How better sleep can protect cardiovascular health

Numer­ous stud­ies have estab­lished a sig­nif­i­cant link between sleep dis­or­ders and car­dio­vas­cu­lar dis­ease. A recent INSERM study, con­duct­ed in col­lab­o­ra­tion with the Cen­tre Hos­pi­tal­ier Uni­ver­si­taire Vau­dois, sheds new light on this asso­ci­a­tion and opens up new avenues for the pre­ven­tion of these diseases.

The num­ber of deaths linked to car­dio­vas­cu­lar dis­ease (CVD) has soared in recent decades. Accord­ing to the World Heart Fed­er­a­tion, it has increased by 60% since 1990, i.e. faster than the world’s pop­u­la­tion. Every year, more than 20 mil­lion peo­ple world­wide die of CVD. This dis­mal fig­ure makes heart dis­ease, which cov­ers a range of dis­or­ders affect­ing the heart and blood ves­sels, the lead­ing cause of death world­wide (and the sec­ond in France).

Pre­vent­ing CVDs is there­fore a major pub­lic health issue. Con­sid­er­able research efforts are being made to bet­ter iden­ti­fy not only the risk fac­tors (fac­tors that con­tribute to the devel­op­ment of dis­ease), but also the risk mark­ers (fac­tors that indi­cate an increased risk, with­out nec­es­sar­i­ly estab­lish­ing a causal link), so that action can be tak­en as ear­ly as possible.

While we undoubt­ed­ly know that smok­ing, dia­betes, harm­ful alco­hol con­sump­tion, poor diet and a seden­tary lifestyle all con­tribute direct­ly to the onset of CVDs, a grow­ing body of sci­en­tif­ic evi­dence also points to sleep as a sig­nif­i­cant risk mark­er. Var­i­ous stud­ies have shown, for exam­ple, that strokes and myocar­dial infarc­tions are ulti­mate­ly more fre­quent in peo­ple who sleep lit­tle or a lot (sleep­ing less than 6 hours or more than 9 hours) or in peo­ple with sleep apnoea than in the rest of the pop­u­la­tion. Can this asso­ci­a­tion be explored in greater depth and used for pre­ven­tion pur­pos­es? This is the ques­tion that the Inte­gra­tive Epi­demi­ol­o­gy of Car­dio­vas­cu­lar Dis­eases team at the Car­dio­vas­cu­lar Cen­tre (Inserm/Université Paris Cité), led by Jean-Philippe Empana, has attempt­ed to answer, in col­lab­o­ra­tion with the Vaud Uni­ver­si­ty Hos­pi­tal Cen­tre in Lausanne.

His work was based on two Euro­pean gen­er­al pop­u­la­tion cohorts: one in France of 10,175 adults aged 50–75; the sec­ond in Switzer­land of 6,733 indi­vid­u­als aged over 35. “Most exist­ing stud­ies focus on a sin­gle com­po­nent of sleep, usu­al­ly its dura­tion or the pres­ence of sleep apnoea. But “good sleep” actu­al­ly encom­pass­es sev­er­al com­po­nents. We have tried to take this into account by adopt­ing a more glob­al approach”, explains Jean-Philippe Empana. The researchers devel­oped a “sleep score” that is sci­en­tif­i­cal­ly robust but delib­er­ate­ly sim­ple so that every­one can adopt it, based on five key mark­ers of the quan­ti­ty and qual­i­ty of sleep: its aver­age dai­ly dura­tion, the pres­ence of exces­sive day­time sleepi­ness, the pres­ence of sleep apnoea, the fre­quen­cy of insom­nia and the chrono­type (the fact of being a morn­ing or evening per­son). Each item is scored 0 or 1, with an opti­mal total pos­si­ble score of 5 cor­re­spond­ing to a sleep dura­tion of between 7 and 8 hours, the absence of insom­nia, apnoea and day­time sleepi­ness, and a morn­ing chronotype.

“Using this score, we want­ed to study the effects of changes in sleep habits over time, as pre­vi­ous stud­ies have tend­ed to focus on the sleep/CVD asso­ci­a­tion at only one giv­en point in time” con­tin­ues the research direc­tor. The sleep score for each indi­vid­ual was assessed at point 0, then two to five years lat­er, and car­dio­vas­cu­lar risk was mon­i­tored for 8 to 10 years. The links between this score and the num­ber of heart attacks, strokes or heart fail­ure were then analysed with­out con­sid­er­ing poten­tial risk fac­tors (smok­ing, dia­betes, etc.), the sex and age of the par­tic­i­pants, and by exclud­ing peo­ple who had already suf­fered from CVD in the past.

The results are clear. The high­er the score obtained, the low­er the num­ber of cas­es of CVD. The sub­groups with scores of 2, 3, 4 and 5 were 10%, 19%, 38% and 63% low­er respec­tive­ly than the sub­group of peo­ple with scores of 0 or 1. But above all, the study shows that what­ev­er the start­ing score, the num­ber of cas­es of CVD falls for par­tic­i­pants who have improved their sleep habits. Each improve­ment in the sleep score, irre­spec­tive of the fac­tor con­sid­ered, cor­re­sponds to a 16% reduc­tion in the num­ber of cas­es of CVD in the group con­cerned. Jean-Philippe Empana is enthu­si­as­tic: “These results high­light two things: first­ly, that improv­ing sleep is asso­ci­at­ed with con­sid­er­able ben­e­fits in terms of reduc­ing the risk of CVD. Sec­ond­ly, it’s nev­er too late to pro­tect your car­dio­vas­cu­lar health by tak­ing action to improve your sleep. It’s a very pow­er­ful mes­sage, and one that we hope every­one can take on board.”

Does this mean that sleep dis­or­ders are one of the caus­es of car­dio­vas­cu­lar dis­ease? “No, and that’s not what the study was try­ing to show. But of course, the hypoth­e­sis remains plau­si­ble since our results do not con­tra­dict it,” explains the research direc­tor. To estab­lish a causal link, we need to be able to show not only that there is indeed an asso­ci­a­tion between sleep and CVD, and that sleep dis­or­ders pre­cede the onset of these patholo­gies (which the study estab­lished), but also to inves­ti­gate in greater depth the phys­iopatho­log­i­cal mech­a­nisms explain­ing this link (oth­er teams are work­ing on this), and then con­firm the results with ran­domised tri­als. So, we shouldn’t be too quick to draw conclusions.

Anne Orliac