Citation: Al Wadee, Z.; Ooi, S.L.; Pak, S.C. Serum Magnesium Levels in Patients with Obstructive Sleep Apnoea: A Systematic Review and Meta-Analysis. Biomedicines 2022, 10, 2273. https://doi.org/10.3390/ biomedicines10092273 Academic Editor: Shaker A. Mousa Received: 5 August 2022 Accepted: 9 September 2022 Published: 14 September 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). biomedicines Systematic Review Serum Magnesium Levels in Patients with Obstructive Sleep Apnoea: A Systematic Review and Meta-Analysis Zahraa Al Wadee 1,2,† , Soo Liang Ooi 1,† and Sok Cheon Pak 1,* 1 School of Dentistry and Medical Sciences, Charles Sturt University, Bathurst, NSW 2795, Australia 2 Smiles Unlimited Dental Clinic, Fairfield, Sydney, NSW 2165, Australia * Correspondence: spak@csu.edu.au; Tel.: +61-2-6338-4952; Fax: +61-2-6338-4993 † These authors contributed equally to this work. Abstract: Aims: Obstructive sleep apnoea (OSA) affects patients’ quality of life and health. Magne- sium (Mg) is an essential mineral and a potent antioxidant. Mg deficiency can worsen oxidative stress caused by sleep deprivation or disorders. The impact of OSA on serum Mg levels and its health consequences remain unclear. Data Synthesis: This study systematically reviewed clinical studies investigating the serum Mg levels of OSA patients and the potential relationships with other biomarkers. Six articles were included for qualitative synthesis and quantitative analysis. Two out of four studies that compared OSA patients to healthy controls found them to have significantly lower serum Mg levels. Our meta-analysis with three studies shows that patients with OSA had significantly lower serum Mg with an effect size of -1.22 (95% CI: -2.24, -0.21). However, the mean serum Mg level of OSA patients (n = 251) pooled from five studies (1.90 mg/dL, 95% CI: 1.77, 2.04) does not differ significantly from the normal range between 1.82 to 2.30 mg/dL. OSA severity appears to affect serum Mg negatively. Serum Mg levels generally improve after treatment, coin- ciding with the improvement of OSA severity. Low serum Mg levels correlate with the worsening of cardiovascular risk biomarkers of C-reactive protein, ischaemia-modified albumin, and carotid intima-media thickness. The serum Mg levels also potentially correlate with biomarkers for lipid profile, glucose metabolism, calcium, and heavy metals. Conclusions: Sleep deprivation appears to deplete Mg levels of OSA patients, making them at risk of Mg deficiency, which potentially increases systemic inflammation and the risk of cardiovascular and metabolic diseases. Keywords: intermittent airway obstruction; sleep disorder; micronutrient deficiency; metabolic risk factor; cardiovascular disease 1. Introduction Human beings spend approximately one-third of their lives sleeping. Adequate and restful sleep is essential for maintaining optimal health. Sleep deprivation resulting from functional disorders can lead to poor quality of life and morbidity. Obstructive sleep apnoea (OSA) is characterised by frequent episodes of partial or complete upper airway collapse during sleep. The disruption of respiratory airflow can occur when there is a physical blockage to the airways caused by the tongue and surrounding soft tissue structures falling back to the throat due to gravity and muscle relaxation. These episodes result in complete or partial reduction of airflow and recurrent arousals from sleep [1,2]. The pathogenesis of OSA is multifactorial, with a combination of both anatomical and non-anatomical causes. OSA patients often have pharyngeal anatomical abnormalities such as narrow pharyngeal airway, increased airway length, and specific pharyngeal lumen shapes. Non-anatomical factors, such as impaired pharyngeal dilator muscle function, low respiratory arousal threshold, and unstable control of breathing, also contribute to upper airway collapse and frequent arousal during sleep [1]. Individuals with OSA may experience symptoms such as snoring, excessive daytime sleepiness, morning headache, Biomedicines 2022, 10, 2273. https://doi.org/10.3390/biomedicines10092273 https://www.mdpi.com/journal/biomedicines