feel a bit like a thunderclap.You're living your life as healthy as a horse, then boom, out of nowhere, illness strikes.Some ills genuinely do strike suddenly. Others, however, may be surreptitiously building for years or even decades before triggering other symptoms – a hidden disease process already underway, if only we knew how to see it.One such condition is atherosclerosis, the gradual buildup of plaque inside the arteries that is the principal driver of cardiovascular disease. Scientists have long known it can develop silently, years before symptoms emerge.What hasn't been clear is just how early that hidden process begins – or how common it is at different stages of our lives.Now, a new study of nearly 17,000 adults in Denmark and Spain, led by cardiologists Henning Bundgaard of Copenhagen University Hospital and Borja Ibáñez of the Spanish National Centre for Cardiovascular Research, has revealed the insidious prevalence of silent atherosclerosis.Among participants with complete imaging, more than 57 percent of those aged 18 to 70 had signs of atherosclerosis – but its prevalence varied dramatically according to age and sex."Because silent atherosclerosis predicts ischemic events and death independent of traditional risk factors, detection in young adults may identify a population at increased long-term risk at a stage at which the benefit of risk-factor control seems greatest," writes the team in a paper published in the New England Journal of Medicine.