Abstract
Purpose
To identify population groups that are most susceptible to obesity-related health conditions at young age.
Methods
For this population-based cross-sectional study, measured weight and height, diagnosis, laboratory, and drug prescription information were extracted from electronic medical records of 1,819,205 patients aged 20–39 years enrolled in two integrated health plans in California 2007–2009.
Results
Overall, 29.9% of young adults were obese. Extreme obesity (BMI ≥ 40 kg/m2) was observed in 6.1% of women and 4.5% of men. The adjusted relative risk for diabetes, hypertension, dyslipidemia, and the metabolic syndrome increased sharply for those individuals with a BMI ≥ 40, with the sharpest increase in the adjusted relative risk for hypertension and metabolic syndrome. The association between weight class and dyslipidemia, hypertension and metabolic syndrome but not diabetes was stronger among 20.0–29.9 year olds compared to 30.0–39.9 year olds (p for interaction: <0.05). For example, compared to their normal weight counterparts of the same age group, young adults with a BMI of 40.0–49.9, 50.0–59.9, and ≥60 kg/m2 had a relative risk for hypertension of 11.73, 19.88, and 30.47 (95%-CI 26.39–35.17) at age 20–29 years, and 9.31, 12.41, and 15.43 (95%-CI 14.32–16.63) at age 30–39 years.
Conclusion
While older individuals were more likely to be extremely obese, the association between obesity-related health conditions was stronger in younger individuals. Hispanics and Blacks are also more likely to be obese, including extreme obesity, putting them at an elevated risk for premature cardiovascular disease and some cancers relative to non-Hispanic whites.
Keywords: Obesity, Type 2 Diabetes Mellitus, Hypercholesterolemia, Metabolic Syndrome X, Hypertension, Young Adult
INTRODUCTION
It is estimated that there are nearly 5 million young adults (6%) with extreme obesity (BMI ≥ 40 kg/m2) in the U.S. (1). Young adults with extreme obesity experience serious chronic diseases that normally occur in much older adults. These diseases include diabetes, dyslipidemia, and hypertension, each potentially leading to premature disability and death with enormous costs to the individual and the society (2–5). For the first time in two centuries, life expectancy may decline due to the rapidly increasing prevalence of obesity (6).
The prevalence of obesity and obesity-related chronic health conditions vary by sex, age group, and race/ethnicity (4, 7, 8). To understand the health consequences of obesity, especially extreme obesity in young adults, will be critical to identify populations at highest risk that may benefit from surveillance programs and prevention strategies (9). However, limited information exists regarding the health consequences of obesity, especially of extreme obesity in young adults. Most population-based studies combine younger and older adults and have limited information regarding obesity class 3 and higher (Body mass index, BMI ≥ 40 kg/m2). Young adults represent a distinctive age group that may experience obesity-related health risks that differ from those observed in older adults, as shown for ischemic heart disease (10).
The overall goal of the present cross-sectional study is to address several knowledge gaps regarding the consequences of obesity in young adults. First, we investigated the prevalence of obesity including obesity class 3 and higher in young adults and how it differed for defined population subgroups. Second, we investigated the prevalence of the consequences of obesity such as diabetes, dyslipidemia, hypertension, and the metabolic syndrome and how they differed for defined population subgroups. The current study was conducted within the framework of the National Cancer Institute (NCI)-funded Cancer Research Network (CRN), and a consortium of 14 health care organizations that participate in innovative population-based cancer research (11). The CRN focuses on cultivating multi-site collaborative efforts that address knowledge gaps in cancer-related research ranging from health care delivery and utilization to epidemiology of cancer and other associated health conditions.
METHODS
Study setting, design, and subjects
Two Cancer Research Network (CRN) sites participated in this project. The Northern and Southern California Divisions of Kaiser Permanente (KPNC and KPSC, respectively), jointly provided medical coverage for approximately 6.3 million members as of Dec. 31st 2009. From these more than 6 million KPNC and KPSC health plan current members, we identified 2,285,278 young adults aged 20–39 years who were members and had at least one medical encounter between January 1, 2007 and December 31, 2009. After excluding members with missing BMI or sex information (n=355,808) and pregnant women (n=110,265), the final analytic population comprised of 1,819,205 young adults that were used for the present cross-sectional analysis. The study population covers 84.4% of KP California members aged 20–39 years and represents about 18.2% of the State of California population in this age group. The study protocol was approved by the Institutional Review Boards (IRB) of KPNC and KPSC.
Body mass Index (BMI)
Based on a validation study including data from over 21 million medical encounters from 2.4 million adults and a manual review of 35,000 medical encounters from 1,026 adults, we removed biologically implausible values for weight and height. For this study an approach combining descriptive analysis of data distribution with stepwise manual review of medical charts was chosen to determine thresholds. Briefly, a height <4 feet or ≥ 7 feet, 2 inches was considered implausible and excluded from the analysis. Weight data were excluded if weight was <30 lbs or ≥1000 lbs. Because implausible combinations of weight and height may be missed by the procedures described above, we additionally excluded BMI values <5 kg/m2 or ≥100 kg/m2 as implausible. The overall error rate before cleaning was <1% of all encounters.
BMI was calculated using the first plausible height and weight measurements in KP’s electronic health record system between January 1st 2007 and December 31st 2009 as weight (kg) divided by the square of height (m2). The first BMI available after January 1st 2007 was used to assemble and characterize this population as only limited weight and height data were available in the KP electronic medical records before this date.
Obesity-related health conditions
Electronic health records were used to obtain the measurements of obesity-related health conditions of interest: Type-2 diabetes mellitus, dyslipidemia, hypertension, and the metabolic syndrome. Algorithms were developed to extract the various outcome measures from the electronic health record system. The algorithms were created based on the definitions of the selected health outcomes. Electronic laboratory data, pharmacy data, and diagnosis data were used to obtain the assorted measures. Records were searched between the dates January 1st, 2007 and December 31st, 2009. However, no information was used that preceded the date of study enrollment (first BMI measurement).
