Eating an apple a day for four weeks led to a 40 percent reduction in blood levels of a substance linked to hardening of the arteries, U.S. researchers say. Lead researcher Robert DiSilvestro of Ohio State University and the Ohio Agricultural Research and Development Center said the study -- funded by the apple industry -- found taking capsules containing polyphenols, a type of antioxidant found in apples, had a similar, but not as large, effect. The study, published online in the Journal of Functional Foods, found apples lowered blood levels of oxidized low-density lipoprotein, the \"bad\" cholesterol. LDL cholesterol interacts with free radicals to become oxidized and as a result the cholesterol is more likely to promote inflammation and can cause tissue damage, or hardening of the arteries, DiSilvestro said. \"We got a tremendous effect against LDL being oxidized with just one apple a day for four weeks,\" DiSilvestro said in a statement. DiSilvestro said daily apple consumption was significantly more effective than other antioxidants he has studied -- including the spice curcumin, green tea and tomato extract -- at lowering oxidized LDL. \"Not all antioxidants are created equal when it comes to this particular effect,\" he said. \"We found the polyphenol extract did register a measurable effect, but not as strong as the straight apple -- because there are other things in the apple that could contribute to the effect, or, in some cases, these bioactive compounds seem to get absorbed better when they\'re consumed in foods.\"