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Comment by danenania | Hacker News Reader

Does anyone know of a rule of thumb for how much time spent in direct sunlight is equivalent to a Vitamin D supplement? Is an hour per day (on average) sufficient?

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It depends on your skin color [0]. For people with light skin, 13 minutes of direct midday sunlight three times a week may be enough. But for people with dark skin, you may need 30 minutes to 3 hours of direct sunlight (the article doesn't make it clear whether that is three times a week or once a day) to get enough vitamin D.

[0] https://www.healthline.com/nutrition/vitamin-d-from-sun#skin...

> 13 minutes of direct midday sunlight three times a week may be enough.

There's a metric left out of this equation.

How much of the body must be exposed?

That little? So my four hours of tennis a week in the hot Greek sun is much more than enough, even with sunscreen on.

Playing four hours of tennis under the hot Greek sun may lead to other health issues though.

Four hours a week? Non-consecutive?

Such as?

Tennis elbow, I'm guessing.

That's one (or two, for each elbow).

Maybe increase your chance of melanoma.

Just 13 min and The time of day is critical..

the sun must be above 50' above horizon for UVB to penetrate the atmosphere to reach the skin. When your skin is exposed to sunlight, it makes vitamin D from cholesterol

https://theralightinc.com/best-time-to-get-vitamin-d-from-su...

https://www.healthline.com/nutrition/vitamin-d-from-sun#time...

I read Michael Holick's book (can't find it at the moment) he was the guy who discovered the circulating form of vitamin D.. IIRC you get vitamin D from the sun in rather large quantities. Just 15 minutes per day with only your face and hands exposed with the sun up at 45 degrees or more will be enough. I'm sure my data is not accurate, but it's in the ballpark. He has tables that depend on how dark your skin is and what latitude you live at.

So, this is only partly true. You need direct sunlight AND the amount varies wildly depending on your skin color. If you're rather pale, it may be only 15 min. But it can go up to several hours if you're dark-skinned.

I've also read that 15 minutes is sufficient. The caveat being that it may need to be strong(ish) sunlight, otherwise you may not generate any at all.

What if it's cloudy? We are lucky to get 3 days a week where the midday sun isn't covered by cloud. Is it still sufficient filtering through the atmosphere?

UV rays penetrate clouds, but the clouds do filter some of it, so you'll likely need to increase the amount of time you spend outside depending on how cloudy it is.

Does one need exposure to direct sunlight, or sunlight coming via glass windows works?

Glass windows block the part of the UV spectrum that is needed to make Vit D.

https://www.nytimes.com/2019/02/08/well/live/does-sunlight-t...

My doctor's advice: 15-30 minutes of sun per day, with more than just your face exposed. So yes, an hour a day might be sufficient. You don't need to sunbathe, luckily, and cloudy days count too.

For me, this only counts from May to August: I'm pretty far north, and there isn't proper sun strength much of the year.

To add to the other replies, it depends on various factors (sun elevation being the most important). This is the best calculator I am aware of: https://fastrt.nilu.no/VitD_quartMEDandMED_v2.html

There are other related calculators linked also.

The Solar Zenith Angle is the most important. This is what changes from winter to summer and morning to night.

Vitamin D production is only made on the UVB range that is highest at midday. Both UVA and UVB causes erythema. Counterintuitively to common sense, it is better to sun bath midday than early in the morning.

If you sunbath at 8 you might need twice as many time to produce the same amount of vitamin D and you be exposed to much more UVA, thus more like to get burn.

I guess an ultraviolet lamp works also? )Or at least the Soviets thought it did).

https://www.nationalgeographic.com/photography/photo-of-the-...

https://fastrt.nilu.no/VitD-ez_quartMEDandMED_v2.html depends on latitude, cloud clover etc

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