Association between social support and health-related quality of life among Chinese seafarers: A cross-sectional study

Background Seafarers have reported impaired health and health-related quality of life (HRQOL). Social support might increase HRQOL, but little is known about this association among Chinese seafarers. The aim of this study was to describe social support and explore its association with HRQOL among Chinese seafarers. Methods A cross-sectional survey was conducted in the ports of Nantong and Rugao, China, from April to December 2013. A total of 917 Chinese seafarers were interviewed on social support, mental distress, perceived occupational stress, and HRQOL using the following self-administered questionnaires: The Social Support Rating Scale, Self-rating Depression Scale, Occupational Stress Questionnaire, and the World Health Organization Quality of Life-BREF (WHOQOL-BREF) questionnaire. Hierarchical linear regression modelling was used to analyze the association between seafarers’ subjective level of social support and their HRQOL. Results Of the 917 male Chinese seafarers included in the study, 40.7% perceived high levels of social support, and 39.1% were highly satisfied with their overall quality of life (QOL). Hierarchical regression analysis showed significant associations between level of social support and all health dimensions in the WHOQOL-BREF, even after adjusting for depressive symptoms, occupational stress, occupational activities, sleep duration, and other relevant covariates. Compared with the medium or low level social support group, seafarers with a high level of social support had better QOL scores in the general facet health and QOL (β = 2.43, p<0.05), and the physical health (β = 3.23, p<0.001), psychological health (β = 5.56, p<0.001), social relation (β = 6.07, p<0.001), and environment domains (β = 4.27, p<0.001). In addition, depression, occupational stress, occupational activities, and sleep duration were found to be determinants of seafarers’ HRQOL. Conclusions Chinese seafarers have poorer HRQOL than the general population, but social support has a significant positive effect on their HRQOL. Efforts to improve social support should be undertaken.

Introduction and social support [19][20][21]. Social support is defined in terms of social network characteristics -such as assistance from family, friends, neighbors, and other community members-that help individuals to cope with everyday life, particularly in response to critical situations [22][23]. Social support could be an important contributor to improve health and HRQOL among elderly people and individuals with chronic diseases [24][25][26][27]. Positive emotional and informational support that may normally be provided is important in maintaining HRQOL [28]. Perceived support seems to be most important [29], especially when stress is experienced [30]. Seafaring workers are usually exposed to mental, psychosocial, and physical stressors that are related to the different duties onboard ships [31]. Little is known about whether social support among seafarers could help them cope with their harsh living conditions and adapt to their environment and lifestyle, as little attention has been focused on the association between social support and QOL of people employed at sea. The aim of this study was to identify current subjective QOL of seafarers and to highlight the relationship between social support and QOL domain scores. Additionally, we assessed the contribution of depressive symptoms, occupational stress, occupational activities, and sleep duration on various dimensions of subjective QOL.

Study population
This cross-sectional study was conducted in the ports of Rugao and Nantong, China, from April to December 2013. The study protocol was approved by the Affiliated Hospital of Nantong University's Committee on Human Experimentation. All participants provided written informed consent.
A cluster sampling strategy was employed to select participants from the Nantong Entry-Exit Inspection and Quarantine Bureau (NTCIQ). Before the health quarantine inspection, captains of the ships were trained to administer the questionnaire and crew members were invited to complete the questionnaire. Since 98% of investigated seafarers were male and the shipboard working situation probably differs by gender, only male seafarers were included. Of the 929 seafarers who consented to participate in the study, 12 questionnaires were voided because participants did not complete more than 20% of the items of the WHO Quality of Life-BREF (WHOQOL-BREF) questionnaire, as recommended by the WHOQOL Group [32]. Thus, 917 (98.7%) valid questionnaires were evaluated.

