the risk of death or heart disease is controversial with some reviews finding benefit and others not. This variation across studies might be driven by low rates of compliance—analyses of those who use CPAP for at least four hours a night suggests a decrease in cardiovascular events. Weight loss Excess body weight is thought to be an important cause of sleep apnea. People who are overweight have more tissues in the back of their throat which can restrict the airway, especially when sleeping. In weight loss studies of overweight individuals, those who lose weight show reduced apnea frequencies and improved apnoea–hypopnoea index (AHI). Weight loss effective enough to relieve obesity hypoventilation syndrome (OHS) must be 25–30% of body weight. For some obese people, it can be difficult to achieve and maintain this result without bariatric surgery. Rapid palatal expansion In children, orthodontic treatment to expand the volume of the nasal airway, such as nonsurgical rapid palatal expansion is common. The procedure has been found to significantly decrease the AHI and lead to long-term resolution of clinical symptoms. Since the palatal suture is fused in adults, regular RPE using tooth-borne expanders cannot be performed. Mini-implant assisted rapid palatal expansion (MARPE) has been recently developed as a non-surgical option for the transverse expansion of the maxilla in adults. This method increases the volume of the nasal cavity and nasopharynx, leading to increased airflow and reduced respiratory arousals during sleep. Changes are permanent with minimal complications. Surgery Several surgical procedures (sleep surgery) are used to treat sleep apnea, although they are normally a third line of treatment for those who reject or are not helped by CPAP treatment or dental appliances. Surgical treatment for obstructive sleep apnea needs to be individualized to address all anatomical areas of obstruction. Nasal obstruction Often, correction of the nasal passages needs to be performed in addition to correction of the oropharynx passage. Septoplasty and turbinate surgery may improve the nasal airway, but has been found to be ineffective at reducing respiratory arousals during sleep. Pharyngeal obstruction Tonsillectomy and uvulopalatopharyngoplasty (UPPP or UP3) are available to address pharyngeal obstruction. The "Pillar" device is a treatment for snoring and obstructive sleep apnea; it is thin, narrow strips of polyester. Three strips are inserted into the roof of the mouth (the soft palate) using a modified syringe and local anesthetic, in order to stiffen the soft palate. This procedure addresses