Introduction

Currently, most of the world’s population has a life expectancy of 60 years or more, which has resulted in an increase in both the number and proportion of older adults (OA). This demographic shift poses significant challenges for health and social care systems in all countries.1 According to the World Health Organization (WHO), by 2050 the global population of people aged 60 and over will experience a twofold increase (1 billion in 2020 vs. 2.1 billion in 2050).1

Although the population aging phenomenon originated in high-income countries, at present middle- and low-income countries, such as countries in Latin America and the Caribbean, are experiencing the most significant changes,1 mainly due to the aforementioned increase in longevity and decline in fertility rates.2 In fact, this demographic trend is expected to continue in the region over the coming decades, with an estimated 80% of older adults living in low- and middle-income countries by 2050.1 It is therefore important to reduce health inequalities; improve the quality of life of this population through strategies such as providing person-centered integrated care and primary health care services that respond to the needs of older adults; and facilitate access to long-term care for older adults who need it.1

In this context, it is essential to understand the factors that directly affect the quality of life and psychological well-being of OAs, especially those related to their physical functioning. Among these factors, muscle mass is particularly important because, due to its fundamental role in locomotion, metabolic function, force production, etc., its decrease is associated with diminished functionality, autonomy, and health, resulting in a reduced quality of life,3 especially in OAs, in whom the annual loss of muscle mass is considerably greater.3,4

Multiple studies have pointed out that this situation is a public health issue because of its link to negative outcomes like decreased physical performance, loss of mobility, osteoarthritis, dementia, and death.5 The loss of muscle mass and strength is considered one of the main contributors to functionality decline in OAs, so much so that a decrease in both is now the primary diagnostic criterion for sarcopenia.6,7

The appendicular muscle mass index (AMMI) is a measure of muscle mass in the upper and lower limbs relative to height and can be calculated using various indirect prediction models (e.g., dual-energy X-ray absorptiometry (DXA), magnetic resonance imaging (MRI), computed tomography (CT), and bioimpedanciometry) and double indirect prediction models (e.g., anthropometry).8 In Chile, where the prevalence of sarcopenia in OAs is 19.1%,9 researchers from the Instituto de Nutrición y Tecnología de los Alimentos (Institute of Nutrition and Food Technology) developed a valid, reliable, and low-cost anthropometric model for predicting ASMM in OAs, obtaining values similar to those calculated using DXA (16.8±4.0 vs. 16.9±3.7), making it a useful tool for detecting this condition in the country.10

Quality of life (QoL) is a broad and multidimensional concept that combines objective and subjective factors. The WHO defines it as “an individual’s perception of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards, and concerns.”11 While this definition hints at the subjective nature of QoL, other definitions acknowledge that other objective factors such as economic, social, and environmental conditions must be considered when evaluating this concept.11

In the context of aging, QoL is related to aspects such as functional status, social inclusion, financial independence, and health policies that affect individual experiences.11 It also integrates individual and macrosocial levels that interact dynamically and are expressed through positive and negative assessments, reflecting the attitude of OAs toward their own aging process.11

The concept of QoL in OAs has been explored mainly regarding biopsychosocial factors, such as psychological well-being, social support, and health. For example, a study that assessed QoL in this population using the World Health Organization Quality of Life (WHOQOL-OLD) instrument reported that people who perceived themselves as ill had lower QoL scores than those who did not, and that self-acceptance, social support, autonomy, and having a purpose in life positively influenced the perception of QoL.12

Psychological well-being (PWB) is defined by Carol Ryff as the fulfillment of personal growth and the achievement of valuable goals that give meaning to life.13 PWB is conceptualized through a eudaimonic perspective and explained by a multidimensional model that includes six domains: self-acceptance, autonomy, environmental mastery, positive relationships with others, a feeling of purpose and meaning in life, and personal growth and development.

