Are you an early riser, or do you stay up until the wee hours of the morning? Could the time you go to bed and eat dinner negatively affect your health? One’s 24-hour clock helps regulate many of the body’s normal functions. As a result, the time you go to bed could negatively impact your health, even leading to an increased risk of heart disease or type 2 diabetes.
Chronotype refers to one’s circadian rhythm, that 24-hour clock that regulates sleep-wake cycles.
Night owls vs. early birds may increase the risk for negative health outcomes, such as diabetes and high blood pressure.
One’s genetics accounts for only 50% of one’s chronotype. Modifications in sleep-wake cycles may improve heart health and lessen the risk of diabetes.
Diabetes and cardiovascular disease
As of 2018, over 23 million Americans have been diagnosed with diabetes mellitus, and almost 82 million can be classified as individuals with prediabetes. According to the Journal of the American Heart Association, patients with diabetes are at a 2-4 times higher risk of dying from heart (cardiovascular) disease than those without. This direct link between diabetes and heart disease risk is well established. Identifying behaviors and factors that individuals can change, such as exercise level, weight management, sleep habits, and even what time one goes to sleep, may improve health outcomes and lessen a person’s chance of diabetes and heart disease.
Circadian rhythm and chronotype
The tendency for a person to go to sleep at a specific moment throughout a 24-hour day is referred to as a person’s chronotype. One’s circadian rhythm is based upon various mental, physical, and behavioral changes throughout the twenty-four-hour cycle. Daylight and darkness play a role in establishing various body rhythms, an example being our sleep and wake cycle.
Numerous studies have evaluated the effects of one’s circadian rhythm and sleep habits on health. Our body’s functions are regulated by many hormones and various physiologic processes within the body. Changes in body temperature, hormone release, and even digestion and eating habits have been shown to relate to one’s chronotype.
Multiple scientists since the 1990s report that about 50% of our displayed chronotype is genetic and beyond our control. However, the remaining 50% occurs based on environmental and behavioral choices that may be changed or adjusted. Therefore, if we control the time of day we eat and sleep, we can influence our health outcomes, both negatively and positively.
Increased diabetes risk in ‘night owls’
A person’s sleep-wake cycle or chronotype can be categorized as early (‘early birds) or late (‘night owls’). However, there can also be an intermediate type that is not always evaluated in research. Those who tend to stay up later may have an increased risk of negative health outcomes, such as high blood pressure and type 2 diabetes.
Increased risk of diabetes secondary to sleep-wake schedule:
- Tendency to eat later in the evening and closer to going to bed.
- Tendency to snack after dinner.
- The tendency to skip breakfast may be higher.
- Tendency to eat larger meals later in the day or in general.
- Shift work.
- Less exposure to morning light.
- Higher evening light exposure (darkness).
- Any additional factors that cause a circadian rhythm mismatch or misalignment – Social changes such as eating out with friends, getting up earlier than normal for a meeting.
Increased inflammation and decreased glucose tolerance
When a person’s 24- hour clock misaligns, studies in healthy individuals have shown an increase in markers of inflammation and decreased glucose tolerance. This suggests increased cardiometabolic risk (concerns for metabolic illnesses such as diabetes and heart problems). Further studies demonstrate this in individuals with an increased risk of type-2 diabetes and those with metabolic syndrome at risk for diabetes.
Glucose and insulin fluctuate based on the time of day
Several studies suggest that those with a later chronotype prefer later in the day for various activities, including later evening meals and later bedtimes. This has been shown to negatively impact glucose metabolism and show increased insulin resistance,
In multiple studies, for example, in a 2013 study by Reutrakal et al, later chronotype and eating larger dinners lead to issues in diabetes management in those with type-2 diabetes regardless of any sleep disturbances, such as sleep apnea, snoring, or other sleep-related disorders.
In a 2015 study by Morris et al., following a meal, glucose levels increased 17% in the evening compared to the morning, while insulin responses were 14% lower at supper than at breakfast. This suggests that the circadian response to eating in the morning vs. evening hours is more effective at controlling sugar levels with improved insulin response.
Therefore, studies to address this decreased glucose tolerance as we shift from morning to evening continue to surface. By focusing on the effect that eating timing and the circadian rhythm have on glucose and insulin levels, researchers continue to demonstrate that the timing of eating, sleeping, and the light-dark cycle does play a role in how one’s body regulates sugar. This helps explain an increased risk of diabetes secondary to one’s chronotype.
It is simple to see how circadian rhythm changes with behaviors and eating habits relative to light and dark. When we evaluate the changes in glucose and insulin levels that arise with daily light and dark cycles, we appreciate how much time one spends awake during daylight vs. dark hours can have negative effects. Spending less time active during the daytime negatively affects one’s overall metabolic function, increasing one’s risk of diabetes.
Higher HgA1c levels in people with prediabetes who go to bed late
A 2017 cross-sectional prediabetes study evaluated hemoglobin A1c levels (HbA1c) measurements. They found that regardless of other sleep disturbances, going to bed later in the evening (late chronotype) was characterized by higher HbA1c levels. Because HbA1c values demonstrate a person’s average blood sugar levels for the preceding 3-month period, those ‘night owls’ were at a greater risk of developing diabetes. The researchers compared an increase in HbA1c with the effect of changing a person’s BMI (body mass index) by 1 unit (BMI being a key recognizable factor in the development of diabetes). This evidence further supports our body’s natural clock’s role in our body’s glucose regulation.
Shift work, a common chronotype misalignment
Numerous studies on those who perform shift work demonstrate increased inflammatory markers and increased risk of heart disease. By default, shift workers are a great example of alterations in the normal circadian rhythm. Those working overnights are awake, eating, and active without much daylight and sleep during light hours. This increases the risk of heart disease and diabetes and shows how other causes of circadian rhythm alterations could also negatively impact health. Note that these changes occur regardless of the duration one sleeps.
Evening chronotypes have an increased cardiovascular risk
In a 2021 study of over 2400 participants, scientists evaluated protein levels associated with insulin resistance and cardiovascular risk. The results demonstrated that proteins linked to cardiometabolic risks were increased in those with evening (‘night owl’) chronotypes.
In addition to the myriad of studies on chronotypes and risks of diabetes, many studies continue to be conducted on increased heart risks associated with evening chronotypes (‘night owls’). Not only did an early study published in 2012 find a 150% increased risk for type 2 diabetes (odds ratio of 2.5), but also a 30% increased risk (1.3 odds ratio) for an elevated resting heart rate and high blood pressure when evening types were compared to morning types.
Studies of varying evidence and quality demonstrate further heart health consequences of evening chronotype, including elevated blood pressure. The research is ongoing and provides a body of evidence for possible lifestyle interventions for cardiovascular disease (heart) prevention.
Should night owls (late chronotypes) alter sleep habits?
Though further research is essential to improve our understanding of the role of one’s circadian rhythm in health outcomes, studies suggest that for those with late chronotypes (meaning those who are more apt to go to bed later), this increases one’s overall cardiometabolic risks.
Therefore, those who stay up late may have an increased risk of diabetes and related metabolic illnesses, compromising their overall heart health. Thus, going to bed late may seriously impact the heart and overall health. With only 50% of a person’s chronotype genetically determined, there is room for change in one’s eating and sleep habits that could decrease the risk of heart disease and diabetes.