Type-2 diabetes mellitus was defined as (1) elevated glucose levels (fasting glucose >126 mg/dL or random glucose ≥ 200 mg/dL) measured on two separate occasions; (2) elevated HbA1C (>7.0%); (3) two or more outpatient visits with ICD-codes (250.XX) for diabetes mellitus; (4) one or more diabetes-related hospital discharge codes; or (5) one or more fills for oral or injected diabetes-specific medications excluding Metformin or any Thiazolidinedione if no other criterion was met. Patients who were pregnant during the enrollment period were only considered diabetic if they met the criterion outside of the pregnancy time period.
Dyslipidemia was defined as (1) at least one prescription for lipid-lowering medication plus an outpatient diagnosis of dyslipidemia (ICD-9 272.0–272.4); (2) at least two outpatient diagnoses of dyslipidemia; (3) at least one prescription for lipid-lowering medication plus at least one elevated LDL cholesterol (≥160 mg/dL); or (4) at least one outpatient diagnosis of dyslipidemia plus at least one elevated LDL cholesterol.
Hypertension was defined as: (1) at least one prescription for an antihypertensive medication plus an outpatient diagnosis of hypertension (ICD-9 401–404); (2) at least two outpatient diagnoses of hypertension; (3) at least one prescription for an antihypertensive medication plus at least one elevated outpatient blood pressure reading (≥140 mm Hg [systolic] or ≥90 mm Hg [diastolic]); or (4) at least one outpatient diagnosis of hypertension plus at least one blood pressure reading of ≥140 mm Hg (systolic) or ≥ 90 mm Hg (diastolic) when no indication of a body temperature ≥100.4 F degrees on the day of the measurement was present.
Metabolic syndrome was defined by three or more of the following health conditions: (1) BMI ≥30 kg/m2; (2) any triglycerides ≥150 mg/dL; (3) any HDL <40 mg/dL for men and <50 mg/dL for women; (4) at least one elevated glucose value (fasting glucose >126 mg/dL or random glucose ≥ 200 mg/dL); (5) any existing diabetes diagnosis; (6) if hypertension criterion was met (12).
Demographic information
All demographic information such as age, sex, and race/ethnicity was retrieved from administrative health records. Individual member’s education and household income were not available from electronic medical records. As measures of socioeconomic status, we used neighborhood household income and neighborhood education through linkage of a member’s address with U.S. census track information via geocoding (13) which have to be interpreted as area-based measures of socioeconomic status. Therefore, these measures do not necessarily reflect each individual’s income or education but have been shown to be strongly associated with disparities in obesity rates (14). Neighborhood household income was classified as likelihood of an individual’s household income of < $15,000, $15,000 to $34,999, $35,000 to $49,999, $50,000 to $74,999, $75,000 to $99,999, $100,000 to $149,999, $150,000 or more. Neighborhood education was categorized as and individual’s likelihood of an education less than high school, high school, some college or associate degree, or Bachelor degree or higher.
Statistical analysis
Weight class was defined as follows: underweight (<18.5 kg/m2), normal weight (18.5 – 24.9 kg/m2), overweight (25–29.9 kg/m2); moderate obesity stratified as class 1 (30.0–34.9 kg/m2) and class 2 (35.0–39.9 kg/m2); and extreme obesity stratified as class 3 (40.0–49.9 kg/m2), class 4 (50.0–59.9 kg/m2), and class 5 (≥ 60 kg/m2).
Log-binomial regression models were used to estimate the association between weight class (BMI <18.5 kg/m2, 18.5–24.9 kg/m2=reference, 25.0–29.9 kg/m2, 30.0–34.9 kg/m2, 35.0–39.9 kg/m2, 40.0–49.9 kg/m2, 50.0–59.9 kg/m2, ≥60 kg/m2) and health conditions of interest. Covariates included in the models included sex, age group (20.0–24.9 years= reference, 25.0–29.9 years, 30.0–34.9 years, 35.0–39.9 years), mutually-exclusive race/ethnicity categories (non-Hispanic White=reference, Hispanic, Black, Asian/Pacific islanders, Others, Unknown), likelihood of education less than 9th grade, and likelihood of household income below $10,000 simultaneously. The associations were expressed as relative risk (RR) and their corresponding 95% confidence intervals (CI). In order to assess whether, and to what extent the relationship between weight class and health conditions was modified by age group, we tested for interaction between age group and weight class in models adjusted for the covariates listed above. Based on these models, we report adjusted RR for all health conditions stratified by age group. All analyses were conducted using SAS release 9.1 (SAS Institute, Cary, NC).
RESULTS
A total of 1,819,205 young adults were included in this cross-sectional analysis. Racial/ethnic minorities constituted about 50% of the study population and were mostly of Hispanic origin (Table 1). Demographics characteristics were comparable between men and women with the exception that women were slightly younger than men.
Table 1.
