NEW YORK (AP) - U.S. health officials have changed their definition of lead poisoning in young children - a move expected to more than double the number of kids with worrisome levels of the toxic metal in their blood.

The more stringent standard announced last week by the Centers for Disease Control and Prevention means the number of children ages 1 to 5 considered to have high blood lead levels will grow from about 200,000 to about 500,000.

Some experts think the change was overdue. The CDC last changed the definition nine years ago and pledged to consider an update every four years. But work on a revision hit obstacles during the Trump administration, said Patrick Breysse, who heads the CDC’s National Center for Environmental Health.

Children can be exposed to lead through bits of old paint, contaminated dust, and - in some cities - drinking water that passes through lead pipes. The metal accumulates in the body, and at very high levels it can damage organs and cause seizures.

But it can have insidious effects at lower levels, too - especially in young children. Kids can absorb four to five times as much lead as adults exposed to the same source, harming children’s brain development and leading to attention and behavior problems.

“There is no safe lead level,” Dr. Marissa Hauptman, a pediatrician at Boston Children’s Hospital.

Lead poisoning is assessed using a measurement of micrograms of lead per deciliter of blood. In the late 1970s, the average blood lead level in U.S. children ages 1 to 5 was 15 micrograms per deciliter. The most recently reported measure, covering the years 2011-2016, was 0.83 micrograms. That drop was attributed to laws that phased out the use of lead in paints and gasoline and other efforts.