Tracy C. Harjo, B.S., Alejandro Perez, B.S., Victor Lopez, M.S., and Nathan D. Wong, Ph.D.

METABOLIC SYNDROME AND RELATED DISORDERS Volume 9, Number 1, 2011 ª Mary Ann Liebert, Inc. Pp. 49 54 DOI: 10.1089/met.2010.0043 Prevalence of Diabetes and Cardiovascular Risk Factors Among California Native American Adults Compared to Other Ethnicities: The 2005 California Health Interview Survey Tracy C. Harjo, B.S., Alejandro Perez, B.S., Victor Lopez, M.S., and Nathan D. Wong, Ph.D. Abstract Background: People with diabetes (DM) are at an increased risk of cardiovascular disease. Although Native American groups have been identified to have among the highest prevalences of DM, such as those located in Arizona, Oklahoma, and North/South Dakota, there is a lack of population data on DM and its cardiovascular risk factor correlates in Native Americans. We sought to examine the prevalence and its cardiovascular risk factor correlates in Native Americans residing in California. Methods: In the California Health Interview Survey 2005 (CHIS), we examined in adults aged 18 years (n ¼ 43,020 projected to 26.4 million, 50.9% female) the prevalence and risk factor correlates of DM, based on selfreported telephone interview information available from CHIS. Results: Among all ethnic groups, the prevalence of DM was highest in Native Americans (14.9%), compared to 10.1% in African Americans, 8.0% in Hispanics, 6.5% in Asians, and 6.0% in Caucasians. From multiple logistic regression, after adjusting for age, gender, other risk factors, and lifestyle characteristics, Native Americans still had the highest likelihood of DM [odds ratio (OR) ¼ 3.09, confidence interval (CI), 1.92 4.96], P < 0.01, when compared to Caucasians). Among adults with DM, Native Americans had the highest prevalence of high cholesterol (42.1%). Age, male gender, lower intake of vegetables and fruits, and high blood pressure were the most important indicators of DM in Native Americans. Conclusions: California Native American adults are more likely to have DM compared to other ethnicities. Education on prevention and further investigation are needed. Introduction Diabetes mellitus (DM) carries an increased risk for heart disease and stroke, and is considered a coronary heart disease (CHD) risk equivalent. 1,2 DM is more prevalent in certain populations. African Americans, Latino/Hispanics, Native Americans, and Asians are more susceptible than Caucasians to develop DM. 3 The ethnic specific incidence of DM is currently being studied across the United States with emphasis on why those differences are present. 4 Several reports have described diabetes prevalence among specific Native American groups within the United States, such as the Pima Indians of Arizona and Northern Plains Indians of the Dakotas 5 7 ; however, there is a lack of population-wide data on diabetes prevalence or its risk factor correlates at either the state or national level. In this report, we seek to examine the prevalence of DM among a representative sample of California Native American adults and the risk factor correlates of diabetes in this population. Methods In the California Health Interview Survey 2005 (CHIS), 8 we examined adults aged 18 and older (n ¼ 43,020 projected to 26.4 million, 50.9% female). CHIS is a telephone survey conducted by the University of California at Los Angeles Center for Health Policy Research. CHIS provides selfreported information on ethnicity, health status, conditions, behavior, mental health, income, and access to health care. The random survey is conducted every 2 years among noninstitutionalized Californians. Data were obtained by dividing California into 44 geographical regions. Of those Heart Disease Prevention Program, Division of Cardiology, Department of Medicine, University of California, Irvine, California. 49