Demographic characteristics of young adults in California by weight status
| Weight class: | Under weight | Normal weight | Overweight | Obesity
|
|||||
|---|---|---|---|---|---|---|---|---|---|
| Class 1 | Class 2 | Class 3 | Class 4 | Class 5 | Total | ||||
| BMI range (kg/m2): | ≤ 18.5 | 18.5–24.9 | 25.0–29.9 | 30.0–34.9 | 35.0–39.9 | 40.0–49.9 | 50.0–59.9 | ≥60.0 | |
|
|
|||||||||
| n | 32,984 | 668,204 | 574,044 | 308,117 | 138,523 | 81,883 | 12,927 | 2,523 | 1,819,205 |
| Sex, % | |||||||||
| Male | 18.8 | 33.5 | 55.0 | 54.6 | 46.0 | 37.9 | 34.2 | 36.9 | 44.8 |
| Female | 81.2 | 66.5 | 45.0 | 45.4 | 54.0 | 62.1 | 65.8 | 63.1 | 55.2 |
| Age Group (years), % | |||||||||
| 20.0–24.9 | 45.3 | 33.5 | 22.0 | 18.9 | 19.4 | 19.2 | 16.5 | 16.9 | 25.7 |
| 25.0–29.9 | 25.2 | 25.5 | 23.8 | 23.0 | 23.1 | 23.4 | 23.7 | 22.8 | 24.3 |
| 30.0–34.9 | 16.9 | 21.0 | 25.4 | 26.6 | 26.6 | 27.0 | 28.3 | 29.0 | 24.0 |
| 35.0–39.9 | 12.5 | 20.0 | 28.8 | 31.5 | 30.9 | 30.4 | 31.5 | 31.3 | 26.0 |
| Race/Ethnicity, % | |||||||||
| Non-Hispanic White | 27.0 | 29.4 | 24.8 | 23.0 | 23.5 | 24.2 | 23.8 | 23.0 | 26.1 |
| Black | 4.5 | 4.4 | 5.4 | 6.9 | 9.0 | 11.5 | 15.6 | 19.1 | 5.9 |
| Hispanic | 21.6 | 26.9 | 37.6 | 43.1 | 43.1 | 41.6 | 39.2 | 36.1 | 34.9 |
| Asian/Pacific Islander | 21.6 | 14.1 | 8.5 | 5.5 | 4.0 | 2.8 | 2.1 | 2.2 | 9.6 |
| Others | 2.1 | 1.8 | 1.6 | 1.5 | 1.6 | 1.7 | 1.8 | 2.3 | 1.7 |
| Unknown | 23.3 | 23.4 | 22.2 | 20.1 | 18.9 | 18.2 | 17.5 | 17.3 | 21.8 |
| Neighborhood education,* % | |||||||||
| Less than High school | 19.3 | 19.9 | 23.6 | 26.0 | 27.0 | 27.7 | 29.0 | 29.4 | 23.1 |
| High school graduate | 19.5 | 19.5 | 20.8 | 21.7 | 22.2 | 22.5 | 22.8 | 22.9 | 20.6 |
| Some college or associate degree | 31.2 | 30.9 | 30.7 | 30.7 | 30.7 | 30.6 | 30.2 | 30.1 | 30.8 |
| Bachelor degree or higher | 30.1 | 29.7 | 24.9 | 21.6 | 20.2 | 19.1 | 18.0 | 17.5 | 25.5 |
| Neighborhood income,* % | |||||||||
| < $15,000 | 10.2 | 10.3 | 11.0 | 11.5 | 11.9 | 12.5 | 13.3 | 13.9 | 11.0 |
| $15,000 to $34,999 | 17.8 | 18.1 | 19.5 | 20.5 | 21.2 | 21.8 | 22.6 | 23.0 | 19.4 |
| $35,000 to $49,999 | 14.0 | 14.1 | 14.8 | 15.3 | 15.5 | 15.8 | 15.9 | 16.0 | 14.7 |
| $50,000 to $74,999 | 19.9 | 20.0 | 20.3 | 20.5 | 20.4 | 20.4 | 20.3 | 20.0 | 20.3 |
| $75,000 to $99,999 | 14.1 | 14.0 | 13.7 | 13.3 | 13.1 | 12.8 | 12.3 | 12.1 | 13.6 |
| $100,000 to $149,999 | 14.6 | 14.3 | 13.2 | 12.4 | 11.9 | 11.3 | 10.7 | 10.2 | 13.3 |
| $150,000 or more | 9.5 | 9.1 | 7.5 | 6.4 | 5.9 | 5.4 | 4.9 | 4.7 | 7.7 |
Neighborhood household income and neighborhood education are area-based measures retrieved through linkage of a member’s address with U.S. census track
Prevalence of Overweight, Obesity, and Extreme Obesity
Overall, 61.5% of young adults had a BMI ≥ 25.0 kg/m2, with 31.6% of young adults classified as overweight, and 29.9% classified as obese (class 1 to 5, Table 2). The prevalence of overweight or obesity was higher in men than in women (71.7% and 53.1% respectively). Obesity was prevalent in 32.9% of men and 27.4% of women (class 1 to 5). Conversely, extreme obesity (classes 3 to 5) affected a higher percentage of women (6.1%) compared to men (4.5%). Overweight and obesity prevalence increased with age; 79.2% of men and 60.0% of women aged 30.0–39.9 years were overweight or obese compared to 63.6% of men and 46.9% of women in the group of 20.0–29.9 years olds. The prevalence of extreme obesity increased from 3.9% in the age group of 20 to 25 years of age to 6.1% in the group of 35 to 39 years of age. While Hispanic young adults have the highest overall prevalence of overweight and obesity, Black young adults had the highest prevalence of extreme obesity class 3–5. Asian/Pacific Islanders had the lowest prevalence of overweight, obesity, and extreme obesity.
Table 2.
Prevalence of overweight and obesity in young adults overall and by age group
| Weight class: | Overweight | Obesity
|
||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Class 1 | Class 2 | Class 3 | Class 4 | Class 5 | Total | |||||||||
| BMI range (kg/m2): | 25.0–29.9 | 30.0–34.9 | 35.0–39.9 | 40.0–49.92 | 50.0–59.9 | ≥60.0 | ||||||||
|
|
||||||||||||||
| Variable | n | % | n | % | n | % | n | % | n | % | n | % | n | % |
| Age 20–29.9 y | 262,702 | 53.4 | 128,952 | 26.2 | 58,866 | 12.0 | 34,888 | 7.1 | 5,200 | 1.1 | 1,002 | 0.2 | 491,610 | 100.0 |
| Sex | ||||||||||||||
| Male | 139,314 | 53.0 | 67,045 | 52.0 | 26,213 | 44.5 | 13,158 | 37.7 | 1,787 | 34.4 | 397 | 39.6 | 247,914 | 50.4 |
| Female | 123,388 | 47.0 | 61,907 | 48.0 | 32,653 | 55.5 | 21,730 | 62.3 | 3,413 | 65.6 | 605 | 60.4 | 243,696 | 49.6 |
| Race/Ethnicity | ||||||||||||||
| Non-Hispanic White | 66,724 | 25.4 | 29,215 | 22.7 | 13,161 | 22.4 | 7,807 | 22.4 | 1,162 | 22.3 | 198 | 19.8 | 118,267 | 24.1 |
| Black | 14,590 | 5.6 | 8,643 | 6.7 | 4,879 | 8.3 | 3,763 | 10.8 | 770 | 14.8 | 186 | 18.6 | 32,831 | 6.7 |
| Hispanic | 96,075 | 36.6 | 54,934 | 42.6 | 25,900 | 44.0 | 15,138 | 43.4 | 2,111 | 40.6 | 390 | 38.9 | 194,548 | 39.6 |
| Asian/Pacific Islander | 19,348 | 7.4 | 7,069 | 5.5 | 2,501 | 4.3 | 1,053 | 3.0 | 116 | 2.2 | 17 | 1.7 | 30,104 | 6.1 |
| Others | 4,188 | 1.6 | 1,862 | 1.4 | 950 | 1.6 | 590 | 1.7 | 93 | 1.8 | 26 | 2.6 | 7,709 | 1.6 |
| Unknown | 61,777 | 23.5 | 27,229 | 21.1 | 11,475 | 19.5 | 6,537 | 18.7 | 948 | 18.2 | 185 | 18.5 | 108,151 | 22.0 |