The World Health Organization Quality of Life-BREF
Subjective QOL was the dependent variable, assessed by means of the Chinese version of the WHOQOL-BREF questionnaire [33], a 26-item self-administered generic questionnaire that is a short version of the WHOQOL-100 scale (S1 Questionnaire). Responses range from 1 (very dissatisfied/very poor) to 5 (very satisfied/very good). This instrument emphasizes the subjective response of individuals rather than objective life conditions, with assessment made over the preceding two weeks. It comprises domains and subdomains (facets). The items on ''overall rating of QOL" and "subjective satisfaction with health", are not included in the domains, but are used to constitute the facet on QOL and general health (general facet). The more popular model for interpreting the scores of WHOQOL-BREF has four domains, namely, physical health (seven items), psychological health (six items), social relations (three items), and environment (eight items). Our analysis was based on this model. The domain scores of the WHO-QOL-BREF can be computed according to WHO guidelines [32]. The mean score of items within each domain is used to calculate the domain score. Mean scores are then multiplied by 4 in order to make domain scores comparable with the scores used in the WHOQOL-100, and are subsequently transformed to a scale from 0-100. In order to understand the status of the seafarers' subjective satisfaction, we employed the definition of subjects' satisfaction as the level of positive appreciation for each item of the WHOQOL-BREF. Previous studies [34][35][36] graded the levels of satisfaction for each item according to the percentage of respondents who positively appreciated the item, as follows: dissatisfaction (<50%), bare satisfaction (50-65%), moderate satisfaction (66-74%), and highest satisfaction (!75%). The WHOQOL-BREF has adequate internal consistency and reliability, and the α-coefficient was 0.92 in this study.

Social support scale
The Social Support Self-Rating Scale (SSRS) (S1 Rating Scale) developed by Xiao is one of most commonly used instruments for measuring social support in China [37]. It consists of 10 items measuring three dimensions: subjective support (four items), objective support (three items), and support-seeking behavior (three items). The SSRS scale can be used in two ways. First, raw scores within each of the three domains are summed, giving a subjective (range: 8-32) and objective (range: 1-22) support score, and a support-seeking behavior score (range: [3][4][5][6][7][8][9][10][11][12]. Second, item scores are simply added up, generating a total support score ranging from 12-66. This total support score is classified into three categories: low ( 22), moderate , and high (!45) levels of support. Our analysis was based on the second model. The internal consistency of the SSRS scale in this study was acceptable (α-coefficient = 0.76).

Occupational characteristics
Occupation-related factors included sailing duration, working area, position, class, occupational physical activity (OPA), and work-related psychosocial stress. OPA was calculated as the time spent engaging in physical activity at work per week divided into three groups: light, moderate, and vigorous OPA. OPA levels were classified as energy expenditure per week, expressed in metabolic equivalent tasks (MET)-minutes per week (MET-minÁwk -1 ) [39]. MET scores of 1.5, 4.0, and 8.0 MET-hourÁwk -1 were classified as light, moderate, and vigorous activity, respectively, and an index was calculated by summarizing the MET-hourÁwk -1 for each physical activity's intensity level [40].
Work-related psychosocial stress has been shown to decrease seafarers' psychological wellbeing [13,21], it may also impact their HRQOL. A self-administered scale was designed, to measure work-related psychosocial stress, based on research and interviews with experts (S2 Questionnaire) [11,31,41]. It comprised 6 items describing psychosocial stress, including concern/anxiety about weather conditions, ship safety, occupational strain, port state control, sea piracy, and family members. Respondents rated each item with regard to how frequently they experienced such concerns during the preceding week using a 3-point Likert scale from 1 (low anxiety) to 3 (severe anxiety). These scores were summed to generate a total score, designated as the "psychosocial stress" variable. The scale has good reliability with an α-coefficient of 0.84. Each item had an α-coefficient ranging from 0.80 to 0.83.

Socio-demographic characteristics
Demographic characteristics included age, marital status, educational level, residence, body mass index (BMI), self-rated health (SRH), sleep duration, and leisure time physical activity (LPA). LPA was calculated as the time spent engaging in leisure activities (such as walking, table tennis, or tai chi) per week on board.
The Chinese version of the whole questionnaire were showed in "S3 Questionnaire". The whole dataset were showed in S1 Data.dta.

Statistical analysis
Analysis was conducted using Stata Statistical Software, Release 12 (College Station, TX: Stata-Corp LP). Data are presented as mean ± standard deviation (SD) for continuous variables and as the number (percent) for categorical variables. First, we assessed the level of satisfaction with the items, using the operational definitions described earlier. Second, the differences between variables for social support were analyzed using independent sample t-tests for continuous variables, χ 2 tests for categorical variables, and Wilcoxon-Mann-Whitney rank sum test for rank variables. Thirdly, hierarchical regression models were employed to explore the association between different levels of social support and HRQOL.
The ordinary least squares (OLS) regression model was constructed as follows: where Y is the measure of the general facet on QOL and health, and the physical health, psychological health, social relation, and environment domain for individuals; X s (social support) is the key independent variable, as the subscales of social support were highly correlated with one another, so the different levels of social support divided by the SSRS total score were used to avoid problems of multicollinearity; X 2 is a vector of other independent variables including depression, occupational characteristics, sleep duration, and LPA; X 3 is set of dummy covariate variables including marital status, educational level, residence, BMI, and SRH with the exception of age and sailing duration; OPA, LPA, sleep duration, and sailing duration had righttailed distributions, so the natural log of these four variables were used in the regression model; and ε is an unobserved error term. The coefficient β 1 is our focused parameter. All statistical tests were two-tailed, and p<0.05 was regarded as being statistically significant.

