Insomnia and sleep duration interact to increase heart disease risk
medwireNews: Long sleep duration and insomnia increase the risk for coronary heart disease (CHD) among postmenopausal women and may interact to almost double the risk, study findings from the Women's Health Initiative (WHI) show.
"This study demonstrated a significant and strong association between long habitual sleep duration and incident CHD among postmenopausal women who report high levels of insomnia," say Megan Sands-Lincoln (University of Pennsylvania Perelman School of Medicine, Philadelphia, USA) and team.
This suggests "characteristics of sleep quality may be an important factor contributing to the observed association between sleep duration and incidence CHD and CVD [cardiovascular disease] reported in previous studies," they add.
Among 86,329 participants of the WHI, aged 50-79 years, approximately 7.9% reported sleeping 5 hours or less per night (short sleepers), while 0.6% reported sleeping at least 10 hours per night (long sleepers).
After accounting for age and race, both short and long sleepers had a significantly greater risk for developing incident CHD (25% and 43% greater, respectively) and CVD (19% and 37%, respectively) than normal sleepers with a midrange sleep duration of 7-8 hours. However, these increased risks were no longer significant after full adjustment for factors such as education, income, depression, diabetes, and body mass index.
Insomnia, on the other hand, was significantly associated with an increased risk for both cardiovascular conditions after adjusting for age and race and after full adjustment for confounding factors.
Indeed, women with a high prevalence, defined as a WHI Insomnia Rating Scale (WHIIRS) score of at least 9, compared with a low prevalence (WHIIRS <3), were 38% more likely to develop incident CHD and 27% more likely to develop CVD. After full adjustment for confounding factors, the risk increases were 19% and 11%, respectively.
But the researchers note in the Journal of Women's Health that there was a significant interaction between sleep duration and insomnia, such that women who had insomnia and were long sleepers had an almost twofold increased risk for CHD.
There were a total of 5359 cases of incident CHD and 7257 cases of incident CVD over 881,888 and 867,513 person-years of follow up, respectively.
"Our analysis extends those of previously reported findings on sleep duration, but also suggests that the impact of sleep duration on cardiac events may be due to comorbid conditions," the researchers conclude.
medwireNews (www.medwirenews.com) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2013
By Lucy Piper, Senior medwireNews Reporter