According to the passage, what is the world’s leading killer?

A new study says that a change in health recommendations might lead to lower cholesterol levels and more treatment for people with high levels of heart disease risk.
    Dr. Pankaj Arora, of the University of Alabama at Birmingham, led the study. The news "is very heartening," Arora said, "but there is more to do."
    Heart disease is the world’s leading killer and high cholesterol is a key risk factor. Doctors have long treated patients based mostly on their level of so-called "bad" cholesterol, known as LDL.
    In 2013, new guidelines in the United States urged doctors to examine people’s overall heart risk. In other words, the guidelines recommended that doctors consider age, blood pressure, diabetes and other factors.
    The idea was that people with the highest risk would get the most benefit from cholesterol-lowering medications called statins.
    The researchers studied records from the Centers for Disease Control and Prevention. These records tracked cholesterol information from more than 32,000 adults between 2005 and 2016.
    Among people taking statins, the average level of "bad" cholesterol dropped 21 percent over the study period. Total cholesterol levels and another kind of fat in the blood also decreased.
    The researchers reported their findings in the Journal of the American College of Cardiology.
    Dr. Michael Miller is a heart disease expert at the University of Maryland Medical Center. He was not involved with the study.
    Miller said, "These are surprisingly impressive results" that together predict a 15 to 20 percent reduction in risk of heart attacks and strokes.
    In addition, there was an increase in statin use by people with diabetes. Over the study period, that number increased from less than half to over 60 percent.
    "It’s very important for those with a diagnosis of diabetes to not get that first heart attack,"
    said Dr. Neil J. Stone of Northwestern University. Stone led the development of the 2013 guidelines from the American College of Cardiology and the American Heart Association. He also co-wrote an update last year.
    Dr. Arora warned that other high-risk groups have not seen an increase in treatment. He added that still too many people do not know if they have a cholesterol problem.
    The advice for patients? Dr. Miller suggested getting a cholesterol check if you have not had one recently.