Vitamin D Strengthened Immune System

Q. I used to catch lots of colds every year. When I was tested for vitamin D a few years ago, it was really low. I took a lot of vitamin D to get into the normal range.
Since then I’ve had only two colds, each three days long. Vitamin D made a huge difference in my immune system.
A. Research shows that vitamin D is extremely important for the immune system. It helps to regulate T cells, which are important immune actors. It also turns on the gene that produces cathelicidin, a natural antimicrobial compound that fights infection (Future Microbiology, Nov. 2009).
Since many Americans don’t get enough vitamin D because we stay out of the sun, recommendations for supplementary vitamin D may rise beyond the current RDA of 400 IU daily. Many experts believe vitamin D intake should be five to ten times higher than that.