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Introduction
The worldwide overweight/obesity has nearly tripled since 1975 and reached 39.0% in 2016.1) Concurrently, obesity prevalence in South Korea has been also rapidly increasing since 1998 and risen by 35.5% in 2016, specifically including the data that middle-aged women (25.2%) showed a higher prevalence of overweight/obesity than younger women (ages 19–29) (13.8%). Furthermore, women may be more likely to have impaired health outcomes associated with overweight/obesity than men.2) Therefore, nurses should pay attention to these issues on overweight/obesity and its health outcomes in a vulnerable group of middle-aged women.
Health-promoting behavior, conceptualized in the Health Promotion Model, was defined as multidimensional action and cognition patterns3) that may reflect an incorporated, comprehensive pattern of health behaviors in individual daily lives. Reportedly, the overweight/obese individuals walked for 30 minutes/day less,4) and had a lower fruit and vegetable intake5) than did the normal-weight group. However, few studies have reported that overweight/obese individuals had more impaired levels of health-promoting behaviors than normal-weight ones,6) specifically among middle-aged, Asian women.
Health-promoting behaviors may be an associate of health-related quality of life (HRQOL). However, evidence of the significant associations was confined within individuals with illness78) or the general population of middle aged-women,9) but not within the overweight/obese groups. Furthermore, no previous studies have reported an association of health-promoting behaviors including comprehensive domains (i.e., spiritual growth, health responsibility, physical activity, nutrition, interpersonal relations, and stress management) with HRQOL, although a few studies reported the association of a single health behavior (e.g., physical activity) with HRQOL among the overweight/obese group.1011) To this point, no studies have examined how comprehensive domains of health-promoting behaviors would be associated with HRQOL among overweight/obese individuals. In this context, identifying such an association may provide basic information for strategically improving HRQOL via enhancing specific domains of health-promoting behaviors associated with HRQOL for overweight/obese individuals.
HRQOL is a comprehensive concept with multiple health dimensions.12) Generally, HRQOL is assessed by generic versus disease-specific measures. The World Health Organization Quality of Life-brief version (WHOQOL-BREF) is the short version of the WHOQOL, and a generic measure used commonly across various populations.13) However, there has been little evidence that overweight/obesity may impair individuals' generic HRQOL as measured by WHOQOL-BREF. Instead of the generic HRQOL, disease-specific HRQOL measures provide a possible choice for capturing small changes in HRQOL among specific populations.14) In particular, obesity-specific HRQOL, i.e., the Impact of Weight on Quality of Life-Lite (IWQOL-Lite), has been developed for overweight/obese populations.15) However, both WHOQOL and IWQOL-Lite have not been assessed in various ethnic populations. Hence, among middle-aged Asian women, comparisons of HRQOLs between overweight and normal-weight groups and associations of health-promoting behaviors with HRQOLs, as measured by various HRQOL measures, may give nurses a comprehensive understanding on nursing strategies for improving their obesity-related health outcomes.
The present study had two aims: 1) to examine firstly if an overweight group significantly had impaired levels of health-promoting behaviors and generic and obesity-specific HRQOLs than a normal-weight group among middle-aged women who are vulnerable to being overweight/obese, and 2) to examine secondly if such health-promoting behaviors were significantly associated with generic and obesity-specific HRQOLs within the overweight group.
Methods
1. Participants
Based on a comparative study, participants were 119 middle-aged, community-dwelling women (56 of normal-weight group and 63 of overweight group) recruited from a community (i.e., a municipal county of Seongbuk-Gu) in Seoul, South Korea. The normal-weight group was recruited and analyzed for the first aim of the present study. The overweight group was obtained from the data of the community-based heart and weight management trial, and used as a secondary analysis for the first and second aims of the present study.
The normal-weight group comprised 56 women who fell into the category of less than 25 kg/m2 of body mass index (BMI), while the overweight group comprised 63 women who fell into either overweight or obese category defined by the World Health Organization (WHO).16) Of 56 of the normal-weight group, six fell into the category of less than 18.5 kg/m2 of BMI with the range 17.0–18.4 kg/m2. The WHO classifies BMI<17.0 kg/m2 into moderate and severe thinness, and reported that about 3–5% of a healthy adult population have a BMI<18.5 kg/m2.17) Based on this, the six women were finally included into the normal-weight group.
The minimum size was determined by using a mean (standard deviation [SD]) of the Health-Promoting Lifestyle Profile II (HPLP II) scores that were obtained from Nies et al.6) study; means (SDs) were 2.42 (0.57) in the overweight group and 2.71 (0.48) in the normal-weight group. Based on this, the minimum sample size was 54 for each group at the levels of statistical power (1−β)=0.80 (Student's t-test) and α=0.05 (two-tailed test).
