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 :)
In the Northern Hemisphere about half the year it's impossible to get enough Vitamin D by going outside.