|Disrupted circadian rhythms contribute to heart disease risk.|
Globally, heart disease is a major threat to human health. The identification of its risk is vital for its prevention. To date, the cluster of risk factors used as an index for predicting heart disease is collectively known as the 'metabolic syndrome'. They include high blood pressure, blood lipids and sugar, and also obesity.
This syndrome is associated with an approximate doubling of risk of incident (new)
cardiovascular disease and premature death in adult populations. Its frequency is increasing worldwide. In Australia, its prevalence in adults exceeds 40% and in China, it was already around 30% in 2016. In European people aged 60 years or above the prevalence of the metabolic syndrome is 25-30%.
However, there is continuing debate on the number of different definitions used globally, and which risk factors are used in each of them. Because of this, a group of researchers led by Professor Zimmet (Monash University) and Professor Zumin Shi (Qatar University) asked an important question, namely, whether there might be a way to better measure heart disease risk.
In 2019, a Monash and Tel Aviv University study led by Professor Zimmet and Professor Noga Kronfeld-Schor (Tel Aviv) pointed out that all of the key metabolic syndrome components including blood sugar and cholesterol and obesity were linked to disruption of circadian rhythm, also known as our “Body Clock”. This might explain how the metabolic risk factors, in combination with a disrupted circadian rhythm, have such an important impact on heart disease risk.
Furthermore, the researchers noted that people who have the metabolic syndrome also often have poor sleep quality and depression which are both known to be objective measures of disturbances of circadian rhythms. So, they suggested adding these measures to the metabolic syndrome and renaming it to create a new entity, “Circadian Syndrome”.
Professor Shi has now compared cardiovascular risk estimates from the Circadian Syndrome against the metabolic syndrome in 9360 adults from the China Health and Retirement Longitudinal Study (CHARLS).
The results have recently been reported in the Journal of Internal Medicine. They have demonstrated that the Circadian Syndrome predicts heart disease better than the metabolic syndrome. So, while both the metabolic syndrome and Circadian Syndrome do predict both prevailing and new cardiovascular disease in the Chinese population, the Circadian Syndrome does it better. Thus, adding sleep quality and depression to the metabolic syndrome equation is likely to boost the risk value.
This could be a cost- and health-effective approach to prevention of heart disease. Zimmet and Shi have pointed out that further studies, now underway in other populations, are required to validate these findings.
They recommend including measures of poor sleep and depression in popular heart disease risk equations which are currently used to provide indication of future risk for heart disease.
As the assessment of short sleep and depression is relatively easy and not expensive, the authors suggest their measurement be included in clinical settings. This approach may have very important implications for the equations used widely and globally for predicting risk of cardiovascular disease, one of the world’s greatest epidemics numerically.
The impact of sleep quality is beginning to be more widely recognised, and if the "Circadian Syndrome" measures are employed by cardiologists and public health experts, it may help save many more lives with more efficient prevention of heart disease in those at highest risk.
- Shi Z, Tuomilehto J, Kronfeld-Schor N, Alberti GK, Stern N, El-Osta A, Bilu C, Einat H, Zimmet P. The circadian syndrome predicts cardiovascular disease better than metabolic syndrome in Chinese adults. J Intern Med. 2020 Dec 19. doi: 10.1111/joim.13204. Epub ahead of print. PMID: 33340184.