Sunlight, Vitamin D, and the Missing Piece in Eco-Friendly Design

Why human health must be part of sustainable architecture:

For most of human history, sunlight shaped how we lived, built, and maintained health. Exposure to natural light regulated sleep, supported immune function, strengthened bones, and influenced mental well-being. In contrast, many modern buildings, particularly those driven by eco-friendly and energy-efficient design strategies, limit direct sunlight exposure in ways that may unintentionally undermine human health.

Recent research highlights a growing concern: as buildings become more efficient, the people inside them are becoming increasingly sunlight-deprived, contributing to widespread vitamin D deficiency and broader wellness challenges.

The opportunity ahead is not to abandon sustainability, but to evolve it, integrating environmental responsibility with biological human needs.

The Role of Sunlight in Human Biology

Sunlight is not merely illumination; it is a biological signal. Different wavelengths of sunlight interact with the body in distinct ways, influencing multiple systems at once.

One of the most critical functions of sunlight is its role in vitamin D synthesis. When skin is exposed to UVB rays, the body produces vitamin D, a hormone-like compound essential for overall health.

Vitamin D supports:

• Bone density and calcium absorption

• Immune system regulation

• Muscle function

• Cardiovascular health

• Mood and cognitive function

  
  

Despite supplementation options, sunlight remains the most efficient and biologically integrated source of vitamin D.

Vitamin D Deficiency: A Widespread and Growing Issue

Over the past five years, research has consistently shown that vitamin D deficiency is prevalent across many populations, even in developed countries and sunny regions. Modern lifestyles, characterized by indoor work, screen-based living, and limited daylight exposure play a major role.

Insufficient vitamin D levels have been linked to:

• Increased risk of respiratory illness and infections

• Fatigue and muscle weakness

• Depression and mood disorders

• Weakened immune response

• Long-term bone and metabolic issues

  
  

Importantly, studies note that diet alone rarely compensates for lack of sun

exposure. Vitamin D production through skin exposure is part of a complex biological feedback loop that supplementation cannot fully replicate.

Sunlight, Circadian Health, and Overall Wellness

Beyond vitamin D, sunlight regulates circadian rhythms, the internal clock that governs sleep, hormone release, metabolism, and immune function. Exposure to natural daylight, especially in the morning, has been shown to improve sleep quality, reduce stress, and enhance cognitive performance.

Artificial lighting, even when carefully engineered, does not provide the same spectral intensity or biological signaling as sunlight. As a result, individuals in low-daylight environments may experience circadian disruption even when visual lighting standards are met.

When vitamin D deficiency and circadian disruption occur together, the effects compound, contributing to long-term health decline rather than isolated symptoms.

How Eco-Friendly Design Can Accidentally Limit Health

Many sustainable building strategies focus on reducing heat gain and energy use by limiting solar exposure. Common approaches include:

• Deep shading systems and overhangs

• Heavily tinted or UV-blocking glass

• Narrow window-to-wall ratios

• Highly sealed building envelopes

While these strategies reduce energy consumption, they can also block beneficial wavelengths of sunlight, including UVB necessary for vitamin D synthesis and visible light critical for circadian regulation. As a result, buildings may achieve environmental certifications while occupants experience reduced daylight access, lower vitamin D levels, and diminished well-being. This reveals a gap between environmental performance metrics and human health outcomes.

The Hidden Cost of Sunlight Deprivation Indoors

When buildings consistently limit sunlight exposure, occupants may experience:

• Chronic vitamin D deficiency

• Poor sleep quality and irregular circadian rhythms

• Increased stress, anxiety, and fatigue

• Reduced productivity and cognitive clarity

• Long-term immune and metabolic impacts

  
  

These effects are subtle and cumulative, often overlooked in building performance evaluations but deeply felt by the people who inhabit these spaces daily.

True sustainability should support long-term human health, not just energy efficiency.

A More Complete Approach: Designing for Planet and People

The future of sustainable design lies in integration, not compromise. Buildings can be energy-efficient while still supporting healthy sunlight exposure.

Evidence-based strategies include:

• Building orientation that prioritizes morning and midday sunlight

• Daylighting systems that allow beneficial light while managing heat

• Glass technologies that balance thermal control with biological light transmission

• Dynamic shading that responds to season and time of day

• Interior layouts that distribute natural light deeper into occupied spaces

  
  

This approach recognizes sunlight as a design resource, not a liability.

Reframing Sustainability Through Human Health

Sustainability has traditionally focused on reducing harm, lower emissions, lower energy use, lower environmental impact. The next evolution of sustainability must also focus on creating health.

Vitamin D sufficiency, circadian alignment, mental clarity, and immune resilience are not optional benefits; they are foundational to a thriving society. Buildings play a direct role in shaping these outcomes.

When design decisions acknowledge the biological relationship between humans and sunlight, they create environments that are:

• Health-supportive

• Energy-conscious

• Emotionally grounding

• Truly sustainable over the long term

  
  

Designing with the Sun, Not Against It

The sun is not something to eliminate from our buildings, it is something to work with intelligently. Responsible exposure supports vitamin D production, regulates biological rhythms, and reconnects people to natural cycles that modern life often disrupts. By integrating human wellness into eco-friendly design, we move beyond efficiency alone and toward environments that sustain both the planet and the people living on it. Sustainability is not complete unless it supports life, and sunlight is central to that equation.

Stay tuned this season for more about sustainability, regenerative design and working with nature to greatly improve our shared spaces!