Good nutritional diet is certainly important unless you have had gastric bypass surgery or anyother type of disease of the colon that causes malabsorption. We cannot correct our Vitamin D deficiency with diet and time in the sun.  Many bypass pts. become lactose intolerant.  We take large doses of Vitamin D to increase our level between 40 and 60.  After we reach our goal, we still remain on prescription doses of Vitamin D.  This is for life.  Within a month and 1/2 of increasing my vitamin D level to 40 I felt better than I have felt in years.  This was after the Vitamin D deficiency destroyed my immune system which caused me to have a high grade lymphoma.  For 18 months following my last chemo treatment we have been checking my Vit. D level every two months.  I am maintaining at 67, feel great, and remain in remission.  The key to finding Vit D deficiency is labs and doctors that are knowledgeable in proper treatment.  My oncologist had no clue.