1. Introduction

Asthma is one of the most common non-communicable chronic diseases, affecting over 260 million people worldwide as of 2019, and is responsible for more than 450,000 deaths annually [1]. In South Korea, the prevalence of asthma increased from approximately 1.6% in 2002 to 2.2% in 2015, with the mortality rate rising from 16.2 to 28 per 100,000 population [2]. Furthermore, recent studies have indicated a gradual increase in asthma prevalence among young adults in their 20s [3].

Asthma imposes substantial economic and social burdens because of medication costs, hospitalization, and productivity loss. For instance, in the United States, the economic burden of asthma increased from USD 56 billion in 2007 [4] to approximately USD 82 billion in 2013 [5]. In South Korea, the estimated health care cost of asthma is approximately USD 646 million [6]. Thus, asthma represents a significant public health issue not only for individuals, but also for society as a whole [7,8].

People with asthma may experience reduced physical activity owing to limitations in daily living and physical functioning, which can lead to muscle weakness and overall physical decline [9]. Prior studies have suggested that patients with chronic respiratory symptoms often find it difficult to engage in muscle-strengthening activities, which further limits their mobility and exacerbates muscle loss [10,11]. Consequently, patients with asthma may be at an increased risk of sarcopenia because of long-term inactivity [12]. Additionally, the long-term use of low-dose inhaled corticosteroids, a core element of asthma management according to the Global Initiative for Asthma (GINA) guidelines [13], has been reported to promote muscle protein breakdown and suppress synthesis, leading to muscle atrophy and reduced exercise capacity [14,15]. These effects may be particularly pronounced in patients with severe asthma undergoing prolonged treatment [16].

Asthma symptoms such as dyspnea, coughing, and chest tightness can limit participation in everyday activities, potentially resulting in impairments across occupational, academic, and recreational domains [17]. Accordingly, asthma has been associated with reduced quality of life (QOL). Inadequately controlled asthma or severe symptoms may also contribute to psychological distress, including anxiety and depression, further lowering QOL [18–22].

Previous research has shown that individuals with low handgrip strength are more likely to experience limited physical activity, difficulty with daily functioning, and psychological distress, all of which are associated with poorer QOL [23–26]. Therefore, improving muscle strength, as reflected by handgrip strength, may represent a potential intervention strategy for enhancing QOL in patients with asthma.

However, few studies have examined the epidemiological association between handgrip strength and QOL, specifically among individuals with asthma. Therefore, this study aimed to investigate the association between handgrip strength and health-related QOL (EuroQol 5-Dimension [EQ-5D]) in Korean adults with asthma and assess whether handgrip strength could serve as a potential target for interventions aimed at improving QOL in this population.

2. Materials and methods

3. Results

Among the 42,853 participants in the 2014–2019 KNHANES, 1,260 individuals reported a physician diagnosis of asthma. After excluding those under 19 years of age, those with a history of cancer (n = 43), and individuals with missing values in key variables (n = 73), a total of 867 participants were included in the final analysis (Fig 1).

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Fig 1. Flow diagram of participant selection from the KNHANES.

https://doi.org/10.1371/journal.pone.0338197.g001

Table 1 summarizes the demographic characteristics of the participants by sex and asthma medication-use pattern. Of the 867 participants, 341 (39.3%) were men and 526 (60.7%) were women. A total of 678 (78.2%) patients reported as-needed medication use, and 189 (21.8%) reported daily medication use. Based on the handgrip strength criteria, 729 (84.1%) participants were classified in the high-handgrip group and 138 (15.9%) in the low-handgrip group. A higher proportion of men (86.8%) belonged to the high-handgrip-strength group compared with women (82.3%; p = 0.072). Additionally, the proportion of participants with high handgrip strength was greater among those with as-needed medication (86.4%) than among those with daily medication (75.7%) (p < 0.001). A total of 474 (54.7%) participants were classified into the high QOL group, and 160 (18.4%) into the low QOL group. Among men, 64.5% were in the high group and 13.2% in the low group; among women, 48.3% were in the high group and 21.9% in the low group. In participants with as-needed medication, 58.4% were classified in the high group and 16.1% in the low group, whereas in those with daily medication, 41.3% were in the high group and 27.0% in the low group.

