According to a study conducted at the University of Gothenburg, Sweden, night owls are almost twice as likely to experience arterial calcification as early risers. The circadian function appears to be particularly important in the early stages of cardiovascular disease.
In atherosclerosis, fatty deposits form on the inside of the arteries, impeding blood flow. The disease develops over a long period and is only noticed when blood clots occur, leading to angina, heart attack, or stroke. Previous research has shown that people with evening habits have an increased risk of cardiovascular disease. However, this is the first study to show the specific effects of circadian rhythms on arterial calcification.
Calcification of the Coronary Arteries
The study, published in the journal Sleep Medicine, involved 771 men and women aged 50 to 64, all of whom were participating in the larger population study SCAPIS. The degree of arterial calcification in the coronary arteries was examined using computed tomography. The participants self-identified their chronotype on a five-point scale: extreme morning type, moderate morning type, neither type, moderate evening type, or extreme evening type.
Out of the 771 participants, 144 identified as extreme morning types and 128 as extreme evening types. The group which was the most awake in the morning had 22.2% showing significant arterial calcification – the lowest prevalence among all five chronotypes. The extreme evening type group showed the highest prevalence of severe coronary artery calcification at 40.6%.
The lead author of the study is Mio Kobayashi Frisk, a doctoral student at the Sahlgrenska Academy, University of Gothenburg:
“Our results suggest that an extreme evening chronotype may be associated not only with poorer overall cardiovascular health, but specifically with calcification in the coronary arteries, calcification and arteriosclerosis,”
Mio Kobayashi Frisk, Doctoral Student at the Sahlgrenska Academy, University of Gothenburg
The statistical analysis considered several factors that can influence the risk of arteriosclerosis, including blood pressure, blood lipids, weight, physical activity, stress level, sleep, and smoking.
The senior author of the study is Ding Zou, a researcher at the Sahlgrenska Academy, University of Gothenburg:
“In addition to previously known factors, individual circadian rhythm appears to be an important risk factor for arteriosclerosis. We interpret our results as evidence that the circadian rhythm is of greater importance in the early stages of the disease and should therefore be given particular consideration in the preventive treatment of cardiovascular diseases,” says Ding Zou.
Those who had suffered a heart attack were excluded from the study, meaning that the study participants were healthier than the general population. Another weakness identified by the researchers is that the participants self-reported their chronotype.
One can say that there is an average time for each chronotype at which half the night’s sleep has elapsed. In a previous study with the same population, although not necessarily the same individuals, this time occurred at 02:55 for the extreme morning type group and at 04:25 for the extreme evening type group. For the other chronotype groups, the mean sleep times fell somewhere between these extremes.
SCAPIS stands for Swedish CArdioPulmonary bioImage Study. It is a research project in the field of cardiovascular and pulmonary diseases. As part of the project, 30,000 randomly selected Swedes aged 50 to 64 underwent comprehensive health examinations, including blood tests, functional tests, and advanced radiological imaging of organs and blood vessels. Six universities and university hospitals lead and operate SCAPIS in close collaboration with the Swedish Heart-Lung Foundation, the main financier of the study.
Kobayashi Frisk, M., et al. (2024). Evening preference is associated with coronary artery calcification in a middle-aged Swedish population. Sleep Medicine. doi.org/10.1016/j.sleep.2023.11.004.