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Living alone makes the heart more vulnerable
  1. James O'Keefe1,2,
  2. Noel Torres-Acosta2,
  3. Carl J Lavie3
  1. 1 University of Missouri-Kansas City, Kansas City, Missouri, USA
  2. 2 Saint Luke’s Mid America Heart Institute, Kansas City, Missouri, USA
  3. 3 Cardiology, John Ochsner Heart and Vascular Institute, New Orleans, Louisiana, USA
  1. Correspondence to Dr Carl J Lavie, Cardiology, John Ochsner Heart and Vascular Institute, New Orleans, LA 70121, USA; clavie{at}ochsner.org

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Homo sapiens is among the most inherently social species on Earth. A proclivity to closely collaborate with other individuals is an instinctive character trait of humans, and this accounts for much of our success as a species. The new study by Chen and colleagues,1 an epidemiological cohort study of 10 000 Swedish twins, found that living alone, regardless of the reason, was associated with a higher risk of cardiovascular disease (CVD) and a shorter leucocyte telomere length (an established biomarker of ageing). However, the observed telomere shortening did not account for the increased risk of CVD among individuals living singly.1

The hypothesis that marriage confers protection against premature mortality and CVD was first proposed over a century ago. Across European, Asian and American cohorts, marriage has been associated with a 1.2-fold to 2.5-fold decreased mortality when compared with widowed, divorced or never-married individuals.2 Also, a prospective cohort of 94 062 Japanese demonstrated a three-fold increased CVD mortality in never-married men when compared with married men.2 A cohort study of 734 626 healthy women reported a significantly lower risk of coronary heart disease (CHD) mortality among married/cohabitating compared with unmarried women, with a relative risk of 0.72 (95% CI 0.66 to 0.80, p<0.0001).2 3 The tendency for marriage to lower mortality extends to divorced individuals. In the Charleston Heart Study, all-cause mortality was lower after remarriage compared with divorced individuals who did not remarry.2

Similarly, Schultz and colleagues4 followed 6051 patients for an average of 3.7 years after they underwent cardiac catheterisation for suspected or confirmed CHD and found that unmarried individuals had higher risk for all-cause mortality (HR 1.24, 95% CI 1.06 to 1.47), CVD death (HR 1.45, 95% CI 1.18 to 1.78), and CVD death or myocardial infarction (MI) (HR 1.52, 95% CI 1.27 to 1.83) (figure 1). When unmarried participants were further stratified, similar increased rates of CVD death/MI were found for people who were divorced or separated (HR 1.41, 95% CI 1.10 to 1.81), never married (HR 1.40, 95% CI 0.97 to 2.03) and widowed (HR 1.71, 95% CI 1.32 to 2.20).4

Figure 1

Kaplan-Meier survival curves for (A) all-cause mortality and (B) cardiovascular (CV) death and myocardial infarction (MI).4

A recently published meta-analysis of 34 prospective cohort studies comprising more than two million participants reported that compared with married participants, unmarried men and women, whether never married, divorced or widowed, had a risk of CVD, with an OR of 1.42 (95% CI 1.00 to 2.01).3 Being divorced was associated with increased risk for CHD (p<0.001), whereas widowers were at increased risk for stroke (p<0.001). Living alone increased the risk for mortality after MI (OR 1.42, 95% CI 1.14 to 1.76) compared with married post-MI participants.3

Protective mechanisms of cohabitation

The underlying protective mechanisms of marriage are not well understood, but cohabitants typically receive social support from their partners, which likely reduces their psychosocial stress (PSS). Also, compared with someone living alone, an individual who is cohabitating is more likely to (1) seek healthcare earlier and more often; (2) be more adherent to prescribed treatment; and (3) be encouraged by their partner to adopt healthier behaviours. Marriage provides emotional support which enhances a person’s resilience to PSS. A large body of scientific data indicates that uncontrolled PSS impairs the parasympathetic/sympathetic nervous system balance, increasing heart rate and blood pressure (BP), and predisposing to hypertension, diabetes, atherosclerotic CVD and major adverse CVD events.5 In the new study by Chen et al,1 the increased stress of living alone may have been at least in part responsible for the shorter telomeres noted among those persons living singly. Indeed, excessive PSS has been associated with accelerated ageing.5

Quality matters too

The quality of close interpersonal relationships has been shown to directly impact CVD risk factors. In a European prospective cohort of men, those who had an improving spousal relationship also had significant reductions in both systolic and diastolic BP, total cholesterol, low-density lipoprotein cholesterol and body mass index (BMI).6 In contrast, men whose spousal relationship was deteriorating showed increased levels of BP, total cholesterol and BMI.6

An interesting study of couples found that when the woman tended to display low levels of warmth during conflict resolution, her husband had more severe atherosclerosis via calcium scoring.7 On the other hand, in couples where the wives or the husbands displayed high levels of control, the husband tended to have more severe atherosclerosis via calcium scoring.7 When both of the partners displayed low levels of control, husbands tended to have a lower calcium score.7

Cardioprotection from your dog

The strong emotional bond that naturally develops between human and dog coinhabitants predictably reduces PSS and can exert therapeutic effects on long-term health and well-being.8 This halo effect on one’s health bestowed by sharing a home with a dog is particularly powerful for individuals living singly, who as noted above are more vulnerable to adverse CVD events. A landmark prospective nationwide cohort study followed 3 432 153 residents of Sweden for 12 years and focused specifically on the effects of dog ownership on survival.9 Individuals living alone with a dog, compared with those living alone without a dog, had a 33% lower risk of all-cause mortality and a 36% lower risk of CVD mortality. These benefits of dog ownership for people living singly were dramatically better than the benefits noted for people living in multiple-person households with or without a dog, where dog ownership reduced risks of all-cause mortality by 11% and CVD mortality by 15%.9 Thus, adopting a dog into one’s home could theoretically be an effective strategy for neutralising CVD risk of living alone (figure 2).2 8–10

Figure 2

Risk reduction of all-cause mortality by type of companionship.2 9 10 Dog ownership: people living singly with a dog versus singly with no dog; cohabitation: living with a partner versus singly; marriage: married and living together versus living singly regardless of marital status (never married, divorced or widowed).

Summary

Living alone appears to be an independent risk factor for early mortality and CVD mortality. Yet this evidence is largely based on observational studies, and correlation does not imply causation. Marital status, like many CVD risk factors, such as tobacco use, hostility, age or family history, is not easily assessed via a randomised controlled trial; thus, we may never have definitive evidence to prove the hypothesis that living alone increases CVD risk. Even so, the advantages of cohabitation for one’s cardiovascular health and longevity might help inform a decision about the pros and cons of living with another person or a canine companion. Two may or may not live as cheaply as one, but two together will probably live longer than one alone.

References

Footnotes

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Provenance and peer review Commissioned; internally peer reviewed.

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