how so tan wrote:
There’s no way runners in places like Portland and Colorado are getting their tan from the sun in the winter. What are they doing? How are runners from non-sunny climates so tan? It’s obviously fake.
Your assumption is understandable but incorrect. It doesn't have to be sunny or hot for UV exposure to happen. Portland is at 45 deg North - it's like southern France, Northern Italy, Croatia, Crimea. Places where Europeans used to go to take sun baths (quite a few are not afraid of skin cancer and still do); all of them are also wine-growing regions as well as Oregon and grapes need a lot of solar energy to grow.
Clouds generally block from 30 to 70 percent of UV radiation so if you spend 12 hours per week running in cloudy weather it's like 6 hours which is still a lot. You're also bound to catch some sunny days. At 45N you're probably still running mostly in daylight even in winter, perhaps using less sunscreen. And that's even before you go to train in Eastern African or South American mountains near equator which is an option when you're a pro.
For some anecdotal evidence, I live in St Petersburg, Russia. November to February we have the sun barely pop out in the sky for 5-7 hours and there are on average 75 sunny days per year (144 for Portland). You hardly ever see UV index different from 0, anything over 1 absolutely never. Locals are mostly pale as vampires. I'm not even a pro but I train up to 10-12 hours per week when preparing for a race and I'm about as tan as (local) people who use tanning beds or spend vacations in Thailand. Maybe less so by March, but generally year round, and I would probably be paler compared to and average white Californian, but you get the idea.