On the other hand, vitamin D is a fat soluble vitamin which can be stored in the body. Your body needs vitamin D to absorb calcium from the diet. If you do not ingest enough vitamin D, your body has hormones which will cause calcium to be withdrawn from the bone so that the amount of calcium in the blood remains normal. In people whose diet is very low in vitamin D and who do not ever go outside without sunscreen, this low vitamin D level can lead to osteoporosis. Even if I did not teach anatomy, I would know this because it happened to my husband. Even though men do not usually develop osteoporosis until their mid-70s, he was not even 65 when he developed severe osteoporosis.
You cannot really overdose on Vitamin C since it is a water soluble vitamin.
Excess vitamin C turns to oxalic acid which can cause kidney stones.
B6 is a water soluble vitamin and can cause long lasting damage.