Can sleep affect cholesterol?
Obstructive sleep apnea (OSA) is a condition in which varying degrees of repetitive upper airway obstruction create disturbances in normal breathing patterns during sleep. The soft tissues of the upper airway can collapse as the muscles in this area become fully relaxed during sleep. Complete or partial obstruction can then occur. This triggers an increased breathing effort against a closed off airway and results in multiple awakenings from sleep. As a result, some common symptoms of OSA include daytime fatigue and somnolence. Other symptoms include depressed mood, morning headaches, increased urination at night, and sometimes insomnia itself. OSA is a common condition that has been under recognized for years. It is estimated that about 25% of adults in the US are at risk for this condition. Some risk factors include obesity, abnormalities of the upper airway such as large tonsils, smoking, and diabetes. OSA can be readily diagnosed by an overnight sleep study (polysomnography) during which time the pulse rate and oxygen levels are recorded during sleep. A severity index can then be generated by counting the number of episodes of disturbed breathing that occurs during a period of sleep. The mainstay treatment for significant OSA is continuous positive airway pressure (CPAP). This therapy is delivered through a nasal or face mask through which continuous air pressure is delivered in order to keep the upper airway open. OSA has become increasingly important in that it has been linked to and may contribute to the development of other serious medical conditions such as hypertension, abnormal heart rhythms, and congestive heart failure. OSA may also increase the risk of heart disease and one possible reason for this is its adverse effects on cholesterol.
In 2006, a pair of articles appeared in the medical literature looking specifically at the relationship between OSA and cholesterol. The US study was a relatively small one that essentially did not demonstrate any significant relationship between cholesterol and OSA in 62 male patients. However, a much larger German study looked at over 400 patients with varying degrees of OSA and concluded that the more severe the OSA, the lower the HDL and higher the triglyceride levels. There was no significant relationship between OSA and total or LDL cholesterol levels. A second part of this German study evaluated the effects of positive airway pressure on lipid levels. In these 86 patients in whom they followed while receiving OSA treatment, the authors observed that as OSA improved, HDL levels rose ~6%. This is not a huge difference but was still significant nonetheless. In the following year, a Greek study also examined the effects of CPAP on cholesterol in patients with OSA. They concluded that CPAP over a 6 month period did lower overall cholesterol and increased HDL levels.
The mechanistic link between OSA and cholesterol is not clearly understood. One thought is that during periods of obstructed breathing, adrenaline levels significantly and chronically are increased. High adrenaline levels have been associated with lower HDL levels and higher triglyceride levels. Another thought involves the effect of OSA on eating habits. A study published this year suggested that OSA promotes poor eating habits and contributes to weight gain and obesity. This results in bad cholesterol levels. Fatigue has been known to be a common trigger for poor dietary habits and OSA patients are often fatigued during the day. In a sense, OSA can be a vicious cycle for obese people in that obesity promotes OSA but OSA can then in turn promote obesity. The effect of CPAP on improving HDL and triglycerides may also be dietary in nature in that as fatigue decreases, better dietary choices are made. Furthermore, less daytime fatigue can lead to more physical activity and exercise. The effects of exercise on cholesterol include lowering triglycerides and increasing HDL.
In conclusion, OSA is a common and under diagnosed disease that can not only be associated with significant symptoms but can also promote the development of other significant diseases that adversely affect heart health. Cholesterol does seem to be adversely affected by OSA and CPAP therapy for OSA can attenuate these effects. In addition, treatment of OSA may promote better eating habits and more physical activity which are critical components in maintaining good cholesterol levels.