‘Night owls’ may have worse heart health, but why?

Some people perform best in the morning, while others feel most awake and productive at night. But growing evidence suggests that the latter group, night owls, may be linked to poorer heart health.

Now, a large study published January 28 in the Journal of the American Heart Association is lending weight to this idea.

Taking information from the UK Biobank, a large repository of data from adults in the UK, researchers followed more than 322,000 adults aged 39 to 74 for almost 14 years. They investigated how chronotypes, such as being a morning person or a night person, are associated with cardiovascular disease risk.

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Participants reported their preferred sleep/wake schedule and were categorized as morning, intermediate, or evening types. Heart health was assessed using the American Heart Association’s Life’s Essential 8 score, which rates heart health on a scale of 0 to 100 based on eight factors: smoking, diet, exercise, blood sugar, weight, blood pressure, cholesterol, and sleep quality. A higher score indicates better cardiovascular health.

Compared to moderate sleepers, those who “reliably slept in the evening” were 79% more likely to have a poor overall score and 16% more likely to have a heart attack or stroke over nearly 14 years of follow-up. Those who were “good morning sleepers” were 5% less likely to have low scores than those who got a moderate amount of sleep.

But what’s behind this link? Is there something about the lifestyle of night owls that worsens heart health, or is there something unique to their biology that plays a role?

How lifestyle affects

In the Biobank study, night owls had worse scores on a variety of lifestyle-related factors compared to middle sleepers. For example, they had 54% higher nicotine exposure, 42% lower sleep, 19% lower physical activity, and 8% poorer diet. In contrast, morning people generally used less nicotine and had better eating habits than intermediate types.

Considering these differences, approximately 75% of the increased cardiovascular risk observed among night owls appears to be related to lifestyle factors rather than chronotype per se. Among these factors, smoking contributed the most (34%), followed by sleep deprivation (14%), hyperglycemia (12%), and diet and weight (11% each).

“Factors of overall cardiovascular health are modifiable, including exposure to nicotine,” study lead author Sheena Kianasi, a postdoctoral fellow at Brigham and Women’s Hospital and Harvard Medical School, told Live Science via email. Other influencing lifestyle factors include physical activity levels, blood pressure and cholesterol, he added.

“So for people who identify as night owls, that’s a good reason to be more proactive about these basics,” he said.

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Previous research suggests that night owls often experience social jet lag, or a mismatch between their body clock and daily life. This discrepancy may be related to habits such as eating late at night, skipping breakfast, sleeping irregularly, and being more dependent on caffeine and nicotine. Furthermore, these behaviors are thought to be associated with factors that increase the risk of heart disease, such as higher body mass index (BMI), higher blood sugar levels, higher insulin resistance, and lower levels of good cholesterol.

Previous research has also shown that adults with irregular sleep patterns have a 26% higher risk of stroke, heart attack, or heart failure than adults with regular sleep patterns, even if they get enough sleep overall.

“Interrupted or inadequate sleep can increase blood pressure, cholesterol, and blood sugar levels, and is often accompanied by weight gain,” Dr. Bibhu Mohanty, an associate professor at the University of South Florida who was not involved in the study, told Live Science via email. “This is mainly due to the following factors.” [the stress hormone] Cortisol mobilizes sugar and fat, which can make recovery difficult once the disease begins. ”

Ecology of night owls

Being a night owl is not a choice. It’s partially hardwired into people’s genes.

Research has linked hundreds of genetic variations to clonotypes. Many of the highlighted genes are involved in regulating the body’s 24-hour clock, or circadian rhythm. These rhythms help control sleep, appetite, hormonal cycles, and heart function throughout the day and night.

People with late chronotypes often have delayed circadian rhythms. This means that levels of the sleep-promoting hormone melatonin rise later in the evening than in earlier chronotypes. Second, cortisol, which helps your body wake up, rises later in the morning than usual.

This change can cause the body to become out of sync with the normal day/night cycle, causing the body’s fight-or-flight system to become overactive. As a result, blood pressure remains high during the night, leading to increased inflammation and oxidative stress. Over time, these changes can damage blood vessels, disrupt blood sugar levels, and promote plaque buildup in the arteries, which can manifest as heart disease, research suggests.

Many of the genes involved in determining clonotype also directly affect lipid and glucose metabolism, or how the body breaks down fats and sugars. Research has shown that night owls have altered expression of these “clock genes,” along with elevated levels of inflammatory markers and triglycerides, a type of fat, compared to morning owls. These patterns may contribute to metabolic problems such as insulin resistance and low cholesterol, both known risk factors for heart disease, but further research is needed to confirm a direct link.

Early evidence also suggests that there are subtle differences in heart structure and function in night owls, although the long-term effects of these differences are still being studied.

Questions to be addressed

Some data from the UK Biobank study suggests that the link between staying up late and poor heart health may be stronger in women than in men. According to the LE8 score, female night owls are 96% more likely to have poor overall cardiovascular health compared to intermediate chronotypes, and male night owls are 67% more likely to have poor overall cardiovascular health.

“This difference may reflect social pressures, biology, or both. This is a sign worthy of further study,” Kianasi said.

A UK Biobank study found a link between chronotype and poor heart health, but being a night owl doesn’t mean you’re doomed to cardiovascular disease.

“We need research that gets closer to causality, using approaches like genetics as well as intervention studies,” Kianasi said. “And it will be important to see whether these patterns also hold true for young adults and other populations with different work schedules and environments.”

For night owls who want to protect their hearts, Mohanty advises them to focus on improving their lifestyle habits wherever possible.

“That means developing healthier sleep habits, exercising, making healthy food choices, avoiding unnecessary snacking and smoking, and potentially using medications to reduce risk if necessary,” he said. A holistic approach to heart health is “probably the best approach to limiting risk.”