What a large rural Chinese study found about sleep and heart disease
The most directly relevant evidence comes from the Henan Rural Cohort in China, which surveyed 27,935 adults and identified 1,506 cases of coronary heart disease [3]. Sleep was measured with the Pittsburgh Sleep Quality Index, a standard questionnaire that scores how poor a person's sleep is, and participants also reported how many hours they slept at night. The study compared people with different sleep-quality scores and different sleep durations to see how their odds of having CHD differed.
The results showed a stepwise pattern for sleep quality: compared with people scoring below 3 on the sleep-quality index, those scoring 3–5 had 1.42 times the odds of CHD, those scoring 6–8 had 1.99 times the odds, and those scoring 9 or higher had 2.56 times the odds, after adjusting for other factors [3]. In plain terms, the worse the sleep quality, the higher the odds of heart disease, and the gradient was consistent across the score ranges.
For sleep duration, the comparison was against people who slept about 7 hours a night. Men who slept less than 5 hours had 1.55 times the odds of CHD, and women who slept less than 5 hours had 1.80 times the odds [3]. The association was described as more obvious in women, and the strongest prevalence of CHD was found in people who both slept short and had poor sleep quality [3].
Why short sleep and poor sleep quality might matter for the heart
The Chinese cohort did not test a biological mechanism, so any explanation of why short or poor sleep would affect the heart is a possibility rather than a demonstrated cause. What the study does show is that the association held after statistical adjustment for other factors, and that it was strongest when short duration and poor quality occurred together [3]. That pattern is consistent with the idea that sleep problems may cluster with other stressors on the heart, but the study design cannot separate cause from consequence.
It is also worth noting what the study did not find clearly: long sleep duration was not highlighted as a risk factor in the results, and the reported duration findings centered on short sleep [3]. So in this population, the signal is mainly about too little sleep and poor quality, not about too much sleep.
What about sleep complaints, and do findings from Western countries apply?
Sleep complaints—such as having told a doctor that you have trouble sleeping—have been studied in US adults, where they were associated with higher all-cause mortality and, among people with a history of cardiovascular disease or cancer, with higher heart disease mortality [1]. In that US study, sleep complaints mainly increased mortality risk among people who slept less than 6 hours or 6–8 hours, not among long sleepers [1]. But that evidence comes from a Western population, so it does not directly answer whether sleep complaints predict heart attacks in non-Western groups.
A separate Chinese cohort looked at sleep duration and cognitive function rather than heart disease, and found a bidirectional association: short or long sleep predicted lower later cognition, and lower cognition predicted short or long sleep, with cognition appearing to be the stronger driver [2]. That study does not address heart attacks, but it reinforces that in a non-Western population, both short and long sleep can be markers of underlying health problems—which is a reason to be cautious about reading sleep duration as a simple cause of heart disease.
What remains uncertain for a general reader
The direct non-Western evidence on heart attacks is essentially one large cross-sectional study from rural China [3]. Because it measured sleep and CHD at roughly the same time, it cannot establish whether poor or short sleep came before the heart disease. The US study on sleep complaints is longitudinal and ties complaints to mortality over time, but in a Western population [1]. Putting these together, the most defensible answer is that short sleep and poor sleep quality are associated with higher heart disease risk in a large non-Western population, while long sleep and sleep complaints remain less clearly established as predictors in that setting.
Sources used in this answer
Association of sleep complaints with all-cause and heart disease mortality among US adults
In US adults, sleep complaints were associated with higher all-cause mortality and, among those with cardiovascular disease or cancer, with higher heart disease mortality, with the association strongest in short and recommended sleep duration groups.
Exploring the Bidirectional Associations Between Short or Long Sleep Duration and Lower Cognitive Function: A 7-Year Cohort Study in China
In a Chinese cohort, short or long sleep duration and lower cognitive function predicted each other over time, with lower cognition appearing to be the stronger driver.
The association of sleep quality and night sleep duration with coronary heart disease in a large-scale rural population
In a large rural Chinese population, poor sleep quality and short night sleep duration were associated with higher odds of coronary heart disease, with the strongest association in short sleepers who also had poor sleep quality.
Denmark’s attack on ‘non-western’ neighbourhoods
This paper examines Denmark's housing legislation and social segregation and does not address sleep or heart attack risk.
Disease etiologies in non-western medical systems
This paper examines disease etiologies in non-Western medical systems from an anthropological perspective and does not address sleep as a predictor of heart attacks.