Final answer:
Decreased alveolar bone density is associated with decreased levels of estrogen, which has a protective effect on bone density by promoting osteoblastic activity.
Step-by-step explanation:
Decreased alveolar bone density is often linked to hormonal changes in the body. Among the hormones listed, estrogen is known to have a protective effect on bone density by promoting the activity of osteoblasts, which are responsible for the deposition of new bone. As estrogen levels decrease, particularly in postmenopausal women, the rate of bone resorption (breakdown of bone tissue) can exceed the rate of bone formation, leading to conditions such as osteoporosis. While parathyroid hormone (PTH) stimulates the release of calcium from bones into the blood and can lead to decreased bone density when levels are high, it is not responsible for the regular maintenance of bone density associated with aging and estrogen levels.