People who consumed one apple a day for four weeks were found to have 40 per cent lower blood levels of a substance linked to hardening of the arteries.
Taking capsules containing polyphenols, a type of antioxidant found in apples, had a similar, but not as large, effect.
Researchers found that the apples lowered blood levels of oxidised LDL - low-density lipoprotein, the "bad" cholesterol.
When LDL cholesterol interacts with free radicals to become oxidised, and is more likely to promote inflammation and can cause tissue damage.
"When LDL becomes oxidised, it takes on a form that begins atherosclerosis, or hardening of the arteries," said lead researcher Robert DiSilvestro, professor of human nutrition at Ohio State University.
"We got a tremendous effect against LDL being oxidised with just one apple a day for four weeks," he said in a statement.
The difference was similar to that found between people with normal coronary arteries versus those with coronary artery disease, he said.
DiSilvestro described daily apple consumption as significantly more effective at lowering oxidised LDL than other antioxidants he has studied, including the spice-based compound curcumin, green tea and tomato extract.
"Not all antioxidants are created equal when it comes to this particular effect," he said.
Researchers recruited non-smoking healthy adults between the ages of 40 and 60 who had a history of eating apples less than twice a month and who didn't take supplements containing polyphenols or other plant-based concentrates.
In all, 16 participants ate a large Red or Golden Delicious apple purchased daily for four weeks; 17 took capsules containing 194 milligrams of polyphenols a day for four weeks; and 18 took a placebo containing no polyphenols.
Researchers found no effect on oxidised LDLs in those taking the placebo.
"We got a tremendous effect against LDL being oxidized with just one apple a day for four weeks," DiSilvestro said.
"We think the polyphenols account for a lot of the effect from apples, but we did try to isolate just the polyphenols, using about what you'd get from an apple a day," he said.
The study was published in the Journal 'Functional Foods'.
