vitamin D prevents colds or does it,is 10,000iu a day safe?

i have suffered from a constant cold for about 8 years now,at it's best it is just a sniffle,but like now it's a full blown cold and doubling my basal rate doing the same with boluses does not seem to make enough of a difference.i read that david mendoza had the same problem untill he started taking vitamin D.He say's he's not had a cold since he started on vitamin D something like 4 years ago,which is incredible,however he also says he takes 10,000 iu a day and ups it to 15,000 if he thinks he needs it.I must admit the amount sounds frightening,but his reaction to it sounds outstanding and after 8 years i am looking for something to cure me,other than taking 6 months off work,i would try anything.What do you suggest,is this amount safe,or am i getting mixed up with an american iu that is different to ours?i am a 50 year old male with type 1 on a pump delivering pork insulin,approx 40 units a day without having to adjust it,i have recently been averaging 60 units a day.i also suffer from depression and chronic insomnia.what do you think about the vitamin D. One last thing ,can i ask you not to recommend i change to human/genetic insulin because i use a pump as it was using genetic insulin with a pen that caused all my problems 8 years ago after having a mostly incident free 16 years mostly on pork prior to being recommended to changing to genetic.