| Age 30–39.9 y | 311,342 | 49.7 | 179,165 | 28.6 | 79,657 | 12.7 | 46,995 | 7.5 | 7,727 | 1.2 | 1,521 | 0.2 | 626,407 | 100.0 |
| Sex | ||||||||||||||
| Male | 176,601 | 56.7 | 101,120 | 56.4 | 37,529 | 47.1 | 17,912 | 38.1 | 2,634 | 34.1 | 534 | 35.1 | 336,330 | 53.7 |
| Female | 134,741 | 43.3 | 78,045 | 43.6 | 42,128 | 52.9 | 29,083 | 61.9 | 5,093 | 65.9 | 987 | 64.9 | 290,077 | 46.3 |
| Race/Ethnicity | ||||||||||||||
| Non-Hispanic White | 75,378 | 24.2 | 41,627 | 23.2 | 19,339 | 24.3 | 11,983 | 25.5 | 1,912 | 24.7 | 382 | 25.1 | 150,621 | 24.1 |
| Black | 16,158 | 5.2 | 12,523 | 7.0 | 7,609 | 9.6 | 5,677 | 12.1 | 1,250 | 16.2 | 297 | 19.5 | 43,514 | 7.0 |
| Hispanic | 119,796 | 38.5 | 77,797 | 43.4 | 33,836 | 42.5 | 18,893 | 40.2 | 2,962 | 38.3 | 521 | 34.3 | 253,805 | 40.5 |
| Asian/Pacific Islander | 29,424 | 9.5 | 9,797 | 5.5 | 3,012 | 3. 8 | 1,270 | 2.7 | 151 | 2.0 | 38 | 2.5 | 43,692 | 7.0 |
| Others | 4,790 | 1.5 | 2,745 | 1.5 | 1,211 | 1.5 | 808 | 1.7 | 136 | 1.8 | 31 | 2.0 | 9,721 | 1.6 |
| Unknown | 65,796 | 21.1 | 34,676 | 19.4 | 14,650 | 18.4 | 8,364 | 17.8 | 1,316 | 17.0 | 252 | 16.6 | 125,054 | 20.0 |
Prevalence of Diabetes, Dyslipidemia, Hypertension, and the Metabolic Syndrome
Overall, men had higher adjusted RR for diabetes, dyslipidemia, hypertension, and the metabolic syndrome than women. This finding was consistent for adults aged 20 to 29 years and 30 to 39 years. The adjusted odd ratios for any of these health conditions increased with age and varied slightly by race and ethnicity. The most striking difference in prevalence of these health conditions among racial/ethnic groups was observed in the for hypertension, which was highest in Black young adults, especially those aged 30.0–39.9 years of age, with 13.1% having hypertension compared to 5.0% of non-Hispanic Whites.
The adjusted RR of diabetes, dyslipidemia, hypertension and metabolic syndrome increased with increasing weight class. The adjusted RR of these health conditions increased sharply for those individuals with a BMI ≥40, with the sharpest increase in the adjusted RR for hypertension and metabolic syndrome. The association between weight class and obesity-related health conditions such as dyslipidemia, hypertension and metabolic syndrome was modified by age with a stronger association among 20.0–29.9 year olds compared to 30.0–39.9 year olds (p for interaction by age <0.001 for dyslipidemia, hypertension, and metabolic syndrome). For diabetes, however, the association with obesity was slightly stronger among 30.0–39.9 year olds than among 20.0–29.9 year olds.
DISCUSSION
This study was consistent with previous findings showing a high prevalence of overweight and obesity in young adults in the U.S., with over 30% of the population in KP having a BMI of 30 kg/m2 or greater. With the large study population and availability of clinical data, a key finding of this population-based cross-sectional study of almost two million young adults is that the risk for obesity-related health conditions increases disproportionately in individuals who are extremely obese with a BMI > 40 kg/m2. But while the prevalence of extreme obesity was higher in older individuals, the association between obesity and obesity-related health conditions was stronger in younger individuals.
Between 1980 and 2008, the prevalence of obesity (BMI ≥ 30 kg/m2) among U.S. adults more than doubled from 15% to approximately 34% (1, 7, 15) although it may have stabilized in recent years at this alarming rate (1). Additional reports based on the NHANES indicate that about 28% to 34% of young adults aged 20 to 39 years are classified as obese, with approximately 5% of the surveyed population categorized as extremely obese (BMI ≥ 40 kg/m2) (1, 7, 16, 17). These estimates are comparable to the present study with 5.4% of young adults classified as extremely obese.
Consistent with the present study, the prevalence of obesity varied markedly by sex. Previous studies identified differences in the prevalence of obesity among different adult population subgroups. Nationwide, more men (63%) than women (55%) are at least overweight (16, 18). However, obesity is more prevalent among women (27%) than among men (21%) (18). The proportion of extremely obese individuals is more than double in women (8.0%) than men (3.1%) (7). Studies focusing on young adults are scant. Recent studies estimated that approximately 7% of women between 20 and 39 years are extremely obese (1). The present study suggests that 4.5% of men and 6.1% of women aged 20–39 years are extremely obese, with 3.9% of men and 5.0% of women in the group of 20–29 year olds compared to 5.0% of men and 7.2% of women in the group of 30–39 year olds.
Consistent with other studies, the prevalence of obesity varied by race/ethnicity. Blacks have the highest prevalence of obesity, reaching rates as high as 50% in Black women (4, 18). Nationwide, obesity class 2 and 3 are most frequent in Black women with approximately 11% and 8% respectively (18). Based on the NHANES 2003–2004, Black women aged 20–39 years have the highest prevalence of extreme obesity with 15.7%, followed by Mexican-American women at 8.6 %, Black men at 7.1%, White women at 6.4%, White men at 3.2% and Mexican-American men at 1.9% (7).
