It could have the most direct effect on the amount of mitochondria in cells and also the system of the membrane.
You absorb vitamin d from sunlight shining on your skin.
Vitamin d can help the absorption of calcium, which is capable for strengthening your bones and teeth.
Therefore if u r lacking of vitamin d, your bones and teeth may be soft, and especially among children, you may get ricket, where the legs are bent outwards.
Their purpose is reproduction.
I think the answer to this is abyssal plane
