Post by Anupam Agarwal, MD, MPH

The link between poor sleep quality and cardiovascular risk is already well documented. However, most studies only consider one or two aspects of sleep (for example, sleep duration or sleep apnea), investigating one sleep pattern at one point in time. A team from Inserm, France's National Institute of Health and Medical Research, published the results of a more complete study of how sleep affects cardiovascular risk. The study examines five sleep patterns that determine sleep quality: sleep duration, insomnia, chronotype ("eveningness" or "morningness"), sleep apnea, and daytime drowsiness. These patterns formed the basis of a questionnaire given to the study participants, providing each with a sleep score between 0 (disturbed sleep) and 5 (perfect sleep). Perfect sleep is characterized by 7-8 hours of sleep per night, getting up early and going to bed early, no insomnia, no sleep apnea, and no excessive daytime drowsiness. Cardiovascular Risk Reduction The questionnaire was given to two cohorts taking part in population surveys. The sleep score was calculated on enrollment and 2 years later for one of the studies and 5 years later for the other. A subgroup of participants also underwent polysomnography testing. The aim of the study was to assess the overall effect on cardiovascular risk of the five sleep patterns and their change over time. The study involved more than 11,000 people aged 53-64 years (44.6% women), and cardiovascular follow-up was conducted for 8-10 years. The data analysis provided three main observations. The first is that the higher the initial sleep score, the lower the cardiovascular risk. The risk is reduced by 18% for each additional point from the initial sleep score (hazard ratio [HR], 0.82). The second finding is that risk is reduced by 16% per additional score point between the two evaluations (HR, 0.84). Finally, the authors estimate that the data collected is evidence that between 30% and 60% of new cardiovascular accidents would be prevented if all participants achieved the maximum level for at least four sleep characteristics.