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Table 1. Demographic and clinical characteristics of study participants by sex and asthma medication-use pattern.

https://doi.org/10.1371/journal.pone.0338197.t001

Table 2 shows the association between handgrip strength and EQ-5D. After adjusting for covariates, participants in the high-handgrip-strength group had higher odds of belonging to the high-QOL group than those in the low-handgrip-strength group (adjusted OR = 2.25; 95% CI: 1.22–4.16). The odds of being in the middle-QOL group were also higher (adjusted OR = 1.68; 95% CI: 0.92–3.04), although the result was not statistically significant.

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Table 2. Multinomial logistic regression of categorical handgrip strength and EQ-5D.

https://doi.org/10.1371/journal.pone.0338197.t002

Table 3 presents the results of the stratified analysis by sex. Among men, high handgrip strength was associated with increased odds of being in the middle-QOL group (OR = 1.59; 95% CI: 0.48–5.28) and the high-QOL group (OR = 1.75; 95% CI: 0.56–5.49); however, these associations were not statistically significant. In contrast, among women, those in the high-handgrip-strength group had significantly higher odds of being in the high-QOL group (OR = 2.89; 95% CI: 1.32–6.29). The odds for the middle-QOL group were also elevated (OR = 1.93; 95% CI: 0.96–3.86), though they were not statistically significant.

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Table 3. Multinomial logistic regression of categorical handgrip strength and EQ-5D by sex.

https://doi.org/10.1371/journal.pone.0338197.t003

Table 4 shows the results stratified by asthma medication-use pattern. Among the as-needed medication group, those with high handgrip strength had significantly higher odds of being in the high-QOL group (OR = 2.36; 95% CI: 1.12–4.99) and moderately higher odds for the middle-QOL group (OR = 1.92; 95% CI: 0.92–3.98), though the latter did not reach statistical significance. Among the daily medication group, the associations between handgrip strength and QOL were not statistically significant (OR = 1.83; 95% CI: 0.58–5.79).

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Table 4. Multinomial logistic regression of categorical handgrip strength and EQ-5D by asthma medication-use pattern.

https://doi.org/10.1371/journal.pone.0338197.t004

Table 5 presents the associations between continuous handgrip strength and EQ-5D. A significant positive association was observed among women, whereas no significant association was found in other subgroups. Comparison between restricted cubic spline and linear models yielded ΔAIC < 2, indicating no evidence of nonlinearity. The direction and pattern of the associations were consistent with those observed in the categorical analyses, showing a higher QOL with greater handgrip strength. However, the effect sizes were smaller in the continuous models, as they represent the change per unit increase rather than contrasts between high and low categories.

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Table 5. Multinomial logistic regression of continuous handgrip strength (per kg and per SD) and EQ-5D.

https://doi.org/10.1371/journal.pone.0338197.t005

4. Discussion

This study investigated the association between handgrip strength and health-related quality of life (EQ-5D) in Korean adults with asthma. Individuals with higher handgrip strength were significantly more likely to report better quality of life, particularly women and those using as-needed asthma medication. These findings suggest that maintaining or improving muscular strength may play an important role in enhancing the quality of life among patients with asthma.

When handgrip strength was analyzed as a continuous variable, the direction of the association with EQ-5D was consistent with that observed in the categorical analyses, showing a higher QOL with increasing grip strength. Although the magnitude of the association was smaller and statistical significance was observed only among women, the overall pattern remained linear and positive.

Handgrip strength was used in this study as a proxy for sarcopenia. Previous studies have established strong correlations between handgrip strength and muscle mass and function, making it a reliable marker of physical capability [40–42]. Prior studies have shown that reduced handgrip strength is associated with lower QOL in specific populations, such as older adults [43] and patients with arthritis [24], chronic obstructive pulmonary disease (COPD) [44], and osteoporosis [45]. However, to the best of our knowledge, no previous study has examined this relationship in patients with asthma. Our findings expand on the literature by showing that lower handgrip strength is also associated with lower QOL in adults with asthma. While earlier studies have reported associations between low handgrip strength and increased mortality in respiratory diseases [46] and severe airflow limitation [47], our findings demonstrated a novel association between handgrip strength and QOL in this population.

