America's No. 1 killer — coronary heart disease — is more likely to afflict women with diabetes than men with diabetes, according to a new study that examined more than 850,000 patients. Across all of those cases, diabetic women were 44 percent more likely to suffer from heart disease than men, though the exact cause is still a mystery.

Heart disease is the leading cause of death in America; it kills about 600,000 people every year, according to the Centers for Disease Control and Prevention. More than half of those are from coronary heart disease, which results from a buildup of plaque in the blood vessels to the heart. The new research, published Thursday in the journal Diabetologia, seems to confirm several previous studies on the topic, which point to a greater likelihood of heart problems and death among women with diabetes, even when variables like age and region are taken out of the equation. 

The authors mention one study that showed diabetic women had a 46 percent higher chance of dying from coronary heart disease than men, according to a press release. In another, diabetic women were more likely to have a stroke than diabetic men by about 25 percent. In the new study, the researchers pulled data going back to 1966, using 64 studies that included 858,507 patients. Their analysis showed the greater likelihood, "independent of sex differences in the levels of other major cardiovascular risk factors."

The trend is clear: Diabetes is more dangerous for women than men. Yet the reason why seems more elusive. Historically, women have been undertreated for risk factors, like obesity and elevated blood pressure during pregnancy, that can lead to heart disease. Yet even when treatment is similar between the sexes, diabetic women are less likely to hit treatment targets. This has led many doctors to conclude that metabolic health deteriorates further for women who become diabetic than men. In other words, women are less healthy when they begin treatment.

"If confirmed, the implementation of sex-specific interventions before diabetes becomes manifest — such as increased screening for prediabetes, especially in women, combined with more stringent follow-up of women at high risk for diabetes, such as women with a history of gestational diabetes — could have a substantial impact on the prevention" of coronary heart disease, wrote the authors, led by Rachel Huxley of the University of Queensland in Australia.

They conclude that "greater awareness of early symptoms of [coronary heart disease] in women ... will be the best way to improve clinical outcomes in both women and men."  Source: Huxley RR, Peters SAE, Woodward M. Diabetes as risk factor for incident coronary heart disease in women compared with men: a systematic review and meta-analysis of 64 cohorts including 858,507 individuals and 28,203 coronary events. Diabetologia. 2014.