Vitamin D is man made just under the skin by sunlight. Vitamin D is a fat soluble vitamin.
For all water soluble vitamins like B and C is much more difficult to be included, because the unnecessary extra amount back to the urine excreted. Of vitamin A and D it is possible in the course of many years to accumulate, which can lead to disease.
Thus vitamin A are teratogenic when used by more than 9 times the RDA per day. A safe daily intake for pregnant women is up 3 to 4 times the RDA (equivalent to approximately 2500 to 3000 ?g (micrograms)) per day. The legal limits for vitamin A in food (well below these levels) the risk of overdose through supplements nil, if one is to keep the recommended dosage. The risk of vitamin A toxicity by regularly eating liver is present. Liver is very rich in vitamin A.