Osteoporosis is a common metabolic bone disease characterized by a loss of bone mass and strength, a deterioration of bone structure and an increased risk of fractures. Bone strength is a reflection of bone mineral density (BMD) and bone quality. Approximately 10% of the world population suffers from osteoporosis, and 30% of post-menopausal women.

 A loss of bone mass with progressing age is expected from the age of 30 as changes in the bone remodelling cycle lead to fragility. The pathophysiology of osteoporosis is linked to a lack of homeostasis between bone formation and bone loss during the continuous remodelling of bone tissue. Bone formation is greater than bone resorption during childhood growth, in early adulthood these processes are relatively equal, and with progressive age bone loss is greater than bone formation, leading to the risk of osteoporosis.

Primary bone cell types include osteoblasts (bone-forming) and osteoclasts (bone-degrading). Several factors are involved in bone remodelling that influence the activities of osteoblasts and osteoclasts.

The formation of osteoclasts depends on the presence of the receptor activator of NF-κB ligand (RANKL), whose expression leads to bone resorption through a cascade of regulatory enzymes and transcription factors. High levels of RANKL are observed in females at the onset of menopause, increasing osteoclast production and bone resorption. The RANKL pathway is modifiable by a variety of hormones and inflammatory cytokines that can influence osteoclast production.

There are multiple risk factors that influence osteoporosis risk including both genetic and environmental factors – unchangeable and variable or preventable factors. In combination, these risk factors can contribute to a loss of bone mass, and ultimately osteoporosis.

Advanced age, the female sex, race and hormone imbalance have all been associated with osteoporosis risk. Dietary factors such as protein, Vitamin D and calcium intake as well as participation in exercise have also been linked to the risk of disease.

Vitamin D

Vitamin D deficiency is correlated with a wide range of diseases including osteoporosis, rickets, cardiovascular disease, autoimmune disease, multiple sclerosis and cancer. A growing awareness of the consequences of Vitamin D deficiency has led to an increase in Vitamin D testing amongst healthcare practitioners. Vitamin D plays an important role in calcium absorption and phosphate metabolism.

The two predominant forms of vitamin D are D2 (ergocalciferol) and D3 (cholecalciferol), both of which are available in small quantities from the diet, and in higher amounts from supplements. In humans the major source of Vitamin D is the endogenous production of the vitamin, prompted by skin exposure to the sun’s ultraviolet rays. Foods naturally high in vitamin D include egg yolk, fatty fish and fish liver oil.

Exercise

An active lifestyle that includes regular (3-4 days/week) weight-bearing exercise is key in preventing osteoporosis. Activity stimulates the mechanoreceptors of the osteocytes to induce remodelling, the removal of damaged bone and synthesis of new bone. Hence a gradual decrease in BMD is observed in sedentary individuals.