Obesity is a known risk factor for diabetes (3, 4, 16, 19–22), dyslipidemia (16), hypertension (16, 23), and metabolic syndrome (16, 24–27). Past reports identified individuals with a BMI ≥ 40 kg/m2 as the weight class group with the highest prevalence of hypertension (52.3 %), diabetes (14.2 %), and metabolic syndrome (39.2%); while individuals with a BMI of 30–39 kg/m2 had the highest prevalence rate of dyslipidemia (20.6%). Adults aged 18–29 years with a BMI ≥40 kg/m2 had the following prevalence rates: hypertension (19.8%), diabetes (0.8%), dyslipidemia (18.2%) and metabolic syndrome (14.9%) (16). Adults aged 30–49 years with a BMI ≥40 kg/m2 had the following prevalence rates: hypertension (47.2%), diabetes (10.8%), dyslipidemia (14.3%) and metabolic syndrome (31.8%). Although dyslipidemia was more prevalent in obese persons compared to normal weight individuals, the prevalence did not increase with increasing weight class beyond the group of individuals with a BMI of 30.0–34.9 kg/m2 in that study (18). In contrast, a study on the association of hypertension, diabetes, dyslipidemia and metabolic syndrome with obesity from NHANES 1999 to 2004 determined that the odds of chronic health conditions increased as BMI increased. The findings indicated that the prevalence of diabetes was more than five times higher in individuals with a BMI ≥40 kg/m2 compared to normal weight individuals (16). Additionally, the study found that individuals with a BMI ≥40 kg/m2 were more than twice as likely as normal weight individuals to have a diagnosis of hypertension, dyslipidemia or metabolic syndrome (16). Similar to some but not all previous reports, findings of our study the prevalence of related-health conditions including dyslipidemia incline steadily with increasing BMI. Young adults with a BMI ≥60 kg/m2 showed the highest prevalence of obesity-related health conditions.
Findings from NHANES 1999–2004 suggested that the association between obesity and some adverse health outcomes was stronger in adults aged 18 to 29 years than in adults aged 30–49 years and ≥50 years (16). In that study, the difference in the prevalence of hypertension, dyslipidemia and metabolic syndrome between normal weight and obese adults was most pronounced in the younger age group while the difference was lowest in the oldest age group (≥50 years) (16). In contrast, the prevalence difference of diabetes between normal weight and obese adults was higher in 30–49 year old adults than in 18–29 year old adults (16). This is consistent with findings from our study suggesting that young adults aged 20 to 29 years who are extremely obese are more likely to have hypertension, dyslipidemia and metabolic syndrome than 30 to 39 years olds when compared to their normal weight counterparts of the same age – even though the absolute prevalence was higher in older adults than in younger adults. This, however, was not observed for diabetes where the relative risks for very obese individuals was comparable for 20–29 year olds and 30 to 39 years olds compared to their normal weight counterparts of the same age.
Our study benefited from an extremely large multi-ethnic population, using data from two large integrated health care delivery systems. These populations represent over 18% of young adults in California. The large population notwithstanding, it is possible that there is a bias in ascertainment of BMI, as these were obtained from electronic medical records. Those individuals who are more likely to seek medical care may also be more overweight or obese, and the prevalence estimates may therefore be overestimated. This is a likely explanation for the larger proportion of women in the study population, as women are likely to undergo more routine care in this age group due to prenatal and postnatal care, and recommended screenings, such as for pap smears. However, height and weight are recorded routinely for the vast majority of visits and not just those related to weight-related health conditions, and the prevalence estimates were similar to those from other studies as described above, albeit with smaller populations. Because of routine recording of height and weight, it is also unlikely that the relative risks observed for the association of BMI and various health conditions are biased due to the health care setting.
In our definition of the metabolic syndrome, BMI >30 kg/m2 (28) had to be used instead of waist circumference which is a better estimate of intra-abdominal visceral adipose tissue and worsened cardiovascular outcomes (12). The inclusion of BMI in the definition of the metabolic may result in an overestimation of relative risks for weight classes.
Because of the cross-sectional design of this study, our findings should be interpreted with care. Both exposure and outcome have been assessed at approximately the same time period, and therefore, no inferences pertaining to causality can be made directly from the observations in this study. Moreover, biological relevance of the differences between groups has to be considered. However, several mechanisms have been suggested to explain the association between obesity and diabetes, dyslipidemia, hypertension and the metabolic syndrome. Obesity is an established risk factor for these health conditions in adults and one of the possible features of the metabolic syndrome (12). Obesity is considered a chronic low-grade inflammatory state and is associated with adypocyte dysfunction which leads to abnormalities in lipid metabolism (29). Chronic inflammation is also often cited as key etiologic factor in the development of the metabolic syndrome (30), insulin resistance and diabetes (31), dyslipidemia (32), and hypertension (33–36).
In conclusion, the current study indicates that the impact of extreme obesity on various health conditions known to be associated with adiposity is higher in the younger age group. Hispanics and Blacks are also more likely to be obese, including extreme obesity, putting them at an elevated risk for premature cardiovascular disease and some cancers relative to non-Hispanic whites. Given the marked elevated associations with increasing obesity class for the health conditions examined in this study, greater attention may need to be directed at preventive screening recommendations and treatment decisions among the extremely obese for these aggravated health conditions.
Table 3.
