HUMAN SKIN COLOUR IS ONE OF THE MOST VISIBLE EXPRESSIONS OF OUR EVOLUTIONARY HISTORY
It reflects where our ancestors lived, the intensity of sunlight they experienced, and how the body adapted to balance protection with the requirement of vitamin D production. In today’s world, however, that ancient balance is often disrupted.
Understanding how skin pigmentation interacts with latitude, season, and modern lifestyles helps explain why vitamin D insufficiency is unevenly distributed across populations — not because of inherent weakness, but because biology evolved for environments very different from the ones many people now inhabit.
PIGMENTATION AS A BIOLOGICAL FILTER
Skin colour is primarily determined by melanin, a pigment that absorbs ultraviolet radiation. Eumelanin, the dominant form in darker skin, is highly effective at filtering ultraviolet B (UVB) radiation — the portion of sunlight required for vitamin D synthesis in the skin.
From an evolutionary perspective, this filtering served a critical role. In regions with intense, year-round sunlight, higher melanin levels helped protect DNA and preserve folate, a nutrient essential for reproduction and development. Vitamin D production remained sufficient because UVB was abundant.
Melanin did not block vitamin D production — it regulated it.
LATITUDE CHANGES THE EQUATION
As humans migrated away from equatorial regions, sunlight became weaker and more seasonal. At higher northern and southern latitudes, UVB intensity drops sharply during autumn and winter and may disappear entirely for several months.
In these environments, skin pigmentation becomes more consequential. Lighter skin allows more UVB to penetrate when sunlight is scarce, supporting vitamin D synthesis during short exposure windows. Darker skin, while still fully capable of producing vitamin D, requires longer or more intense UVB exposure to achieve the same effect.
This difference is not a flaw. It is the result of adaptation to different ancestral environments.
THE MODERN MISMATCH
Today, many people live far from the environments in which their skin pigmentation evolved. Global migration, urbanisation, and the widespread shift toward indoor living have created conditions that differ sharply from those under which the human vitamin D system developed.
In higher latitudes, sunlight is already limited by season, with long periods during autumn and winter when UVB radiation is too weak to support vitamin D production in the skin. Modern lifestyles compound this limitation. Time spent indoors, protective clothing, window glass, and reduced outdoor activity further narrow the opportunities for meaningful sun exposure.
For individuals with higher levels of melanin living in these regions, the window for effective vitamin D synthesis becomes even smaller. The skin remains fully capable of producing vitamin D, but the environmental signals it relies on arrive less frequently and with lower intensity. This is not a biological deficiency, but a mismatch between inherited adaptation and present-day conditions.
VULNERABILITY WITHOUT PATHOLOGY
In scientific terms, vulnerability does not imply disease or deficiency as an inevitability. It describes a greater sensitivity to environmental constraints.
Darker-pigmented skin evolved in contexts where UVB was plentiful and reliable. When that reliability disappears — as it does in high-latitude winters or indoor-dominated lives — the biological system receives less of the signal it evolved to expect.
Population studies consistently show that lower average vitamin D status is more common in darker-skinned groups living at higher latitudes. These observations reflect environmental exposure patterns, not biological inadequacy.
The body is responding appropriately to the conditions it encounters.
NORTHERN AND SOUTHERN LATITUDES: A SHARED CHALLENGE
Although discussions about vitamin D often focus on the northern hemisphere, similar patterns emerge in southern latitudes far from the equator. In regions such as southern Australia, New Zealand, and parts of South America, seasonal declines in UVB radiation limit vitamin D production for extended periods of the year.
Across both hemispheres, the underlying dynamic is the same. As the sun sits lower in the sky during winter months, the atmosphere filters out much of the UVB needed for vitamin D synthesis. Skin pigmentation influences how much of this already limited radiation reaches the deeper layers of the skin, shaping individual responses to seasonal light availability.
In these environments, vitamin D status becomes less about daily sunlight and more about how the body navigates long intervals of low exposure. This shared challenge highlights that latitude, season, and modern living conditions play a central role in shaping vitamin D variability, regardless of hemisphere.
MODERN LIFE AND BIOLOGICAL EXPECTATIONS
The human vitamin D system evolved under open skies. It assumes regular exposure to unfiltered sunlight, adjusted by skin pigmentation and season. Modern life has changed those conditions rapidly.
The result is not a failure of biology, but a reminder that physiology is shaped by context. Skin colour, latitude, and lifestyle now interact in ways evolution did not have time to recalibrate.
Recognising this interaction allows for a more accurate, less simplistic understanding of vitamin D variability across populations.
CONCLUSION
Skin pigmentation is an evolutionary adaptation to sunlight, not a determinant of health in isolation. Its influence on vitamin D production depends on where people live, how much sunlight reaches their skin, and how modern environments shape exposure.
In northern and southern latitudes, seasonal light scarcity affects everyone — but its impact is modulated by pigmentation and lifestyle. What appears as vulnerability is often a reflection of environmental mismatch rather than biological limitation.
Vitamin D reminds us that the human body is deeply connected to light, and that understanding this connection requires attention to evolution, geography, and the realities of modern life.
DISCLAIMER
This article is for educational and informational purposes only. It does not constitute medical advice or promote any specific product. Readers concerned about vitamin D or sun exposure should consult a qualified healthcare professional.
