Which factor inhibits bone synthesis?

Cortisol is a hormone released by the adrenal glands during stress and has several metabolic effects, including a notable impact on bone health. An increase in cortisol levels inhibits bone synthesis by promoting the breakdown of bone tissue (a process known as bone resorption) and decreasing the proliferation and activity of osteoblasts, the cells responsible for bone formation.

High cortisol levels can lead to conditions such as osteoporosis, where there is a net loss of bone density due to the imbalance between bone resorption and formation. Additionally, cortisol can impair the absorption of calcium in the intestines and decrease renal tubular reabsorption of calcium, further contributing to the inhibition of bone synthesis.

In contrast, the other factors mentioned—growth hormone, insulin, and estrogen—have beneficial roles in bone synthesis. Growth hormone stimulates the growth of bone and cartilage, insulin has anabolic effects that promote the uptake of glucose and amino acids necessary for bone formation, and estrogen is crucial for maintaining bone density by inhibiting bone resorption. Therefore, their increases would typically support rather than inhibit bone synthesis.