Trends in anthropometry and severity of sleep-disordered breathing over two decades of diagnostic sleep studies in an Australian adult sleep laboratory.

OBJECTIVE: To document trends in subject demographics, anthropometry and sleep disorder severity over 21 years of diagnostic sleep studies.

DESIGN, PARTICIPANTS AND SETTING: A retrospective observational study of consecutive subjects undergoing initial diagnostic polysomnography for investigation of possible sleep disorders in a university-affiliated tertiary public metropolitan hospital in the Hunter New England region of New South Wales between 1987 and 2007.

MAIN OUTCOME MEASURES: Body weight, body mass index (BMI) and severity of sleep-related breathing disorders (apnoea-hypopnoea index [AHI]).

RESULTS: Between 1987 and 2007, 14 648 new diagnostic sleep studies were performed. The median age of subjects (51 years; interquartile range, 41-61 years) did not change over time and the proportion of women increased from 20% to 39%. Median body weight increased from 89 kg to 99 kg for men (11%) and from 73 kg to 85 kg for women (16%), equating to a yearly increase in median BMI of 0.15 kg/m(2) for men and 0.14 kg/m(2) for women. The proportion of subjects who were morbidly obese (BMI > or = 40) increased from 3% in 1987 to 16% in 2007. Median AHI progressively increased from 1992-1995 to 2004-2007 (from 6.5 events/h to 14.3 events/h; P < 0.001), indicating increasing disease severity. Over the same period, for every unit increase in BMI, AHI increased by 5.5 events/h for men and by 2.8 events/h for women. About 80% of the observed variance in AHI over this period was attributable to variance in BMI.

CONCLUSION: There is a continuing trend towards increasing body weight and BMI in people undergoing diagnostic sleep studies. Our data do not support the hypothesis that increased accessibility to diagnostic services and increased awareness of sleep disorders are resulting in a decline in disease severity. These findings are consistent with the premise that worsening severity in sleep-disordered breathing is primarily attributable to increasing obesity.