The perception of PWB is influenced by sociodemographic factors such as age, sex, marital status, and educational level.13 With aging, the life purpose and personal growth domains may decline due to losses (e.g., of interests and capabilities) and limited contextual opportunities, while autonomy and environmental mastery tend to be more stable.13 It has been reported that men tend to excel in the areas of autonomy, personal growth, and self-acceptance, while women show better well-being in social relationships. Married people score higher in several domains, and a higher level of education is associated with better perceived health, more self-acceptance, purpose in life, and personal growth due to access to more resources for coping with challenges and self-regulation.13

Ryff’s Psychological Well-Being Scales are a useful tool for measuring PBW14,15 that has been adapted and validated in different languages, including Spanish.16

Although the relationship between muscle mass and functionality has been extensively studied, there is little evidence on its association with psychosocial aspects such as QoL and PWB, especially in non-institutionalized OAs in Latin America. This gap warrants local research that integrates physical and subjective dimensions of aging to guide more comprehensive intervention strategies. Therefore, the objective of this study was to evaluate the correlation between ASMM and QoL and PWB in non-institutionalized older adults in Chile.

Materials and methods

Study type

Cross-sectional correlational study.

Study population and sample

The study population consisted of non-institutionalized OAs (≥65 years) registered in the social services department of the Estación Central district of Santiago, Chile. Individuals with evident cognitive impairment were not considered eligible due to their inability to follow instructions. Convenience sampling was used to include OAs who, after agreeing to participate in the study, accepted to have their anthropometric measurements taken and the instruments administered at their homes (n=59).

Procedures and variables

The OAs were contacted by telephone to invite them to participate in the study. After agreeing, a home visit was scheduled to take anthropometric measurements and assess QoL and PWB using the instruments described below. These procedures were performed by three duly trained evaluators after confirming that they did not suffer from any cognitive impairment. The following information was also collected: age, biological sex, marital status, educational level, and living arrangements (with relatives, partner, children, alone, or others). Each assessment lasted approximately 30 to 40 minutes.

Instruments used

In order to estimate the ASMM, the following anthropometric parameters were measured: weight (kg), knee height (cm; measured at the left knee with a height gauge and with the subject seated with the left leg flexed at 90°. The fixed part of the caliper was placed under the heel and the movable part was placed parallel to the fibula on the malleolus and behind the fibula, pressing the two blades to compress the soft tissue), calf circumference (cm), muscle strength (kg; measured using a handgrip strength test), and hip circumference (cm). The ASMM was calculated using the following predictive equation: ASMM (kg) = 0.107(weight kg) + 0.251(knee height cm) + 0.197(calf circumference cm) + 0.047 (dynamometry kg) - 0.034 (hip circumference cm) + 3.417(sex male) - 0.020 (age years) - 7.646 (R2=0.89).10

QoL was assessed using the validated Chilean versions of the abbreviated WHOQOL (WHOQOL-BREF)17 and WHOQOL-OLD,18 which are described below.

The Spanish version of the WHOQOL-BREF questionnaire used has 26 items covering four domains: Physical Health (7 items), Psychological Health (6 items), Social Relationships (3 items), and Environment (8 items). In addition, the first two items refer to the perception of QoL and satisfaction with health status, respectively. Each question is evaluated using a 5-point Likert scale (1-5), which provides a raw score for each item. The average score for each domain is then calculated and these values are converted into a scale between 4-20 (comparable to WHOQOL-100 scores) or between 0-100, thus obtaining scores for the four domains and for two individual items (health status and perception of quality of life), where a higher score indicates a better QoL. The overall score of the instrument is the average of the converted scores. The interpretation of the instrument depends on the scores obtained in each domain and their comparison with reference values, where a high score indicates a better QoL. More information on how to calculate the score on this instrument can be found in the official WHO documents.19