We recruited the normal-weight group first, and then extracted the age-group matched overweight group. Between July 2013 and August 2013, the normal-weight group was recruited using a convenience sampling by community lay health advisors who were working for the Seongbuk-Gu Community Health Center. The inclusion criteria were 1) women aged between 30 and 65 years, 2) those without current health problems (i.e., cardiovascular diseases or cancers), and 3) those without obesity-related health problems (i.e., hypertension, dyslipidemia, or diabetes). The final sample recruited was 56 with an age range between 30 and under 50 (mean age=38.7 years).
Based on characteristics of the final sample of the normal-weight group (i.e., 30–49 years of age), the overweight group was recruited from a baseline sample (n=110) of the Community-Based Heart and Weight Management Trial (ISRCTN46069848).18192021) The trial was a single-center, randomized controlled trial (RCT) that examined differential effects of three exercise modes on cardiovascular markers in weight management.18192021) The sample of the trial was recruited during the period from September 2010 to November 2011 in the Seongbuk-Gu community. Among the sample of the trial (n=110), we extracted overweight/obese women with ages between 30 and ≤49 years (mean age=39.2 years). The final sample for the overweight group was 63.
2. Measurements
Participants' general characteristics were collected: socio-demographic variables such as age, education levels, employed status, monthly household income, married status, religion; and health-related variables such as BMI, current smoking, alcohol drinking, post-menopausal status, and obesity-related health problems. BMI was obtained by using the formula of body weight (kg)/height (m)2. For the overweight group, body weight and height were measured using the Tanita bioelectrical impedance scale (Tanita Corporation of American, Inc., Arlington Heights, IL, USA) and a stadiometer, respectively. For the normal-weight group, body weight and height were self-reported. Obesity-related health problems included hypertension and dyslipidemia.
1) Health-promoting behaviors
The levels of health-promoting behaviors were measured by using the Korean version of the HPLP II after permission from the HPLP II developers22) and translation of the English version.20) The HPLP II consisted of 52-items indicating the frequency with which they engaged in each behavior on a 4-point Likert scale, and 6 subscales comprising spiritual growth, health responsibility, physical activity, nutrition, interpersonal relations, and stress management. Means for total and 6 subscales were obtained, ranging from 1 to 4; higher means indicate higher levels of health-promoting behaviors. Cronbach's alpha for the total score was 0.90 in a community-based sample of women.6) Cronbach's alpha was 0.91 in this study.
2) Generic health-related quality of life (HRQOL)
Generic HRQOL was measured by the Korean version of WHOQOL-BREF that was obtained under the user agreement with the WHO.23) The WHOQOL-BREF comprises of 26 items, which are self-reported on a five-point Likert scale (1–5) based on four domains: physical, psychological, social, and environmental domains. Scores for each domain were calculated by multiplying the mean of all item scores in each domain by a factor of 4. The possible scores for total and each domain ranged from 4 to 20. Higher scores indicate higher levels of WHOQOL-BREF. Cronbach's alphas were 0.68–0.82 for the four domains in a previous study (11,830 adults; undertaken in 23 countries).24) Cronbach's alphas were 0.66–0.82 for the four domains in this study.
3) Obesity-specific health-related quality of life (HRQOL)
Obesity-specific HRQOL was measured by the Korean version of the IWQOL-Lite that was obtained under the license agreement with the Duke University.15) The IWQOL-Lite is a self-reported measure consisting of: 31 items and five subscales of weight-related concerns, i.e., physical function (11 items), self-esteem (7 items), sexual life (4 items), public distress (5 items), and work (4 items). Each scale was scored with a 5-point Likert scale. The possible scores ranged from 0 (worst) to 100 (best) after converting the raw scores of the IWQOL-Lite.25) In a previous study,15) Cronbach's alphas were 0.96 and 0.90–0.94 for total and subscale scores, respectively. In the present study, Cronbach's alpha was 0.97 and 0.89–0.97 for total and subscale scores, respectively.
