Date of Award

1-1-2011

Document Type

Campus Access Dissertation

Department

Epidemiology and Biostatistics

Sub-Department

Epidemiology

First Advisor

James R Hebert

Abstract

Chronic diseases, such as heart disease, diabetes, and cancer, account for over 2/3 of deaths in the United States. Overweight and obesity have been shown to be associated with a number of chronic diseases, coronary artery disease, type 2 diabetes mellitus, and various cancers. Currently in the United States, over 2/3 of the population is considered overweight or obese. Overweight and obesity have also been shown to be strongly associated with chronic inflammation, an uncontrolled process linked to the development of cardiovascular disease. Chronic inflammation has also been associated with diabetes and cancer.

Compared to European Americans, African Americans have been shown to be at a higher risk for a number of chronic conditions, including type 2 diabetes mellitus and colorectal cancer (CRC). Also, after CRC diagnosis, African Americans have a mortality rate that is 1.4 times higher compared to European Americans. Consistent with the negative effects of overweight and obesity on health outcomes, African Americans are also more likely to be overweight and obese. 2007-2008 National Health and Nutrition Examination Survey (NHANES) data found the prevalence of overweight among European Americans to be 66.7% compared to 73.8% and 77.9% among African Americans and Hispanics, respectively.

As we can see, there are differences in the risk of chronic disease outcomes by race/ethnicity. Also, a major contributor to the development of many chronic diseases, overweight and obesity, is more prevalent among African Americans compared to European Americans. In this dissertation, the goal was to assess the associations along the pathway from overweight and obesity to chronic diseases, such as diabetes and cancer, while assessing differences by race/ethnicity.

First, data from NHANES was used to estimate the prevalence of elevated C - reactive protein (CRP), a marker of inflammation, among the United States population by race/ethnicity and gender. Next, using CRP as a 3 level outcome (< 1 mg/L, 1 to 3 mg/L, and > 3 mg/L), we carried out analyses to identify risk factors for moderate and high levels of CRP. Second, using data from South Carolina, we assessed the association between excessive weight and risk of gestational diabetes mellitus (GDM) by race/ethnicity. We also calculated the population attributable fraction (PAF) for overweight, obesity, and extreme obesity. Third, we assessed the association between type 2 diabetes mellitus and CRC by race/ethnicity among Medicaid individuals in South Carolina. Differences in survival after CRC diagnosis between individuals diagnosed with type 2 diabetes mellitus and individuals that were diabetes free was also assessed. Results show that 28.7% of the population had an elevated level of CRP. The African-American population had the highest proportion of individuals with elevated CRP, followed by Mexican Americans, other Hispanics, and then European Americans. Also, the results reveal a significantly higher prevalence of elevated CRP among women compared to men, with similar differences among racial/ethnic groups within each gender. Overweight, obese, and extremely obese individuals were significantly more likely to be in the moderately elevated and elevated CRP groups compared to normal weight individuals. Extremely obese individuals were 8 times and 33 times more likely to be in the moderately elevated and elevated CRP groups than in the low CRP group compared to normal weight individuals, respectively. Among Hispanic women, the adjusted risk of GDM among the extremely obese was 3.62 times higher compared to normal weight women. Among European American and African American women the risk of GDM among extremely obese women was 2.00 and 1.71 times higher, respectively. Overweight among Hispanic women explains almost three times as much of the GDM cases compared to European American and African American women (14.22 %, 5.08 %, and 6.84 %, respectively). Similarly, obesity among Hispanic women explains almost twice as much of the GDM cases compared to European American and African American women (15.55 %, 7.33 %, and 8.31 %, respectively). Overall, individuals with type 2 diabetes mellitus were ~1.5 times more likely to be diagnosed with colon cancer, especially proximal colon cancer. When results were stratified by race, associations were stronger among African Americans, while associations among European Americans were both attenuated and no longer significant. Individuals with type 2 diabetes mellitus were significantly more likely to be diagnosed with in situ or local CRC, colon cancer, proximal colon cancer, and distal colon cancer.

The results of this dissertation show that almost 1/3 of the United States population has elevated levels of inflammation and that obesity is strongly associated with having moderately elevated and, even more so, elevated CRP. Pre-pregnancy Overweight and obesity increases the risk of GDM among women in South Carolina, with stronger effects among Hispanic women. Also, we see that type 2 diabetes increases the risk of proximal colon cancer among African Americans, but may not significantly increase the risk among European Americans.

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