101 Facts About Ageing #33: Bones Become Weaker With Age

As Daniel Patrick Moynihan, an American sociologist, politician, and diplomat once said: “Everyone is entitled to his own opinion, but not his own facts”. And we wholeheartedly agree. A shared set of facts is the first step to building a better world with longevity for all. In that spirit, we are creating a series that covers 101 indisputable facts about ageing, health and longevity.

The mass and strength of the bones declines with age, starting around middle-age. This makes them more fragile and less able to absorb shocks. Bones also take longer to heal as ageing progresses. If not addressed, these changes may progress to osteoporosis, a disease in which severe weakening of the bones leads to frequent fractures and therefore potentially chronic pain. Women are more susceptible to this disease, as their bone mass represents a lower proportion of total body weight at a given age, and declines more rapidly on average after reaching its peak.

The skeleton isn’t just an inert scaffold that supports our flesh – bones are made from living tissue, just like any other organ of the body. Within the bone, cells called osteoblasts and osteoclasts work together to remodel and repair bone tissue, including the microscopic fractures that occur as a result of normal, everyday forces which the skeleton must withstand. Osteoclasts resorb (reabsorb) damaged tissue, while osteoblasts deposit new tissue. With age, osteoclast activity begins to outstrip osteoblast activity, which leads to a net loss of bone tissue.

Several factors may contribute to this change. Oxidative stress increases with age, leading to the apoptosis (self-destruction) of osteoblasts. Stem cells in the bone marrow begin to produce fewer osteoblasts in favour of fat cells. Hormonal changes (such as increased production of parathyroid hormone) affect the activity of osteoblasts and osteoclasts. Calcium and vitamin D, which are both required for bone production, are less well absorbed due to the ageing of the digestive system. Inflammation increases with age (fact #29), which promotes bone resorption. Since mechanical loading stimulates osteoblasts, lack of exercise due to old age may decrease production of new bone.