Available data indicate that cardiovascular disease has become the leading cause of death in American Indians. However, limited information is available on cardiovascular disease incidence, prevalence, and risk factors in this population. Reported cardiovascular disease rates vary greatly among groups in different geographic areas. These rates have been obtained from studies of varying sizes and different methodologies. The Strong Heart Study, which uses standardized methodology, is designed to estimate cardiovascular disease mortality and morbidity rates and the prevalence of known and suspected cardiovascular disease risk factors in American Indians. The study population consists of 12 tribes in three geographic areas: an area near Phoenix, Arizona, the southwestern area of Oklahoma, and the Aberdeen area of North and South Dakota. The study includes three components. The first is a mortality survey to estimate cardiovascular disease mortality rates for 1984-1988 among tribal members aged 35-74 years, and the second is a morbidity survey to estimate incidence of both first and first or recurrent hospitalized myocardial infarction and stroke (cerebrovascular disease) among tribal members aged 45-74 years in 1984-1988, and the third is a clinical examination of 4,500 tribal members aged 45-74 years in order to estimate the prevalence of cardiovascular disease and its associations with risk factors. Family history, diet, alcohol and tobacco consumption, physical activity, degree of acculturation, and socioeconomic status are assessed in personal interviews. The physical examination includes measurements of body fat, body circumferences, and blood pressure, an examination of the heart and lungs, an evaluation of peripheral vascular disease, and a 12-lead electrocardiogram. Laboratory measurements include fasting and postload glucose, insulin, fasting lipids, apoproteins, fibrinogen, and glycated hemoglobin. Also measured are serum and urine creatinine and urinary albumin. DNA from lymphocytes is isolated and stored for future genetic studies.

The Strong Heart Study, a study of cardiovascular disease among American Indians, was conducted to determine cardiovascular disease rates and the prevalence of risk factors among members of 13 tribal groups in South Dakota/North Dakota (SD/ND), southeastern Oklahoma, and Arizona. From 1989 to 1992, 4,549 tribal members aged 45-74 years (62% of eligible participants) were surveyed and examined for cardiovascular disease and its risk factors. Mean total cholesterol concentrations were over 20 mg/dl lower among the men and 27 mg/dl lower among the women than national mean levels for the same age groups. Cholesterol levels varied by tribal group; Arizona Indians had mean levels more than 20 mg/dl lower than those of SD/ND Indians. The prevalence of hypercholesterolemia was almost twice as high among SD/ND Indians as among Arizona Indians, but the rates for all three groups were much lower than total US rates (all races). Mean levels of high density lipoprotein cholesterol were lower among Indian men and women than in the US population as a whole. The prevalence of hypertension among Arizona and Oklahoma Indians was higher than that for the entire United States. SD/ND Indians had significantly lower mean blood pressures and prevalence rates of hypertension than Oklahoma and Arizona Indians and the United States as a whole. The prevalence of cigarette smoking was higher for all Indian groups except Arizona women in comparison with US rates. Smoking rates were highest in SD/ND and lowest in Arizona. Indian smokers smoked fewer cigarettes per day than the average US smoker. Arizona Indians had the highest prevalence of diabetes mellitus; over 60% of those participants were diabetic. In Oklahoma and SD/ND, one third of the men and over 40% of the women were diabetic. In addition, 13-20% of the participants had impaired glucose tolerance. Proteinuria was also a common problem; almost half of the Arizona Indians had micro- or macroalbuminuria, and 20% of Oklahoma and SD/ND Indians had significant proteinuria. The prevalence of obesity was high in all three groups, with Arizona Indians having the highest rates and the highest mean body mass indices. The prevalence of current alcohol use was lower among Indians than in the nation as a whole, but binge drinking was common among those who used alcohol. These results indicate that cardiovascular disease risk factors vary significantly among tribal groups. Prevention programs tailored toward decreasing the prevalence of risk factors are recommended for long-term reduction of cardiovascular disease rates in American Indian communities.

Although coronary heart disease (CHD) is currently the leading cause of death among American Indians, information on the prevalence of CHD and its association with known cardiovascular risk factors is limited. The Strong Heart Study was initiated in 1988 to quantify cardiovascular disease and its risk factors among three geographically diverse groups of American Indians. Members of 13 Indian communities in Arizona, Oklahoma, and South and North Dakota between 45 and 74 years of age underwent a physical examination that included medical history; an electrocardiogram; anthropometric and blood pressure measurements; an oral glucose tolerance test; and measurements of fasting plasma lipoproteins, fibrinogen, insulin, hemoglobin A1c, and urinary albumin. Prevalence rates of definite myocardial infarction and definite CHD were higher in men than in women at all three centers (p < 0.0001) and higher in those with diabetes mellitus (p = 0.002 in men and p = 0.0003 in women). Diabetes was associated with relatively higher prevalence rates of myocardial infarction (diabetic:nondiabetic prevalence ratio = 3.8 vs. 1.9) and CHD (prevalence ratio = 4.6 vs. 1.8) in women than in men. Prevalence rates of heart disease were lowest in the communities in Arizona; prevalence rates were similar in Oklahoma and South Dakota/North Dakota and were two- to threefold higher than those in Arizona. By logistic regression, prevalent CHD among American Indians was significantly and independently related to age, diabetes, hypertension, albuminuria, percentage of body fat, smoking, high concentrations of plasma insulin, and low concentrations of high density lipoprotein cholesterol. In contrast to reports from other non-Indian populations, diabetes was the strongest risk factor. The lower prevalence of CHD among Indians in Arizona is distinctive in view of their higher rates of diabetes, obesity, hypertension, and albuminuria, but it may be partly related to their low frequency of smoking and their low concentrations of total and low density lipoprotein cholesterol. These findings from the initial Strong Heart Study examination emphasize the importance of diabetes and its associated variables as risk factors for CHD in Native American populations.

Community mortality surveillance for 1984-1988 was conducted by researchers of the Strong Heart Study, which examined the incidence, prevalence, and risk factors of cardiovascular disease in three American Indian populations, aged 45-74 years, in Arizona, Oklahoma, and South/North Dakota. All-cause and cardiovascular disease mortality rates were determined through the use of death certificate data. Cardiovascular disease deaths were confirmed by independent systematic review of medical records. In all three populations, men had higher all-cause and cardiovascular disease mortality rates than did women. Oklahoma exhibited slightly lower 5-year, age-adjusted, all-cause mortality (96/1,000) than did Arizona (107/1,000) and South/North Dakota (114/1,000). The leading cause of death among both sexes in Oklahoma and in South/North Dakota was cardiovascular disease. Diabetes mellitus led among Arizona women. The other major causes of death were cancer, liver disease including cirrhosis, and injury. When compared with the rates in each state, average annual all-cause mortality rates were higher for the American Indian populations in almost every age group. The all-cause annual mortality rates in the three Indian populations were close to rates in the US black population and higher than the rates of the entire US population and of US whites. This trend was amplified in the 45- to 64-year age group. Only in the 65- to 74-year age group did mortality rates in the Indian population approach those of the US population. Cardiovascular disease mortality rates were close to the US averages in Arizona and Oklahoma, but they were more than two times higher in South/North Dakota among those between 45 and 64 years of age. Thus, American Indians in Arizona, Oklahoma, and South/North Dakota exhibit high all-cause mortality rates. In particular, the South/North Dakota population cardiovascular disease death rate appears to present a potential target for community-based programs to intervene on known risk factors to promote healthy lifestyles.