"The overall prevalence rate of vitamin D deficiency was 41.6%, with the highest rate seen in blacks (82.1%), followed by Hispanics (69.2%)." -Prevalence and correlates of vitamin D deficiency in US adults
Alarmed? Based on these numbers it's safe to assume that Vitamin D deficiency is common among runners and indirectly impacting performance. This doesn't mean you'll run faster just by popping a Vitamin D pill, however according to this Runners Connect article Vitamin D is involved in calcium absorption, muscle contraction, nerve stimulation, support of a healthy immune system, and inhibiting inflammatory response in individuals with asthma or allergies.
If you're serious about running fast or considering a supplement, get a 25-hydroxy vitamin D blood test.
Recommended Reading on Vitamin D
What Is Vitamin D Good For and Why Do I Need It?- Runners World
Eat These Foods to Boost Your Vitamin D- Runners World
Vitamin D Council
12 Ways to Get Your Daily Vitamin D-Health.com