It appears that vitamin D decrease your chances of dying by about 7%. While that does not seem like a lot, it is statistically significant. In simple terms, you are likely to live about another 5.7 years.
The cancer rates for breast and bowel cancer diminish. As do the mortality rates from diabetes and cardiovascular disease. These diseases account for 60-70% of deaths in developed countries.
You should be taking 400IU-1000IU daily of vitamin D. This varies because people in northern climates do not get as much sun exposure as those that live in warmer climates.