The WHOQOL-OLD is a specific module for OAs that complements the WHOQOL-100 and WHOQOL-BREF versions by including specific aspects related to the aging experience.18 The instrument comprises 24 items rated on a 5-point Likert scale, which are divided into the following six domains: Sensory abilities (4 items); Autonomy (4 items); Past, present, and future activities (4 items); Social participation (4 items); Death and dying (4 items); and Intimacy (4 items). Fang et al.20 validated three abbreviated versions of this instrument, and the present study employs the version translated into Spanish from version 3 of Fang et al.20 and validated in the Chilean population by Urzúa et al.,18 which includes six items from the WHOQOL-OLD (questions 4, 6, 17, 19, 20, and 24), one for each domain. Similar to the WHOQOL-BREF, the score obtained for each question is converted to a 0-100 scale, and the overall score is the average of the converted scores. The interpretation of the instrument depends on the scores obtained in each domain and their comparison with reference values, where a high score indicates a better QoL.

PWB was measured using the version of the Ryff’s Model of Psychological Well-being validated in the Spanish population by Díaz et al.,16 which is a Spanish adaptation of the version proposed by Van Dierendock21 (6-8 items per scale for a total of 39 items). The version developed by Díaz et al.16 comprises 29 items (4-6 per scale) and, with the exception of the “Personal Growth” scale (α=0.68), it has good internal consistency in the remaining scales (α=0.71-0.83). The instrument consists of six scales: Self-acceptance (four items), Positive relationships with others (five items), Autonomy (six items), Environmental mastery (five items), Purpose in life (five items), and Personal growth (four items).16 Each item is answered using a 6-point Likert scale, where 1 means strongly disagree and 6 means strongly agree. The score for each scale is the sum of the scores obtained in the respective items, and the overall score of the instrument (Ryff total) is the sum of the scores obtained in the six scales. The higher the score, the better the PWB.

Both the invitation to participate in the study and data collection took place between October 2019 and March 2020.

Statistical analysis

Data are described using absolute and relative frequencies for qualitative variables and means and standard deviations for quantitative variables depending on the data distribution (Shapiro-Wilk test). The two-sample Wilcoxon rank-sum test was used to compare the means of the variables between different sexes. In addition, Spearman’s correlation coefficient was used to measure the relationships between ASMM (dependent variable) and the scores obtained in our instruments (by domain and overall). Data analysis was performed using the STATA® 15.1 program, and a statistical significance level of p<0.05 was considered.

Ethical considerations

This study followed the ethical principles for biomedical research involving human subjects established in the Declaration of Helsinki.22 It was also approved by the Scientific Ethics Committee of the Servicio de Salud Metropolitano Oriente (Eastern Metropolitan Health Service) of the Chilean Ministry of Health by means of a resolution issued on August 4, 2020.

Results

Most participants were female (77.97%; n=46) and 42.37% (n=25) were married. The most common educational levels were incomplete and complete secondary education (each n=17; 28.81%), while the most common type of living arrangement was with children (n=20; 33.90%) (Table 1).

Table 1. Sociodemographic characteristics of the participants (n=59).

Variable		n (%)
Sex	Male	13 (22.03)
	Female	46 (77.97)
Marital status	Single	7 (11.87)
	Married	25 (42.37)
	Separated	3 (5.09)
	Divorced	1 (1.69)
	Widowed	23 (38.98)
Educational level	Incomplete primary education	6 (10.17)
	Complete primary education	16 (27.12)
	Incomplete secondary education	17 (28.81)
	Complete secondary education	17 (28.81)
	Incomplete university education	3 (5.08)
Living arrangement	Alone	8 (13.56)
	With partner	16 (27.12)
	With children	20 (33.90)
	With relatives	14 (23.73)
	Other	1 (1.69)

The mean values for age, ASMM, weight, knee height, calf circumference, hip circumference, and grip strength were 75.68±7.49 years, 15.27±3.77kg, 69.63±11.42kg, 46.02±5.13cm, 37.36±3.64cm, 108.67±15.74cm, and 19.44±5.51, respectively. Statistically significant differences between males and females were observed in all these variables, except for age (Figure 1, Table 2).

Figure 1. Appendicular skeletal muscle mass by sex.

