Over the past 50 years, the incidence of heart disease has decreased in most of the U.S. population. Unfortunately, however, it has increased among American Indians to the point that it is now double that of the general population.
This finding is just one of many revealed about the health of the American Indian population as part of the Strong Heart Study, the largest and longest epidemiologic investigation in this population to examine heart disease and its risk factors. The study, sponsored by the National Heart, Lung, and Blood Institute (NHLBI), is shedding new light on this health disparity and shows promise for reducing levels of heart disease in this at-risk group, researchers say.
The Strong Heart Study, now in its 27th year, is comparable to the landmark Framingham Heart Study, also supported by NHLBI. The Framingham study was the first to identify risk factors for heart disease in the general U.S. population.
To date, Strong Heart has identified several risk factors that may account for the high rates of heart disease in the American Indian population. As with the general population, key factors include diabetes, high blood pressure, high cholesterol, and cigarette smoking. Researchers believe that many of these risk factors may have increased among the American Indians because of cultural changes that have taken place among this group over the past 50 years. Those cultural changes include a reduction in physical activity, changes in diet, and increased rates of smoking.
“Studies of cardiovascular disease in American Indians such as the Strong Heart Study offer great scientific value in multiple ways,” said Richard R. Fabsitz, Ph.D., former deputy chief of the NHLBI Epidemiology Branch and a past member of the Strong Heart Steering Committee. “They fill a void in our understanding of the burden of disease and associated risk factors and their solutions in this understudied group.”
The study, which began in 1988, includes health data from more than 7,600 volunteers (males and females ages 15 and older) among 13 communities in parts of Arizona, Oklahoma, and North and South Dakota.
“When this study began, people thought that American Indians were somehow protected from heart disease and had lower rates,” said Barbara Howard, Ph.D., a principal investigator for the study and a researcher with the MedStar Health Research Institute in Hyattsville, Maryland. A review of records from the Indian Health Service from the 1960s showed very low rates of heart disease, noted Dr. Howard, who is also a professor of medicine at Georgetown University School of Medicine in Washington, D.C.
“The Strong Heart Study proved that these earlier assumptions were wrong,” she said. “Heart disease is no longer a rarity in the American Indian population and more intensive efforts are now needed to prevent and reduce its burden.”
Researchers compared cardiovascular disease rates in the Strong Heart Study to those of other U.S. populations. Investigators found that cardiovascular disease rates in the American Indian population were almost twice as high as the rest of the U.S. population.
In addition, the researchers also found that diabetes is a key risk factor for the development of heart disease among American Indians. Although scientists have known for some time that diabetes is a risk factor for heart disease in the general population, the Strong Heart Study represents the first time that this link has been shown in the American Indian population, the researchers noted. Also, the study showed the major role that diabetes plays in heart disease in populations with high rates of diabetes, Dr. Howard added.
Investigators involved in the Strong Heart Study are currently trying to identify a genetic basis for heart disease in the American Indian population. Using blood samples, the scientists collected DNA to gain a better understanding of how genes might affect cholesterol and blood pressure as well as other factors related to heart disease. This could lead to new approaches for preventing or treating heart disease in the future, researchers said. In addition, Strong Heart has done much work to understand the impact that diabetes had on cardiac structure and function; its contributions in the field of cardiology have been recognized for many years.
The study directly benefits the American Indian community. Participants in the study receive health exams that can lead to early detection of congenital heart disease and even cancer. Health care workers use data from the Strong Heart Study to support preventative health counseling, including smoking cessation programs as well as diet and exercise programs. Health care workers have also developed brochures about heart-healthy habits and made them available in waiting rooms, nutrition centers, and schools throughout the community.
These education efforts appear to be paying off. “This study helped me quit smoking, increased my exercise levels, and raised my awareness about the importance of monitoring my cholesterol levels,” said Francine Red Willow, a member of the Oglala Sioux Tribe. “As a Native American, I commend this study for raising awareness of health disparities in the Indian population.”
Everett Rhoades, M.D., a former director of the Indian Health Service and a member of the Kiowa Nation of Oklahoma, said that the study is also notable for empowering the Indian community to take charge of its own health. The study has trained and employed dozens of American Indian investigators as part of its active research team. Members of the community are also exercising control over how data derived from that research are utilized and shared, which enhances the value of the research findings for the community, he said.
“The Strong Heart Study provides a reason to be optimistic that the health of the American Indian people will improve in the future,” added Dr. Rhoades. “More and more Indians are now adopting positive health habits, including better fitness and diet, than in the past. And there’s a growing perception that this study is saving lives. However, real progress will depend upon continued clinical or epidemiologic studies such as that exemplified so splendidly by the Strong Heart Study, which has set the standard for such studies conducted among American Indian populations.”
Today, researchers are continuing to hone in on the risk factors of diabetes and heart disease in the American Indian population involved in the Strong Heart Study. In 2012, a research team with the Strong Heart Study found that diabetes risk is raised among American Indian men and women who eat a diet that is high in processed meats, such as hot dogs, lunch meat, sausages, and canned meats. Participants who ate canned meat twice a week had double the risk of diabetes compared with those who ate canned meat only twice a month, the researchers said. That study was led by Amanda Fretts, Ph.D., M.P.H., an American Indian epidemiologist and an assistant professor at the University of Washington Department of Epidemiology.
“Many American Indians live on rural reservations, where it is difficult to get access to fresh, healthful foods,” notes Dr. Fretts, a member of the Mi’kmaq tribe, which is based in eastern Canada. “Our study suggests that limiting processed meat should be part of a heart healthy diet. Although these analyses used data from the Strong Heart Study, the findings may be useful to other underserved or rural communities throughout the United States. The Strong Heart Study continues to be a valuable health resource.”
Dr. Fretts led another Strong Heart-related study showing that American Indians who regularly walk have a lower risk of diabetes. Walking might help people maintain a healthier weight, which could help keep both diabetes and heart disease at bay, she explained
Over the past two decades, the Strong Heart Study has raised awareness about American Indian health and the health of rural America and underserved communities. Researchers continue to analyze data from the study and expand upon its findings in an effort to reduce the burden of heart disease, diabetes, and other conditions that disproportionately affect American Indians as well as many other populations.