3. Statistical analysis
Data were analyzed using SPSS 23.0 (SPSS Inc., Chicago, IL, USA). A P-value of less than 0.05 was considered significant. To report participants' general characteristics, descriptive statistics were performed with frequencies, percentages, means, SDs and SEs. To examine the differences in general characteristics between overweight and normal-weight groups, either χ2 tests/Fisher's exact test or Student's t-test was performed by categorical versus continuous variables. To examine the differences in the outcome variables (i.e., HPLP II, WHOQOL-BREF, and IWQOL-Lite) between the two groups, the general linear model was performed using two models (i.e., crude and adjusted models). The adjusted models were controlled for married status, which significantly differed by group. Finally, to examine the associations between the HPLP-II and WHOQOL-BREF scores, a multiple regression analysis was conducted with adjusted models; “religion” was selected as covariates with a P-value of <0.1 were based on the results of the crude associations between the HPLP II and WHOQOL-BREF scores. To examine the associations between the HPLP II and IWQOL-Lite scores, the multiple regression analysis was performed with adjusted models; “age”, “job”, and “religion” were selected as covariates with a P-value of <0.1 in the associations.
Results
1. Participants' general characteristics
Participants' mean age was 39.0 years (Table 1). Of the participants, 93.3% were married, 59.7% were college-educated or higher, and 42.0% had a monthly household income of at least 4,000,000 Korean won (approximately USD 3,752).26) The overweight and normal-weight groups had mean BMIs of 29.3 kg/m2 and 21.0 kg/m2, respectively; BMIs differed significantly by group (P<0.001). The overweight and normal-weight group had 87.3% and 100.0% of married women, respectively (χ2=7.62, P=0.006). The overweight group was 3.2% post-menopausal, and had 17.5% with obesity-causing health problems, while the normal-weight group was 100% pre-menopausal and had no obesity-causing health problems.
2. Levels of health-promoting behaviors and HRQOL between groups
Comparisons were conducted in crude models and adjusted models (Table 2). The total HPLP-II scores were lower in the overweight group than normal-weight group, but did not differ significantly by group (Table 2). Among the HPLP II subscales, physical activity, nutrition, and stress management scores significantly differed by group (Ps<0.05), showing significant lower levels in the overweight group.
The total WHOQOL-BREF score was significantly lower in the overweight group than normal-weight group (P<0.001) (Table 2). Except for the environmental domain score, all physical, psychological, and social relationship domain scores remained significantly lower in the overweight group compared to the normal-weight group (Ps<0.001). The total IWQOL score was significantly lower among the overweight group compared to the normal-weight group (P<0.001) (Table 2). All the IWQOL subscales of physical function, public distress, self-esteem, sexual life, and work remained significantly lower in the overweight group than normal-weight group (Ps<0.001).
3. Associations between health-promoting behaviors and HRQOLs in the overweight group
Among the overweight group, lower scores for total HPLP-II had significant associations with lower scores for total WHOQOL-BREF after adjusting for religion (β=2.72, P<0.001), but were not associated with the total IWQOL scores (Table 3). Lower subscale scores for stress management (β=1.58, P=0.003), spiritual growth (β=2.00, P<0.001), and interpersonal relations (β=2.88, P<0.001) revealed significant associations with lower scores for total WHOQOL-BREF. Lower subscale scores for spiritual growth (β=9.65, P=0.011) and interpersonal relations (β=12.38, P=0.013) had significant associations with lower total IWQOL-Lite scores. Lower subscale scores for stress management had significant associations with lower scores for its self-esteem subscale (β=11.58, P=0.034).
Discussion
Among community-dwelling middle-aged women, the overweight group showed not only lower levels of health-promoting behaviors, but also lower levels of both generic and obesity-specific HRQOLs than the normal-weight group. Moreover, the overweight women with low scores of stress management, spiritual growth, and interpersonal relations (i.e., a subscale of health-promoting behaviors) showed significantly low levels of both generic and obesity-specific HRQOL levels.
We found that the overweight and normal-weight women showed no significant variations in total HPLP II scores, but significant variations in some HPLP II subscales including nutrition, physical activity, and stress management. Unlike our findings, Nies and colleagues6) found between-group differences in all HPLP II subscales among 86 American women.6) The discrepancy in HPLP-II subscales between the two studies may be attributable to the different BMI levels of the study participants. Our study participants fell into the overweight category, whereas those of Nies and colleagues6) fell into the severely obese category (i.e., a mean of BMI, 40.3–41.3 kg/m2) according the WHO criteria of obesity and overweight categories.16) This may be based on the postulation that health-promoting behaviors may be more comprehensively impaired with increasing obesity status.
In our findings, the overweight women showed significantly lower total scores for the generic HRQOL (i.e., WHOQOL-BREF) compared to the normal-weight women. Particularly, we found such lower scores in the three domains except for the environmental domain, whereas Dinc and colleagues27) found them in all sub-domains including the environmental domain among 1,602 women recruited from the 11th largest city in Turkey. Such a discrepancy in the environmental domain between studies might be attributed to different sociocultural backgrounds in the research settings. Among the four domains of the WHOQOL-BREF, the environmental domain is characterized by fulfilment with the surrounding neighborhood; the availability of medico-social care; possibilities for the acquisition of new information and skills; and possibilities for transportation.13) In this context, our sample was recruited from the largest metropolitan city in South Korea, Seoul, which is particularly characterized by high accessibility to mass media, the Internet, a convenient transportation system and medical service.282930) Based on this, environmental WHOQOL-BREF may not be related to obesity-related health outcomes in Korean women.
