Introduction To investigate whether nocturnal intermittent hypoxia (NIH), a surrogate marker for sleep apnoea, is associated with cardiovascular risk factors, we conducted epidemiological studies.

Methods The CIRCS is a prospective cohort study across Japan since 1963 to examine risk factors for cardiovascular disease. Subjects aged 40–69 years were recruited to the sleep study in three communities. NIH was estimated by hourly occurrences of oxygen desaturation of ≥3% (3% oxygen desaturation index [3% ODI]) by a pulse-oximeter during a night's sleep in the participant's own home. We defined no, mild and moderate-to-severe NIH by 3% ODI as <5, 5 to <15 and ≥15 events/h, respectively. We conducted cross sectional studies on hypertension among 1424 men, on CRP among 1422 men and 2466 women and on metabolic syndrome among 1710 men and 2896 women, and a prospective study on type 2 diabetes among 1603 men and 2795 women.

Results Compared with no NIH, the multivariable OR of hypertension was 1.63 (95% CI 1.1 to 2.5) for moderate-to-severe NIH. The prevalence of a high CRP (≥1.0 mg/l) was 1.4 to 1.7-fold higher for mild to severe NIH in both sexes. The multivariable ORs of metabolic syndrome was 3.2 (2.2 to 4.7) for moderate-to-severe NIH among men and 5.8 (3.4 to 9.8) among women, respectively. The multivariable-adjusted HRs of developing type 2 diabetes was 1.3 (0.9 to 1.8) among those with mild NIH and 1.7 (1.0 to 2.8) among those with moderate-to-severe NIH.

Conclusion NIH was associated with hypertension, elevated serum CRP levels, the accumulation of metabolic risk factors, and increased risk of developing type 2 diabetes among middle-aged Japanese.