*p<0.05

Table 2. Anthropometric measurements, grip strength, and age.

Variable	Total (n=59)	Female (n=46)	Male (n=13)	p-value
Weight	69.63±11.42	67.05±10.62	78.31±10.03	0.001
Knee height	46.02±5.13	45.13±5.32	49.15±2.79	0.002
Calf circumference	37.36±3.64	36.42±3.37	40.66±2.50	0.001
Hip circumference	108.67±15.74	106.63±16.14	115.86±12.21	0.003
Grip strength	19.44±5.51	18.00±5.175.17	24.53±3.28	0.000
Age	75.68±7.49	76.26±7.67	73.62±6.62	0.257
Appendicular skeletal muscle mass	15.27±3.77	13.73±2.32	20.74±2.64	0.002

The mean score on the WHOQOL-BREF was 58.80±11.21, and “Psychological health” was the domain with the highest mean score (59.82±10.49). No statistically significant differences were found between males and females in any of the domains or in the overall score (Table 3).

Regarding the WHOQOL-OLD, the mean score was 65.54±12.11, and “Intimacy” was the domain with the highest mean score (69.92±21.16). There were no statistically significant differences between males and females in the overall score, but a statistically significant difference was observed in the score for the “Death and dying” domain (82.69±15.76 vs. 65.76±26.01; p=0.025) (Table 3).

With regard to PWB, the overall mean score was 105.68±20.91 (females: 106.91±22.43 vs. males: 101.31±14.15). The only domain in which a statistically significant difference in scores between males and females was observed was “Positive relationships with others” (13.00±2.27 vs. 15.93±4.41; p=0.016) (Table 3).

Table 3. Perception of quality of life and psychological well-being in non-institutionalized older adults in Chile.

Variable		Total (n=59)	Females (n=46)	Males (n=13)	p-value
WHOQOL-BREF (mean±SD)	Quality of life	56.36±20.55	57.61±22.28	51.92±12.34	0.424
	Satisfaction with health status	55.08±19.02	54.35±19.93	57.69±15.76	0.672
	Physical health	58.84±11.38	58.31±11.88	60.71±9.56	0.672
	Psychological health	59.82±10.49	59.51±10.85	60.90±9.40	0.934
	Social relationships	56.50±16.31	56.70±17.00	55.77±14.18	0.565
	Environment	59.64±14.74	58.70±14.45	62.98±15.88	0.401
	Overall score	58.80±11.21	58.34±11.50	60.43±10.40	0.781
WHOQOL-OLD (mean±SD)	Autonomy	69.49±16.13	68.93±16.38	75.00±14.43	0.162
	Death and dying	69.49±25.03	65.76±26.01	82.69±15.76	0.025
	Social participation	63.46±21.93	60.87±22.14	63.46±21.93	0.801
	Past, present, and future activities	66.10±17.22	65.76±17376	67.31±15376	0.894
	Sensory abilities	56.78±16.63	57.61±18.16	53.85±9.39	0.464
	Intimacy	69.92±21.16	69.02±23.09	73.08±12.34	0.648
	Overall score	65.54±12.11	64.50±12.54	69.23±10.00	0.256
Ryff’s Model of Psychological Well-being (mean±SD)	Self-acceptance	17.51±4.11	17.28±4.25	18.31±3.59	0.455
	Positive relationships with others	15.29±4.21	15.93±4.41	13.00±2.27	0.016
	Autonomy	17.97±4.38	18.43±4.76	16.31±2.02	0.070
	Environmental mastery	17.39±3.77	17.72±4.15	16.23±1.59	0.761
	Personal growth	16.1±3.45	16.07±3.64	16.23±2.80	0.831
	Purpose in life	21.44±5.39	21.50±5.68	21.23±4.40	0.963
	Ryff total	105.68±20.91	106.91±22.43	101.31±14.15	0.493