Additionally, we found that the overweight women had significantly lower scores for obesity-specific HRQOL (i.e., IWQOL-Lite) than the normal-weight women, across total and all subscale IWQOL-Lite scores. These findings were consistent with those of Kolotkin and Crosby31) and Caixàs et al.32) Meanwhile, our participants in the overweight group mostly fell into the overweight category (68%), as those in previous two studies were mostly in the obese category. Nevertheless, the obesity-specific IWQOL-Lite has easily captured vulnerability to impaired HRQOL with increasing BMI levels among Korean women. Choo et al.2) reported gender differences in obesity-related HRQOL among a Korean population group; women had significantly low obesity-related HRQOL, but men did not.
We found that the overweight women with low scores for stress management (a HPLP-II subscale) was significantly more likely to have low scores for total WHOQOL-BREF and self-esteem IWQOL-Lite subscale. Such an association has not been reported in previous studies, whereas the association between perceived stress and HRQOL had been previously reported. Wang et al.33) found that obese individuals with high scores of perceived stress were more likely to have low scores of the mental component of HRQOL. As a result, stress management behavior may be impaired with overweight/obesity (as shown with our empirical data), and its impaired levels may explain impaired HRQOL levels among the overweight/obese women. Therefore, enhancing stress management skills for overweight women should be first prioritized for improving impaired HRQOL among overweight middle-aged women.
In addition, our findings showed that higher scores for interpersonal relations and spiritual growth of HPLP-II subscales were significantly associated with higher scores for the WHOQOL-BREF and IWQOL-Lite in the overweight group. Wu et al.34) reported a significant positive correlation between classmate support and total IWQOL-Kids scores among obese adolescents. Additionally, Saffari et al.35) reported that spiritual/religious factors were significantly related to HRQOL in patients undergoing hemodialysis. Similarly, Jafari et al.36) had reported that the levels of spiritual well-being were significantly associated with generic HRQOL among Iranian women with breast cancer undergoing radiation therapy. Therefore, health-promoting behaviors for interpersonal relations and spiritual growth may be essential to improve HRQOL among overweight/obese women.
Our study has some strengths. First, we used two measures of generic and obesity-specific HRQOLs simultaneously to identify any variations in HRQOLs between overweight and normal-weight groups. Second, we firstly revealed a significant finding that health-promoting behavior may be an associate of HRQOL among overweight individuals. However, the study also had some limitations. First, our results may not be representative of Korean women because of our convenience sampling method, and have limited generalizability to other ethnic groups. Second, body weight measures self-reported among the normal-weight group may be underestimated compared to those measured among the overweight women; however, self-reported body weight may have a bias of <3% to estimate obesity prevalence in women aged 30–49 years, compared to measured body weight.37) Based on this, it may be small on the results of between-group differences in study outcome variables. Finally, as a control group, the normal-weight group was separately recruited from the overweight women in a community, with the interval of one and half years. This time-effect may result in a bias. However, there were no events to be considered as influencing factors on sociodemographic and health-related characteristics of the community-dwelling group. Further, there was little difference in the prevalence of overweight/obesity within the interval, showing from 26.6% to 25.0%.38)
Overweight middle-aged women showed lower scores for both generic and obesity-specific HRQOLs and more impaired levels of nutrition, physical activity and stress management behaviors compared to normal-weight women. Community nurses need to provide health counseling and education to improve health-promoting behaviors of nutrition, physical activity and stress management for the overweight/obese women. Moreover, low levels of stress management, interpersonal relations, and spiritual growth were significantly associated with low levels of HRQOL levels among overweight/obese middle-aged women. Based on this, we could take note of the result that overweight women showed low levels of stress management behaviors, which, in sequence, were significantly associated with low HRQOL levels. Therefore, enhancing health-promoting behaviors for stress management skills could be the first strategy for improving impaired HRQOL levels among community-dwelling middle-aged women who are overweight/obese. As the second strategy, improving health-promoting behaviors of interpersonal relations and spiritual growth may help increase HRQOL levels among the middle-aged women. As a result, community nurses should be cultivated for the knowledge and skills for developing and conducting these two behavioral strategies to improve HRQOL for overweight/obese middle-aged women.
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