A normal blood oxygen level during sleep is approximately 94 to 98 percent, according to Sleep Apnea Guide. Levels below 90 percent oxygen saturation are dangerous to the human body. The human brain can only survive four minutes without oxygen before cell death occurs.
Sleep apnea causes short pauses in breathing that can cause oxygen levels to drop as low as 80 percent. Some side effects of low oxygen saturation induced by sleep apnea include weight gain, high blood pressure, impotency, loud snoring, depression, irritability and cardiovascular issues, according to Central California Ear, Nose and Throat. While most commonly found in middle-age men, sleep apnea is worsened by obesity.