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