Vitamin D Reduces Winter Colds
Even a little vitamin D supplementation reduces children’s colds by 50% in winter:
143 children’s daily glasses of milk were fortified with 300 IU of vitamin D … These same children reported half as many incidences of ARIs
300 IU is almost nothing. I take 5000 IU/day (it’s better for sleep to do so in the morning than evening, apparently). You probably should take vitamin D too if you’re not getting plenty of sunlight on your skin. 10000 IU might be overdoing it (best to test your blood rather than blindly take that much, as there’s an optimal range you won’t want to exceed by too much).