Center of Division Ring is Subfield

Theorem
Let $$\left({K, +, \circ}\right)$$ be an division ring.

Then $$Z \left({K}\right)$$, the center of $$K$$, is a subfield of $$K$$.

Proof
For $$Z \left({K}\right)$$ to be a subfield of $$K$$, it needs to be a division ring that is commutative.

Thus the result follows directly from Center of Ring is Commutative Subring.