The presence of insomnia symptoms increases the likelihood of cardiovascular or cerebrovascular disease during approximately 10 years of follow-up, according to a large cohort study of adults in China. A greater number of insomnia symptoms is associated with increased risk, and this relationship is more evident in younger adults and in adults without hypertension at baseline, researchers reported Nov. 6 in Neurology.

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“These results suggest that, if we can target people who are having trouble sleeping with behavioral therapies, it’s possible that we could reduce the number of cases of stroke, heart attack, and other diseases later down the line,” study author Liming Li, MD, professor of epidemiology at Peking University, Beijing, said in a news release.

To clarify the relationships between individual insomnia symptoms, cardiocerebral vascular diseases, and potential effect modifiers, Dr. Li and colleagues analyzed data from the China Kadoorie Biobank Study. For this study, more than 500,000 adults in China aged 30-79 years completed a baseline survey during 2004-2008. The present analysis included data from 487,200 participants who did not have a history of stroke, coronary heart disease, or cancer at baseline.

For the baseline survey, participants answered questions about whether specific insomnia symptoms occurred at least 3 days per week during the past month. The symptoms included difficulty initiating or maintaining sleep (that is, sleep onset latency of 30 minutes or more after going to bed or waking up in the middle of the night); waking too early and being unable to fall back asleep; and trouble functioning during the day because of bad sleep.

The researchers assessed the incidence of cardiocerebral vascular diseases through 2016 by examining disease registries, national health insurance claims databases, and local records. Investigators identified participants with any cardiocerebral vascular disease and assessed the incidence of ischemic heart disease, acute myocardial infarction, hemorrhagic stroke, and ischemic stroke. The researchers followed each participant until the diagnosis of a cardiocerebral vascular disease outcome, death from any cause, loss to follow-up, or Dec. 31, 2016. The researchers used Cox proportional hazard models to estimate hazard ratios for the association between each insomnia symptom and cardiocerebral vascular disease outcomes. They adjusted the models for established and potential confounding factors, including age, income, smoking status, diet, and physical activity.

More than 16% had any insomnia symptom

Of the 487,200 participants, 11.3% had difficulty initiating or maintaining sleep, 10.4% had early morning awakening, and 2.2% had daytime dysfunction attributed to poor sleep. Compared with participants without insomnia symptoms, participants with insomnia symptoms tended to be older and were more likely to be female, not married, and from a rural area. In addition, those with insomnia symptoms were more likely have depression or anxiety symptoms, lower education level, lower household income, and lower body mass index. They also were more likely to have a history of diabetes mellitus. During a median follow-up of 9.6 years, 130,032 cases of cardiocerebral vascular disease occurred, including 40,348 cases of ischemic heart disease and 45,316 cases of stroke.

After adjustment for potential confounders, each insomnia symptom was associated with greater risk of cardiocerebral vascular disease. For difficulty initiating or maintaining sleep, the hazard ratio was 1.09. For early-morning awakening, the HR was 1.07. For daytime dysfunction, the HR was 1.13. Each insomnia symptom was associated with increased risk of ischemic heart disease and ischemic stroke, whereas only difficulty initiating or maintaining sleep was associated with increased risk of acute MI.

In all, 16.4% of participants reported any insomnia symptom; 10% had one symptom, 5.2% had two symptoms, and 1.2% had three symptoms. “Compared with those without any insomnia symptoms, participants with one, two, or three symptoms had a 7%, 10%, or 18% higher risk of total [cardiocerebral vascular disease] incidence, respectively,” the authors wrote. “Our study is the first large-scale cohort study that identified positive dose-response relationships between the number of insomnia symptoms and risks of [cardiocerebral vascular diseases, ischemic heart disease] and stroke incidence.”

Opportunity for intervention

Compared with clinical diagnostic criteria for insomnia, “individual insomnia symptoms are better defined and more feasible to assess with questionnaires in large-scale population studies and clinical practice,” Dr. Li and colleagues wrote. “Moreover, it is reasonable that insomnia symptoms are more modifiable and precisely targetable through behavioral therapies before developing into clinically significant insomnia disorder. Therefore, future clinical trials or community-based intervention studies should be conducted to test whether lifestyle or sleep hygiene interventions for insomnia symptoms can reduce subsequent [cardiocerebral vascular disease] risks.”

The results suggest that efforts aimed at early detection and intervention should include a focus on younger adults and people who do not have high blood pressure, Dr. Li said.

The self-reported insomnia symptoms used in this study have not been fully validated, the investigators noted. The researchers also lacked information about potential confounders, such as shift work and obstructive sleep apnea, that are risk factors for coronary heart disease or stroke and may interfere with insomnia symptoms. In addition, the study did not capture changes in insomnia symptoms over time.

This study was supported by the National Key Research and Development Program of China, the Chinese Ministry of Science and Technology, and the National Natural Science Foundation of China. The China Kadoorie Biobank surveys were supported by grants from the Kadoorie Charitable Foundation and the U.K. Wellcome Trust. The authors had no relevant disclosures.

SOURCE: Zheng B et al. Neurology. 2019 Nov 6. doi: 10.1212/WNL.0000000000008581.