50 HARJO ET AL. regions, 41 were defined by single counties whereas three regions were defined by combining smaller counties. Within each region, random-digit dialing selected participants. Within each household dialed, one adult (aged 18 and over) was selected at random. Interviews were conducted in multiple languages (English, Spanish, Chinese [Mandarin and Cantonese dialects], Vietnamese, and Korean). Native American ethnicity was defined according to if the respondent self-described themselves as American Indian or Alaskan Native. Subjects were also questioned as to whether they belonged to one of the following specific tribes, including Apache, Blackfoot, Cherokee, Choctaw, Mexican American Indian, Navajo, Pomo, Pueblo, Sioux, or Yaqui. Information was also available on whether they lived in an urban or rural community and belonged to a California or non-california tribe and if they were enrolled in a federally recognized tribe. Information on proportion Native American ancestry was unavailable. DM was defined as currently taking diabetic pills to lower blood sugar, taking insulin, or self-reported DM. The telephone survey also asked whether the respondent has been told by a doctor if he/she has had high cholesterol, heart disease, stroke, or heart failure. A response of yes to any of the previous questions was used to classify individuals as having that condition. High blood pressure was defined as currently taking medicine to control high blood pressure and having been told by a doctor that they have high blood pressure. In addition, other questions related to mental health (including feelings of depression and hopelessness), health behavior (obesity, smoking, consumption of the daily recommended fruit and vegetable servings), levels of exercise, and health insurance coverage were asked. Participants were also asked about their cigarette smoking behavior (current, past, or never), height, and weight (from which body mass index [BMI] was calculated as weight in kilograms divided by the square of height in meters). Normal weight was classified as a BMI from 18.5 to <25, overweight was defined as a BMI 25.0 to <30, and obese was defined as BMI 30. Analysis of publically available, nonidentifiable data, including the current study, does not fulfill the criteria for Human Subject Research by the University of California, Irvine, and is exempt from review by the Institutional Review Board. Statistical analysis The Chi-squared test of proportions or analysis of variance (ANOVA) was used to compare the extent of risk factors by gender and ethnicity. Multivariable logistic regression was used to examine which risk factors and ethnicity (relative to Caucasians) remained independently associated with the likelihood of DM. SAS version 9.1.3 (SAS institute, Cary, NC) and SUDAAN software (RTI International, Research Triangle Park, NC) were used for analysis and computation of weighted estimates for projection to the California population. Results Our study sample consisted of 28,979 Caucasians (weighted to 13.6 million [M]), 6,369 (6.8 M) Hispanics, 3,941 (3.3 M) Asians, 1,954 (1.5 M) African Americans, and 554 (0.26 M) Native Americans. Of our Native American respondents, 65% declared themselves as living in an urban community (versus 35% rural), 21% as belonging to a California tribe (versus 72% belonging to a non-california tribe and 7% unknown), and 42% stated they were enrolled in a federally recognized tribe. The prevalence of DM across ethnicities and by gender is summarized in the Fig. 1. Overall, DM is most prevalent in the California Native American population (14.9%) when compared to African Americans (10.1%), Hispanics (8.0%), Asians (6.5%), and Caucasians (6.0%) (P < 0.01). These ethnic differences are also consistent for men (P < 0.01) and for women (P < 0.01). Native American men have a higher FIG. 1. Prevalence of diabetes (DM) among California adults aged 18, overall and by gender: California Health Interview Survey 2005. Bar labels represent percentages. P < 0.01 across ethnic groups, overall and by gender.

DIABETES IN CALIFORNIA NATIVE AMERICANS 51 Table 1. Logistic Regression Examining Ethnicity and Other Factors in Relation to the Likelihood of DM (n ¼ 41,491) (CHIS 2005) Variables Odds ratio Confidence interval P value Age (in 10-year increments) 1.53 1.47 1.59 <0.0001 Gender (male vs. female) 1.69 1.49 1.91 <0.0001 Native American verus Caucasian 3.09 1.92 4.96 <0.0001 Asian versus Caucasian 1.63 1.28 2.07 0.0001 Latino/Hispanic versus Caucasian 2.20 1.85 2.61 <0.0001 African American versus Caucasian 1.62 1.30 2.03 <0.0001 Current smoker versus nonsmoker 1.07 0.92 1.25 0.3892 Daily serving of fruits/vegetables: <5 vs. 5 0.99 0.86 1.13 0.8829 One or more alcoholic drink(s) per day versus zero alcoholic drinks per day 0.48 0.42 0.54 <0.0001 Weekly vigorous physical