Exposure to Light at Night, Nocturnal Urinary Melatonin Excretion, and Obesity/Dyslipidemia in the Elderly: A Cross-Sectional Analysis of the HEIJO-KYO Study

Obesity and exposure to light at night (LAN) have increased globally. Although LAN suppresses melatonin secretion and disturbs body mass regulation in experimental settings, its associations with melatonin secretion, obesity, and other metabolic consequences in uncontrolled home settings remain unclear.The aim of this study was to determine the association of exposure to LAN in an uncontrolled home setting with melatonin secretion, obesity, dyslipidemia, and diabetes.A cross-sectional study was performed in 528 elderly individuals (mean age, 72.8 yr).The intensity of LAN in the bedroom was measured at 1-min intervals during two consecutive nights, along with overnight urinary melatonin excretion and metabolic parameters.Compared with the Dim group (average <3 lux; n = 383), the LAN group (average ≥3 lux; n = 145) showed significantly higher body weight (adjusted mean, 58.8 vs. 56.6 kg; P = 0.01), body mass index (23.3 vs. 22.7 kg/m(2); P = 0.04), waist circumference (84.9 vs. 82.8 cm; P = 0.01), triglyceride levels (119.7 vs. 99.5 mg/dl; P < 0.01), and low-density lipoprotein cholesterol levels (128.6 vs. 122.2 mg/dl; P = 0.04), and showed significantly lower high-density lipoprotein cholesterol levels (57.4 vs. 61.3 mg/dl; P = 0.02). These associations were independent of numerous potential confounders, including urinary melatonin excretion. Furthermore, LAN exposure is associated with higher odds ratios (ORs) for obesity (body mass index: OR, 1.89; P = 0.02; abdominal: OR, 1.62; P = 0.04) and dyslipidemia (OR, 1.72; P = 0.02) independent of demographic and socioeconomic parameters. In contrast, urinary melatonin excretion and glucose parameters did not show significant differences between the two groups.Exposure to LAN in an uncontrolled home setting is associated with impaired obese and lipid parameters independent of nocturnal urinary melatonin excretion in elderly individuals. Moreover, LAN exposure is associated with higher ORs for obesity and dyslipidemia independent of demographic and socioeconomic parameters.