Body Clock Day (Tainai Tokei no Hi) — 3/31, from "31 = Circadian"

What Is Body Clock Day?

March 31st is celebrated every year as "Body Clock Day." Just before the start of the new fiscal year in Japan, this day was established by DOCOMO Healthcare, Inc. (as it was then known) with the wish that people adjust their daily rhythms and get a healthy fresh start. The number "31" is also a wordplay — read as "thirty-one," it echoes the sound of "circadian" (rhythm). It's a meaningful day to turn your attention to your body's own rhythm during the busy end-of-fiscal-year period.

Scientific Facts About the Circadian Rhythm

Our bodies have a precise system that keeps time even without looking at a clock.

• A 24-hour regulatory cycle: The circadian rhythm refers to physiological changes that fluctuate on roughly a 24-hour cycle. In fact, sleep, body temperature, blood pressure, and hormone secretion are all governed by this rhythm, forming the foundation of health.
• The resetting effect of light: The human body clock actually runs slightly longer than 24 hours (about 24.2 hours). Exposure to sunlight in the morning stimulates the brain's "master clock," resetting this small daily discrepancy.

Facts About Hormones and Sleep Mechanisms

Having the right hormones released at the right times is essential for mental and physical stability.

• The role of melatonin: Melatonin, the "sleep hormone" released at night, has its production suppressed by exposure to bright light. This is why using a smartphone before bed lowers sleep quality — blue light tricks the brain into thinking it's daytime, throwing off the body clock.
• Fluctuations in core body temperature: Following the body clock, our temperature begins to drop before sleep and starts rising in the early morning before activity. When this temperature rhythm is disrupted, it can cause trouble falling asleep or reduced concentration during the day.

Interesting Facts About the Body Clock

• "Secondary clocks" in your organs: Besides the master clock in the brain, organs like the heart and liver each have their own "peripheral clocks." Keeping meal times consistent helps regulate these peripheral clocks and smooths out metabolism.
• Morning or night types are partly genetic: A person's chronotype (morning or night type) has a genetic component. Rather than forcing yourself to change, understanding your own tendencies and designing your lifestyle around them can improve performance.
• "Social jetlag" from weekend sleep-ins: Sleeping in on weekends to make up for weekday sleep deprivation actually causes "social jetlag," disrupting the body clock and leading to that heavy, tired feeling on Monday mornings.
• A 15-hour delay: Melatonin is released roughly 15 hours after you wake up and get morning sunlight. In other words, how you spend your morning already determines the quality of that night's sleep.
• Diet and the body clock: Research in "chrono-nutrition" shows that when you eat matters as much as what you eat. Eating protein at breakfast, in particular, sends a powerful signal that resets the body clock.

Tips for Spending Body Clock Day

• On the morning of March 31st (Body Clock Day), open your curtains and soak in plenty of sunlight, signaling to your brain and body that a new day has begun
• Ahead of the new fiscal year, put away digital devices 1-2 hours before bed and spend quiet time under warm lighting to encourage melatonin release for deep sleep
• Keep your meal times as consistent as possible to regulate your internal organ rhythms, improving digestion and building up stamina from within
• Track your sleep duration and how you feel upon waking to objectively understand your weekly rhythm and discover your own "golden rhythm" for feeling your best

Harmonizing With Your Inner "Life Clock" Sets You Up for Your Best Condition Tomorrow

March 31st is a day to step away from the noisy outside world and listen to the quiet rhythm ticking within you. We all carry a remarkable clock inside us, synced with nature and the cosmos. Rather than ignoring that rhythm and pushing through, aligning with it lets you unlock your full potential. A well-tuned body clock brings stability to your mind, vitality to your body, and a glow to your expression. Take care of your rhythm as you would care for yourself, and step into the bright new season feeling completely refreshed.