activity (no vs. yes) 1.42 1.20 1.68 <0.0001 Underweight (BMI 0 to <18.5) versus normal weight (BMI 18.5 to <25) 0.93 0.56 1.56 0.7933 Overweight (BMI 25 to <30) versus normal weight (BMI 18.5 to <25) 1.40 1.16 1.69 0.0073 Obese (BMI 30) versus normal weight (BMI 18.5 to <25) 3.62 3.01 4.35 <0.0001 Insurance status (uninsured vs. insured) 0.95 0.79 1.14 0.6030 High blood pressure (yes vs. no) 2.34 2.03 2.70 <0.0001 High cholesterol (yes vs. no) 1.56 1.37 1.78 <0.0001 DM, diabetes mellitus; CHIS, California Health Interview Survey; BMI, body mass index. prevalence of DM compared to Native American women (16.8% vs. 13.4%). When examining the likelihood of DM, age, male gender, ethnicity, alcohol use, physical inactivity, overweight/obesity, high blood pressure, and high cholesterol were significant indicators of DM (P < 0.0001) (Table 1). After adjustment for these and other demographic, risk factor, and behavioral correlates, compared to Caucasians, Native Americans had the highest likelihood of DM (odds ratio [OR] ¼ 3.09, confidence interval [CI], 1.92 4.96], P < 0.01), followed by Hispanics (OR ¼ 2.20, CI, 1.85 2.61, P < 0.01), Asians (OR ¼ 1.63, CI, 1.28 2.07], P < 0.01), and African Americans (OR ¼ 1.62, CI, 1.30 2.03, P < 0.01). Compared to individuals with normal BMI (18.5 to <25), overweight (BMI 25 to <30, OR ¼ 1.40, CI,1.16 1.69], P < 0.01), and obese persons (BMI >30, OR ¼ 3.62, CI, 3.01 4.35], P < 0.01) were significantly more likely to have DM. Compared to individuals who did not consume any alcoholic drinks per day, those who consumed one alcoholic drink (OR ¼ 0.48, CI, 0.42 0.54, P < 0.01) were less likely to have DM. Smoking, consumption of fruits/vegetables, and health insurance status did not significantly predict the likelihood of DM. When separately examining the likelihood of DM in Native Americans, multiple regression analyses showed age (OR ¼ 1.5, CI, 1.0 2.2], P < 0.05), male gender (OR ¼ 2.6, CI, 1.0 6.9, P < 0.05), <5 vs. >5 servings per day of fruits/ vegetables (OR ¼ 2.3, CI, 1.1 4.8, P < 0.05, 2 or more vs. 0 alcoholic beverages per day (OR ¼ 0.28, CI, 0.04 1.7), hypertension (OR ¼ 2.8, CI, 1.1 7.4, p < 0.05) to be independently associated with DM. Risk factors among Californians with DM are shown in Table 2. The mean age for individuals with diabetes was youngest in Hispanics (52.4 7 years), followed by Native Americans (57.2 3.4 years), African Americans (58.5 1.2), Asians (59.5 1.5 years), and Caucasians (61.8 0.5 years) (P < 0.01). Among Native Americans with DM, 49.4% were female. The prevalence of high cholesterol was highest (42.1%) in Native Americans and lowest (35.4%) in Caucasians (P ¼ 0.66). Hypertension prevalence was highest among whites (66.1%), African Americans (65.9%), and Native Americans (64.1%) and lowest in Asians (56.9%) and Hispanics (54.1%) (P < 0.01). Obesity was prevalent in over 48% of those with DM among all ethnicities except for Asians (19.6%). The proportion of current smokers was highest in Native Americans with DM (19.6%), followed by Caucasians (15.9%), African Americans (15.8%), Hispanics (9.1%), and Asians (7.4%) (P < 0.01). Additionally, Native Americans had the lowest percentage among Californians for consuming (5) daily recommended servings of fruits and vegetables (37.3%) compared to Latino/Hispanics, of which 53.8% eat proper servings (P < 0.05 across ethnicity). The percentage of individuals living below the federal poverty level was 30% for Hispanics, 23% for African Americans, 19% for Asians, 17% for Native Americans (17%), and 8% for Caucasians (P < 0.01) (Table 2). Levels of insured individuals were lowest in the Latino/Hispanic population (76.4%), followed by Native Americans and Asians (94.8% and 90.9%, respectively, P < 0.01 across ethnicity). Although 94.8% of Native Americans were insured, the Indian Health Service covered only 20.6% of those. Of the remainder, 20% were covered by a health maintenance organization (HMO; Kaiser), 39% by other private insurance, 9% by Medicare, and 11% by MediCal. We did not have information on Indian Health Services operated clinics and hospitals in California, nor did we have information on whether or not the high DM prevalence was due to poor compliance to recommended health care, medications, or other reasons. However, our results do not show health insurance status to be an independent predictor of DM, nor is the proportion of Native Americans below the federal poverty level greater than other major ethnic groups. With respect to mental health, the percentage of individuals reporting feelings of hopelessness some of the time was lowest among Native Americans (6.7%); however, not having any feelings of hopelessness was second lowest (66.0%) (Table 2). Similarly, feelings of depression most of the time was highest (11.7%) among Native Americans compared to other ethnicities (P < 0.01). Discussion We have shown that in California the prevalence of DM was highest in Native Americans (14.9%), and that a

