Heart disease is the number one killer in America, and although rates of the disease have declined, some areas of the country are at far greater risk than others. New research, published in the journal Circulation, highlights the disproportionate decline of heart disease-related deaths across the United States.

"Despite the overall decline in heart disease death rates, heart disease remains one of the most widespread and costly health problems facing the nation,” said the study’s lead author Michele Casper, an epidemiologist at the Centers for Disease Control and Prevention, in a statement. “More than 600,000 people die of heart disease in the United States every year -- that's one in every four deaths."

The research team examined data from Americans in more than 3,000 U.S. counties between 1973 and 2010. In the beginning of the study, the greatest concentration of death rates were found in the Northeast, in parts of the Midwest, and along the coasts of North Carolina, South Carolina, and Georgia. But by the end of the study, researchers found a geographical shift that stayed primarily in the south.

Over the course of the study, death rates in each county dropped anywhere between 9.2 and 83.4 percent. However, looking more closely, these statistics split the country in half. The slowest declines in death rates (between 9.2 and 49.6 percent) were found in southern state counties — specifically, in Alabama, Mississippi, Louisiana, Arkansas, Oklahoma, and Texas. Counties in the northern half of the country showed the greatest rate of decline, between 64.1 and 83.4 percent.

"These findings provide local communities with important historical context regarding their current burden of heart disease," Casper said, “and emphasize the importance of local conditions in heart disease prevention and treatment efforts.”

According to the National Heart, Lung, and Blood Institute, there are certain risk factors or habits that make a person more or less likely to develop heart disease. Some of the major risk factors include high blood pressure, cholesterol, diabetes, smoking, being overweight or obese, being physically inactive, eating an unhealthy diet, or having a family history of heart disease. By addressing heart disease risk factors based on patients' geographical location, the entire country may see a dramatic drop in the death toll.

One way to start is by cutting back on unhealthy foods and replacing them with a more healthful, colorful diet. This may not only impact obesity in the population, but also reduce high blood pressure, diabetes, and cholesterol rates. Many of the same states that have exhibited a slow decline of heart disease also have the highest rates of adult obesity, including Arkansas, Mississippi, Louisiana, Alabama, and Oklahoma. According to Casper, emphasizing geography-based prevention and treatment may be the way to reduce rates over the next 40 years.

As of yet, further research is needed to uncover the risk factors those living in southern counties face. The researchers believe by implementing systematic changes into at-risk areas they could begin to chip away at the death rates associated with heart disease. Measures that have the potential to influence change may include public health policies, such as increasing the opportunity for physical activity, promoting smoke-free environments, and increasing access to healthy foods and health care.

Source: Casper M, Kramer MR, Quick H, Schieb LJ, Vaughan AS, and Greer S. Circulation. 2016.