Light exposure at night is associated with subclinical carotid atherosclerosis in the general elderly population: The HEIJO-KYO cohort

Epidemiological and cellular biological studies indicate the influence of impaired circadian biological rhythmicity on atherosclerosis. Increased exposure to light at night (LAN) is common in modern life, and LAN exposure is the most important environmental cue for circadian misalignment. However, the association between LAN exposure and atherosclerosis has never been explored in humans. In this cross-sectional study, we measured nighttime light intensity in the bedroom along with the intima-media thickness (IMT) of the common carotid artery using ultrasonography in 700 elderly individuals (mean age 71.6 years). Averages of mean and maximal carotid IMT were 0.88 +/- 0.15mm and 1.09 +/- 0.32 mm, respectively. Median intensity of LAN exposure was 0.74 lux (interquartile range, 0.08-3.34). Both mean and maximal carotid IMT significantly increased across quartiles of increasing LAN intensity (p for trend = 0.002 and <0.001, respectively). After adjustment for confounding factors, including age, gender, body mass index, current smoking status, hypertension, diabetes, dyslipidemia, sleep medication, estimated glomerular filtration rate, nocturia, bedtime, duration in bed (scotoperiod), day length (photoperiod), urinary 6-sulfatoxymelatonin excretion and daytime and nighttime physical activity, multivariate linear regression models revealed significant associations of LAN exposure with carotid IMT measurements [mean: beta, 0.032 (fourth versus first quartiles); 95% confidence intervals (CI), 0.002-0.061; p = 0.037; maximal: beta, 0.100 (fourth versus first quartiles); 95% CI, 0.034-0.165; p = 0.003]. In conclusion, these results suggested that LAN exposure in home settings is significantly associated with subclinical carotid atherosclerosis in the general elderly population.