[Cletus.D.Yokel]

What I assume you intend is to say that if you are NORTH of 55-LATITUDE, you will not get enough [direct] sunlight to metabolize your natural levels of Vit-D.

Latitudes are measured from zero at the equator and encircle the globe, extending to 90-North and 90-South.

At latitudes above 55 North (90-35), the sun does not traverse the sky higher than 35-degrees.
55-North is somewhere in Canada (Hudson Bay, maybe?)

[numberonepal]

North of 35 degrees latitude.

[LonePalm]

Your guess about Hudson's Bay for 55N is excellent. Belfast Northern Ireland is just south and Moscow is just North of 55 degrees north.

WWG1WGA

Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
(Keep the Faith, my friends! We are the saviors of the Republic! Now and Forever!)
LonePalm, le Républicain du verre cassé (The Broken Glass Republican)

[LittleLinda]

There’s an app called D Minder that helps you determine how much vitamin D you’re getting in any given situation. You enter some personal information (skin tone, age) and then which city you’re in and your percentage of skin coverage that day. It accesses weather/UV information, date, location and time of day to calculate how many IU’s of vitamin D you’re getting, and it warns you when you’re in danger of getting sunburned. It’s free and it’s useful but you need an electronic device.