Here's why:

* Cyclic Forms: Glucose exists primarily in its cyclic forms (alpha and beta) in solution.

* Mutarotation: These cyclic forms can interconvert through a process called mutarotation. In solution, an equilibrium is established between the alpha and beta anomers.

* Equilibrium: At equilibrium, beta-D-glucose is the more stable form and is present in a higher concentration (approximately 63%) compared to alpha-D-glucose (approximately 37%).

Therefore, while both alpha and beta forms exist in blood, beta-D-glucose is the predominant form.