What is the goal of the SHS?
The Strong Heart Study (SHS) is a study of cardiovascular disease and its risk factors among American Indian men and women, and is one of the largest epidemiological studies of American Indians ever undertaken. Cardiovascular disease remains the leading cause of death of American Indians overall. The prevalence and severity of cardiovascular disease among American Indians has been particularly challenging to study due to the small size of American Indian communities, as well as the relatively young age, cultural diversity, and wide geographic distribution of the population. The SHS is designed to overcome challenges to estimating cardiovascular disease mortality and morbidity, as well as the prevalence of known and suspected cardiovascular disease risk factors, among American Indians. The study also works to assess the significance of these risk factors over an extended period of time.
In the early 1980s, a review of existing data by the Subcommittee on Cardiovascular and Cerebrovascular Disease of the Secretary of Health and Human Service’s Task Force on Black and Minority Health concluded that information on cardiovascular disease in American Indians was inadequate and strongly recommended epidemiologic studies of this problem. In response, and with collaboration from members of the participating American Indian communities, the SHS began.
- The SHS is the largest and longest study of heart disease and risk factors for American Indians.
- The study found that heart disease among American Indians has increased over the past 50 years and is now double that of the general U.S. population.
- The SHS has had more than 7,600 participants from 13 American Indian communities from Arizona, Oklahoma, and North and South Dakota.
- Study findings have helped show the impact of diabetes on heart structure and function and have contributed to the cardiology field for years.
What are the key findings from the SHS?
The SHS has identified several risk factors that may account for the high rates of heart disease in American Indian populations. As with the general population, key risk factors include having type 2 diabetes, high blood pressure, and high cholesterol, as well as engaging in smoking. However, the study identified unique factors, such as having albuminuria, or high amounts of albumin protein in the urine. Such factors have led to new clinical calculators that doctors can use to assess the risk of developing coronary heart disease and diabetes.
In addition, the study found type 2 diabetes to be the strongest risk factor for cardiovascular disease in American Indians, providing a warning of higher future rates of cardiovascular disease in other populations with a high prevalence of diabetes. The study recently found diabetes and prediabetes in young adults to be independently associated with early adverse effects on heart structure and function.
SHS investigators are also trying to understand how genetics might affect blood cholesterol, blood pressure, and other factors related to heart disease. The study has shown that American Indians in the SHS have genetic risk factors related to heart disease that are both common to—and different from—other population groups. These results suggest that prevention and treatment efforts developed through the study of other population groups might not be as effective for American Indians. They have led to current efforts to better understand the unique set of genetic and environmental risk factors faced by American Indians.
The SHS is pioneering research to investigate the role of the environment—especially the presence of certain metals—in cardiovascular disease development. The SHS has found, for example, that arsenic and cadmium exposures are prospectively associated with higher cardiovascular risk. The SHS has also conducted brain magnetic resonance imaging (MRI) that showed that adverse cardiovascular events in the brain, such as stroke, are highly common in American Indian elders. Nearly 90 percent of these findings are subclinical, meaning they were not detected by routine health care or immediately recognized as stroke events; however, these subclinical strokes may contribute to cognitive or physical decline.
The NHLBI continues to encourage the use of anonymized SHS data and specimens to spur new scientific discovery in collaboration with the communities. The NHLBI invites researchers to utilize the valuable resources that have been collected since the study began in 1988. Learn more about utilizing SHS resources through the study website.
How is the SHS conducted?
The study includes 13 American Indian tribes and communities in three geographic areas: Arizona; Oklahoma; and North and South Dakota. In its initial stages, the SHS included three components. The first was a survey to determine cardiovascular disease mortality rates from 1984 to 1994 among tribal members aged 35 to 74 years who lived in the three study areas. The second was the clinical examination of 4,549 eligible tribal members. The third component was the morbidity and mortality surveillance of these 4,549 participants. The SHS has completed three clinical exams of the original cohort. Because genetics plays an important role in cardiovascular diseases, the SHS has expanded its research into genetic epidemiology with its Strong Heart Family Study (SHFS).
The SHFS was conducted to investigate the genetic contributions to cardiovascular disease and its risk factors. From 2001 to 2003, the SHFS recruited a total of 3,776 individuals from 94 extended families (about 1,200 members of extended families who were at least 15 years of age were recruited from each of the field centers), including 825 family members from the original SHS cohort. The SHFS completed two clinical exams. The original and family cohorts combined (over 7,600 participants) comprise the SHS. The SHS currently focuses on the continuation and expansion of the surveillance of the original and family cohorts.
In addition to conducting valuable research, the study directly benefits the American Indian community. Participants in the study receive health exams that can lead to early detection of risk factors, heart disease and even cancer. Findings from the SHS are routinely shared with the communities to help support programs such as those that promote preventative health counseling, smoking cessation, and healthy eating, and physical activity. The SHS has developed brochures about heart-healthy habits and made them available in waiting rooms, nutrition centers, and schools throughout the community.
Similar to other groups in the United States, many American Indians today have become disconnected from their traditional ways of eating. Canned meats and sugary snacks have largely replaced healthy diets once rich in fresh fruits and vegetables. That shift, along with increasingly sedentary lifestyles, has dramatically affected the health of many now living in rural communities.