Telomeres for a Longer, Healthier Life - book mentions vitamin D - 2010
The Immortality Edge: Realize the Secrets of Your Telomeres for a Longer, Healthier Life
Hardcover and Kindle versions Dec 2010
Looking inside of the book finds 16 hits for "Vitamin D"
Can read first chapter for free on any Kindle reader - including PC, MAC

See also VitaminDWiki
Telomeres improved when obese blacks took 2000 iu of vitamin D daily – Oct 2011
Lupus in blacks associated with low vitamin D AND short telomeres – May 2013
Telomeres (which extend life) appear to be extended by Vitamin D - March 2015
Vitamin D appears to keep telomeres long (longer life) – Jan 2021