How Can You Be Vitamin D Deficient in One of the Sunniest Places on Earth?

By Tina Chagoury, Clinical Dietitian · 6 min read · 2026-08-21

It is the question I hear most in clinic. Sunshine and vitamin D production are not the same thing, and the difference explains everything.

"How can I possibly be deficient in vitamin D? I live in Dubai."

I hear this in clinic more than almost anything else, and I understand why. On the surface it makes no sense at all.

It makes complete sense once you understand one thing: sunshine and vitamin D production are not the same thing.

Your skin responds to UVB, not to sunshine

Your skin contains a compound called 7-dehydrocholesterol. When UVB radiation hits it directly, your body converts it into vitamin D3, the same vitamin D your cells use for immune function, mood regulation and hormonal signalling. Your skin was quite literally designed to do this.

The critical word is directly. UVB has to reach your skin without passing through anything. Not through your car window. Not through the glass at home. Not through your office window. Glass blocks UVB almost completely.

Now think about how people in the Gulf actually live

You leave home before the peak UVB hours specifically to avoid the heat. You spend the day indoors, in an office, in a mall, in a car. You exercise in an air conditioned gym. When you are outside, you are covered or in the shade, because it is fifty two degrees.

Then add sunscreen, skin pigmentation, age and body composition, all of which reduce how much vitamin D your skin can synthesise.

The sun is everywhere. The UVB is not reaching you.

Why you cannot eat your way out of it

This is the second question I always get: can I just eat more eggs and salmon? It is the right instinct and the wrong conclusion. Let us do the arithmetic.

One egg contains roughly 40 international units of vitamin D. Two eggs, 80. Five eggs, around 200 IU. We have not moved very far.

A salmon fillet contains somewhere between 400 and 600 IU depending on type, variety and weight. Two fillets gets you to about 1,000 IU.

Now consider that someone who is genuinely deficient may need substantially more than that, sometimes in the region of 5,000 IU per day, to restore levels.

You can see the problem. Vitamin D was never designed to come primarily from food. Your body has a built in manufacturing system. Your skin is the production facility, sunlight runs it, and food supports the process. Food is support, not the solution.

What blocks absorption even when you do get sun

Several factors reduce how much you actually end up with:

• Elevated body fat, because vitamin D is fat soluble and gets sequestered
• Older age, because skin synthesis becomes less efficient
• Gut malabsorption
• Chronic inflammation
• Certain medications

This is why someone can eat salmon three times a week, walk outside regularly, and still test deficient.

What low vitamin D feels like

None of these feel like a sun problem, which is exactly why it gets missed:

• Tired no matter how much you sleep
• Low mood with no obvious cause
• Hair falling more than usual
• Getting ill repeatedly
• Poor recovery after workouts
• Premenstrual symptoms that are harder to manage

What about sunscreen?

One side of the internet says avoid the sun completely. The other says sunscreen is toxic. Both are wrong.

Sunscreen was designed to block UV radiation, and UVB is the exact wavelength that triggers vitamin D production, so there is a genuine trade off. Some chemical sunscreen ingredients have raised legitimate questions in the research around endocrine disruption.

My own approach, and what I usually recommend, is a mineral sunscreen with zinc oxide. It works as a physical barrier on the skin rather than being absorbed, and its safety profile is well established.

Protect your skin, know what is in your products, and test your levels. Make informed choices, not fear based ones.

The one rule I never break

I never assume vitamin D status based on geography. I test, every single time. And when supplementation is needed, it is taken with the main meal of the day, because absorption improves substantially when it is taken with food.

This article is nutrition education, not medical advice. Dosing should be guided by your own test results and your doctor.

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About the author. Tina Chagoury is a licensed clinical dietitian based in Dubai, specialising in women's hormonal health, metabolism and nutrient status. She is the creator of the Hormone Reset Method™. Learn more about the Hormone Reset Method.