Vitamin D is well absorbed if you take it in gelcap form, as it's fat soluble. Many people take it from "dry" tablets and that's why it's not well absorbed.

This can be verified with blood tests.

Having a substance in your blood doesn't imply that your body is benefiting from it, or even using it.

No, but it's better than not having it even get to your blood, especially if you test for the bio-available compound in the blood.

Northern climes don't get enough sun.

Vitamin D supplements (at normal daily doses) are recommended.

This is especially important for pregnant women and children under 5. Also for people with limited access to sun ('cultural dress' for example.)

Somali women are dressed in all-over black covers, and as a consequence, there is even something called "the Swedish disease" among Somali immigrants to Scandinavia. It's autism and there is a suspected link with vitamin D deficiency.

http://www.thelocal.se/32862/20110328/ http://www.scientificamerican.com/article.cfm?id=vitamin-d-a...

It shouldn't be a problem if you have enough vitamin K in your diet: http://articles.mercola.com/sites/articles/archive/2011/03/2...

Sunlight comes with increased cancer risks so even if it's more efficient and cheaper than D it's not nessisarily better. Also, studies have demonstrated that eskimos get significant quantities do D from there diet so diet can work.

I met a doctor recovering from a very bad breast cancer. Her opinion, for what it's worth, was "get lots of sun, and inspect for skin cancers - they are easy."

you can balance both. the amount of sun you need is quite limited, apparently. see http://www.nhs.uk/Livewell/Summerhealth/Pages/vitamin-D-sunl...

15 min, 3 times a week is enough to give you all the D you need. Not nearly enough sun to worry about skin cancer.

Vitamin D is critical to health and should be called something else, not a vitamin.

BTW, as you get older, your body loses the ability to convert sunlight to Vitamin D. Of course no one who reads HN would have this issue :-)

All vitamins are crucial to health.

But less crucial than a normal diet. I mean a diet consisting of a little piece of meat with fat bought on the market, cooked at home with some fresh vegetables, etc. Etc.

What? I don't understand what you mean. What do you mean by "vitamins"?

That little bit of meat and vegetables will contain vitamins.

Those vitamins are a crucial part of a normal diet.