Hi
Vit
B12 & D3 are both micro nutrients. Which are if at low levels can create nutritional deficiencies l. They can be treated by supplements. Vit B12 is responsible for the development of brain & nerve cells. Vit D is responsible for
calcium absorption in the body. Once they have reached the required targets, then they could be maintained by Dietary & lifestyle changes. Once you've reached the required amounts needed by the body, its advised to stop consuming otherwise they might prove toxic.
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Thanks