Participant characteristics
In 917 male participants (Table 1), the total SSRS mean score was 42.2 (SD 7.0), with 0.5%, 58.8%, and 40.7% of participants categorized as having low, moderate, and high levels of social support, respectively. The mean age of participants was 33.5 years; 55.1% had junior college education or above; 67.8% were from rural areas; the mean sailing duration was 91.6 months; 42.7% worked in the deck department; and 57.3% were ordinary crew, with no differences between the high support group and low or moderate support group. The groups differed in terms of SRH, LPA, psychosocial stress, depression, and HRQOL scores. Participants in the high support group had better SRH and HRQOL, were engaged in more LPA, had lower psychosocial stress, and a lower incidence of depressive symptoms. Regarding depressive symptoms, 51.0% of participants scored in the normal range, with 23.2%, 24.1%, and 1.6% scoring in the mild, moderate, and severe depression range. In the study, respondents felt moderately or severely nervous about: their financial situation (55.4%), ship safety (64.3%), occupational strain (52.7%), port state control (51.5%), sea piracy (59.5%), and family members (66.5%).

Satisfaction with circumstances of life
Using the criteria previously defined, seafarers were generally not satisfied with their life circumstances; only 39.1% participants were satisfied with their overall QOL (Table 2). Less than 50% of participants identified 15 items (of the total 26 items) with which they felt satisfaction.

Social support and health-related QOL
The OLS regression analysis revealed a significant association between social support and HRQOL (Tables 3 and 4). In Model 1, high-level social support was significantly associated with all domains of the WHOQOL-BREF, as well as the general facet QOL and health. Social support explained 8.6-13.1% of the total variance among the four domains and 5.4% of the total variance in the general facet QOL and health. However, social support explained a larger share of the total variance in the psychological health (R 2 = 13.1%) than the other domains (physical health, R 2 = 9.4%; social relations, R 2 = 9.6%; and environment domain, R 2 = 8.6%). After including the other independent variables and adjusted for covariates (Model 5), the association between social support and HRQOL persisted (p<0.05

Depression and health-related QOL
Depressive symptoms were significantly associated with impaired HRQOL (p<0.01). Compared with participants with no depressive symptoms, those with depressive symptoms had

Psychosocial stress and HRQOL
Psychosocial stress was a significant independent determinant of HRQOL (p<0.05), even after adjusting for other control variables (Tables 3 and 4). For each 1-unit increase in psychosocial stress score, the score of general facet of QOL and health decreased by 0.46 units (p<0.05). Similar results were found in four domains: decreased by 0.71 units for the score of   1.07, p<0.05). In addition, seafarers who reported good or very good health also showed higher scores of HRQOL in all domains (p<0.01), as well as in the general facet QOL and health (p<0.001). Seafarers who were married were more likely than those who were single, separated, divorced, or bereaved to report better QOL in all domains (p<0.05) except the social relation domain (data not shown). The independent variables in Model 1 and Model 5 were the same as that in Table 3. The control variables were age at interview, education, marital status, self-rated health, and body mass index.

