Michelle Turner-Young began struggling with sleep after having twin girls at the age of 16. Her daughters are 23 years old now. Committed to a lifestyle that prioritizes mental and physical well-being, Turner-Young is a Boston-based dance fitness instructor. She combines yoga and meditation in a practice she refers to as “mindful dance fitness.” She began offering classes in 2020, around the time that she first used singing bowls, or sound baths, as a way to confront her chronic sleeplessness.

“Sound bowls have been the only thing that have put me [to sleep] faster,” Turner-Young explained, referring to an 11-hour sound bath YouTube video that has her unconscious in 15 minutes. Today, a careful balance of sound baths, meditation and exercise allow her to stay healthy alongside her other commitments.

It took Turner-Young years postpartum to discover a routine that improved her sleep, but a healthy lifestyle continues to evade most adults worldwide. The CDC reports that 36.8% of adults in the U.S. get fewer than the recommended seven hours of sleep a night as of 2022. At the same time, nearly half of adults in the U.S. have some form of heart disease as well as obesity . A recent statement by the American Heart Association (AHA) suggests that these two health concerns may be more connected than previously thought.

Specifically, the AHA emphasizes the importance of “circadian health,” which includes sleep, in mitigating the risks of cardiometabolic diseases, or diseases related to heart health and metabolism. In fact, it asserts the astounding statistic that a one-hour increase in variability in sleep onset timing was associated with 25% higher odds of central obesity.

In other words, a sleep timing variation of just one hour is associated with a greater risk of metabolic disease.

“[Large studies] show that, if people have their sleep onset in an irregular fashion,” they are more susceptible to suffering major health consequences, said Sina Kianersi, a postdoctoral research fellow at Brigham and Women’s Hospital. “Meaning that one night they go to sleep, maybe at 10 p.m., another night they go to sleep at midnight. Then that alone... may increase their risk of cardiometabolic outcomes,” he said.

Kianersi’s research focuses on circadian health, a broad topic that, among other things, reflects a person’s internal clock. Sleep, meal timing, light exposure and exercise all influence circadian health. Ideally, internal biological processes associated with circadian rhythm align with triggers from the external environment. When lifestyle doesn’t align with the internal clock, it results in circadian misalignment, contributing to diseases such as obesity, type 2 diabetes, hypertension and cardiovascular disease.

Kristen Knutson, an associate professor of neurology and preventive medicine at Northwestern University and chair of the writing committee for the AHA statement, made a distinction between circadian health and sleep. “Circadian health and sleep health are related to each other, but they are not identical, and I think that is sort of a misconception some people have,” she said.

Sleep health refers to consistent sleep patterns, including bedtime routines and sleep duration. It’s narrower than circadian health, which refers to an entire 24-hour cycle. Knutson described circadian health as an organism’s way of preparing for sunup and sundown.

Light from the sun or from screens serves as a key external regulator that communicates wake or sleep periods. When someone stays awake late, eating meals or staring at screens, external input tells their body it’s daytime. Internal clocks likely indicate the opposite. Light at night confuses the central internal clock in the brain, the suprachiasmatic nuclei (SCN) in the hypothalamus. The SCN then communicates with peripheral clocks through neural and hormonal signals such as melatonin, cortisol, norepinephrine and epinephrine.

“[Cortisol and melatonin] tend to interact with a lot of metabolic processes, so if those hormones tend to be out of rhythm, or, you know, [are] desynchronized from the environment, that could lead to some metabolic impacts,” said Christopher Kline, a co-author on the AHA statement and associate professor of health and human development at University of Pittsburgh.

Circadian health researchers identified a number of genes associated with these biorhythms, nicknamed “clock” genes, including several in humans and other mammals as well as in fish, fruit flies and cyanobacteria.

What’s revelatory, Kline explained, is that a combination of physiological and behavioral tendencies contributes to the association between circadian health and cardiometabolic disease risk.

“Maybe your diet is relatively the same, when you stay up later versus when you go to bed earlier. But maybe your ability to metabolize that meal is slightly impaired if you've got highly variable sleep timing,” said Kline.

Those with highly variable sleep patterns also tend to have a higher daily caloric intake and live a more sedentary lifestyle compared to the rest of the population, according to the AHA’s data. Kline surmised that this may be due to having less energy during the day to exercise because of poor sleep health.

But it’s not always easy for the average person to maintain a consistent schedule between sleep, meals and light exposure.

Individuals who engage in shift or night work have a higher risk of circadian disruption and cardiometabolic diseases. Studies have even suggested that night shift work may be a carcinogen. Furthermore, data suggest that certain demographics are at greater risk than others.

Non-white Americans, especially Black Americans, are more likely to do shift work. They are also at a disproportionately high risk of cardiometabolic diseases.

“It's not biological, let's just put that out there,” Knutson asserted. “This is a sociocultural phenomenon. Any individual or group of individuals who are going to be at an increased risk of experiencing circadian disruption are going to be at an increased risk of the consequences of circadian disruption.”

Everything from neighborhood light exposure, noise levels, socioeconomic stature and job status threaten circadian disruption. It’s a health equity concern.

Additionally, not everyone has the same internal clock.

Knutson explained that for people who naturally stay up late, “they're more like night owls, [while] some of us [have] earlier [rhythms].” These variations are our chronotypes. The problem is, technology to determine one’s chronotype is not easily accessible to the public. Researchers at University of Pittsburgh recently developed an app to calculate 24-hour circadian rhythm cycles using wearable devices such as an Apple Watch. The app is now on the Apple App Store, available for public use.

Turner-Young, the mother-of-two who uses sound baths to sleep, used a Google Pixel Watch to discover that her sleep is inconsistent. Without the watch, she may not have identified what was impacting her energy throughout the day. As a dance fitness instructor, it’s important for her to have the energy to exercise efficiently.

Research connecting exercise with circadian rhythm remains in its infancy, according to Kline. “The timing of exercise could have importance to the circadian system,” he continued. “But we don't know whether that's person-dependent, or if recommending everyone exercise in the morning would be best.”

Regardless of timing, Knutson and Kline agree some exercise is better than none. Every little bit counts.

“But really, just [adjusting your] overall environment, [or] trying to minimize light exposure in those hours leading up into bedtime” goes a long way to preserve circadian health, assured Kline. “Obviously, it helps you sleep better, but it also keeps the timing of your circadian system relatively stable. So, you know, clinical recommendations... are recommendations that don't cost too much.”

21st century technology use, demanding work schedules and socioeconomic stressors interfere with the ability to prioritize health recommendations, but small changes go a long way. The AHA statement helped draw attention to the importance of timing and consistency in maintaining a healthy lifestyle.

“Yeah, most of us are not going to be able to have a perfectly timed breakfast, sleep, lunch, everything, always at the same time every day. That's just not realistic. But it's our first little step,” concluded Knutson. “You want to gradually try to change your lifestyle in steps that are achievable, so that you're motivated towards making changes that are realistic.”