Tag sunlight

Let There Be Light: Circadian Rhythm

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Natural sunlight is one of the most powerful regulators of human biology. At the center of this system is the circadian rhythm—an internal, roughly 24-hour cycle that governs sleep, hormone release, metabolism, body temperature, and even cognitive performance. While this rhythm is generated internally, it is synchronized to the external world primarily through exposure to natural light.

Sunlight as the master “time-setter”

Specialized cells in the retina detect light—especially blue wavelengths present in morning sunlight—and send signals directly to the brain’s “master clock,” the suprachiasmatic nucleus (SCN) in the hypothalamus. This signal does two critical things:

  • Suppresses melatonin (the sleep hormone) in the morning
  • Reinforces wakefulness, alertness, and cortisol release at appropriate times

In the absence of consistent natural light cues, the circadian system begins to “free-run,” drifting away from the 24-hour day. This is why people in artificially lit environments—or those who spend most of their time indoors—often experience sleep disturbances, fatigue, or reduced mental clarity.

A famous example comes from isolation experiments, including one involving a medical student who lived for weeks in a sensory deprivation bunker without access to natural light or time cues. Over time, their sleep–wake cycle lengthened beyond 24 hours, demonstrating that while the body has an internal clock, it depends on sunlight to stay properly aligned.

Genetic basis of circadian regulation

At a deeper level, circadian rhythms are governed by a network of “clock genes” that operate through feedback loops in nearly every cell of the body. Key genes include:

  • CLOCK and BMAL1: activate transcription of other clock genes
  • PER (Period) and CRY (Cryptochrome): accumulate over time and then inhibit CLOCK/BMAL1 activity

This creates a self-regulating oscillation: genes turn on, proteins build up, then shut the system down, and the cycle repeats roughly every 24 hours.

These genetic rhythms are not limited to the brain. Peripheral tissues—like the liver, heart, and muscles—also have their own clocks, which are coordinated by the SCN and influenced by environmental signals such as light, food intake, and activity.

Disruptions to these genes or their expression have been linked to:

  • Sleep disorders
  • Metabolic diseases (e.g., obesity, diabetes)
  • Mood disorders
  • Increased risk of certain cancers

This highlights that circadian regulation is not just about sleep—it is a fundamental organizing principle of physiology.

Architecture and natural light: the Fuji example

The importance of sunlight extends beyond biology into the design of human environments. The Fuji Kindergarten is a well-known example of architecture intentionally designed to optimize natural light exposure. Its open, circular structure, expansive windows, and indoor–outdoor flow ensure that children are continuously exposed to daylight throughout the day.

This design aligns with circadian principles:

  • Bright daylight exposure supports alertness and learning
  • Gradual transitions in natural light help regulate energy levels
  • Reduced reliance on artificial lighting maintains a more biologically natural environment

Such spaces are increasingly seen as beneficial not just for children, but for workplaces, hospitals, and homes.

Putting it all together

Natural sunlight acts as the synchronizing force that keeps our genetically encoded circadian machinery aligned with the Earth’s day–night cycle. Without it, the internal clock drifts; with it, physiology, cognition, and behavior become more stable and efficient.

In modern life—where artificial lighting and indoor living dominate—this connection is often weakened. Understanding both the environmental (light exposure) and genetic (clock gene feedback loops) aspects of circadian regulation underscores a simple but powerful point: regular exposure to natural daylight is not just beneficial—it is biologically essential.

Low Vitamin D Levels Linked to Macular Degeneration Risk

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Vitamin D has gotten more attention in recent years, as a result of extensive research which has explored the impact of a deficiency in this important substance. A meta-analysis on vitamin D deficiency which was published earlier this year in Maturitas revealed a possible correlation between low levels of 25-hydroxyvitamin D in the body and increased risk for development of age-related macular degeneration (AMD). Furthermore, scientists surmise that if a vitamin D deficiency is corrected well before any signs of AMD are present, the disease’s prognosis is much improved.

The meta-analysis revealed that individuals with macular degeneration had vitamin D levels which were an average of 15% lower than levels in individuals without the disease. Another analysis revealed that subjects with highest circulating levels of vitamin had 50-80% lower odds of developing AMD compared with those who had the lowest circulating vitamin D levels.

However, despite all of these findings, it is not yet clear whether vitamin D supplementation would have a protective effect against AMD. In addition, the lower vitamin D levels found in some subjects may have resulted from the pathophysiology of AMD itself.

