If anyone is thinking about taking vitamin d to avoid sickness i would personally recommend it.

I used to live in California and got plenty of sun, ate healthy, etc. However, my immune system was always very weak and i sometimes found myself getting very sick every month. I decided to get my vitamin d levels checked and found them to be very low... I've been taking vitamin d now for 6 or 7 months and i haven't gotten sick since, while taking it (i way 155 lbs and take 4,000 to 6,000 iou daily).
I should probably get my levels checked soon to see where they're at tho...!