In 2021, the proportion of older adults aged ≥ 65 years in most major Organization for Economic Cooperation and Development countries exceeded 7%, marking the transition into an aged society [1]. The consequences of population aging, such as an increase in the incidence of functional impairment due to various chronic diseases, an increase in medical expenditure, and intergenerational conflict, have prompted a global effort to devise strategies to address the challenges of an aging society. Notably, the onset of sarcopenia, a well-known health issue among older adults, commences as early as the age of 50 years [2], with an estimated annual muscle loss rate of 1%–2% [3], [4]. Sarcopenia causes various problems in older adults, including decreased mobility [5], limitations in the activities of daily living [6], and a decline in the overall quality of life [7]. As a result, the World Health Organization (WHO) assigned a disease classification code for sarcopenia in early 2017, acknowledging sarcopenia as an officially recognized disease.

Sarcopenia was initially described in the late 20th century as an age-related degenerative decrease in muscle mass [8]. It causes decreased overall physical function and activities, ultimately leading to a loss of autonomy and an inability to maintain an independent lifestyle, which in turn significantly impacts quality of life [9]. According to Yuan and Larsson (2023), sarcopenia affects an estimated 10%–16% of older adults worldwide[10], with a prevalence of approximately 5%–13% among those aged 60–79 years and increasing up to 50% among those aged ≥ 80 years [11]. Numerous previous studies have highlighted the association between sarcopenia and low bone mineral density (BMD) [12], [13]. Moreover, the risk of fracture and falls is more than twice as high in older adults with sarcopenia than in women without sarcopenia [13], [14]. Therefore, sarcopenia poses a potentially life-threatening risk by elevating the susceptibility to falls and fractures and jeopardizing musculoskeletal health [9], [15], [16]. Recent studies have focused on the combined use of exercise and supplement intake as a method for delaying and improving sarcopenia [17], [18]. Protein supplements are an excellent dietary source for addressing protein deficiencies due to their high proportion of essential amino acids. They have been reported to contribute to increased muscle mass in older adults [19], [20]. Given the synergistic effect of vitamin D and leucine in enhancing protein anabolism, the combination of protein and vitamin D supplements can be beneficial in enhancing physical functions and increasing muscle mass [18], [21]. Accordingly, various previous studies reported that combining exercise with protein and vitamin D supplementation enhanced gait function, muscle mass, and lower extremity strength in older adults [18], [22].

Studies that have been published to date have emphasized the need for combining exercise and vitamin D and protein supplementation for enhancing the musculoskeletal system and physical fitness in older adults. However, a meta-analysis approach that encompasses all three components is lacking. In light of this gap, this study conducted a meta-analysis of previous studies related to changes and improvements in body composition and physical fitness after interventions combining exercise and supplement intake. This study aimed to verify the reliability and validity of the results reported in those studies and contribute to suggesting directions for enhancing the musculoskeletal system and physical fitness in older adults.