Vitamin D. Make Your Own.
Vitamin D is not a vitamin. It is a hormone.
Your skin produces D3 — the form of vitamin D made through UVB exposure. Your liver and kidneys then convert it into its active hormonal form — 1,25(OH)D.
Prerequisites
- Bare skin exposed to UVB light (290–315nm).
- UV index of 3 or above — ideally between 3 and 8.
- Cholesterol for D3 synthesis.
- Magnesium for activation.
- Dietary fat for transport.
Factors
- Skin type — the biggest variable. Fair skin needs significantly less time than dark skin.
- UV index — the higher the index, the less time needed.
- Body surface area exposed — more skin, faster synthesis.
- Age — older skin produces D3 less efficiently.
How
- Check the UV index — aim for 3 to 8.
- Expose arms and legs at minimum — more skin means faster synthesis.
- Direct sunlight only — no glass between you and the sun.
As a rough guide — arms and legs exposed, UV index 5:
- Fair skin — around 10–15 minutes.
- Medium skin — around 20–25 minutes.
- Dark skin — around 35–40 minutes.
UV index 3 roughly doubles these times. UV index 8 roughly halves them. Use an app like dminder for your specific dose.
Caveats
- Sunscreen blocks up to 95% of UVB.
- Window glass blocks UVB entirely.
- Age reduces D3 production capacity.
- Darker skin requires longer exposure.
- Skin burning degrades the D3 already produced — stop before that point.