52 HARJO ET AL. Table 2. Prevalent Diseases and Risk Factors Among Californian Adults 18 Years with DM by Ethnicity (n ¼ 3,229) (CHIS 2005) %(n) Native American (n ¼ 74) Asian (n ¼ 262) Latino/ Hispanic (n ¼ 595) Caucasian (n ¼ 2,055) African American (n ¼ 243) P value Percent female 49.4 (44) 48.0 (135) 44.3 (340) 44.5 (1,074) 52.7 (142) 0.3514 Hard/vigorous exercise in past 7 days 33.3 (10) 18.9 (41) 13.4 (72) 11.9 (249) 14.3 (28) 0.3181 High cholesterol 42.1 (28) 37.1 (104) 39.7 (223) 35.4 (700) 35.8 (88) 0.656 High blood pressure 64.1 (45) 56.9 (159) 54.1 (324) 66.1 (1,391) 65.9 (173) 0.0016 Stroke 7.6 (9) 9.0 (27) 4.9 (31) 9.5 (205) 12.2 (32) 0.0125 Heart disease 10.4 (19) 26.1* (53) 13.9 (87) 26.0** (553) 19.4 (49) <0.001 Current smoker 19.6 (13) 7.4 (29) 9.1 (60) 15.9 (289) 15.8 (38) 0.0019 Insured 94.8 (65) 90.9 (232) 76.5** (475) 95.0 (1,963) 95.4 (232) <.0001 Consume one or more alcoholic drink(s) per day 70.7 (48) 66.9 (167) 62.2 (395) 56.5 (1171) 74.5 (175) 0.0003 Consume daily serving fruit/vegetables (5) 37.3 (30) 38.3 (108) 53.8 (268) 47.6 (931) 42.2 (102) 0.0304 Below federal poverty level (0 99%) 17.0 (13) 19.2 (59) 29.9 (194) 7.6 (163) 23.0 (55) <0.0001 Three times or greater than FPL (300%) 39.9 (29) 42.8 (105) 17.2 (118) 57.1 (1,149) 40.6 (100) Hopeless some of the time 6.7 (9) 9.0 (33) 11.6 (76) 8.7 (166) 8.6 (29) 0.0532 Not hopeless at all 66.0 (48) 69.0 (179) 65.6 (376) 75.9 (1,560) 81.1 (179) Depressed most of the time 11.7 (4) 3.1 (11) 4.6* (27) 2.2 (42) 1.9 (4) 0.0001 Not depressed at all 52.0 (51) 71.7 (170) 65.3* (372) 79.2 (1,633) 78.4 (184) Overweight (BMI 25 30) 19.0 (24) 30.7* (93) 31.0 (197) 33.6* (694) 27.0 (75) <0.0001 Obese (BMI 30) 49.8 (40) 19.6* (45) 49.2 (292) 48.1* (967) 53.4 (123) *p < 0.05 and **p < 0.01 when compared to Native Americans. DM, diabetes mellitus; CHIS, California Health Interview Survey; FPL, federal poverty level; BMI, body mass index. three-fold increased odds of DM persists in Native Americans compared to Caucasians, even after adjustment for ethnic differences in age, gender, other risk factors, and health behaviors. Our prevalence rate is slightly higher than that reported among Native Americans (based on epidemiologic studies) by the American Heart Association (13.6%). 9 We also find DM more prevalent in California Native American men versus women (16.8% vs. 13.4%), with greater prevalences also seen in men versus women of other ethnicities. Males of each race had higher rates of being overweight and obese than of females of the same race except for African Americans. Self-reported high cholesterol (42.1%), current smokers (19.6%), and depression (11.7%) were highest in Native Americans with DM. Additionally, Native Americans had the lowest percentage of consuming (5) daily recommended servings of fruits and vegetables (37.3%) when compared to the other ethnicities. Health education programs targeted in a culturally sensitive manner toward Native Americans may be an important way to help reduce their burden of DM. One study found that the advice given by physicians and that of Native American healers varied and that the patients viewed the healers advice in a greater light, 10 suggesting that if programs were more culturally sensitive toward Native American values and there was better dialogue between physicians and Native American healers, efforts to reduce disease burden may be more successful. It is also important for comprehensive screening of cardiovascular risk factors to become standard of practice in Native American communities because DM-related complications can be lowered if risk factors are controlled. The Strong Heart Study, which focuses on Native American communities in Arizona, Oklahoma, and North/South Dakota, found more women recognized the risks of DM; therefore, increased efforts toward educating men are needed. They also noted higher rates of low physical activity levels and higher BMI levels among Native Americans. Additional studies of Northern Plains Indians also show similar results of higher prevalence of DM, smoking, obesity, and low physical activity levels compared to Caucasians. 