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Comment by adammichaelc | Hacker News Reader

"you only need 15 minutes"

It's important to qualify that this is only true of people with lower levels of melanin (ie white people). For Hispanics and Asians/Indians the number is probably closer to 60 minutes, and for those of African descent the number is closer to 120 minutes.

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Yes! It's also important to note that sunlight through glass DOES NOT COUNT.

Why not?

Probably because glass filters UV light.

That's evolution in action, folks. Just look at where each ethnicity originates from, and it makes perfect sense. When you live in northern Europe, you may not get much sun, and have to make the most of it.

I'm in Scotland, what is this "sun" thing you speak of?

Possibly your skin can make vitamin D from rain ?

I believe we Scots are adapted (or at least attempting to adapt) to produce the necessary vitamins from a combination of alcohol and deep fried food. (e.g. deep fried pizzas and Mars bars).

Fish & Chips actually contain quite a bit of vitamin D!

The Scots have adapted to harsh modern environments containing hazards like the deep fat fryer, but what of more recent technological hazards? (And Hollywood!)

http://www.youtube.com/watch?v=5FFRoYhTJQQ

It's a large, blazing fiery mystic beast that is greatly feared for its ability to kill masses of people through silent, sneaky death via waves. Many people are convinced one day it will destroy everything.

You're missing out, really.

Come to Phoenix, AZ. I'll give you a demo.

An interesting addition to that point is the fact that it's the unique combination of little sun + arable land that set the stage for whiteness to develop in northern Europe. Take northern Native Americans-- they had little sun but also couldn't grow grains and so got plenty of vitamin D through their meat-only diet. There was an article here on HN about this some time ago.

Way more details on that: http://knol.google.com/k/why-are-europeans-white-e1#

Inuit in particular are especially dark because seal fat is soaked in Vitamin D.

Season and location are factors too.

In the winter in the SF bay area, it's very unlikely your skin can make enough vitamin D.

After one winter here, I my D levels were at 20 ng/ml -- way below what many believe is the sufficient level of 30 ng/ml.

Also it is important to keep in mind that the sun has a lower altitude over the horizon in winter (for europeans), you need more exposure then.

Do you have sources for those numbers? They seem very high.

A quick google search found this:

http://www.google.com/search?q=%223-6+times%22+%22vitamin+d%...

My battery is about to die in the iPhone, so I don't have time to curate the list, but from a quick glance a couple of the sources from the google search look credible.

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