Vitamin D enrichment is required for most milk in the USA, and according to wikipedia virtually all first world countries have a similar law.

Alas, some of us are lactose intolerant or just don't drink milk. So we supplement with vitamin D pills.

Note: Sweden does not have total darkness for half of the year. Firstly, 85% of Sweden is below the arctic circle, and does get daylight every day. Secondly, the 15% that is above the arctic circle is the most remote and least populated part of Sweden. Thirdly, even above the arctic circle in wintertime, it seldom actually gets dark as you might imagine; the sun is just below the horizon much of the time, and you merely get a sort of twilight/early morning light.