I live in Wyoming. I used to work in an office and I would catch every bug that came into town. But in 2006 I got a job working in the oil/gas field. I work outside all day 4 days a week (in and out of a truck), and I've been notably sick once in 6 years. I swear by viamin D by the sun. I've never suplimented my D, but when I started hearing the studies linking vitamin D to testosterone I'm considering it. There's more science to go, but here is one test.
Effect of vitamin D supplementation on testos... [Horm Metab Res. 2011] - PubMed - NCBI