Discussion
To the best of our knowledge, this is the first study to explore the association between social support and HRQOL among seafarers. The main findings show that social support is significantly associated with HRQOL. We also demonstrated that as a group, seafarers were not satisfied with their life circumstances, especially in terms of availability of money for their needs, leisure-time physical activity, medical treatment, and availability of information to meet daily needs. Seafarers were shown to have worse QOL than the general population in all four domains of the WHOQOL-BREF. Their mean scores in the physical health, psychological health, social relations, and environment domains were 67.8, 64.3, 63.8, and 52.5, respectively. In a study among 37,740 Chinese male adults, the respondents reported mean scores in the four domains of 75.0, 67.5, 66.4, and 57.1, respectively [42]. In addition, Chinese seafarers reported poorer QOL in the four domains than Polish seafarers [43]. Among items in the four domains, satisfaction with items in the environment domain was poorer than that in other domains (7/8 items were unsatisfying). Only 16.9% of seafarers were satisfied that the money they earned was enough to meet their needs; their wages were considered inconsistent with their occupation. As the wage gap between seafaring and onshore work decreases, some seafarers (mainly those who registered low level of support) have reported low self-esteem and experience of mental health imbalance [43], which can contribute to distress. Additionally, <25% of participants were satisfied with these two items: leisure-time activities and information acquisition. This may result in increased loneliness and may affect mental health.
In the present study, 49% of the respondents had self-rated depressive symptoms; this rate was much higher than that among the general Chinese population (21.8%) [44], but it was consistent with that in a previous study of seafarers [45]. A large number of qualitative studies have reported that seafarers have poorer mental health with possible associated health damage [46,47]; the present study provided quantitative evidence for this. We found depressive symptoms had a significantly negative effect on seafarers' HRQOL (p<0.01) after controlling for confounders. In fact, many reports have demonstrated that depressive symptoms are negatively related to a subject's health and HRQOL in patients and the children [48][49][50]. Anxiety and depressive mood disorders may impact on seafarers' mental health; hence, effective prevention programs should be strengthened to improve their psychological wellbeing.
Previous studies showed that seafarers are exposed unique psychosocial stressors, such as diverse climate and long term separation from family, which are related to their ill-health [10,51]. In this study, we found that seafarers were most worried about family members (66.5%), ship safety (64.2%), and sea piracy (59.5%). A comprehensive literature search indicated that, from 2002-2012, 3,806 ships were attacked and 7,635 incidents involving human victims occurred; this threatens maritime security and health [52]. Ziello et al. assessed psychological consequences of kidnapping in a group of Italian seafarers held in captivity: all the victims showed high scores of anxiety and social adjustment disorder, and, even more seriously, somatic disorders, depression, and post-traumatic stress disorder [53,54]. Our study robustly confirmed that psychosocial stress at work has an adverse effect on seafarers' HRQOL. Marriage satisfaction and anxiety levels among seafarers also mediate their work-related stresses and sense of purpose in life [55]. Therefore, more attention should be paid to preventive occupational measures in coping with strain on order to improve the QOL of seafarers.
Social support is an important factor affecting QOL, as has been reported in previous studies. Strine et al. found that inadequate social support was associated with adverse health behaviors, impaired HRQOL, and dissatisfaction with life [56]. Our research confirmed that increased social support was associated with a higher QOL in all domains. According to a social support theory raised by Cobb [57]; Cohen and Willis [58], social support can protect people in crisis from a wide variety of pathological states. The specific character of maritime work has many factors conducive to stress, overload, fatigue, and emotional tension, all of which can negatively influence subjective QOL. Social support could provide a positive effect to improve their health. This study has verified the direct effect of social support among seafarers. However, social support is also a mediator to alleviate the damage caused by stress and depression. Previous research has empirically demonstrated that social support serves as a buffer against the adverse effects of stressors and increases QOL in patients [59,60]. Maritime work-related stress and depressive symptoms are very common, so the buffering effect of social support should be the subject of further studies.
The strengths of this study include a large sample size in seafaring workers, and a comprehensive data collected to detect association of QOL with social support and its four domains, and extensive information on confounders. However, the major limitation is its cross-sectional design. Therefore, the causal interpretation of associations should be made with caution. In addition, owing to the subjective assessment made by Chinese seafarers in this research, the usual limitations inherent to self-report research are explicit, such as memory bias, reporting bias, common method variance, and social desirability bias. Furthermore, comparatively fewer objective indicators were applied in the presented study and the analysis was based strictly on the subjective indicators of QOL, both the aim of our research and one of the reasons for criticism thereof.

Conclusions
The study contributes new knowledge about social support and QOL among seafarers. One finding was that Chinese seafarers experienced low QOL and that social support can effectively improve their QOL. Attention should be paid to the status quo of Chinese seafarers. First, base facility construction should be undertaken by shipping companies. Such facilities should include a workers' exercise center, electronic network equipment, and better medical services, as these would improve the occupational environment of seafarers. Second, emphasis should be placed on the mental health of the crew, providing professional counseling to resolve seafarers' psychological difficulties. In addition, cultural entertainment activities, interpersonal contact training, or psychological quality training could significantly improve seafarers' subjective levels of support. The crew themselves, should adjust their mentality, find joy and fulfillment in their careers, and broaden their social interaction, in order to improve subjective levels of support and support utilization. Last, the study findings are an indication to health planners that there is need to focus on proper measures aimed at improving the QOL and occupational conditions of seafarers.