A study into the body clock’s effect on cardiovascular risk factors has found that timing truly counts.
Exercise has long been shown to lower the risk of heart disease, stroke and diabetes – by lowering cholesterol and blood sugar levels and making the heart work harder.
But now experts at the University of Edinburgh say it’s not just about what type of exercise you do, but when you do it – with early exercise sessions benefitting morning people, and vice-versa for night owls.
The study, published in the Open Heart journal, found that timing exercise to match a person’s chronotype – the natural predisposition to morning or evening alertness – may lower heart disease risk.
People already at risk of heart disease- such as those with high cholesterol – were able to reduce their risk by simply shifting the time they worked out to match their internal body clock.
The researchers concluded: ‘Integrating the principle of ‘chrono-exercise’, may trigger a novel and impactful approach to enhancing outcomes in preventive cardiovascular and metabolic health.’
The study tracked 150 participants, aged 40 to 60-years-old, who had at least one cardiovascular risk, such as high cholesterol or obesity, and led a sedentary lifestyle.
Those with a family history of premature heart disease – affecting a first degree male or female relative before the age of 55 or 65 respectively – were also included.
Working around your body clock could boost the beneficial effects of exercise, new research suggests
Participants completed the Morningness-Eveningness questionnaire, which uses questions like ‘what time would you get up if you were entirely free to plan your day,’ to ascertain their chronotype.
Their core body temperature was also measured over a 48 hour period.
Participants were randomly assigned to exercise at a time that either matched their chronotype or at a time that didn’t, between 8-11am or 6pm-9pm.
For 12 weeks, participants had to do five sessions of supervised moderate-intensity aerobic exercise, such as brisk walking, each lasting 40 minutes.
At the end of the study period, 134 participants had completed all 60 exercise sessions.
Of these, 70 were morning larks – just under half of which had been matched to their chronotype; 64 were night owls, 30 of whom exercised in the evening.
Blood pressure, heart rate variability (HRV), fasting blood sugar, VO2 max, bad cholesterol levels and sleep quality were all measured before the start of the trial and three days after it finished.
Results showed that heart disease risk factors, aerobic fitness and sleep quality improved in both groups with 12 weeks of exercise.
But matching exercise with chronotype produced more significant improvements in blood pressure, heart rate variability, aerobic capacity, metabolic markers and sleep quality than mismatched exercise.
The scientists said this could be because aligning exercise with the body’s clock can ‘entrain peripheral clocks in skeletal muscle, adipose tissue and vasculature more effectively, enhancing metabolic efficiency and reducing inflammation.’
This was particularly true for sleep quality, and systolic blood pressure – which measures the pressure at which blood pushes against the artery walls when the heart beats.
A normal blood pressure is usually considered to be between 90/60mmHg and 120/80mmHg, whilst high blood pressure starts at 140/90mmHg.
After 12 weeks of exercise, those who matched their workout time to their chronotype experienced a 10.8mmHg drop in systolic blood pressure, compared with a drop of just 5.5mm Hg in people whose exercise sessions had been mismatched .
The fall in systolic pressure was even larger among those who had high blood pressure to begin with.
In this group, who exercised according to their body clock, systolic blood pressure fell by an average of 13.6mmHg, almost double the decrease experienced by those who exercised out of sync with their chronotype.
Overall, the effect was most significant among morning people than night owls.
The team acknowledged that the results lack generalisability – due to the fact that intermediate chronotype – people who are neither a morning nor evening person – were excluded.
Furthermore, the study only included participants from hospitals in Lahore.
But, they concluded: ‘This study adds to a growing body of evidence suggesting that the timing of exercise when aligned with an individual’s internal biological clock can significantly enhance health outcomes.’
Commenting on the findings, Dr Rajiv Sankaranarayanan a consultant cardiologist from the British Cardiovascular Society, said: ‘From a UK perspective, the study’s findings are highly relevant to preventive cardiology within the NHS, where scalable, cost effective inventions are essential.
‘Incorporating simple chronotype assessment into lifestyle advice could enhance adherence and outcomes, particularly in patients with hypertension or cardiometabolic risk.’
However, he warned, before widespread implementation, validation in more diverse, real-world populations is needed.
Dr Nina Rzechorzek, a clinician scientist from the University of Cambridge, echoed his concerns, stating that the sleep findings in particular should be interpreted with caution, as the researchers relied on self-reported sleep quality rather than clinically objective measures.
She added: ‘In practical terms, this does not mean exercise is currently being prescribed at the wrong clock time, or that everyone now needs formal chronotype testing.
‘Most people who exercise routinely already do so when they prefer to or when their schedule allows, so the realistic implication is more modest.’
Dr Jeffery Kelu, from King’s College London, who wasn’t involved in the current study labelled the findings ‘important’.
He said: ‘This study brings bringing personalised medicine into a very practical context by asking not only what intervention to prescribe, but when to prescribe it.
Around eight million people in the UK are living with cardiovascular disease, with an estimated 1.2million thought to be overweight.
It is often caused by a build-up of fat in the arteries, restricting blood flow.
Smoking, drinking alcohol, being overweight and leading a sedentary lifestyle can all increase the risk.
Heart disease remains one of the biggest killers, claiming more than 460 lives a day – roughly one every three minutes.
