The story of our skin – folate, sunlight and evolution

Human skin colour is not just a matter of aesthetics – it is a record of thousands of years of evolution, in which sunlight and nutrients such as folate shaped our health and survival.

Research shows that the balance between protecting folate and synthesising vitamin D was one of the key driving forces behind the evolution of skin pigmentation.

“The story of our skin” is a journey through evolution, migrations, and genes that shaped the diversity of human pigmentation across the world.

In the previous articles, we explored melanin and pigmentation genes. Now it’s time for the next piece of the puzzle: folate (vitamin B9) – a vitamin whose role in the evolution of skin colour was just as crucial as that of vitamin D.

Why did human skin have to find the golden balance between protecting DNA from folate degradation and maintaining the ability to synthesise vitamin D? This question takes us to the very heart of pigmentation evolution. Only in recent decades has science uncovered how UV light influences not just vitamin D, but also folate.

Folate – what it is and why it matters

Folate, also known as vitamin B9, is one of the essential vitamins for life. It plays a crucial role in building nucleotides – the basic “building blocks” of DNA and RNA. Thanks to folate, cells can divide and renew, and the body can grow and regenerate. Without it, the production of new blood cells and the proper development of tissues would not be possible.

  • Folate ≠ folic acid – folate is the natural form (from food), while folic acid is a synthetic supplement that must be converted in the body into active forms.
  • Why does this matter? Without adequate folate levels, DNA replication processes are disrupted, which is critical for reproductive health and overall well-being.

A lack of folate is especially harmful during pregnancy. During this period of intense cell division, B9 deficiency can lead to neural tube defects in the fetus – severe malformations of the brain and spinal cord. Supplementation can reduce this risk by up to 70% (WHO, 2015). That’s why folate intake is recommended for all women planning pregnancy. From an evolutionary perspective, protecting folate was essential for the survival of our species.

Although folate is most often associated with pregnancy supplementation, its role is much broader:

  • It supports the proper functioning of the nervous system,
  • It impacts cardiovascular health (by lowering homocysteine levels),
  • it aids cellular repair and regeneration.

Note: Excessive intake of synthetic folic acid can mask vitamin B12 deficiency, which is why supplementation should always be monitored.

Sweet and sour mix of citrus fruits source of folian

Dietary sources of folate

It’s relatively easy to obtain folate through food, especially when including a variety of fresh, plant-based ingredients:

  • Green leafy vegetables – spinach, kale, and chard are among the richest sources; even a small serving can significantly contribute to daily requirements.

  • Root vegetables and legumes – beets and beans are excellent plant-based sources of folate, valued both nutritionally and culinarily.

  • Citrus fruits – adding fresh citrus to the daily diet provides not only folate but also vitamin C, which supports absorption and overall health.

  • A variety of vegetables, nuts, seeds, and eggs – while they contain smaller amounts individually, together with the above foods, they build a strong nutritional foundation.

Sun, folate, and skin colour – an evolutionary story

Ultraviolet (UV) radiation can break down folate circulating in the blood. A deficiency of this vitamin weakens the body’s capacity for DNA replication, which in the past – when no supplementation was available – had serious consequences: increased risk of birth defects and reduced fertility.

This is why, in regions of intense sunlight such as equatorial Africa, darker skin served a protective role. Melanin acted like a “natural umbrella,” shielding the body not only from burns and skin cancer but also from folate degradation – thus safeguarding the ability to reproduce and pass on life.

In areas with little UV exposure, the situation was reversed. The priority shifted to vitamin D synthesis, so evolution “favoured” lighter skin, which made this process more efficient.

The balance between folate and vitamin D is a dual foundation that shaped the evolution of human skin pigmentation.

Migrations and modern challenges

Today, migrations and lifestyle disrupt this natural balance:

  • People with dark skin living in Scandinavia, Canada, or even Poland are particularly at risk of vitamin D deficiency.
  • People with very fair skin living in the tropics lose folate more quickly and are more vulnerable to DNA damage.
  • Modern lifestyles – office work, commuting by car – further reduce exposure to natural sunlight, deepening deficiencies.

Conclusion – the two pillars of skin evolution

The history of skin pigmentation is not just a story of colour, migration, and genes. It is also the story of balancing two vitamins-folate (B9) and vitamin D.

Dark skin in regions of high UV protected folate and DNA. Light skin in areas of low UV facilitated vitamin D synthesis. This evolutionary compromise shaped human health for thousands of years.

Today, we know this balance still matters – both for people migrating across climates and for modern populations living in offices and under artificial light. Just as evolution sought equilibrium, personalised medicine – nutrigenomics and genetics – now aim to restore it by tailoring recommendations and supplementation to the individual.

Sources: