Generally the more far you are from the equator, the less Vitamin D from the sun you can get. If you live above latitude 35 north/south this means you almost do NOT make any Vitamin d from the sun during winter.

At Latitude 40 (parallel) north (or south) or above, you virtually can not make any Vitamin D at all, all year round. Like for example, all of Canada, New York, Boston, Chicago, and Seattle in North America. And Scandinavia, UK, Ireland, and Germany in Europe.

At latitude 30, if you live in the northern half of the earth, you can make vitamin d 10 months a year (probably no enough uv-b rays in January & February). Southern US cities, such as, Miami, Dallas, Phenix and others, are  good examples of those.

When we talk about sun here, we have to mention that we are talking about noon. The best time to get some sunshine is between 10 am – 2 pm. Or you might use this as a rule of thumb: if the shadow of anything is shorter than its real height, you can make Vitamin D.

If you are a light skinned/light eyed person, you need to be cautious. People with these characteristics can get skin cancer from extensive sun exposure. In this case it’s recommended that you get vitamin from supplements. To be more accurate, it’s probably your only way, as food generally does not contain enough.