Middle-aged and older adults who are more active at night are more likely to have poorer cardiovascular health than those who are more active during the day, a study has found.
The new research, published in the Journal of the American Heart Association, analysed health data from more than 300,000 adults (average age 57) taking part in the UK Biobank.
It examined how chronotypes – a person’s natural preference for sleep and wake times – influence cardiovascular health.
Around 8% of participants identified as ‘definitely evening types’, typically going to bed very late (for example, at 2am) and reaching peak activity later in the day.
By contrast, about 24% described themselves as ‘definitely morning types’, meaning they were more active earlier in the day and tended to go to bed earlier (for example, at 9pm).
The remaining 67% were classified as having an ‘intermediate’ chronotype, either because they were unsure or did not identify strongly as either morning or evening types.
Cardiovascular health was assessed using the American Heart Association’s Life’s Essential 8 metrics, which identify behaviours and health factors associated with optimal heart health.
These include a healthy diet, regular physical activity, not smoking, good sleep quality, and healthy levels of body weight, cholesterol, blood sugar and blood pressure.
The analysis found that, compared with people with an intermediate chronotype, evening types had a 79% higher prevalence of poor overall cardiovascular health scores.
Night-active individuals also had a 16% higher risk of suffering a heart attack or stroke over an average follow-up period of around 14 years, compared with those in the intermediate group.
Stronger effect in women
Meanwhile, the association between an evening chronotype and lower cardiovascular health scores was stronger in women than in men.
Much of the increased risk of heart disease among night-active individuals was linked to unhealthy behaviours and risk factors, particularly nicotine use and insufficient sleep.
By contrast, morning types had a 5% lower prevalence of poor cardiovascular health scores compared with people who did not have a strong morning or evening preference.
‘Evening types often experience circadian misalignment, meaning their internal biological clock may not match the natural day–night light cycle or their usual daily schedules,’ said lead study author Dr Sina Kianersi, a researcher in the Division of Sleep and Circadian Disorders at Brigham and Women’s Hospital and Harvard Medical School in the United States.
‘Evening types may be more likely to engage in behaviours that affect cardiovascular health, such as poor diet, smoking, and inadequate or irregular sleep.’
Not all bad news
The findings are not entirely negative for night owls, notes Kristen Knutson, volunteer chair of the American Heart Association’s 2025 scientific statement The Role of Circadian Health in Cardiometabolic Health and Disease Risk, who was not involved in the study.
‘These findings show that the higher risk of heart disease among evening types is partly driven by modifiable behaviours such as smoking and sleep,’ she explained.
‘Therefore, evening types have options to improve their cardiovascular health. Evening types are not inherently less healthy, but they face challenges that make it especially important for them to maintain a healthy lifestyle.’
The American Heart Association scientific statement led by Knutson suggests that individual chronotype should be considered when determining the timing of interventions or treatments.
‘Some medications or therapies work better when aligned with specific circadian rhythms, and this timing will vary depending on whether someone is a morning, intermediate or evening type,’ she said.
‘Targeted programmes for people who tend to stay up late could help them improve lifestyle habits and reduce their risk of cardiovascular disease.’
