Bone biology is not an independent process but instead interacts closely with the functioning of a number of other systems in the body. As a result there are a number of factors that can affect bone health and hence determine the risk of developing Osteoporosis and the rate of progression when disease is present. Furthermore, it should be noted that osteoporosis is a systemic disease, affecting all bones in the body, which further supports the fact that bone biology is balanced by the body system in general.
Two major factors that determine your bone biology and hence risk of Osteoporosis is your age and gender. It is true that peak bone mass is achieved in the early adult years and thereafter is characterized by slow but progressive decline.
It is estimated that 2-3% of bone mass is lost on an annual basis. As mentioned in the section ‘What is Osteoporosis?’, bone is a living organ that is continually undergoing remodeling. This involves a balance between bone formation and bone resorption. Until early adulthood bone formation is greater than bone resorption allowing bones to grow and strengthen, but thereafter the pendulum swings in the opposite direction causing overall loss of bone mass. In addition to age, gender plays an important role.
Obviously gender is genetically determined, but how those genes result in sexual differences is of greater interest in Osteoporosis. The sex genes determine, in essence, what sexual hormones are in abundance, being either oestrogren in females or testosterone in males. These hormones have an important role to play in the balance between bone formation and bone resorption, and hence bone mass. In females, the production of oestrogen dramatically falls at the time of menopause since the ovaries, which is the primary site at which the hormone is made, effectively stops working at this time. However, males continue to produce testosterone their entire lives. For this reason, Osteoporosis is more common in females than in men! Nevertheless, men can and do still develop the disease although the condition is often (unfortunately) not considered for the reasons mentioned above
In addition to your age and gender there are a number of other risk factors for developing Osteoporosis. There are a few of these that relate directly to the hormone oestrogen as introduced above. As mentioned, oestrogen is a sex hormone that is produced in women that has an important role in bone health. Therefore, the amount and duration that this hormone is present can predict, to a degree, the risk of developing osteoporosis. Time of menarche (age at first menstrual cycle) and menopause (age of last menstruation) is useful information as well as any interruption to the menstrual cycle that does or can occur with pregnancy, anorexia, or any serious medical illness.
The latter of which can also have an independent negative affect on bone, especially when the infirm person is bed bound. This relates to the importance of load as a stimulus to build and maintain bone. This is perhaps most famously appreciated by the bone loss that astronauts experience during their adventures into space, during which gravity (and hence load) is not present. A more common scenario, however, is the immobility that often affects the elderly of our community. Admittedly, these are extreme examples to highlight the principle that the greater the load on bones the stronger they become.
Other factors affecting risk of Osteoporosis will be discussed in other sections.