IJGG Journal

Introduction

The age-related decline of strength and muscle mass, also known as sarcopenia, is a major contributor to weakness, disability, and diminished standard of life in senior individuals [1-2]. It is considered that the number of people suffering from sarcopenia and related healthcare costs will increase as the global population ages, making it an important issue for the public. Since sarcopenia has been linked to an increased risk of falls, fractures and mortality, it is crucial to develop effective interventions to prevent or manage this condition [2]. Nutritional interventions play a significant role in maintaining and improving muscle health in older adults [3]. Previous research has highlighted the importance of adequate protein intake in the elderly to preserve muscle mass and function [4-5]. Inadequate protein intake may exacerbate the age-related decline in muscle mass, leading to the development or worsening of sarcopenia [6]. Moreover, higher protein intake has been associated with reduced frailty and improved physical performance in older individuals [7-8]. However, the optimal amount, type and distribution of protein intake for preventing and managing sarcopenia remain topics of ongoing debate among researchers and healthcare professionals.

Besides protein, other nutrients, such as essential amino acids, vitamins and minerals, have also been suggested to play a role in maintaining muscle health and combating sarcopenia. Leucine, an essential amino acid, has been shown to stimulate muscle protein synthesis and improve muscle function in older adults [912]. Furthermore, omega-3 fatty acids, vitamin D, magnesium and antioxidants have all been investigated for their potential benefits in preventing and managing sarcopenia [16-28]. However, the evidence regarding the effectiveness of these nutrients in mitigating sarcopenia remains inconsistent, necessitating further research to understand better their roles and potential synergistic effects in combination with resistance training. In addition to nutrient supplementation, resistance training has been established as an effective intervention for improving muscle mass and strength in older adults [29]. The combination of nutritional interventions and resistance training is believed to have additive or synergistic effects on muscle health, potentially leading to better outcomes in the prevention and management of sarcopenia. Nevertheless, research on the optimal combination of nutritional interventions and exercise for older adults with sarcopenia is still limited.

In this review, the aim is to provide a summary of the current evidence regarding nutritional interventions for preventing and managing sarcopenia in older adults. We will discuss the role of protein intake, including the optimal amount, type and distribution, as well as the potential benefits of other nutrients, such as essential amino acids, omega-3 fatty acids, vitamin D, magnesium and antioxidants. Additionally, we will examine the interaction between nutritional interventions and resistance training and the potential additive or synergistic effects on muscle health in this population. By synthesizing the available evidence, this review seeks to guide healthcare professionals and researchers in the development of effective strategies to combat sarcopenia in the aging population.

Methods

Search Strategy

A comprehensive literature search was conducted using electronic databases, including PubMed, Scopus, Cochrane Library and Web of Science, to identify relevant articles published up to March 2023. The search strategy incorporated both Medical Subject Headings (MeSH) terms along with associated keywords. sarcopenia, older adults, nutritional interventions, and resistance training. The search terms included “sarcopenia,” “muscle mass,” “muscle strength,” “muscle function,” “older adults,” “elderly,” “geriatrics,” “nutrition,” “dietary intervention,” “protein,” “amino acids,” “omega-3 fatty acids,” “vitamin D,” “antioxidants,” “resistance training,” “exercise” and “physical activity.” The search was restricted to English-language articles only

Study Selection

12 independent reviewers screened the titles and abstracts of the retrieved articles to determine their eligibility for inclusion in this review. The eligibility of the complete texts of possibly pertinent articles was then determined using the following criteria for inclusion: (i) randomized controlled trials (RCTs) or observational studies; (ii) conducted in older adults (≥ 60 years of age); (iii) investigating the effects of nutritional interventions (protein, essential amino acids, omega-3 fatty acids, vitamin D, magnesium or antioxidants) on muscle mass, strength or function; and (iv) reporting muscle-related outcomes. Studies were excluded if they were: (i) conducted in younger populations (< 60 years of age); (ii) not focused on nutritional interventions or resistance training; (iii) not reporting muscle-related outcomes; or (iv) review articles, editorials or case reports. Any discrepancies between the reviewers during the study selection process were resolved by discussion and consensus or by consulting all reviewers, if necessary.