Concerning the relationship between ASMM and the perception of QoL assessed with the WHOQOL-BREF (Table 4 and Figure 2), the following was found: i) for the entire sample, there was a negative correlation with the overall score (r=-0.07) and with the score for each domain (r=-0.08 to -0.37), being the correlation with the score obtained in the “Quality of life” domain statistically significant (r=-0.37; p=0.040); ii) in females, there was a negative correlation with the overall score (r=-0.32) and with the scores for the 5 domains (r=-0.17 a -0.42); iii) in females, there was a statistically significant correlation with the scores obtained in the domains “Quality of life” (r=-0.42; p=0.00), “Social relationships” (r=0.37; p=0.012), and “Environment” (r=0.44; p=0.020); iv) in males, there was a positive correlation with overall score (r=0.57), which was statistically significant (p=0.037); and v) in males, there was a positive correlation with scores in four domains (r=0.43 to 0.55), being statistically significant in the “Physical health” domain (r=0.55; p=0.040).

With respect to the relationship between ASMM and the perception of QoL assessed with the WHOQOL-OLD (Table 4 and Figure 2), the following was evidenced: i) the correlations with the overall WHOQOL-OLD score and with the scores of the 6 domains were not statistically significant for the sample; ii) in females, the correlation with the overall score was negative but not statistically significant (r=-0.23; p=0.130); iii) in females, the correlation was negative with 5 domains (r=-0.10 to -0.36), being statistically significant in the domain “Social participation” (r=-0.36; p=0.015); iv) in males, a positive and statistically significant correlation was observed with the overall score (r=0.62; p=0.031); and v) in males, the correlation was positive in 5 domains (r= 0.21 to 0.65), being statistically significant in the domains “Sensory abilities” (r=0.63; p=0.022) and “Intimacy” (r=0.65; p=0.017).

Importantly, a negative correlation between ASMM and QoL means that a higher ASMM is associated with a lower perception of QoL, while a positive correlation means the opposite (a lower ASMM is associated with a higher perception of QoL).

As for the relationship between ASMM and PWB (Table 4 and Figure 3), the following was found: i) the correlation with the overall score was negative and statistically significant in both the sample (r=-0.37; p=0.004) and in females (r=-0.46; p=0.001), whereas it was positive (r=0.08) but not significant in males; ii) in the sample, the correlation was negative with the score obtained on the 6 scales (r=-0.20 to -56), being statistically significant in “Positive relationships with others” (r=-0.56, p=0.00), “Autonomy” (r=-0.38, p=0.003), “Environmental mastery” (r=-0.33, p=0.012), and “Personal growth” (r=-0.29, p=0.024); iii) in females, the correlation was negative and statistically significant on all scales (r=-0.32 to -0.51; p<0.005); and iv) in males, the correlation was positive with the overall score (r=0.08) and with the scores of 4 domains (r=0.05 to 0.35), but no correlation (positive or negative) was statistically significant.

Similar to QoL, a negative correlation between ASMM and PWB means that a higher ASMM is associated with a lower perception of PWB, while a positive correlation represents the opposite.

Table 4. Correlation between appendicular skeletal muscle mass, quality of life, and psychological well-being by sex and dimensions.

