Single nucleotide polymorphisms were analysed from blood samples taken from 385,292 healthy participants of the UK Biobank Project which were used to create a genetic risk score to determine whether the participant’s risk level of cardiovascular problems of being either high, low, or intermediate.
A new healthy sleep score was also created by asking participants whether they were a morning or night person, how long they slept for, if they snored/frequency, excessive daytime sleepiness, and if they suffered from insomnia; sleep scores ranged from 0-5 with five being the healthiest sleep pattern, typically representing a morning person who slept between 7-8 hours per night without snoring, insomnia, or daytime sleepiness.
“We wanted to test whether the relation between sleep scores and cardiovascular outcomes was different according to the genetic risk. This is the first time this has been done,” said Professor Lu Qi, Director of Tulane University Obesity Research Center at Tulane University. “We also wanted to estimate the proportion of cardiovascular problems that would not have occurred if all participants had a healthy sleep pattern, if we assume there is a causal relationship.”
Participants were followed for an average of 8.5 years, during which there were 7280 cases of stroke or heart disease. Participants with a score of 5 were found to have a 35% decreased risk of cardiovascular disease, and a 34% decreased risk of stroke and heart attack compared to those with unhealthy sleep scores of 0-1.
“If the link between sleep and cardiovascular disease proves to be causal, then more than a tenth of all heart disease and strokes would not have occurred if all the participants had a healthy sleep score of 5. Among people with a healthy sleep score of 5, there were nearly seven fewer cases of cardiovascular disease per 1000 people per year compared to those with a sleep score of less than 5,” said Professor Qi.
When investigating the combined effects of genetic susceptibility and sleep score on cardiovascular disease those with both poor sleep patterns and high genetic risk were found to have more than a 2.5 fold increased risk of heart disease and a 1.5 fold increased risk of stroke than those with healthy sleep patterns and low genetic risk. Meaning that there were 11 more cases of heart disease and 5 more cases of stroke per 1000 people annually among those with high genetic risks that are poor sleepers. However, according to the researchers having a healthy sleep pattern appeared to slightly compensate for a high genetic risk with their risk being 2.1 fold greater for heart disease and 1.3 fold greater for stroke. Those with a low genetic risk with an unhealthy sleep pattern were found to be at 1.7 fold greater risk of heart disease and 1.6 fold greater risk of stroke.
“We found that a high genetic risk could be partly offset by a healthy sleep pattern,” said Prof Qi. “In addition, we found that people with a low genetic risk could lose this inherent protection if they had a poor sleep pattern.”
The possibility of poor sleep patterns being an indicator of an underlying and/or undetected health problem that may play a role in the increased risk for cardiovascular disease can’t be excluded; the researcher tried to minimise this by excluding all participants with cardiovascular disease at the beginning of the study, and by taking into account factors which could affect the results, such as gender, age, ethnicity, smoking, BMI, alcohol, other health problems, and family history.
Prof Qi concluded: “As with other findings from observational studies, our results indicate an association not a causal relation. However, these findings may motivate other investigations and, at least, suggest that it is essential to consider overall sleep behaviours when considering a person’s risk of heart disease or stroke.”
The study was noted to be limited by relying on participants to report sleeping patterns, which only occurred at the start of the study and did not include all sleep problems such as restless leg syndrome, and the majority of the Biobank participants were of European descent, which may affect the generalisation of their findings to other populations.
The mechanisms responsible for the link between sleep and the risk for cardiovascular disease are not clear, the researchers say that sleep may upset the hormonal or metabolic regulation of the body, increase the fight or flight responses in the body, increase inflammation, and disrupt the natural circadian rhythm.
