In Obstructive Sleep Apnea, Gender Makes a Difference
Current statistics of obstructive sleep apnea (OSA) reveal that 24 percent of the male population and 9 percent of women suffer from this disease, and that many women go undiagnosed.
This was a prospective study done on 6,000 government employees who responded to a questionnaire and agreed to have a sleep study. The group was followed for several years and valuable data was obtained about the natural history of the disease if left untreated. The percentages (24 percent of men and 9 percent of women) were derived from the number of positive sleep studies that confirmed the diagnosis.
When along with a positive sleep study, symptoms were taken into account, specifically excessive daytime somnolence, the percentages of disease (Obstructive Sleep Apnea Syndrome or OSAS) was 4 percent of men and 2 percent of women. In other words, OSAS may be only twice as common among men as among women, contradicting the widely held belief that it’s far more rare among women.
A follow up of this population conducted in 2008 showed a three-fold increase in “all-cause mortality” for those left untreated. There also was a clear association with increased rates of hypertension, heart disease and strokes.
Much more has been learned about OSA since then, and different approaches to management and treatment have also evolved. Much has been learned about the different presentation in women as compared to men, which may cause clinicians to reassess what is known about the prevalence of the disease, specifically in women. These differences include: obesity, upper airway anatomy, breathing control, hormones and physiological changes that come with aging.
Women may not show the classic symptomatology of daytime sleepiness and when they do, it is often accompanied by other complaints that (erroneously) lead to a diagnosis of depression or other illness. Women also are more reluctant to complain of snoring, as they believe it is a masculine trait, or embarrassing.
What are some of the specific gender differences?
Women with OSA have longer sleep latencies (it takes them longer to fall asleep), fewer awakenings, and their OSA events are primarily during the REM phase of sleep, while men are routinely awakened by the apnea events (which are more position-related in origin). This may be why men suffer more from daytime somnolence, while women have more fatigue, which leads to other diagnoses.
The U.S. Centers for Disease Control and Prevention has found that 70 percent of the U.S. population is overweight or obese. In the National Health and Nutrition Examination Survey (NHANES) dataset, the percentage of women diagnosed with obesity is higher than men (33.4% for women and 27.55% for men). One would therefore expect these statistics to correlate with rates of OSA, but this is not the case.
There is a more positive correlation between Body Mass Index and OSA in men than women. This may be due to differences in the distribution (location) of fat. Studies done with MRI confirmed that there is obese women tend to have less fat in the pharynx and neck thanobese men. A large neck is a risk factor for OSA.
Respiratory control stability
The brain controls breathing based on feedback from levels of oxygen and carbon dioxide. The receptors that sense the changes are called chemoreceptors and they send signals to the breathing center.. With OSA, this feedback relationship becomes less stable, which may lead the brain to cease stimulating the lungs, resulting in Central Sleep Apnea (CSA).
Among women, significant differences are noted between pre- and post-menopausal women. Women post-menopause have worse breathing control stability. This suggests a hormonal influence in breathing, which can also explain why pregnant women tend to hyperventilate. It also seems to explain the sudden increase in OSA in menopausal women.
Current literature suggests that higher levels of progesterone and lower levels of testosterone may be protective against OSA. This may be due to the ventilator stimulation effects of progesterone and the effects of testosterone on fat distribution.
Currently, there’s controversy about using hormone therapy to treat some patients at risk of OSA. Studies done with the use of progesterone failed to show that it made a difference.
Aging in itself is associated with many physiological changes particularly with sleep. Primarily there is worsening of sleep efficiency. The fact that older people are less active during the day leads to the incorrect assumption that they need less sleep. This actually makes them more vulnerable for more severe OSA.
In both genders, there is an increase in the pharyngeal fat pads, independent of increases in BMI. Additionally, because there is less concern about daytime performance, there is less compliance in treatment with CPAP. The biggest motivator for treatment is the association with heart disease and the focus on this unhealthy link is more prominent in men.
This imbalance in identification of disease results is a higher risk for cardiovascular disease in women because more are left untreated. Overall, prevalence of sleep apnea increases with age, but the clinical significance and severity of the disease decreases.
In conclusion, there are clear gender differences in sleep-related breathing disorders which currently may lead to the condition being undiagnosed or underdiagnosed in women. This places women at higher risk for cardiovascular and neurocognitive consequences. The associated decrease in quality of life is difficult to measure, because it is highly subjective.
This places the burden of responsibility on health care providers to be aware of these gender differences. Different options for treatment should always be considered, and they include oral appliances, surgical approaches and improving sleep hygiene.