Preheat the oven to 375°F (190°C) and line or grease a 12-cup muffin tin.
In a large bowl, combine the whole wheat flour, wheat bran, brown sugar, flax, cinnamon, baking powder, baking soda, and salt.
Add the orange zest, orange juice, oil, and vanilla to the bowl and mix until just combined. Don't over mix.
Add frozen blueberries to the muffin batter and gently fold them in until evenly incorporated.
Scoop the batter into the 5 muffin cups as evenly as possible. Bake for 25-30 minutes, or until the top of a muffin springs back when lightly touched.
Cool the muffins for 5 minutes before removing from the tin and cooling fully on a wire rack. They'll last a few days in an airtight container at room temperature and freeze well.