I also had a vitamin D deficiency that was found after a particularly bad string of colds, my Dr told me to take a supplement(5000ius daily) of vitamin D and have not seen anything like it since. Apparently windows cars/office block sunlight's ability to create vitamin D in a person so a car ride or sitting near an office window does not provide any help. And if you are in a office job you are def. not getting enough vitamin D.