Nursing Research and Obesity as Cardiovascular Risk
Obesity and Worldwide Statistics
or obese, and with the medical costs attributable to obesity ranging upwards
from $100 billion per year, the national, indeed global, crisis of obesity
stands in the ignominious position of being the one epidemic that nursing
research has virtually ignored.
In the last few years there has been a slow
increase in the number of studies and publications by nurses that focus on
obesity. While cardiovascular disease (CVD) and many of its risk factors have
been prominent in the nursing literature for quite some time, the intersection
of obesity and cardiovascular risk has been virtually unexplored from a nursing
perspective.
The most common approach of nurses studying obesity and CVD has
been to include body weight, either directly measured or self-reported, in
descriptive studies of CVD risk factors. This data point is subsequently
analyzed as Body Mass Index (BMI), calculated as weight/height (kg/m).
In Children
Children. Among 340 elementary school children, 53% had one or more
risk factors for CVD (Cowell, Warren, & Montgomery, 1999). Moreover, 25% of
the children were obese, and among the children who were obese, 47% had
additional risk factors for CVD.
Despite a low prevalence of poor fitness, 84%
of the low fitness children also had high blood pressure or were obese. In a
study involving 32 third grade children ( Skybo & Ryan-Wenger, 2002), the
most prevalent risk factors for heart disease were high body fat percentage and
environmental tobacco smoke in the home.
Few children had a body fat percentage
within the healthy range. Thus, the investigators suggested that the
third-grade children possessed some of the known risk factors for CVD, with
some of the risk factors being under the control of the child. Women.
A study
was conducted to determine whether there was a difference between
African-American and Caucasian women in the self-reported CVD risk factors of
obesity, physical inactivity, and smoking (Harrell & Gore, 1998).
In that
study of 1,945 women aged 23-53 years, African American women of low and middle
socioeconomic status (SES) were much more likely than high SES African
Americans to be obese, inactive, and smokers.
Among Caucasian women, however,
only those with low SES had the greatest prevalence of these three risk factors
for CVD. After controlling for income and education, African-American women
were more than twice as likely as Caucasian women to be obese and inactive.
A
secondary analysis of the Canadian National Population Health Survey (Cycle 1:
1994/95; Cycle II: 1996/97) focused on the CVD risk factors of physical
inactivity, hypertension, cigarette smoking, diabetes, obesity, and
socioeconomic status (SES) among women aged 20 years and older (Wong &
Wong, 2002).
Results indicated an increased prevalence of obesity, diabetes,
hypertension, and physical activity from Cycle I to Cycle II, and supported
previous studies that there is an SES gradient for CVD risk factors. In this
study age, physical activity, hypertension, and household income but not
obesity emerged as significant predictors of heart disease.
Older adults
In a study of patients after coronary artery bypass
grafting (CABG), female sex (odds ratio 4.7) and obesity (odds ratio 3.7) significantly
predicted hospital readmission (Sabourin & Funk, 1999).
Other investigators
used a cross-sectional design to assess CVD risk factors in Korean-American
elderly, aged 60-89 years, who resided in a large city in the eastern United
States (Kim, MT, Juon , Hill, Post, & Kim , 2001).
In these older adults,
hypertension was the leading CVD risk factor, followed by high blood
cholesterol, overweight, sedentary lifestyle, and smoking.
Intervention studies
Intervention studies of obesity as a CVD
risk factor where major dependent variables were physiological, were only found
when nurses appeared as members of multidisciplinary investigator teams. One of
these teams (McMurray, Ainsworth, Harrell, Griggs, & Williams, 1998)
examined cardiovascular fitness (VO) and physical activity (PA) rather than
obesity perse as CVD risk factors in young adult men and women.
A
cross-sectional analysis revealed that those in the highest tertial of VO2 had
a reduced relative risk for elevated cholesterol, blood pressure, and obesity,
while those in the highest tertial of self-reported PA only had a lower
relative risk for high systolic blood pressure (BP).
After a 9-week exercise
program for low fit young adults, only those who increased VO had a reduction
in relative risk for high cholesterol and systolic BP, but not for diastolic BP
or obesity.
Obesity and Post Menopausal Women
From a research program focusing on obesity and sedentariness as
major risk factors for CVD in postmenopausal women, and the corresponding
lifestyle modifications of weight loss and physical activity to mediate these
risks, Nicklas and colleagues reported the physiological aspects of these
phenomena in numerous publications.
The sequential effects of a 2-month
American Heart Association (AHA) Step I diet and subsequent weight loss through
6 months of hypocaloric AHA diet and low-intensity walking were examined for
their effects on lipoprotein lipids in obese, postmenopausal women (Nicklas,
katzel , Bunyard , Dennis, & Goldberg, 1997).
