The Dawn of a New Day

 

When the child of morning, rosy-fingered Dawn, appeared, Odysseus rose and led the way to the place of assembly, which was near the ships.

Book VIII, The Odyssey

Homer

 

The phrase “rosy-fingered dawn” is an epithet (a descriptive term) used many times by Homer in both the Iliad and the Odyssey to say, “the break of day”. The term also signifies a fresh start to a new day and a tribute to the trials and tribulations of the day. How does the body handle the “rosy-fingered dawn” and rising from sleep to face a new day? What physiologic changes occur and how do those changes impact heart health?

 

The human body ticks to a 24-hour clock. This clock determines changes in our bodily functions which guide us between a rest stage (sleep) and an active stage. Our internal rhythms are synchronized with the world through interactions with light. These variations are called circadian rhythms (the term circadian is from Latin, circa which means around and dies which means day; around the day). As the rosy-fingered dawn breaks, we sense the presence of light. This results in the secretion of a number of hormones which serve to rouse us, “rev” us up, to get ready for a new day. The hormones include adrenaline and cortisol, which result in an increase in blood pressure and heart rate, increase our wakefulness, increase body temperature and get us ready to be become active. On the other hand, as light fades, the body secretes melatonin and decreases adrenaline and cortisol, getting us ready for the rest phase, sleep. Disruptions to the well-controlled circadian rhythm can lead to various chronic illnesses including heart disease. 

 

Circadian rhythms are controlled by a number of biological clocks. A central clock is located deep in the brain and regulates the clocks located throughout the body. These peripheral clocks are found in nearly all of the tissues of the body, especially in the gastrointestinal system, the nervous system, the liver and the heart. The circadian clocks are molecules within the cell that provide feedback loops timed to a 24-hour cycle. There are clocks in the heart muscle as well as in the wall of blood vessels. The heart muscle clocks orchestrate cellular processes, ensuring that they occur at the right time of the day. Growth and repair of heart tissue takes place during sleep or rest periods. If this circadian pattern is broken, then cardiac pathology ensues. During a normal day, there are fluctuations of up to 20% in various cardiac parameters. For example, blood pressure is lowest during sleep and highest in the early morning hours.  This is due to the release of the hormones responsible for rousing us at the beginning of the day.  Similarly, the greatest risk for a heart attack or stroke is around 6 AM. This is a direct result of the early morning changes with increased blood pressure and heart rate leading to increased stress with the heart’s blood vessels and an increase in clotting factors caused by the release of hormones. In addition, life threatening arrhythmias and sudden cardiac arrest peak around 6 AM.  

 

Maintaining normal circadian periodicity is important for preventing disease and maximizing longevity. Disruption of the normal circadian rhythm is detrimental and leads to a variety of chronic illnesses. Disruption can be genetic, environmental or behavioral. Irregular sleep and eating schedules misalign the clocks. It is important to keep sleep timed with lack of light, i.e. night-time. Irregular sleep schedules throw off the biological clocks so they can’t synchronize properly with the light-dark cycle. Changes such as jet lag and daylight savings time can disturb internal clocks and lead to cognitive impairment and increased risk for heart attack.  Shift workers who sleep during daytime are especially prone to circadian disturbances. Shift work is a risk factor for heart disease, diabetes, obesity and hypertension. It increases cholesterol and triglyceride levels and increase inflammation. Sleep timing is important as well. Evening types, people who have later wake up and bedtimes, are at increased risk compared to morning people. Evening types have a higher incidence of cardiac disease, diabetes and obesity. Therefore, it is important to keep a regular sleep schedule. Meal timing is another factor as food serves to synchronize the biological clocks. Eating late at night also leads to cardiac disease, diabetes, obesity and high cholesterol. Shifting food toward the beginning of the day reduces those risks. This was proven in a recent study. Late eaters, people whose largest meal of the day was after 12:38 PM, had higher risk for obesity than people whose main meal is at lunch time. Having smaller meals throughout the day was better than eating three “square” meals. In addition, intermittent fasting, food intake restricted to early morning to 6 PM with an overnight fast, can reduce weight and protect against metabolic disease. 

 

To every rule, there is an exception. In this case, the exception lies in a Blue Zone. Blue Zones are areas around the world where there is exceptional longevity, with many people in the population reaching 100 years of age. Blue Zones have been identified in Japan, Costa Rica, California and on the Mediterranean island of Ikaria, Greece. The Mediterranean lifestyle seems to counter the circadian rhythms noted above. Dinner is served after 9 PM at night and bedtime occurs late as well. In addition, there is a day time siesta, so sleep patterns are irregular. On the other hand, the main meal is lunch. 

 

There are numerous factors involved in greeting many rosy-fingered dawns. Listening to our biologic clocks and following our circadian rhythms can help stave off disease and increase longevity. In order to do this, regular sleep habits and timing sleep patterns to light and dark seem prudent. In addition, shifting caloric intake to earlier in the day, eating smaller meals and doing some overnight fasting will improve the chances of seeing the dawn of a new day.