Sleep is commonly known to be important to good health; adults who sleep fewer than 7 hours each night are more likely to report having health problems such as heart attack, asthma, and depression. Studies have been conducted to examine sleep duration as a potential predictor of cardiovascular events, including stroke. One such study enrolled 9,692 individuals aged 40-79 years who had not previously had a stroke. Individuals were selected to join the study from a list of patients registered at primary care offices in Norfolk, England. Participants completed questionnaires to provide data about themselves, including information about their typical sleep duration in a 24-hour period (six response options: <4, 4-6, 6-8, 8-10, 10-12, >12 hours) and about whether they generally sleep well (two response options: yes, no). Over the 10-year duration of the study, 346 of the study participants suffered strokes.

Based on the collected data, researchers concluded that individuals who reported sleeping more than 8 hours per day were 45% more likely to have had a stroke than those who reported sleeping 6-8 hours; this calculation controlled for age and sex as potential confounders.

1. From these results, is it possible to conclude that sleeping more than 8 hours per day causes increased risk of stroke?