Vitamin DGlobal Solar Explorer

Vitamin D from the sun in San Francisco

In San Francisco you can synthesize vitamin D from February to October.

From November to January synthesis isn't possible — this is when a supplement can help.

More precisely: February 2 – November 13.

Year-round profile in San Francisco

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Daily hours with enough sun to synthesize vitamin D across the year.

Seasonal windows

  • March: between 10:00 and 16:00, about 9 min for 1000 IU.
  • June: between 09:00 and 17:00, about 5 min for 1000 IU.
  • September: between 10:00 and 16:00, about 8 min for 1000 IU.
  • December: synthesis isn't possible.

Estimated for Fitzpatrick type III skin, arms and face exposed, clear sky.

When to supplement in San Francisco

During the months without solar synthesis, vitamin D comes only from food or a supplement. It is usually taken as D3, often with magnesium — which the body needs to activate it — and vitamin K (as K2), which contributes to the maintenance of normal bones.

Calculate my window in San Francisco

Frequently asked questions about vitamin D in San Francisco

Can I get vitamin D from the sun in winter in San Francisco?
In San Francisco you can synthesize vitamin D from February to October.
How many minutes of sun do I need in San Francisco?
In summer, about 9 minutes with arms and face exposed is enough for 1000 IU (Fitzpatrick type III skin, clear sky).
Built by Javier Aguilar