The relationship between ratio of serum triglyceride to high-density lipoprotein cholesterol and frequency of sarcopenia in Chinese community adults

Background In a previous study, the high ratio of serum triglyceride to high-density lipoprotein cholesterol (TG/HDL-C) was relevant to a high risk of sarcopenia in Korean old males. In this study, the purpose was to discover the association in Chinese community adults. MethodsChinese adults who had physical examinations from May 2016 to August 2017 at the First Aliated Hospital of Wenzhou Medical University were involved in this study. The univariable and multivariable logistic regression analyses were applied to evaluate possible effect. ResultsIn total, 2613 adults were involved in the study, with 13.85% presenting sarcopenia. The separate results for TG and HDL-C displayed that OR for TG was 0.67(95%CI: 0.51-0.87), and OR for HDL-C was 1.97(95%CI: 1.49-2.61). Additionally, the ratio of TG/HDL-C was independently associated with sarcopenia status(OR: 0.63; 95%CI: 0.49-0.81).ConclusionsIt was indicative that TG was negatively associated with the frequency of sarcopenia in Chinese community population, but HDL-C was positively associated with it. Besides, the negative association was discovered between sarcopenia and TG/HDL-C ratio.


Introduction
The reduction of muscle mass and function relevant to age, referred to "sarcopenia," has drawn public attention all over the world (1)(2)(3)(4)(5). The Asian Working Group for Sarcopenia (AWGS) put forward a concept of sarcopenia in 2014. It referred to reduction of muscle mass and function, or low physical capability relevant to age (5). In 2019, AWGS regarded either reduced muscle strength or reduced physical capability as "possible sarcopenia". Sarcopenia is incrementally general in the society, with a prevalence rate of 5.5%-25.7% (6)(7)(8). Sarcopenia has become a public health issue gradually.
Serum lipid pro le is commonly tested in a clinical setting, including fasting serum triglyceride (TG) and cholesterol. A meta-analysis by Jaekyung No et al. on sarcopenia and blood lipid pro les was recently published, which con rmed that TG had a positive relation with sarcopenia, whereas high-density lipoprotein cholesterol (HDL-C) had a negative effect (16). Tae-Ha et al. demonstrated that the higher ratio of TG/HDL-C was relevant to an increased rate of sarcopenia in elderly Korean men (17). Given this nding, the purpose of this research was to discover a potential association between serum lipid pro le and sarcopenia in Chinese community adults.

Study population
This cross-sectional study involved in individuals having routine health examinations from May 2016 to August 2017 at the First A liated Hospital of Wenzhou Medical University. Subjects with age≥18, having serum lipid pro le and bioelectrical impedance analysis (BIA) measures were involved in our study.
Exclusion criteria included individuals with aged<18 years; taking lipid-lowering medicine; with a history of stroke, malignant tumor, chronic kidney or liver disease, or thyroid disease.
The research was agreed by the Institutional Review Board (IRB) of the hospital. Given its cross-sectional nature, the consent was waived by the IRB and the medical privacy was protected. All data were reviewed complying with the Declaration of Helsinki.

Data collection
Data regarding the health examinations were collected, including questionnaires concerning to lifestyles and pre-existing conditions, and results of BIA, blood, biochemical and anthropometric measurements.
Living habits contained smoking and drinking. Alcohol drinking higher than 70 g per week for women and higher than 140 g per week for men were regarded as heavy drinking. The 3 kinds of smoking status were de ned as follows: current smoker (currently smokes and has smoked for at least the past 6 months or who abandoned smoking <2 years ago), past smoker (smoked in the past and had quitted smoking for at least 2 years) and never (never smoked).
Pre-existing conditions included diabetes mellitus (DM), hypertension (HTN), and hyperuricemia. DM was referred to random plasma glucose(PG), fasting plasma glucose (FPG) or 2-h PG equal or greater than 200 mg/dL, 126 mg/dL, or 200 mg/dL, respectively (18). Every individual took a blood pressure measure at the morning of medical examination, containing systolic blood pressure (SBP) and diastolic blood pressure (DBP). HTN was referred to SBP ≥140 mmHg or DBP ≥90 mmHg (19). Hyperuricemia was referred to serum uric acid (UA) levels higher than 6 mg/dL in females and higher than 7.0 mg/dL in males (20). Additionally, past morbidities included medical histories of DM, HTN or hyperuricemia or taking corresponding medications from self-reports.
To monitor appendicular skeletal muscle mass (ASM; kg), every subject carried out BIA detection (InBody770; InBody Japan Inc., Tokyo, Japan). Then, skeletal muscle mass index (SMI; kg/m 2 ) was computed through following formula: ASM(kg)/height 2 (m 2 ). Additionally, according to the AWGS 2019 Consensus(1), males with SMI lower than 7.0kg/m 2 and females with SMI lower than 5.7kg/m 2 were diagnosed as sarcopenia. Subjects with Body mass index (BMI) higher than 25 kg/m 2 were regarded as with status of overweight.

