> This is only in the winter that you can't produce vitamin D at high latitudes. The line drawn on that map you linked applies to the winter solstice, above th

> This is only in the winter that you can't produce vitamin D at high latitudes. The line drawn on that map you linked applies to the winter solstice, above that line there is at least one day where you don't make vitamin D. Also, worth taking into account is elevation; a +5000 ft elevation in Denver your skin receptors are not functioning the same way they are at in sea level Manhattan. Hell, I try to make it to 10,000+ ft elevation in the Winter when I'm in CO in the Winter for this very reason (I'm from SoCal) that is below the 37th parallel where you can tan all year around. My emphasis was on Vitamin D during my undergrad in biology, and while their has been some vitamin D exposure in the media every now nd ten, it's hardly what this hormone deserves and it's vital role in so many metabolic processes. The truth is that even it's erroneous classification goes to show how very little impact it has had in modern medicine despite a lengthy breadth of studies since at least the 70s on the topic tat sow its implications on Human physiology. If people are really wanting to delve into this topic in earnest, as you should after COVID, this was my bible for my last 2 years of undergrad and something I always keep around to read [0]. Its out of print so it's costly, but chances are if you're familiar with SciHub you should be able to find it too. As for US vs European production, mine is anecdotal but I know for sure my body was starting fall apart wen I was in the UK in the winter, it felt like my thyroid stopped working altogether: i was getting sick easily, I was sluggish and my mood was just despondent, it was really hard to get out of bed. I got tons of exercise and I was outdoors all the time, despite the floods happening that year (2014), so I could definitely tell a difference of being that far North at sea-level in the Winter. 0: https://www.amazon.com/s?i=stripbooks&rh=p_27%3ARoger+Bouillon&s=relevancerank&text=Roger+Bouillon&ref=dp_byline_sr_book_2 https://www.amazon.com/s?i=stripbooks&rh=p_27%3ARoger+Bouill...