Rather than take a chance, I would prefer to promote vitamin D supplementation under the assumption that low vitamin D levels are a causative factor in the development of AMD. I also lean strongly towards a brief amount of exposure to sunlight daily in order to boost vitamin D levels naturally. In order for such exposure to be effective, sunscreen cannot be used around the clock. My recommendation is to sit in the sun for 3 minutes daily.

The Origins Of Daylight Savings Time

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Now that most of the nation is taking a break from Daylight Savings Time (Arizona and Hawaii are exempt from the twice yearly clock shift) and is also recovering from the Presidential Election, I thought it might be fun to review the history of Daylight Savings Time.

ROOTS OF DAYLIGHT SAVINGS TIME

The concept of Daylight Savings Time (DST) originated in ancient civilizations as our ancestors referenced the daylight hours and adjusted their daily schedules accordingly. However, the practice of conserving daylight hours over the centuries was sporadic. The idea resurfaced in the 18th century when American politician and inventor Benjamin Franklin wrote an essay in 1784 called “An Economical Project for Diminishing the Cost of Light” which he submitted to the editor of The Journal of Paris. Franklin suggested that candle usage could be minimized by adjusting clocks to get people out of bed earlier in the morning in an effort to use natural sunlight instead.

More than a century later, a New Zealand scientist by the name of George Vernon Hudson proposed a two-hour shift in time forward in October with a corresponding two-hour shift backward in March, but the idea never took off. Ten years later, a more dizzying concept of adjusting clocks was suggested by a Brit by the name of William Willett. Willett came up with the idea of setting clocks ahead 20 minutes on each Sunday in April, then switching them back on each Sunday in September. His idea was then introduced to the House of Commons in 1908, with the first Daylight Saving Bill drafted the following year and presented to Parliament. The United Kingdom did not put DST into effect until 1916, a year after Willett died.
More recently, Germany developed DST and introduced it on April 30, 1916 by turning the clocks forward by one hour. This was done in an effort to conserve fuel normally used for artificial lighting so that it would be used for the war effort during World War I.

The United States followed suit two years later by instilling the Standard Time Act, which ran from March through the summer. President Woodrow Wilson signed DST, also known as “Fast Time”, into law to support the war effort during WWI. However, it was not a popular idea and was revoked by the end of WWI. Other countries, like France and the United Kingdom, had also embraced the concept of DST but also abandoned it after WWI.

By World War II, however, President Franklin D Roosevelt implemented year-round DST, also called “War Time”, from February 9th, 1942, until September 30th, 1945 throughout the United States and Canada. The different time zones throughout the United States were referred to as “Pacific War Time”, “Central War Time”, “Mountain War Time”, and “Eastern War Time”. The time zones were renamed “Peace Time” in August of 1945 after Japan’s surrender.

The United Kingdom took a slightly different approach, employing the use of “Double Summer Time” during WWII which meant setting clocks two hours ahead of Greenwich Mean Time (GMT) during the summer, and one hour ahead of GMT during the winter.

AMERICANS PLAYING WITH DAYLIGHT – 20TH CENTURY AND BEYOND

After WWI and WWII, the United States dropped the federal mandate on DST, leaving it up to individual states and cities to decide if they wanted to practice DST, and how to implement it. In 1954, only two states, California and Nevada, had statewide laws regarding DST. By 1966, there were 100 million Americans who observed DST based on their local laws, but a federal law was still lacking. Congress decided to end the confusion by establishing a pattern which applied throughout the country. The Uniform Time Act was signed into law in April of 1966 by President Lyndon Johnson, thus creating the modern version of Daylight Saving Time. It specified the beginning as the last Sunday of April and the end as the last Sunday of October. The law was not mandated, so any state which wanted to be exempt from DST could do so by passing a state law.

Congress revised the Uniform Time Act in 1972 to enable a state which was in two or more time zones to exempt one portion of the state in one time zone while observing DST in another part of the state. When the oil embargo of 1973 hit, Congress decided to extend DST to a period of ten months in 1974, then eight months in 1975, in an effort to save energy. Federal law was again revised in 1986 to change the beginning of DST to the first Sunday in April.

The current United States DST schedule, which was adopted in 2007, followed the Energy Policy Act of 2005, which extended the period of DST by about one month. The current DST guidelines are as follows:

Begins at 2:00 a.m. on the second Sunday of March

Ends at 2:00 a.m. on the first Sunday of November

There are over 70 countries worldwide which use Daylight Savings Time, with many variations on beginning and end dates. However, the European Union (EU) implemented a standardized EU-wide DST schedule in 1996 which begins the last Sunday in March and ends the last Sunday in October.