A short-term increase in cancer risk associated with daytime napping is likely to reflect pre-clinical disease: prospective cohort study
Menée en Grande Bretagne sur une cohorte de 795 238 femmes âgées de 50 à 64 ans (20 058 cas de cancer du sein et 31 856 autres cas de cancer ; durée moyenne de suivi : 7,4 ans), cette étude prospective montre, sur une courte période, une augmentation du risque de cancer associé à la sieste diurne, puis suggère que cette augmentation s'explique par la présence d'une maladie au stade pré-clinique
Background : Sleep disturbance, a correlate of which is daytime napping, has been hypothesised to be associated with risk of breast and other cancers. Methods : We estimated relative risks (RR) of breast and other invasive cancers by the reported frequency of daytime napping in a large prospective cohort of middle-aged women in the UK. Results :During an average of 7.4 years of follow-up, 20 058 breast cancers and 31 856 other cancers were diagnosed. Over the first 4 years of follow-up, daytime napping (sometimes/usually vs rarely/never) was associated with slightly increased risks of breast cancer (RR=1.10, 95% CI 1.06–1.15) and of other cancers (RR=1.12, 1.08–1.15), but the RRs decreased significantly with increasing follow-up time (P=0.001 and P=0.01, respectively, for trend). Four or more years after baseline, there was no elevated risk of breast cancer (RR=1.00, 0.96–1.05), and only marginally greater risk of other cancers (RR=1.04, 1.01–1.07). Conclusion :The effect of pre-clinical disease is a likely explanation for the short-term increased risk of breast and other cancers associated with daytime napping.