Variable		Total (n=59)		Females (n=46)		Males (n=13)
		r	p-value	r	p-value	R	p-value
WHOQoL-BREF	Quality of life	-0.37	0.040	-0.42	0.003	-0.44	0.130
	Satisfaction with health status	-0.11	0.403	-0.22	0.150	-0.20	0.510
	Physical health	-0.10	0.474	-0.27	0.072	0.55	0.040
	Psychological health	-0.08	0.554	-0.17	0.250	0.43	0.148
	Social relationships	-0.26	0.050	0.37	0.012	0.48	0.094
	Environment	-0.10	0.436	-0.34	0.020	0.55	0.052
	WHOQOL-BREF total	-0.07	0.611	-0.32	0.280	0.57	0.037
WHOQol-OLD	Autonomy	0.02	0.907	-0.21	0.163	0.22	0.465
	Death and dying	0.16	0.217	0.04	0.8091	-0.16	0.600
	Social participation	-0.19	0.155	-0.36	0.015	0.21	0.500
	Past, present, and future activities	-0.07	0.582	-0.19	0.218	0.46	0.116
	Sensory abilities	-0.23	0.085	-0.28	0.057	0.63	0.022
	Intimacy	0.00	0.491	-0.10	0.523	0.65	0.017
	WHOQOL-OLD total	0.09	0.500	-0.23	0.130	0.62	0.031
Ryff’s Model of Psychological Well-being	Self-acceptance	-0.20	0.127	-0.45	0.002	0.35	0.227
	Positive relationships with others	-0.56	0.000	-0.51	0.000	-0.15	0.516
	Autonomy	-0.38	0.003	-0.32	0.031	-0.19	0.541
	Environmental mastery	-0.33	0.012	-0.47	0.001	0.05	0.741
	Personal growth	-0.29	0.024	-0.49	0.001	0.12	0.5768
	Purpose in life	-0.25	0.062	-0.36	0.014	0.09	0.726
	Ryff total	-0.37	0.004	-0.46	0.001	0.08	0.714

r: Spearman’s correlation coefficient.

Figure 2. Correlation between appendicular skeletal muscle mass and overall quality of life by sex.

ASMM: appendicular skeletal muscle mass; PWB: psychological well-being.

Figure 3. Correlation between appendicular skeletal muscle mass and overall psychological well-being by sex.

ASMM: appendicular skeletal muscle mass; PWB: psychological well-being.

Discussion

This study evaluated the correlation between ASMM and QoL and PWB in non-institutionalized OAs in Chile.

One of the noteworthy findings is the predominance of females in the sample (n=46; 77.97%), which is consistent with national and international population data.23,24 In Chile, for example, the estimated female-to-male ratio in 2020 was 134.4 women for every 100 men in the population aged 60 and over.23

Regarding QoL perception, the mean scores on the WHOQOL-BREF and WHOQOL-OLD instruments were 58.80±11.21 and 65.54±12.11, respectively. Furthermore, although no statistically significant differences were observed between sexes in overall scores or in most domains, there was a significant difference in the “Death and dying” domain of the WHOQOL-OLD (p=0.025), with higher scores in males (82.69±15.76 vs. 65.76±26.01).

The scores obtained in this study differ from those reported by other studies. For example, in Peru, Hernandez-Huayta et al.,25 in a study conducted on 447 older adults (207 from rural areas and 240 from urban areas), lower scores were reported in all domains on both instruments, for both urban and rural populations (57.42 and 52.65 on the WHOQOL-BREF and 61.3 and 59.3 on the WHOQOL-OLD). In contrast, in Germany, Hussenoeder et al.,26 in a study of 805 individuals over the age of 60, reported higher mean values on both instruments (69.65 on the WHOQOL-BREF and 68.41 on the WHOQOL-OLD). It should be noted that, although the WHOQOL-BREF version used by Hussenoeder et al.26 also has 26 items, unlike the instrument used in our study, QoL is assessed in 5 domains and not 4: physical health, psychology, social relationships, environment, and overall quality of life. The heterogeneity in QoL levels observed across studies could be explained by social and economic differences between countries, as Germany is a high-income country and, although Chile and Peru are considered middle-income countries, the former has better social and economic indicators.27

With regard to differences between sexes, our results are in line with the findings reported by Santos et al.,28 who, in a study conducted in Brazil with 100 OAs, also found no significant differences between males and females in the WHOQOL-BREF and WHOQOL-OLD scores (11.21 vs. 11.32 and 11.63 vs. 11.63, respectively). In turn, Pacheco et al.,29 evaluated QoL in 450 OAs from Mexico (n=238) and Ecuador (n=212) using the WHOQOL-OLD, finding no statistically significant differences between sexes (3.79 vs. 3.90).

