In order for your hips to be building bone density through the day, they need to be supporting the weight of your pelvis and torso in a certain alignment.
A common pattern we see with resting standing positions is standing with the pelvis pushed slightly forward (as in the first picture). It is subtle but has major implications for bone health of the hips (not to mention the long term impact of this position on foot health, core strength, and balance).
Shifting the pelvis back so your body weight is carried over the heels (second picture) and maintaining this position throughout the day allows for optimal bone health. However, getting to this position if this is not your usual requires taking a closer look at the muscle groups that attach to the pelvis.
A quick and simple test to help you determine where you carry your center of mass: make a plumb line from string with something weighted at the bottom. Position yourself facing sideways toward a mirror and find the boniest part of the outside of the hip. Drop your plumb line from that spot. If the weight falls in front of the ankle, you are likely standing with your pelvis pushed forward! Back your hips up until the plumb line falls in line with the ankle to get in a better position for weight-bearing hips.
Just getting to this position drastically changes the muscle groups you use in standing. Improving alignment requires mindfulness throughout the day in combination with the strengthening and stretching need to maintain this position.
Building bone density takes time, so there is no better time to start than today!