And now we finally get a glance at Nirin's mom! 

  I've noticed some debate concerning the anthropology and genetics of cultural height differences.  First, I'll say this: Saengor has pretty harsh winters and the North is not frozen year-round. The only real difference between these places is the amount of daylight.  Did you know that blond-haired people absord vitamin D from the sun much easier than dark-haired people?  

  Rather than focusing on the effect of cold temperatures on overal bodymass, I would think diet plays a larger role.  The Rethuii have far more meat (beef, venison, rabbit, poultry, moose, bear, etc.) and potatoes in their diet since they can't grow as many vegetables.  They also drink cow's milk while Saengorians don't have cows.  Mizha and Azhari are lactose-intolerant.  Saengorian food is mostly rice, vegetables, fruits, lamb, and poultry.

By the way, you need vitamin D to absorb calcium.