Vitamin D has been well known for decades to improve the fertility of many animals A systematic review published Jan 2012 showed, yet again, that Fertility improved with Vitamin D

See VitaminDWiki

• All items in category Fertility and Sperm 18 items as of Jan 2012
• Testosterone increased with daily 3332 IU vitamin D – Dec 2010
• Clinical Trial vitamin D levels and IVF success – May 2011 good overview
• Hypothesis – Fatigue the day after sex is due to deficiency of vitamin D or Magnesium
• Overview Conception and vitamin D highlights are listed below
  Vitamin D increases fertility of BOTH the man and the woman.
  Each 1 ng increase in blood level of vitamin D increases fertility by 1%.
  Vitamin D has been used by zoos and vets for a long time to improve fertility.
  You may not have heard much about vitamin D and fertility since it has been patented

Vitamin D Council has a page about the topic and the study

need to subscribe to their Newsletter to read it - $5 a month

Interesting to note that some of the IVF (In vitro fertilisation) clinics are in regions with lots of UVB (vitamin D) People come to the clinic then magic, they can get pregnant.