6 Increased DM and obesity prevalence have been identified among all Native American tribes, including those in Alaska, the Atlantic, Great Lakes, Pacific, Southern Plains, and Southwest areas. 11 Education programs that emphasize the importance of physical activity and nutrition as well as improved control of high cholesterol, blood sugar, and smoking habits among those with DM may also reduce risk of cardiovascular disease in Native American communities. 12 When compared to other ethnic groups in California, higher prevalence rates of DM among Native Americans may be due to numerous factors, including lifestyle and environment. Significantly higher poverty levels in Native Americans, compared to Caucasians who have the lowest prevalence of DM, may be partially to blame due to unequal accessibility to healthy foods and education about nutrition and diet. 13 Poverty and access to healthy foods may negatively impact lifestyle and diet, which contributes to increase prevalence of DM. Environmental factors such as living in rural versus suburban communities may also impact mental health, as well as income and transportation issues. 14 In the Havasupai, a Native American tribe, higher rates of DM were found to be linked to malnutrition. By examining the Havasupai tribe in a historical context, it is believed that the higher rate of DM in newborns may be the result of generations of malnourished women caused by social factors. 15 The prevalence of DM among the Pima Indians of Arizona is approximately 50% 16 and may be due to historical environmental factors. The Pima Indians of Arizona were able to maintain a traditional lifestyle mostly dependent on agriculture and farming. However, in the late 19 th century, their water supply was diverted, and they had to depend more heavily on lard and flour food rations provided by the

DIABETES IN CALIFORNIA NATIVE AMERICANS 53 U.S. government. This led to the adoption of a Western lifestyle, which included a diet high in fat, processed foods, and less physical activity; levels of obesity rose dramatically. 17 In contrast, by studying the Pima Indians of Mexico, who did not undergo a change in lifestyle and are genetically the same as the Pima Indians of Arizona but have much lower levels of DM, one can infer that DM is greatly influenced by environmental conditions. 16 More longitudinal studies that are culturally sensitive across the United States would further contribute to the present knowledge of DM and related causes. The prevalences of many diseases are often associated with socioeconomic status, which in many cases, is also intertwined with race. 18 Research involving ethnic categories can still provide insight on the prevalence of disease and where medical prevention programs should be targeted. Further studies should be conducted to better understand the health disparities among the adult Native American population as well as other ethnicities in California. Studying social and environmental factors may provide insight on the many complexities associated with disease. Limitations of our study include the lack of measured variables, such as for cholesterol, blood pressure, and glucose, because the CHIS survey was based on self-reported information and consisted mostly of true-or-false questions; however, self-reported information on treatment, which formed the basis for much of the clinical information, has been widely used in other large surveys, such as the National Health and Nutrition Examination survey. There may, however, be a chance that the individual taking the survey may not answer the questions truthfully. 