Sarcopenia is a progressive condition common in older adults and is characterized by loss of muscle strength, muscle mass, and physical performance. It is associated with an increased risk of falls, disability, reduced independence, and poorer quality of life. Nutritional interventions are recommended as part of sarcopenia management; however, evidence regarding the role of specific micronutrients remains limited. Magnesium is an essential mineral involved in muscle contraction, neuromuscular function, energy production, and inflammation regulation. Low magnesium status is frequent in older adults and may contribute to muscle impairment and physical decline.

This study aims to evaluate the effects of magnesium supplementation on muscle strength, muscle mass, and physical performance in older adults with sarcopenia living in the eastern Algarve region of Portugal. In addition, the study will assess the prevalence of low magnesium status and sarcopenia in this population.

The study will be conducted in two phases. In the first, observational phase, community-dwelling adults aged 70 years or older will be assessed for sarcopenia according to established diagnostic criteria. Blood samples will be collected to measure serum and erythrocyte magnesium levels and C-reactive protein as an inflammatory marker. Participants diagnosed with sarcopenia and presenting low magnesium levels will be eligible for the second phase.

In the second phase, eligible participants will be randomly assigned to receive either oral magnesium supplementation (400 mg/day of magnesium citrate) or a placebo for 12 weeks, in a double-blind and controlled design. After the intervention period, participants will be reassessed for muscle strength, muscle mass, physical performance, magnesium status, and inflammation.

The results of this study are expected to clarify the role of magnesium supplementation as a nutritional strategy in sarcopenia. Findings may contribute to improving nutritional recommendations and supporting interventions aimed at preserving muscle health, physical function, and quality of life in older adults.

Inclusion Criteria:

• Adults aged 70 years or older
• Community-dwelling individuals residing in the eastern Algarve region of Portugal
• Not hospitalized at the time of recruitment
• Ability to participate in study assessments, regardless of mobility status
• Ability to provide written informed consent, either personally or via a legally authorized representative when applicable
• Adequate cognitive ability to collaborate with study procedures, as determined by screening assessment

Exclusion Criteria:

• Alcoholism
• Acute gastrointestinal conditions with symptoms of diarrhea and/or vomiting
• Presence of conditions associated with magnesium imbalance, including: Electrolyte disorders, Hyperthyroidism, Type 1 diabetes mellitus, Renal disease, Hyperaldosteronism, Short bowel syndrome or history of intestinal resection, Gastric bypass surgery
• Use of medications known to affect magnesium metabolism, including: Loop or thiazide diuretics (e.g., furosemide, thiazides), Proton pump inhibitors (e.g., omeprazole, pantoprazole, esomeprazole), Cytotoxic agents (e.g., cisplatin, carboplatin, gallium nitrate), Antimicrobial agents such as aminoglycosides, Immunosuppressive agents, Beta-adrenergic agonists (e.g., theophylline, salbutamol, rimiterol), Cetuximab, Cyclosporine A, Pamidronate.

Individual participant data will not be shared due to ethical and data protection constraints. The study involves an older population considered potentially vulnerable, and informed consent for participation did not include consent for data sharing beyond the research team. In addition, the risk of re-identification cannot be fully excluded given the detailed clinical and contextual data collected. Data will be used exclusively for the purposes defined in the approved protocol and in accordance with applicable data protection regulations.