Data Extraction

The admissibility of the full texts of potentially relevant articles was subsequently assessed using the inclusion criteria listed below, which included the following information: study design, population characteristics (age, sex, health status), sample size, type and duration of nutritional intervention, resistance training protocol, muscle-related outcomes (muscle mass, strength, function), and main findings. One reviewer was responsible for data extraction, while a second reviewer verified its accuracy.

Quality Assessment

Risk of bias was evaluated in seven domains that include random sequence generation, allocation concealment, blinding of subjects and personnel, outcome assessment blinding , insufficient outcome data, selective reporting, along with other potential sources of bias. The standard of observational investigations was evaluated by Newcastle-Ottawa Scale (NOS), which evaluates the quality of non-randomized studies based on three domains: selection, comparability, and outcome. Each study was assigned a quality rating (low, moderate, or high) based on the overall risk of bias or the total score on the NOS.

Data Synthesis

Based on the effects of dietary modifications and resistance exercise on strength, mass and function of muscle in elderly people with sarcopenia, a narrative assessment of the data was conducted. Due to the heterogeneity of the included studies in terms of study design, population characteristics, nutritional interventions and outcome measures, a meta-analysis was deemed inappropriate. Instead, the findings from individual studies were summarized and the consistency of the evidence was discussed.

Protein Intake

A sufficient amount of protein is necessary for older individuals to maintain their muscle mass and function. [4]. The Recommended Dietary Allowance (RDA) for protein is 0.8g/ kg/day; however, some experts suggest higher protein intakes of 1.0-1.2g/kg/day for older adults to preserve muscle mass [5]. Recent studies have demonstrated that increased protein intake is associated with improved muscle strength and function [6], reduced risk of frailty [7] and decreased incidence of sarcopenia [8]. Additionally, the distribution of protein intake throughout the day, rather than consuming the majority in one meal, has been shown to optimize muscle protein synthesis in older adults [9-10].

Protein Quality and Sources

Protein quality and sources also play a significant role in promoting muscle health in older adults. High-quality proteins, such as animal-based proteins (e.g., dairy, meat, poultry and fish), provide a complete amino acid profile and have higher digestibility, possibly contributing to more remarkable muscle protein synthesis [30-32]. Although less digestible and lower in some essential amino acids, plant-based proteins can still contribute to muscle health when consumed with other protein sources [33, 34]. A recent systematic review by van Vliet et al. [35] reported that both animal and plant-based proteins could be effective in supporting muscle health in older adults when consumed in adequate amounts.

Protein Timing and Distribution

In addition to the total protein intake, the timing and distribution of protein consumption have been shown to impact muscle protein synthesis in older adults. Consuming protein evenly across meals (i.e., breakfast, lunch and dinner) has been demonstrated to enhance muscle protein synthesis compared to a skewed protein distribution [36]. Additionally, a study by Mamerow et al. [37] found that consuming 30g of protein per meal resulted in a greater stimulation of muscle protein synthesis compared to consuming 10g or 90g of protein per meal. This suggests that a balanced protein distribution throughout the day may optimize muscle protein synthesis and support muscle health in older adults.

Essential Amino Acids

Essential amino acids (EAAs), particularly leucine, are crucial in stimulating muscle protein synthesis [11]. Leucineenriched supplements have been shown to enhance muscle protein synthesis and reduce muscle protein breakdown in older adults [12-13]. A meta-analysis by Xu et al. [14] found that EAA supplementation significantly increased muscle mass and strength in older adults with sarcopenia. Moreover, EAA supplementation has been shown to improve functional outcomes in older adults, such as walking speed and chair rise performance [15-16].

Leucine Threshold

The concept of the leucine threshold has been proposed to explain the age-related decline in muscle protein synthesis response to dietary protein intake. Older adults may require higher leucine concentrations to stimulate muscle protein synthesis than younger individuals [38]. Studies have shown that consuming approximately 2.5-3.0g of leucine per meal may help older adults overcome the leucine threshold and optimize muscle protein synthesis [39-40]. This can be accomplished by consuming protein sources rich in leucine or by taking leucine-rich supplements.