19 Also, because the survey excluded cell phones and noninstitutionalized subjects, only individuals who had a home phone and were not in prison, hospitals, nursing homes, or other institutions were eligible to participate. Information on the proportion of Native American heritage or whether or not the respondent lived on an Indian reservation was unavailable. Strengths of the study include its multiethnic sample, including Asian and Native Americans, its large sample of Californians, and the ability to project to California population. Conclusion California Native Americans are more likely to have DM compared to other races, even after adjustment for risk factor and other differences. Our data are consistent with other reports of DM prevalence in U.S. Native Americans on the basis of other epidemiologic studies. However, the much higher rates of DM prevalence in Native Americans, as compared to other ethnic groups, warrants an increased need for examining and intervening on factors that may be responsible for this excess prevalence. Along with the higher levels of poverty, smoking, and the absence of adequate fruit and vegetable consumption, other lesser understood risk factors may also be responsible for the increased prevalence of DM in Native Americans. The Latino/Hispanic and African American populations in California also experience higher levels of obesity and poverty than Caucasians and may also play a part in their higher rates of DM as well. Health professionals and educators should be aware of these ethnic disparities to implement aggressive measures in education, prevention, treatment, and control. Acknowledgments The authors thank the participants of the California Health Interview Survey and the staff from the UCLA Center for Health Policy who conducted the survey. This study was presented in part at the 2009 CAMP Statewide Symposium, Irvine, California, February 28, 2009, and at the 2009 Native Health Research Conference, Portland, Oregon, August 3, 2009. Author Disclosure Statement Dr. Wong has received research funding related to diabetes from Bristol Myers Squibb thorough the University of California, Irvine. None of the other authors have any disclosures. N. Wong conceived of the study and supervised all aspects of its implementation. T. Harjo and A. Perez assisted with the study and completed the analysis. T. Harjo and V. Lopez led the writing. All authors helped to conceptualize ideas, interpret findings, and review manuscript drafts. References 1. Haffner SM, Lehto S, Ronnemaa T, Pyorala K, Laakso M. Mortality from coronary heart disease in subjects with type 2 diabetes and in nondiabetic subjects with and without prior myocardial infarction. N Engl J Med 1998;339:229 234. 2. 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54 HARJO ET AL. 12. Burrows, NR, Geiss, LS, Engelgau, MM, Acton, KJ. Prevalence of diabetes among Native Americans and Alaska Natives, 1990 1997: An increasing burden. Diabetes Care 2000; 23:1786 1790. 13. Lautenschlager L, Smith C. Low-income American Indians perceptions of diabetes. J Nutr Educ Behav 2006;38:307 315. 14. Bell RA, Smith SL, Arcury TA, Snively BM, Stafford JM, Quandt SA. Prevalence and correlates of depressive symptoms among rural older African Americans, Native Americans, and whites with diabetes. Diabetes Care 2005;28:823 829. 15. Chaufan, C. How much can a large population study on genes, environments, their interactions and common diseases contribute to the health of the American people? Soc Sci Med 2007;65:1730 1741. 16. Schulz LO, Bennett PH, Ravussin E, Kidd JR, Kidd KK, Esparza J, Valencia ME. Effects of traditional and western environments on prevalence of type 2 diabetes in Pima Indians in Mexico and the U.S. Diabetes Care 2006;29:1866 1871. 17. National Institute of Diabetes and Digestive and Kidney Diseases. The Pima Indians: Pathfinders to Health. National Institutes of Health 2002 [Article Online]. Accessed at http:// diabetes.niddk.nih.gov/dm/pubs/pima/index.htm/, July 30, 2008. 18. Burchard EG, Ziv E, Coyle N, Gomez SL, Tang H, Karter AJ, Mountain JL, Pérez-Stable EJ, Sheppard D, Risch N. The importance of race and ethnic background in biomedical research and clinical practice. N Engl J Med 2003;348:1170 1175. 19. Stone, AA, Bachrach CA, Jobe JB, Kurtzman HS, Cain VS, Turkkan J. The Science of Self-report: Implications for Research and Practice. Mahwah, New Jersey: Lawrence Erlbaum Associates; 1999. Address correspondence to: Nathan D. Wong, Ph.D. Heart Disease Prevention Program Department of Medicine C240 Medical Sciences University of California Irvine, CA, 92697 E-mail: ndwong@uci.edu