Sun goes up at 09:34 and down at 15:16, most of us are at work. And that doesn't include the mountains blocking the sun, some weeks it barely goes above them. So there's light, but no direct sun light. And when it's -10C, only a few square centimeters of my skin is exposed to the elements, not really producing any vit D.
Indeed, I had no problems with vitamin D levels when living in Georgia (the state), especially since I regularly ran or otherwise exercised outdoors after work and most weekends year round (even when it got cold, it didn't get that cold, and there was no ice to speak of south of Atlanta). But during my first winter in Colorado, hah! Good luck getting sunlight during the week when the sun sets by 4:40pm and the sidewalks and trails you run on are covered with ice even if you do get outside before then.
A quick search online suggests that Russians also tend to be at higher risk for vitamin D deficiency and that the local climate/weather is a large contributing factor. I feel pretty comfortable saying that people who live in northern climates like Russia should be getting their Vitamin D levels checked, and potentially taking supplements or using sun lamps.
Big cats especially need proper nutritional intake, or they'll turn into small malnourished ones :)
