By Dr Amrita Jesurasa
Ever since our most ancient ancestors left Africa to populate the rest of the world the appearance of their descendants has changed.
Height, facial features, hair type, body size and shape, and invisible genes that can protect from or predispose to disease have developed and differentiated racial groups. But the most profound (and superficial) change has to be in the colour of our skin as people migrated and settled around the world.
Skin colour forms a strong part of our physical and social identity, at times unifying people but more distressingly, causing division. The legacy of this evolutionary change has left its scars on human history in the last few hundred years and continues to cause tension in the present. Ethnic inequalities in health are well recognised and yet we perhaps fail to recognise the true message from history: why did skin colour change?
Current theory suggests that this phenomenon arose as a result of our need for vitamin D. As our early ancestors migrated to northern latitudes, they experienced the severe consequences of vitamin D deficiency. These included bone deformities that affected their ability to walk, breathe and – crucially – to give birth (the latter the result of changes to the female pelvis).
In Europe, natural selection began to favour lighter skin that allowed ultraviolet radiation to be more readily absorbed, vitamin D to be synthesised and ultimately our species to survive in Europe and other northern climes.
Fast-forward to the 21st century and rapid technological advances have transformed the way we live. Some of these developments, including air travel, have facilitated evolutionary shortcuts, enabling the humans of today to live in environments that are totally different to that of even the previous generation. But other advances have affected the behaviour of us all by encouraging a more indoor lifestyle than that of our ancestors, creating fear of the adverse effects of the sun and altering our dietary habits.
This perfect storm has allowed vitamin D deficiency to become a population-wide issue, but one which has the greatest impact on those with darker skin. The irony is that this disproportionate effect within the population marginalises the issue of vitamin D deficiency, creating an ethnicity-related health inequality.
To raise the profile of vitamin D deficiency, universal issues need to be addressed and universal solutions provided. While improving access to vitamin D supplements must be part of this strategy, there are worrying common pitfalls associated with an exclusively medical approach.
Instead, a simple message may resonate more with both the public and policy-makers. This could mean promoting a basic principle that “like plants, we need food, water and sunshine to thrive”. With a more holistic approach we can relate prevention of vitamin D deficiency to other important and well-recognised public health concerns, thereby raising the priority of this historically important issue.
- Dr Jesurasa is a Specialty Registrar in Public Health Medicine/ Honorary Clinical Lecturer in Public Health, University of Sheffield