Prevalence, relative risks (RR) and 95% confidence intervals (CI) of dyslipidemia in young adults overall and by age group
|
|
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|---|---|---|---|---|---|---|---|---|---|---|---|---|
| All | Age 20–29.9 y | Age 30–39.9 y | ||||||||||
|
|
||||||||||||
| n | % | RR | 95% CI | n | % | RR | 95% CI | n | % | RR | 95% CI | |
| All ages | 33,975 | 1.9 | -- | -- | 5,218 | 0.6 | 1.00 | -- | 28,757 | 3.2 | -- | -- |
| Sex | ||||||||||||
| Male | 21,297 | 2.6 | 1.89 | (1.85–1.93) | 2,746 | 0.7 | 1.36 | (1.29–1.44) | 18,551 | 4.4 | 2.01 | (1.96–2.06) |
| Female | 12,678 | 1.3 | 1.00 | Ref. | 2,472 | 0.5 | 1.00 | Ref. | 1.00 | Ref. | ||
| Age group, y | ||||||||||||
| 20.0–24.9 | 1,811 | 0.4 | 1.00 | Ref. | ||||||||
| 25.0–29.9 | 3,407 | 0.8 | 1.77 | (1.68–1.88) | ||||||||
| 30.0–34.9 | 8,945 | 2.0 | 4.27 | (4.06–4.49) | ||||||||
| 35.0–39.9 | 19,812 | 4.2 | 8.40 | (8.01–8.82) | ||||||||
| Race/Ethnicity | ||||||||||||
| Non-Hispanic White | 8,329 | 1.8 | 1.00 | Ref. | 1,353 | 0.6 | 1.00 | Ref. | 6,976 | 3.0 | 1.00 | Ref. |
| Black | 2,466 | 2.3 | 1.11 | (1.06–1.16) | 354 | 0.7 | 0.98 | (0.87–1.10) | 2,112 | 3.9 | 1.14 | (1.08–1.19) |
| Hispanic | 13,792 | 2.2 | 1.06 | (1.03–1.09) | 2,096 | 0.7 | 0.97 | (0.91–1.04) | 11,696 | 3.6 | 1.07 | (1.04–1.10) |
| Asian/Pacific Islander | 3,997 | 2.3 | 1.60 | (1.54–1.66) | 578 | 0.7 | 1.55 | (1.41–1.71) | 3,419 | 3.6 | 1.60 | (1.54–1.67) |
| Others | 704 | 2.3 | 1.37 | (1.27–1.48) | 124 | 0.8 | 1.44 | (1.20–1.73) | 580 | 3.8 | 1.36 | (1.25–1.47) |
| Unknown | 4,687 | 1.2 | 0.64 | (0.62–0.66) | 713 | 0.3 | 0.56 | (0.51–0.61) | 3,974 | 2.2 | 0.66 | (0.63–0.68) |
| BMI, kg/m2 | ||||||||||||
| <18.5 | 96 | 0.3 | 0.55 | (0.45–0.67) | 39 | 0.2 | 0.72 | (0.53–1.00) | 57 | 0.6 | 0.48 | (0.37–0.62) |
| 18.5–24.9 | 4,721 | 0.7 | 1.00 | Ref. | 955 | 0.2 | 1.00 | Ref. | 3,766 | 1.4 | 1.00 | Ref. |
| 25.0–29.9 | 10,758 | 1.9 | 1.91 | (1.84–1.98) | 1,441 | 0.5 | 2.07 | (1.91–2.25) | 9,317 | 3.0 | 1.85 | (1.78–1.92) |
| 30.0–34.9 | 9,091 | 3.0 | 2.88 | (2.77–2.98) | 1,266 | 1.0 | 3.68 | (3.38–4.01) | 7,825 | 4.4 | 2.71 | (2.60–2.82) |
| 35.0–39.9 | 5,165 | 3.7 | 3.88 | (3.73–4.04) | 841 | 1.4 | 5.49 | (5.00–6.03) | 4,324 | 5.4 | 3.60 | (3.44–3.76) |
| 40.0–49.9 | 3,429 | 4.2 | 4.64 | (4.44–4.85) | 541 | 1.6 | 6.10 | (5.48–6.78) | 2,888 | 6.1 | 4.36 | (4.15–4.57) |
| 50.0–59.9 | 584 | 4.5 | 4.97 | (4.57–5.40) | 112 | 2.2 | 8.39 | (6.90–10.19) | 472 | 6.1 | 4.46 | (4.06–4.89) |
| ≥60 | 131 | 5.2 | 5.58 | (4.73–6.59) | 23 | 2.3 | 8.82 | (5.86–13.27) | 108 | 7.1 | 5.10 | (4.25–6.12) |
Table 4.
Prevalence, relative risks (RR) and 95% confidence intervals (CI) of hypertension in young adults overall and by age group
|
|
||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| All | Age 20–29.9 y | Age 30–39.9 y | ||||||||||
|
| ||||||||||||
| n | % | RR | 95% CI | n | % | RR | 95% CI | n | % | RR | 95% CI | |
| All ages | 60,027 | 3.3 | -- | -- | 11,985 | 1.3 | -- | -- | 48,042 | 5.3 | -- | -- |
| Sex | ||||||||||||
| Male | 31,319 | 3.8 | 1.32 | (1.30–1.34) | 6,360 | 1.6 | 1.50 | (1.45–1.56) | 24,959 | 5.9 | 1.28 | (1.26–1.31) |
| Female | 28,708 | 2.9 | 1.00 | Ref. | 5,625 | 1.1 | 1.00 | Ref. | 23,083 | 4.8 | 1.00 | Ref. |
| Age group, y | ||||||||||||
| 20.0–24.9 | 4,293 | 0.9 | 1.00 | Ref. | ||||||||
| 25.0–29.9 | 7,692 | 1.7 | 1.68 | (1.62–1.75) | ||||||||
| 30.0–34.9 | 15,963 | 3.7 | 3.16 | (3.06–3.27) | ||||||||
| 35.0–39.9 | 32,079 | 6.8 | 5.43 | (5.26–5.60) | ||||||||
| Race/Ethnicity | ||||||||||||
| Non-Hispanic White | 17,108 | 3.6 | 1.00 | Ref. | 3,638 | 1.5 | 1.00 | Ref. | 13,470 | 5.8 | 1.00 | Ref. |
| Black | 8,683 | 8.1 | 1.59 | (1.55–1.63) | 1,579 | 3.0 | 1.46 | (1.38–1.55) | 7,104 | 13.1 | 1.63 | (1.59–1.67 |
| Hispanic | 18,597 | 2.9 | 0.69 | (0.67–0.70) | 3,782 | 1.2 | 0.63 | (0.60–0.66) | 14,815 | 4.5 | 0.70 | (0.69–0.72) |
