try and do some research on vit d3. i take 5000 iu per day. it has helped me immensely. i used to get bronchitis or pneumonia every winter until i started with the d3 about 6 years ago. haven't had either since. and, i very rarely get sick anymore. and, if i do, my recovery time is very quick--just the onsets of sickness then quickly better.
good luck!