Carole Baggerly is the founder of Grassroots Health, a non-profit organization conducting research into the effects of vitamin D. 

According to her research:

35% of our healthcare costs will decrease if everyone has adequate levels of vitamin D.

Randomised Controlled Trials have shown that 2000IU of vitamin D given IV daily decreased the incidence of all cancers by 77%.

Breast cancer incidence decreases 75% when serum vitamin D level is maintained at or above 50ng/ml.

Serum level of 30ng/ml and above corresponds with 50% lower incidence of cancer recurrence.

Diabetes Mellitus incidence decreases 60% at levels of 40ng/ml and above.

So, Simple!! Just ensure adequate intake and blood level of Vitamin D, and Stay Healthy!!