Vitamin D

Vitamin D deficiency is prevalent in older adults and is associated with reduced muscle strength and an increased risk of sarcopenia [17]. It has been established that supplementation with vitamin D enhances muscle function and stamina in elderly individuals with a deficient vitamin D status [18].A meta-analysis [19] reported that vitamin D supplementation significantly increased muscle strength, particularly in those with baseline 25-hydroxyvitamin D levels below 30 nmol/L. Moreover, vitamin D supplementation has been associated with reduced fall risk in older adults, particularly when combined with calcium supplementation [20].

Vitamin D and Calcium Interaction

The interaction between vitamin D and calcium is crucial for maintaining bone health and may also play a role in muscle function. Vitamin D enhances intestinal calcium absorption, whereas calcium is essential for efficient muscle function. [41].

A systematic review by Muir and Montero-Odasso [42] found that combined vitamin D and calcium supplementation was more effective in improving muscle strength and reducing falls risk in older adults than vitamin D supplementation alone.

Omega-3 Fatty Acids

Omega-3 fatty acids, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have been shown to modulate muscle protein metabolism and improve muscle mass and function in older adults [21-22]. Smith et al. [23] reported that omega-3 supplementation increased muscle protein synthesis in healthy older adults. Furthermore, a recent meta-analysis [24]. found that omega-3 supplementation significantly improved muscle strength and function in older adults, particularly when combined with resistance training [25]. In addition, omega-3 fatty acids in particular have demonstrated anti-inflammatory properties, which may help mitigate the chronic low-grade inflammation associated with sarcopenia [26].

Omega-3 Fatty Acids and Resistance Training

The combination of omega-3 fatty acid supplementation and resistance training has been shown to provide synergistic benefits in improving muscle health in older adults. A study by Da Boit et al. [43] found that omega-3 supplementation enhanced the gains in muscle strength and function following a 12-week resistance training program in older women. This suggests combining omega-3 supplementation and resistance training may be a promising strategy for preventing and managing sarcopenia in older adults.

Antioxidants

Oxidative stress contributes to the development and progression of sarcopenia by promoting muscle protein breakdown and impairing muscle function [27]. Antioxidants such as vitamins C as well as E, carotenoids and polyphenols have been suggested as possible therapies to reduce the effects of oxidative stress and enhance the health of muscles in older people [28]. Some studies have reported positive effects of antioxidant supplementation on muscle strength and function [29-30]; however, the evidence is inconsistent, with other studies showing no significant benefits [31, 32]. To elucidate the function of antioxidants in the prevention and management of sarcopenia, more research is required.

Antioxidant-rich Foods

In addition to antioxidant supplements, the consumption of antioxidant-rich foods, such as fruits, vegetables, whole grains, nuts and seeds, may also prevent and manage sarcopenia. Carotenoids, polyphenols and the vitamins C and E, among the other bioactive substances in these foods, have demonstrated antioxidant and antiinflammatory properties [44]. A study by Cesari et al. [45] found that higher adherence to a Mediterranean-style diet, characterized by high consumption of antioxidant-rich foods, was associated with better muscle strength and physical performance in older adults.

Potential Limitations of Antioxidant Supplementation

While antioxidants may play a role in mitigating oxidative stress and preserving muscle health, excessive antioxidant supplementation may have potential drawbacks. Some studies have reported that high-dose antioxidant supplementation may interfere with the adaptive response to exercise training, potentially impairing the improvements in muscle strength and endurance [46-48]. Therefore, it is essential to consider the potential risks and benefits of antioxidant supplementation in the context of sarcopenia prevention and management.

Conclusion

In conclusion, this review highlights the importance of nutritional interventions in preventing and managing sarcopenia in older adults. Adequate protein intake, essential amino acids, vitamin D and omega-3 fatty acids have improved muscle mass, strength and functional performance in older adults. Antioxidants also show potential benefits, but the evidence is inconsistent and requires further investigation. It is crucial for healthcare professionals to consider the role of nutrition in maintaining muscle health and preventing sarcopenia in older adults, particularly in combination with other interventions such as resistance training and physical activity.

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