The AHA diet alone lowered
concentrations of total, low-density lipoprotein (LDL-C) and high-density
lipoprotein (HDL-C) cholesterol. Weight loss increased HDL-C concentrations,
but brought no additional changes in total cholesterol or LDL-C, Reductions in
total cholesterol and LDL-C were significant for participants with
hypercholesterolemia, but not for normocholesterolemic women.
The investigators
conjectured that because the AHA diet alone lowered HDL-C in the total sample
of women, a low-fat diet without substantial weight loss may not be beneficial
for improving lipoprotein lipid risk factors for CVD in obese, postmenopausal
women with normal lipid profiles .
In research to determine the specific
dietary factors associated with the decrease in HDL-C on an AHA diet alone (
Bunyard , Dennis, & Nicklas, 2002), the one significant dietary change was
the increase in the percent of energy consumed from simple sugar.
There were no
relationships between changes in HDL-C and changes in the percentage of energy
consumed from total, saturated, polyunsaturated, or monounsaturated fat.
Findings from a study of racial differences in resting metabolic
rate (RMR) fat oxidation and VO in obese, postmenopausal women showed that RMR,
adjusted for differences in lean mass, fat oxidation rate, and VO were
significantly higher in white than in black women ( Nicklas, Berman, Davis,
Dobrovolny, & Dennis, 1999).
In a multiple regression model including race,
body weight, lean mass, and age, lean mass was the only independent predictor
of RMR, while race was the only independent predictor of fat oxidation. The
best predictors of VO were lean mass and race.
The efficacy of a 6-month
hypocaloric AHA diet and low-intensity walking in improving CVD risk factors in
obese Caucasian and African-American post-menopausal women was evaluated by
measurements of body composition (dual-energy x-ray absorptiometry), abdominal
fat areas (computed tomography scan), lipoprotein lipids, insulin, glucose
tolerance, and blood pressure (Nicklas, Dennis, et al., 2003).
Although
absolute weight loss was similar in the two races, Caucasian women lost
relatively more fat mass. Women across the sample decreased fat in the
abdominal region with no differences in magnitude by race.
The intervention
decreased triglycerides and increased HDL-C in both races, and decreased total
and LDL-C in the Caucasian women. Fasting glucose and glucose area during an
oral glucose tolerance test decreased in Caucasian women, whereas there were no
racial differences in the decreased insulin area.
Blood pressure decreased the
most in women with higher blood pressures at baseline. Changes in lipids,
fasting glucose, and insulin, their responses during the oral glucose tolerance
test, and blood pressure were not different between racial groups of low-intensity
walking intervention, 458/832.
High Cholesterol and Insulin Levels
The accumulation of visceral fat, independent of total body
obesity, is widely acknowledged for its association with the development of
dyslipidemia, hypertension, glucose intolerance, and hyperinsulinemia in women.
Examining whether the loss of visceral adipose tissue (VAT) was related to
improvements in VO during a hypocaloric di and colleagues (Lynch, Nicklas,
Berman, Dennis, & Goldberg, 2001) found significant declines in visceral as
well as subcutaneous adipose tissue areas, with no change in lean body mass.
Women with an average of 10%. Increase in VO reduced VAT by an average of 20%,
significantly more than women who did not increase VO despite comparable
reductions in total body fat, fat mass, and subcutaneous adipose tissue area.
In a cross-sectional analysis of peri- and post-menopausal women 45-65 years
old, who ranged widely in adiposity and fat distribution (Nicklas, Penninx , et
al., 2003), women in the lowest quintile for VAT (< 105 cm³) had
significantly higher concentrations of HDL-C, lower LDL-C/HDL-C ratios,
triglyceride concentrations, fasting glucose, and insulin concentrations than
women in the four remaining quartiles.
Women in the two highest VAT quintiles
(2,163 cm) had the highest glucose and insulin concentrations. A VAT greater
than 105 cm² was associated with a higher risk of having low HDL-C, while a VAT
greater than 163 cm² also was associated with a higher risk of having a high
LDL-C/HDL-C ratio and a higher risk of being glucose intolerant.
Weight Loss and Lipid Level
Findings from additional studies in over weight and obese
postmenopausal women conducted by this same multidisciplinary research team
suggested that a reduction in adipose tissue lipoprotein lipase activity
(AT-LPL) with weight loss was associated with improvements in lipid metabolic
risk factors from weight loss and decreased weight regain.
In genetic studies,
variations in the lipoprotein lipase gene Pull were associated with ATLPL
activity and lipoprotein lipid and glucose concentrations, which resulted in a
more problematic CVD risk factor profile for these women.
Women with variation
in the peroxisome proliferator activated receptor (PPAR) gamma2 gene (Pro12Ala)
regained more weight during follow up than those who were homozygous for the
Pro allele.
Obesity Etiology
Obesity is a global epidemic with a complex etiology of
physiologic, metabolic, genetic, cognitive, psychological, behavioral,
environmental, social, and political factors. Obesity also is a major risk
factor for CVD, the leading cause of mortality in women as well as men.