Looking for calcium in coronary arteries could provide an early warning of future heart attacks in people still in the prime of life, research has shown.
Even small amounts of calcium can identify men and women in their 30s and 40s who are at an increased risk of a fatal or non-fatal heart attack in the next 12 and a half years, say scientists.
A fifth of study participants with high levels of calcium in the major vessels supplying the heart with blood went on to die from a heart attack.
Calcium is one component of deposits, or plaques, made from cholesterol, fat and other substances, that build up on the walls of the arteries and restrict blood flow.
Lead researcher Dr Jeffrey Carr, from Vanderbilt University Medical Centre in the US, said: "We always thought you had to have a certain amount of this plaque before you were at risk of having events.
"What we showed was that, for younger people, any amount of coronary artery calcium (CAC) dramatically and statistically significantly increased risk of clinical heart disease.
"The presence of any coronary artery calcification, even the lowest score, was associated with between a 2.6 and 10-fold increase in clinical events over the next 12.5 years.
"And when it comes to those with high CAC scores, the incidence of death was 22%, or approximately one in five."
He added: "Very few times do you get a biomarker, be it genetic or imaging, that predicts death at a level of 22% over 12.5 years."
The findings, published in the journal Jama Cardiology, emerge from a major US investigation into heart disease risk in young adults.
Computed tomography (CT) scans, which provide 3D X-ray images, were carried out on a total of 3,330 individuals whose progress was followed for an average 12.5 years.
Dr Carr pointed out that coronary artery calcium could easily be spotted on routine CT scans of the chest performed for other reasons.
"For example, a 45-year-old woman with a cough might receive a routine CT scan that shows the presence of a calcified plaque in her coronary arteries," he said.
"With this new information, the doctors don't need to know the CAC score or do additional tests.
"With the information that any CAC is present, she and her health care team could assess her risk and determine the optimum prevention strategy."
Rather than screening everyone for coronary artery calcium, the researchers suggested targeting young adults considered to be at high risk.
Genetic factors, increased age, diabetes and chronic kidney disease can all raise the chances of calcium being deposited in the arteries.