Clinical Context

Poor sleep has been associated with a number of poor health outcomes in terms of mental and physical health, and sleep quality certainly plays a role in obesity and insulin resistance. A previous review by Reutrakal and Van Cauter, published in the July 2018 issue of Metabolism, assessed the evidence for these relationships.^[1]

Poor sleep duration is strongly associated with increased hunger and food intake. Excessive caloric intake in cases of poor sleep goes beyond simply eating more to provide energy during increased wake time. However, the effects of sleep quality on hormones such as leptin and ghrelin are less clear. Reduced sleep duration also is associated with higher degrees of insulin resistance, but sleep fragmentation alone may not affect this outcome. Finally, increases in sleep duration through behavioral change can reduce appetite and improve glucose metabolism, but the use of pharmacotherapy to aid sleep is less likely to help metabolic outcomes.

The result of the negative metabolic effects of poor sleep can be a higher rate of cardiovascular disease. However, the effects of sleep duration on the risk for myocardial infarction (MI) are inadequately quantified. The current study addresses this issue.

Study Synopsis and Perspective

Insomnia, or difficulty falling or staying asleep, was associated with a 69% greater risk of having a MI than seen among adults without insomnia, according to new research.

Those who slept 5 or fewer hours per night had the highest risk for MI, and those with both diabetes and insomnia had double the risk for MI compared with patients without these comorbidities.

The findings are from a meta-analysis of studies in more than 1 million patients, almost all of whom were without prior MI and were, on average, in their early 50s and were followed up for 9 years.

“Insomnia and ≤5 [hours] of sleep are highly associated with increased incidence of MI; an association comparable to that of other MI risk factors and as such, it should be considered as a risk factor for MI and to be incorporated into MI prevention guidelines,” the researchers conclude.

“We believe that [insomnia] should be screened and patients should be educated about the importance of sleep because nowadays insomnia is no longer a disease--sleep deprivation could also be a life choice,” Dean told a press conference before the meeting.

“Clinicians must educate the patients about the importance of sleep in maintaining a healthy heart and encourage proper sleep hygiene,” Dean reiterated in an email to theheart.org | Medscape Cardiology.

“And if a patient still has insomnia, other methods should be considered such as cognitive behavior therapy for insomnia (CBT-I).”

This study does not allow any conclusion about whether treating insomnia will reduce heart attack risk, Jennifer L. Martin, PhD, president of the American Academy of Sleep Medicine, noted in an email to theheart.org | Medscape Cardiology. Nor does it report the diversity of study participants, as insomnia is also a health equity issue, she noted, and insomnia symptoms and comorbidities were self-reported.

However, this analysis “adds to the growing evidence that poor quality or insufficient sleep is associated with poor health,” said Dr Martin, professor of medicine at UCLA’s David Geffen School of Medicine, Los Angeles, who was not involved with this research.

The study reinforces the recommendation from the American Heart Association, which includes “Get Healthy Sleep“ as one of “Life’s Essential 8“ for heart health, Dr Martin noted.

“Particularly in primary care, where disease prevention and health promotion are important, clinicians should be asking all patients about their sleep--just like they ask about diet and exercise--as a key aspect of maintaining heart health,” she said.

Advice about basic sleep hygiene advice is a first step, she noted.

When improved sleep hygiene is not enough to address chronic insomnia, the American Academy of Sleep Medicine’s clinical practice guidelines and the guidelines of the VA/Department of Defense recommend first-line treatment with CBT-I, typically offered by a sleep specialist or mental health clinician.

Similarly, the American College of Physicians suggests that sleeping pills should be reserved for short-term use in patients who may not benefit sufficiently from CBT-I.

“Studies have found that insomnia and subsequent sleep deprivation puts the body under stress,” Dean said. “This triggers cortisol release, which could accelerate atherosclerosis” and increase risk for MI.

For this analysis the researchers identified 9 observational studies, published from 1998 to 2019, with data on incident MI in adults who had insomnia.

The diagnosis of insomnia was based on International Classification of Diseases, Ninth Revision, Clinical Modification, diagnostic codes or on the Diagnostic and Statistical Manual of Mental Disorders , which defines insomnia as the presence of any of the following 3 symptoms: difficulty initiating sleep, difficulty maintaining sleep, or early morning awakening with inability to return to sleep.

Patients with sleep apnea were excluded.

The studies were in populations in China, Germany, Norway, Taiwan, United Kingdom, and United States, in 1.1 million adults aged 18 and older and 13% reported insomnia.

During follow-up, 2406 of 153,881 patients with insomnia and 12,398 of 1,030,375 patients without insomnia had an MI.

In the pooled analysis, patients with insomnia had a significantly increased risk for MI (relative risk [RR], 1.69; P<.00001), after adjusting for age, sex, diabetes, hypertension, high cholesterol, and smoking.

Sleeping 5 hours or less was associated with a greater risk for MI than sleeping 6 hours, or 7 to 8 hours, but sleeping 9 hours or more was just as harmful.

Table. Risk for MI with Different Sleep Durations

Patients who had difficulty initiating and maintaining sleep (2 symptoms of insomnia) had a 13% increased risk for MI compared with other patients (RR = 1.13; P=.003).

However, patients who had nonrestorative sleep and daytime dysfunction despite adequate sleep, which is common, did not have an increased risk for MI compared with other patients (RR = 1.06; P=.46).

Women with insomnia had a 2.24-fold greater risk for MI than other women, whereas men with insomnia had a 2.03-fold greater risk for MI than other men.

Patients with insomnia had a greater risk for MI than those without insomnia in subgroups based on patients’ age (<65 and >65 years), follow-up duration (≤5 years and >5 years), and comorbidities (diabetes, hypertension, and hyperlipidemia).

The authors have disclosed no relevant financial relationships.

Clin Cardiol. Published online February 25, 2023.

Clinical Implications

• Clinicians should encourage patients with sleep disorders to take steps to mitigate causative factors. Poor sleep duration is strongly associated with increased hunger and food intake. However, the effects of sleep quality on hormones such as leptin and ghrelin are less clear. Individuals with sleep dysfunction might benefit from a referral to a nutritionist and holistic evaluation of causative factors.
• The current study finds that sleep duration of 5 hours or less or 9 hours or more was associated with an increased risk for MI, as was difficulty initiating or maintaining sleep. However, nonrestorative sleep and daytime dysfunction because of poor sleep were not related to a higher risk for MI.
• Implications for the healthcare team: The healthcare team should counsel patients that MI is a potential complication of insomnia when providing education about the importance of sleep hygiene.

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