Concerning PWB, the overall score on the Ryff’s Psychological Well-Being Scales was 105.68±20.91, being slightly higher in females (106.91±20.91 vs. 101.31±14.15; p=0.493). A statistically significant difference between females and males was only observed in the domain “Positive relationships with others” (15.93±4.41 vs. 13.00±2.27; p=0.016). These results differ from what was reported by Palma-Candia et al.30 in a study that evaluated PWB using the Ryff scale adapted by Van Dierendonck21 in 101 OAs (aged 60-88) in Magallanes (Chile), in which the overall score was slightly higher in males (194.33±19. 09 vs. 193.24±20.79; p=0.86), with no statistically significant differences between sexes in any domain.

It is worth noting that, since Palma-Candia et al.30 use a longer version of the scale (39 items), it is expected to have a higher overall score (193.70±19.96); however, when converting this figure to a 29-item scale, such as the one used in our study, the score is still much higher (144.50). Furthermore, the finding regarding higher scores in females also differs from the findings reported by Vivaldi&Barra31 and Slavinski32 in studies conducted in OAs (≥60 years) in Chile and Israel, respectively, which reported higher overall scores on the Ryff scale in males.

In the present study, ASMM was not significantly correlated with overall scores on the WHOQOL-BREF or WHOQOL-OLD instruments, but it was correlated with the “Quality of Life” domain of the WHOQOL-BREF (r=-0.37; p=0.040). The analysis stratified by sex revealed the following: in females, ASMM was significantly correlated (p<0.00) with scores in the domains “Quality of life” (r=-0,42), “Social relationships” (r=0.37) and “Environment” (r=-0.34) from the WHOQOL-BREF and “Social participation” (r=-0.36) from the WHOQOL-OLD, but the correlation with the overall scores on both instruments was not significant. In males, correlations were significant with overall scores on both instruments (r=0.57 and r=0.62) and with the domains “Physical health” (r=0.55) from the WHOQOL-BREF and “Sensory abilities” (r=0.63) and “Intimacy” (r=0.65) from the WHOQOL-OLD.

Even though no studies evaluating the correlation between ASMM and QoL with these instruments were found in our literature review, studies on the impact of muscle mass on QoL in OAs do exist. For example, Trombetti et al.,33 in a study conducted on 48 OAs (26 with mobility limitations and 22 without limitations) in the United States, reported that muscle mass loss contributes independently to the deterioration of QoL as measured using the Short Form-36 questionnaire (p=0.024), while Sayer et al.,34 in a study of 2 987 non-institutionalized OAs (aged 59-73) in the United Kingdom, stated that lower grip strength is associated with poor health-related QoL (assessed using the Short Form-36), as the probability of reporting poor general health, compared to excellent health, was significantly higher in individuals with lower grip strength (odds ratio [OR] for each kilogram reduction in grip strength = 1.13, 95%CI: 1.06-1.19; p<0.001 in males, and OR for each kilogram reduction in grip strength=1.13, 95%CI: 1.07-1.20; p<0.001 in females). However, in a study conducted on 83 OAs (29 pre-frail and 54 frail) in Austria by Haider et al.,35 ASMM was not significantly associated with overall QoL (overall score on the WHOQOL-BREF; p=0.352) or with any of the domains assessed in the WHOQOL-BREF and WHOQOL-OLD.

Furthermore, ASMM had a negative and statistically significant correlation with the overall PWB score (r=-0.37; p=0.00) and the score obtained on the domains “Positive relationships with others” (r=-0.56; p=0.000), “Autonomy” (r=-0.38; p=0.003), “Environmental mastery” (r=-0.33; p=0.012), and “Personal growth” (r=-0.29; p=0.024); likewise, it showed a statistically significant correlation with all domains in females (r=−0.32 to −0.45; p< 0.05). Similar to the association between ASMM and QoL, we found no studies evaluating the correlation between ASMM and PWB measured with the Ryff’s Psychological Well-being Scales.

