Many people are genuinely surprised: "I spend all summer in the sun — why do I still have a vitamin D deficiency?"

At First Glance, It Seems Strange. After All, Vitamin D Is Called the "Sunshine" Vitamin — It’s Synthesized in the Skin Under UV Rays. But Reality Is More Complex: Even Spending a Lot of Time Outdoors Doesn’t Guarantee Adequate Vitamin D Levels.

What prevents proper synthesis in the body:

– Sunscreen
SPF blocks UVB rays — the very ones needed for vitamin D production. Even SPF 15 reduces synthesis by over 90%. This isn’t a reason to skip sun protection, but it's a factor to keep in mind.

– Clothing and Shade
If most of your body is covered by clothes, hats, or you're always in the shade, synthesis is almost zero. Sunlight must hit the bare skin directly.

– Dark Skin
The more melanin, the slower the skin makes vitamin D. Dark-skinned individuals need 3–5 times more sun exposure than fair-skinned — even in sunny countries.

– Climate and Geography
Living in cloudy regions, places with short summers, or high pollution levels limits UVB exposure. Even in countries like the Czech Republic, UV levels may be too low in spring or autumn.

– Age-Related Changes
After age 60, skin produces vitamin D 2–3 times less efficiently. Seniors often require supplementation.

– Digestive and Liver Diseases
Conditions affecting fat absorption (e.g. celiac disease, Crohn’s, liver or gallbladder issues) prevent vitamin D absorption from food or supplements.

What to Do:

– If you're at risk (fair or dark skin, age 50+, chronic illness, modest clothing) — don’t guess. Get a blood test.
– If deficient, a doctor can prescribe supplements in the right dose.
– Sun is important, but a tan ≠ vitamin D prevention.
– Don’t rely on sunbathing as a substitute for medical screening.

Vitamin D affects immunity, bones, mood, and energy. Its deficiency often goes unnoticed — until it becomes serious.

Signs of Vitamin D Deficiency That Are Easy to Miss:

Vitamin D is not just about bones. It affects immunity, mood, metabolism, and even sleep. But deficiency develops quietly.

Watch out for:
– Frequent colds
– Fatigue and apathy
– Muscle and joint pain
– Poor sleep
– Hair loss
– Slow wound healing
– Increased anxiety or irritability

If you check off 2–3 of these — it’s not a diagnosis, but a reason to get tested.
Especially in spring, when winter reserves are depleted.