Gender difference and laterality of sleep position.

OBJECTIVE: A higher incidence in women (approximately 7:3) and a predominant involvement of the right ear (approximately 7:5) are interesting features of BPPV (benign paroxysmal positional vertigo). It is speculated that these features are related to sleep position. The first aim of this study was to compare the frequency of position shifts during sleep between men and women. The second aim was to elucidate any differences in sleep position between men and women. The third aim was to clarify the laterality of sleep position.

METHODS: We retrospectively selected the data of 30 males (mean, 53.1 years) and 22 females (mean, 50.6 years) diagnosed as mild or moderate obstructive sleep apnea. A position sensor was attached to the patient's anterior chest. Supine position was defined as less than 45° tilt, and lateral position was defined as more than 45° tilt. A single overnight laboratory polysomnography provided the number of position shifts, total sleep time, sleep time spent in the supine position (S), sleep time spent in the right-side-down lateral position (R), and sleep time spent in the left-side-down lateral position (L).

RESULTS: The mean value and standard deviation of the number of position shifts per hour was 2.4±1.3 in males, and 2.3±1.1 in females. There was no significant difference between males and females. Twelve cases (40%) were lateral type (S<R+L), and 18 (60%) were supine type (S>R+L) in males. Ten cases (45%) were lateral type, and 12 (55%) were supine type in females. There was no significant difference between males and females. Seventeen cases (56.6%) were right-dominant type (R-L>0), and 13 (43.3%) were left-dominant type (R-L<0) in males. Thirteen cases (59%) were right-dominant type, and 9 (41%) were left-dominant type in females.

CONCLUSION: Body position and the number of position shifts during sleep differ substantially between individuals. There is no gender difference in the frequency of position shifts. Although the supine type is more common than the lateral type, there is no gender difference in sleep position. Therefore, the reason of higher incidence in women is not related to sleep. The right-dominant type occurs more than the left-dominant type in both genders. It is possible that this behavior is the reason for the predominant involvement of the right ear in BPPV.