However, some studies have addressed the association between muscle loss and mental health deterioration. For example, Wang et al.,36 in a study of 865 non-institutionalized Chinese OAs, reported that sarcopenia was significantly associated with the presence of depressive symptoms (OR=2.23. 95%CI: 1.06-4.92), while Gariballa & Alessa,37 in a study of 432 critically ill OAs in England, found that low muscle strength was significantly associated with a greater presence of depressive symptoms during acute illness and recovery (p=0.087). Nevertheless a Korean study of 7 364 adults (2 124 ≥60 years) participating in a national health and nutrition survey found no association between sarcopenia and depression or depressive symptoms in any age group.35

The strong negative association between ASMM and PWB observed in females suggests that psychosocial and cultural factors such as body perception and social roles may be modulating this relationship. In males, the lack of significant correlations could be caused by sample limitations or differences in the subjective perception of well-being.

This study has several strengths, including its multidimensional approach, the use of internationally validated instruments, and the stratified analysis of QoL and PWB by sex, which allowed us to identify key differences between males and females. Still, it has several limitations.

First, its cross-sectional design prevents us from establishing causal relationships and limits our ability to infer temporal directionality between the variables analyzed. Second, although convenience sampling was appropriate given the logistical conditions of the study, it reduces the representativeness of the sample and may introduce selection biases. Third, the small sample size restricts the generalizability of the findings. An additional significant limitation is the high sex disproportion of the sample, with a female predominance; however, this can be explained both by the higher proportion of females aged 60 years or older in Chile21 and by a probable reduced disposition of males to participate in studies of this nature.27,28,32

Despite the fact that our findings partially agree with the findings of studies conducted in developed countries such as the United Kingdom, the United States, and Austria, it is worth noting that differences in sociocultural contexts, healthcare systems, and living conditions may influence perceptions of QoL and well-being, since factors such as access to services, support networks, and functional expectations at older ages vary considerably between countries, thus limiting the direct comparison of results. In this regard, further studies are needed to address the relationship between ASMM, QoL, and PWB in OAs of the region to better understand this phenomenon in Latin America.

Finally, although some of the correlations found were statistically significant (p<0.05), their magnitude was low (r≈±0.3), indicating a weak association. Therefore, the results should be interpreted with caution, bearing in mind that statistical significance does not necessarily imply clinical relevance. This remark is key to avoiding overinterpretation of the findings and highlights the need for studies with larger samples and multivariate analyses to assess the robustness and true relevance of the identified associations.

Conclusions

ASMM was not correlated with WHOQOL-OLD or any of its domains in non-institutionalized OAs in Santiago. In the case of WHOQOL-BREF, only a statistically significant correlation was observed with the “Quality of life” domain, which was negative. As for PWB, negative and significant correlations were found with the overall score and in four domains of the Ryff’s Psychological Well-Being Scales.

When analyzing the data by sex, significant differences were observed: in females, ASMM was negatively correlated with the “Quality of life” and ‘Environment’ domains of the WHOQOL-BREF and “Social participation” of the WHOQOL-OLD and positively correlated with the “Social relationships” domain of the WHOQOL-BREF, but the correlations with the overall scores were not significant. In males, the correlation was statistically significant and positive with the overall score on both instruments and with the domains “Physical Health” on the WHOQOL-BREF and “Sensory abilities” and “Intimacy” on the WHOQOL-OLD. In the case of the PWB, none of the correlations (Ryff total and individual scales) were statistically significant in males, while all correlations in females were negative and statistically significant.

Finally, it should be noted that these results are preliminary and do not provide sufficient basis for proposing specific intervention strategies, as the limitations of the study, including a small sample size, sex imbalance, and lack of adjustment for confounding variables, restrict the possibility of drawing applied conclusions. However, the patterns observed can serve as a guide for future research that explores sex differences in OAs in Chile and other countries of the region in terms of functionality and subjective well-being in greater depth and with more methodological rigor.

Conflicts of interest

None stated by the authors.

Funding

None stated by the authors.

Acknowledgments

None stated by the authors.

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