Stratified analyses revealed that the association between handgrip strength and QOL was significant only in women. This may be because of sex-specific differences in muscle mass and the prevalence of sarcopenia. Research has shown that sarcopenia is more prevalent in women than in men as age increases [48], possibly because of hormonal factors. Testosterone levels in men rise sharply after puberty, leading to greater muscle mass and strength than in women of the same age and training level [49,50]. Men also tend to have a larger cross-sectional area of muscle and slower rates of muscle loss with age [32]. In contrast, postmenopausal women experience a decline in estrogen levels, which contributes to reduced muscle mass and joint pain in nearly 77% of women [33]. Studies have also reported that women with low handgrip strength are significantly more likely to experience mobility issues (OR = 2.12) and limitations in daily activities (OR = 2.04) [34].

Moreover, women may experience greater psychological benefits from physical improvement than men. Increased muscle strength in women has been linked to reduced stress and improved emotional stability [35,36], and women are generally more prone to depression and anxiety, which may further influence their QOL [37].

Interestingly, the association between handgrip strength and QOL was significant only in participants with as-needed medication use. This finding is consistent with those of previous studies on patients with respiratory disease, where those with milder disease severity showed stronger associations between physical function and QOL [38]. One possible explanation is that patients with severe chronic diseases, such as advanced COPD, may experience limited QOL improvements despite treatment, as disease progression often outweighs the benefits of physical improvement [39]. Although the exact mechanisms remain unclear, these findings suggest that physical interventions may be more effective in improving the QOL of patients with less severe asthma.

Several biological mechanisms may underlie the reduced muscle strength observed in adults with asthma–chronic systemic inflammation (IL-6, TNF-α) [51,52], intermittent hypoxia with ventilatory limitation during exacerbations [53], physical deconditioning driven by fear of dyspnea [53], and steroid-induced myopathy with prolonged corticosteroid exposure [54,55]. These processes can reduce skeletal-muscle function and exercise capacity, leading to mobility limitations, greater fatigue, and lower performance of daily activities, which are reflected in EQ-5D domains; this pathway provides biological plausibility for the observed association between lower handgrip strength and lower quality of life in asthma.

Overall, this study has several important public health and clinical implications. First, asthma is associated with substantial reductions in QOL owing to both physical and psychological burdens. Previous studies have shown that QOL decreases as asthma severity increases [56,57], and even with adequate treatment, many patients with asthma report lower QOL than patients without asthma [58] . Therefore, improving the QOL of patients with asthma remains a crucial goal. Our findings indicate that interventions to improve muscle strength, particularly handgrip strength, may be a promising strategy to support better health outcomes, especially for women and individuals with mild asthma. Rehabilitation programs or physical activity interventions designed to enhance muscular strength can be integrated into routine asthma care.

To our knowledge, this is one of the few studies to explore the relationship between handgrip strength and QOL in patients with asthma using nationally representative data. Stratified analysis by sex and asthma severity provided additional insights into the subgroups that may benefit most from strength-based interventions. These findings may support the development of tailored strategies to manage asthma and enhance patient-centered outcomes.

However, this study has some limitations. First, its cross-sectional design precluded the determination of a causal relationship between handgrip strength and QOL. Second, although multiple covariates were adjusted for, the potential for residual confounding variables remains because some were unmeasured. Third, because the study population was limited to Korean adults, the generalizability of the findings to other ethnic or cultural groups may be limited. Future longitudinal and interventional studies are needed to confirm whether improving handgrip strength leads to improvements in QOL and to expand on these findings to broader populations. Fourth, EQ-5D was analyzed as a categorical variable (low, intermediate, and high) rather than as a continuous score. Although this approach was chosen to address the marked right-skew and ceiling effect commonly observed in EQ-5D data, it may have resulted in a loss of statistical power and information compared with treating EQ-5D as a continuous variable. Finally, the distinction between as-needed medication and daily medication was based on the self-reported frequency of use. While practical, this measure does not fully reflect the GINA-defined multidimensional severity and may involve misclassification due to differences in adherence.

5. Conclusion

This study demonstrated a significant association between handgrip strength and QOL (EQ-5D) in Korean adults with asthma. Individuals with higher handgrip strength were more likely to report a better QOL, particularly women and those with mild asthma severity. These findings highlight the potential value of incorporating muscle-strengthening interventions into asthma management strategies to improve patient well-being. Strengthening programs targeting specific subgroups, such as women and those with less severe disease, may be especially effective. Future longitudinal and intervention-based research is needed to further explore causal relationships and assess the impact of muscular strength improvements on QOL in diverse asthma populations.