Statistical analysis
Continuous and categorical factors were displayed as medians (ranges) and frequencies (percentages), respectively. Through receiver operating characteristic (ROC) curves, the diagnostic accuracies of lipid pro le for sarcopenia were assessed. The optimal indicator was selected, based on area under curve (AUC) and Youden index. The subjects were grouped according to the selected indicator(high and low group). The differences of the continuous factors were compared with the Mann-Whitney test, while the differences of the categorical factors was compared with the χ2 test. Through univariate and multivariate logistic regression models, the effects of the factors on the risk of sarcopenia were evaluated. Backward stepwise selection with the Akaike information criterion(AIC) was performed to identify variables for the multivariable logistic regression models. Interaction term in the multivariable logistic regression analysis was also conducted to get rid of confound factor. In addition, individuals were strati ed by quartiles, χ 2 test was utilized to compare the different rate of sarcopenia. R version 3.6.1 was utilized to perform statistical analyses (https://www.r-project.org/). All analyses were 2-sided, and a P value <0.05 was regarded as signi cance level.

Population features
In total, 2613 subjects were involved in the research. The medians of ASM and SMI were 20.14 (8.9-32.98) and 7.27 (4.35-11.50 Table 1. The high group showed higher ASM (p<0.01), SMI (p<0.01) and BMI (p<0.01), and a greater proportion of elderly (p<0.01) and male (p<0.01) subjects, compared to the low group.
When the TG/HDL-C ratio was a continuous predictor in multivariable logistic regression analysis (Table   3), it continued to exert an independent effect on sarcopenia (OR: 0.75, 95%CI: 0.63-0.89), with C-index of 0.75.

Discussion
The negative association between sarcopenia and the TG/HDL ratio was discover in this study. In a research by Tae-Ha et al., the ratio of TG/HDL-C was positively relevant to the rate of sarcopenia in Korean old males, along with insulin resistance. However, this study was limited to older age and sexbased differences in general (17). A larger number of subjects were involved in our study, including men and women, with a median age of 48 years. Genetic and lifestyle factors among different populations contribute to interindividual variations in serum cholesterol and triglyceride levels. Previous studies have veri ed some special loci in different populations. For instance, there were novel loci near MYL2 and HECTD2 associated with HDL-C in Korean individuals (21). The missense variants at PNPLA3 and PKD1L3 were discovered to be correlated to TG and LDL-C in the Chinese population (22). Although the different distribution of genetic polymorphism between Chinese and Korean have not been illustrated yet, the difference of lipid pro le between Chinese and Korean adolescents have been demonstrated. Korean adolescents had higher levels of TC, LDL-C, TC/HDL-C, and LDL-C/HDL-C, compared to Korean-Chinese adolescents (18). Additionally, lifestyle factors, such as alcohol abuse, dietary habits, and physical activity, may have effect on lipid pro les (23).
The lipid pro le, a widely used test, is a group of easy and economic parameters. Among lipid pro le, it was found that medium-chain TG could be a feasible nutrient for sarcopenia, as medium-chain TG could enhance muscle strength through motivating ghrelin (24). Besides, it was proposed by Stella et al. that muscle loss could be attenuated by plasma TG, which was generated from omega 3 fatty acids. (25).
HDL-C was discovered to be negatively relevant to muscle function improvement (26)(27)(28). According to these ndings, a negative association between the ratio of TG/HDL-C and risk of sarcopenia should be took into account. Thus, appropriate supplementation of fatty foods could be good for building muscle function; however, further researches are needed to determine the degree of supplementation that is required.

Study strengths and limitations
This was a large cross-sectional study investigating in 2613 Chinese individuals, and provided new and opposite results compared to the Korean study (17). Our results indicate that the relationship may be relevant to different nationalities and territories.
However, there were some limitations. First, since its cross-sectional nature, causality could not be determined, and there is a possibility of reverse causality bias. Additionally, the study was not registered in a database of clinical studies. Second, due to the lack of data, the new de nition was not taken into consideration, which proposed that the diagnosis of sarcopenia included 2 elements: low muscle mass and function (1). Third, many of the individuals involved in this study with age younger than 65 years and without any severe diseases. Thus, our results may not apply to older and critically ill patients. Finally, the cutoff was determined by the ROC curve, with restrictive sensitivity and speci city.

Conclusion
In general, a low ratio of TG/HDL-C was a potential risk marker for sarcopenia regardless of whether it is a continuous variable or a categorical variable. In clinical practice, to lessen the impact and frequency of sarcopenia, the supplementation of TG and control of HDL could be put into effect, especially in Chinese patients.
Prospective studies with more comprehensive data and a larger sample size are requisite to validate the relationship in the future.

Declarations
Ethics approval and consent to participate The study was approved by the IRB of the First A liated Hospital of Wenzhou Medical University. Given its cross-sectional nature, the consent was waived by the IRB and the medical privacy was protected.

Consent for publication
Not applicable.

Availability of data and materials
The datasets used and analyzed during the current study will be provided by the corresponding author upon reasonable request.

Competing interests
The authors declare that they have no competing interests.

Funding
This study was supported by grants from the Wenzhou Municipal Sci-Tech Bureau's program(No.Y20170063).

Authors' contributions
Na Wang, Mengjun Chen, and Danhong Fang contributed to the conception and design of the work. Na Wang and Mengjun Chen contributed to the acquisition, analysis, or interpretation of data. Na Wang drafted the manuscript. Danhong Fang critically revised the manuscript. All authors gave nal approval and are accountable for all aspects of the work and its integrity and accuracy.