Hormonal influences. Women have a lower bone mass than men, and this difference increases following the menopause. The factors that influence skeletal development and determine gender differences have been assumed to be related primarily to sex steroid action. Sex steroids are synthesised in response to signals from the brain. It is this stimulus from the hypothalamus to the pituitary gland which releases hormones that target the reproductive organs [77]. Luteinising hormone (LH) and follicle-stimulating hormone (FSH) stimulate the synthesis of progesterone and oestrogens in the female ovaries and testosterone in the male testes [77-79]. With the onset of puberty, hormones contribute to gender differences and the greater bone mass in men [70]. Studies have shown that gonadal hormones can increase bone formation [80] particularly in cortical areas, and the absence of androgen action has been related to lower bone mass and smaller size [81]. Testosterones are known to influence weight and muscle mass and therefore also indirectly affect skeletal development. Oestrogens slow the rate of bone remodelling and help to maintain a balance between bone formation and resorption by increasing the release of osteoclast and osteoblast progenitor cells in the bone marrow [82-84]. Conversely, oestrogen deficiency causes an increase in bone remodelling where osteoclastic activity is increased coupled with a reduction in osteoblastic activity, resulting in increased resorption and reduced formation leading to bone loss [85].