| Asian/Pacific Islander | 5,937 | 3.4 | 1.31 | (1.27–1.35) | 1,033 | 1.3 | 1.11 | (1.03–1.18) | 4,904 | 5.1 | 1.35 | (1.31–1.40) |
| Others | 1407 | 4.7 | 1.28 | (1.22–1.34) | 298 | 2.0 | 1.26 | (1.12–1.41) | 1,109 | 7.4 | 1.28 | (1.21–1.36) |
| Unknown | 8,295 | 2.1 | 0.59 | (0.57–0.60) | 1,655 | 0.8 | 0.48 | (0.46–0.51) | 6,640 | 3.6 | 0.62 | (0.60–0.63) |
| BMI, kg/m2 | ||||||||||||
| <18.5 | 240 | 0.7 | 0.87 | (0.77–0.99) | 127 | 0.5 | 1.28 | (1.07–1.53) | 113 | 1.2 | 0.66 | (0.55–0.80) |
| 18.5–24.9 | 6,627 | 1.0 | 1.00 | Ref. | 1,800 | 0.5 | 1.00 | Ref. | 4,827 | 1.8 | 1.00 | Ref. |
| 25.0–29.9 | 14,186 | 2.5 | 2.08 | (2.02–2.14) | 2,610 | 1.0 | 2.00 | (1.88–2.13) | 11,576 | 3.7 | 2.07 | (2.00–2.14) |
| 30.0–34.9 | 15,330 | 5.0 | 4.04 | (3.92–4.16) | 2,723 | 2.1 | 4.25 | (4.00–4.51) | 12,607 | 7.0 | 3.95 | (3.82–4.08) |
| 35.0–39.9 | 10,894 | 7.9 | 6.47 | (6.28–6.67) | 2,056 | 3.5 | 7.18 | (6.74–7.65) | 8,838 | 11.1 | 6.25 | (6.04–6.47) |
| 40.0–49.9 | 9,806 | 12.0 | 9.80 | (9.50–10.10) | 1,979 | 5.7 | 11.73 | (11.01–12.51) | 7,827 | 16.7 | 9.31 | (8.99–9.64) |
| 50.0–59.9 | 2313 | 17.9 | 13.54 | (12.97–14.12) | 525 | 10.1 | 19.88 | (18.11–21.82) | 1,788 | 23.1 | 12.41 | (11.82–13.03) |
| ≥60 | 631 | 25.0 | 17.25 | (16.20–18.37) | 165 | 16.5 | 30.47 | (26.39–35.17) | 466 | 30.6 | 15.43 | (14.32–16.63) |
Table 5.
Prevalence, relative risks (RR) and 95% confidence intervals (CI) of diabetes in young adults overall and by age group
|
|
||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| All | Age 20–29.9 y | Age 30–39.9 y | ||||||||||
|
| ||||||||||||
| n | % | RR | 95% CI | n | % | RR | 95% CI | n | % | RR | 95% CI | |
| All ages | 28,545 | 1.57 | -- | -- | 7,061 | 0.78 | -- | -- | 21,484 | 2.36 | -- | -- |
| Sex | ||||||||||||
| Male | 13,802 | 1.69 | 1.14 | (1.11–1.16) | 3,118 | 0.80 | 1.05 | (1.00–1.10) | 10,684 | 2.52 | 1.16 | (1.13–1.19) |
| Female | 14,743 | 1.47 | 1.00 | Ref. | 3,943 | 0.76 | 1.00 | Ref. | 10,800 | 2.22 | 1.00 | Ref. |
| Age group, y | ||||||||||||
| 20.0–24.9 | 3,020 | 0.65 | 1.00 | Ref. | ||||||||
| 25.0–29.9 | 4,041 | 0.92 | 1.26 | (1.20–1.32) | ||||||||
| 30.0–34.9 | 7,577 | 1.73 | 2.16 | (2.07–2.25) | ||||||||
| 35.0–39.9 | 13,907 | 2.94 | 3.51 | (3.37–3.65) | ||||||||
| Race/Ethnicity | ||||||||||||
| Non-Hispanic White | 7,102 | 1.50 | 1.00 | Ref. | 2,171 | 0.90 | 1.00 | Ref. | 4,931 | 2.13 | 1.00 | Ref. |
| Black | 2,727 | 2.54 | 1.24 | (1.18–1.29) | 715 | 1.35 | 1.19 | (1.10–1.30) | 2,012 | 3.71 | 1.26 | (1.20–1.33) |
| Hispanic | 12,046 | 1.90 | 1.09 | (1.06–1.13) | 2,615 | 0.85 | 0.80 | (0.75–0.84) | 9,431 | 2.87 | 1.22 | (1.18–1.26) |
| Asian/Pacific Islander | 2,935 | 1.68 | 1.50 | (1.44–1.57) | 583 | 0.74 | 0.96 | (0.88–1.06) | 2,352 | 2.44 | 1.77 | (1.68–1.86) |
| Others | 675 | 2.24 | 1.47 | (1.361.59) | 194 | 1.28 | 1.37 | (1.19–1.59) | 481 | 3.19 | 1.51 | (1.38–1.66) |
| Unknown | 3,060 | 0.77 | 0.53 | (0.51–0.55) | 783 | 0.37 | 0.40 | (0.37–0.44) | 2,277 | 1.24 | 0.59 | (0.56–0.62) |
| BMI, kg/m2 | ||||||||||||
| <18.5 | 141 | 0.43 | 0.80 | (0.68–0.95) | 93 | 0.40 | 0.96 | (0.78–1.18) | 48 | 0.49 | 0.57 | (0.43–0.76) |
| 18.5–24.9 | 4,022 | 0.60 | 1.00 | Ref. | 1,665 | 0.42 | 1.00 | Ref. | 2,357 | 0.86 | 1.00 | Ref. |
| 25.0–29.9 | 6,532 | 1.14 | 1.63 | (1.57–1.70) | 1,676 | 0.64 | 1.48 | (1.38–1.58) | 4,856 | 1.56 | 1.77 | (1.69–1.86) |
| 30.0–34.9 | 6,895 | 2.24 | 3.09 | (2.97–3.22) | 1,434 | 1.11 | 2.54 | (2.37–2.73) | 5,461 | 3.05 | 3.48 | (3.31–3.65) |
| 35.0–39.9 | 5,287 | 3.82 | 5.36 | (5.14–5.59) | 1,038 | 1.76 | 3.99 | (3.69–4.32) | 4,249 | 5.33 | 6.20 | (5.89–6.53) |
| 40.0–49.9 | 4,466 | 5.45 | 7.76 | (7.43–8.10) | 898 | 2.57 | 5.76 | (5.31–6.25) | 3,568 | 7.59 | 9.01 | (8.55–9.49) |
| 50.0–59.9 | 977 | 7.56 | 10.48 | (9.79–11.22) | 201 | 3.87 | 8.39 | (7.27–9.70) | 776 | 10.04 | 11.93 | (11.03–12.91) |
| ≥60 | 225 | 8.92 | 12.14 | (10.69–13.78) | 56 | 5.59 | 11.97 | (9.24–15.51) | 169 | 11.11 | 13.09 | (11.30–15.16) |
Table 6.
