Late-night habits of "night owls" raise the risk of heart disease

A recent study from the University of Gothenburg sheds new light on the relationship between circadian rhythms and cardiovascular health. The study reveals a startling correlation between late-night habits and the risk of coronary artery calcification, a critical factor in the development of atherosclerosis.

“Cardiovascular disease (CVD) is a major cause of morbidity and mortality worldwide. Approximately 49 million people in the European Union live with CVD, which accounts for 37% of all deaths in the region,” wrote the study authors.

The research, involving 771 people aged 50 to 64, is part of the larger SCAPIS population study. It meticulously assessed the degree of artery calcification in the heart’s coronary arteries using computer tomography. 

Key insights 

Participants self-reported their chronotype – whether they were extreme morning types, moderate morning types, intermediate types, moderate evening types, or extreme evening types.

The results were striking. Among those who classified themselves as extreme morning types, only 22.2% exhibited pronounced artery calcification. 

By contrast, the extreme evening types showed a significantly higher prevalence, with 40.6% having severe coronary artery calcification.

Study significance 

Atherosclerosis involves the accumulation of fatty deposits inside arteries, impeding blood flow. This disease develops over an extended period, often going unnoticed until causing severe conditions like angina, heart attacks, or strokes.

Previous studies have linked late-night habits with an increased risk of cardiovascular disease. However, this is the first research to specifically connect circadian rhythms to artery calcification, an early stage of cardiovascular disease.

“Our results indicate that extreme evening chronotype may be linked not only to poorer cardiovascular health in general, but also more specifically to calcification in the coronary arteries calcification and atherosclerosis,” said study first author Mio Kobayashi Frisk, a doctoral student at Sahlgrenska Academy.

Contributing factors

In assessing the risk of atherosclerosis, the study accounted for various factors, including blood pressure, blood lipids, weight, physical activity, stress level, sleep quality, and smoking habits. 

“As well as the previously known factors, the individual circadian rhythm also appears to be an important risk factor for atherosclerosis. We interpret our results as indicating that circadian rhythms are more significant early in the disease process. It should therefore particularly be considered in the preventive treatment of cardiovascular diseases,” said study co-author Ding Zou.

Self-reported chronotypes

An interesting aspect of the study is the reliance on self-reported chronotypes. While this could be seen as a limitation, it provides valuable insight into personal sleep patterns and their impact on health. The study excluded individuals who had experienced a heart attack, focusing on a healthier subset of the general population.

Chronotypes represent the average time when half of the night’s sleep has passed. For extreme morning types, this occurred around 02:55 AM, whereas for extreme evening types, it was around 04:25 AM.

The results highlight the need for further research into how our internal clocks influence our overall health, particularly concerning life-threatening conditions like atherosclerosis. 

The study is published in the journal Sleep Medicine.

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