Prevalence, relative risks (RR) and 95% confidence intervals (CI) of Metabolic Syndrome in young adults overall and by age group
|
|
||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| All | Age 20–29.9 y | Age 30–39.9 y | ||||||||||
|
| ||||||||||||
| n | % | RR | 95% CI | n | % | RR | 95% CI | n | % | RR | 95% CI | |
| All ages | 76,468 | 4.20 | -- | -- | 18,399 | 2.02 | -- | -- | 58,069 | 6.38 | -- | -- |
| Sex | ||||||||||||
| Male | 38,805 | 4.76 | 1.14 | (1.12–1.15) | 8,697 | 2.23 | 1.08 | (1.05–1.12) | 30,108 | 7.09 | 1.15 | (1.14–1.17) |
| Female | 37,663 | 3.75 | 1.00 | Ref. | 9,702 | 1.87 | 1.00 | Ref. | 27,961 | 5.76 | 1.00 | Ref. |
| Age group, y | ||||||||||||
| 20.0–24.9 | 6,881 | 1.47 | 1.00 | Ref. | ||||||||
| 25.0–29.9 | 11,518 | 2.61 | 1.41 | (1.37–1.45) | ||||||||
| 30.0–34.9 | 21,573 | 4.93 | 2.29 | (2.23–2.35) | ||||||||
| 35.0–39.9 | 36,496 | 7.72 | 3.32 | (3.24–3.40) | ||||||||
| Race/Ethnicity | ||||||||||||
| Non-Hispanic White | 20,131 | 4.25 | 1.00 | Ref. | 4,831 | 1.99 | 1.00 | Ref. | 15,300 | 6.60 | 1.00 | Ref. |
| Black | 5,841 | 5.45 | 0.81 | (0.79–0.83) | 1,279 | 2.42 | 0.73 | (0.69–0.77) | 4,562 | 8.41 | 0.83 | (0.81–0.86) |
| Hispanic | 33,416 | 5.26 | 0.96 | (0.94–0.97) | 8,299 | 2.70 | 0.91 | (0.88–0.94) | 25,117 | 7.65 | 0.97 | (0.95–0.98) |
| Asian/Pacific Islander | 5,900 | 3.37 | 1.43 | (1.39–1.46) | 1,261 | 1.60 | 1.27 | (1.19–1.34) | 4,639 | 4.82 | 1.46 | (1.42–1.50) |
| Others | 1,577 | 5.22 | 1.18 | (1.121.23) | 408 | 2.70 | 1.21 | (1.10–1.34) | 1,169 | 7.75 | 1.16 | (1.10–1.23) |
| Unknown | 9,603 | 2.42 | 0.59 | (0.57–0.60) | 2,321 | 1.09 | 0.53 | (0.51–0.56) | 7,282 | 3.95 | 0.60 | (0.59–0.62) |
| BMI, kg/m2 | ||||||||||||
| <18.5 | 49 | 0.15 | 0.65 | (0.49–0.86) | 30 | 0.13 | 1.34 | (0.92–1.94) | 19 | 0.20 | 0.40 | (0.25–0.63) |
| 18.5–24.9 | 1,708 | 0.26 | 1.00 | Ref. | 384 | 0.10 | 1.00 | Ref. | 1,324 | 0.48 | 1.00 | Ref. |
| 25.0–29.9 | 6,480 | 1.13 | 3.90 | (3.70–4.12) | 1,086 | 0.41 | 4.13 | (3.67–4.64) | 5,394 | 1.73 | 3.58 | (3.37–3.80) |
| 30.0–34.9 | 30,010 | 9.74 | 32.93 | (31.36–34.58) | 6,742 | 5.23 | 51.94 | (46.86–57.57) | 23,268 | 12.99 | 27.16 | (25.69–28.70) |
| 35.0–39.9 | 19,614 | 14.16 | 48.86 | (46.51–51.33) | 4,980 | 8.46 | 84.70 | (76.34–93.96) | 14,634 | 18.37 | 39.24 | (37.10–41.50) |
| 40.0–49.9 | 14,840 | 18.12 | 63.45 | (60.37–66.68) | 4,060 | 11.64 | 117.59 | (105.93–130.53) | 10,780 | 22.94 | 49.98 | (47.24–52.89) |
| 50.0–59.9 | 3,058 | 23.66 | 81.05 | (76.62–85.73) | 881 | 16.94 | 170.33 | (151.55–191.44) | 2,177 | 28.17 | 61.90 | (58.05–66.02) |
| ≥60 | 709 | 28.10 | 92.79 | (86.05–100.06) | 236 | 23.55 | 237.86 | (204.92–276.08) | 473 | 31.10 | 67.10 | (61.29–73.45) |
Acknowledgments
The present study is supported by the National Cancer Institute through the HMO Cancer Research Network (U19 CA079689, Dr. Ed Wagner, Group Health Research Institute, PI) as a Pilot Project to Dr. Koebnick, and by the Kaiser Permanente Southern California Direct Community Benefit Fund.
Abbreviations
- CI
confidence interval
- BMI
Body mass index
- CRN
Cancer Research Network
- ICD-9
International Classification of Disease, 9th modification
- KP
Kaiser Permanente
- NCI
National Cancer Institute
- RR
Relative Risk
Footnotes
Author contributions:
Design and conduct of the study: Koebnick, Kushi.
Collection, management, analysis and interpretation of data: Koebnick, Kushi, Smith, Martinez, Huang, Clancy, Williams.
Preparation of the manuscript: Koebnick, Martinez.
Critical revision of the manuscript for important intellectual content: Kushi, Smith, Huang, Clancy, Williams.
Conflict of interest:
Lawrence Kushi: (Relevant Relationship) Employment (other than primary affiliation, e.g., consulting) <10,000 - Adjunct Professor, UC Davis Medical School
Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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