Osteoporosis: Why Bones Weaken With Age and What May Really Be Driving It

Osteoporosis is one of the most common age-related conditions, affecting millions of people worldwide. Osteoporosis is what happens when bones gradually lose their strength, making them more likely to crack, break, or fracture from injuries that once would have caused little to no damage. Although osteoporosis can affect both men and women, it disproportionately affects women, who account for about 80% of all cases. The risk rises significantly with age, particularly during and after the menopausal transition, when important hormonal changes begin to influence the body's ability to maintain healthy bone.

For many people, the first sign of osteoporosis is a broken bone after a seemingly minor fall. A fracture that once would have been insignificant suddenly becomes life-changing. Hip fractures, in particular, are associated with loss of independence, prolonged disability, and increased mortality in older adults.

But before that fracture happened, the bones had been evolving every single day. Osteoporosis is the result of years of changes occurring beneath the surface.

Bone Is Constantly Being Rebuilt

Many people think of bone as an inert structure, but bone is actually one of the most metabolically active tissues in the body.

Every day, your skeleton is being remodeled through the coordinated actions of two specialized cell types:

• Osteoclasts, which break down and remove old or damaged bone.
• Osteoblasts, which build new bone and strengthen the skeleton.

When these two processes remain balanced, bone remains healthy and strong. Problems arise when bone breakdown begins to outpace bone formation.

As we age, this balance often shifts. The body may continue removing old bone, but it becomes less efficient at replacing it. Over time, bones become thinner, weaker, and more susceptible to fracture.

The question is: what causes this shift in the first place?

Chronic Stress and the Skeleton

One of the most overlooked contributors to bone loss may be chronic stress.

Stress can create a measurable physiological changes throughout the body, including alterations in hormone production that directly affect bone metabolism.

Research has shown that U.S. military veterans suffering from post-traumatic stress disorder (PTSD) have higher rates of osteoporosis than the general population. These findings suggest that prolonged activation of the stress response may accelerate bone loss.

One mechanism involves parathyroid hormone (PTH), a hormone responsible for regulating calcium levels in the blood. Under chronic stress, PTH levels can rise. While PTH plays an essential role in calcium regulation, persistently elevated levels can promote bone breakdown in order to maintain calcium availability.

This is why physicians frequently monitor PTH levels in patients with osteoporosis and osteopenia.

Stress also increases production of cortisol, often referred to as the body's primary stress hormone. Elevated cortisol has long been recognized as a contributor to bone loss. Studies have repeatedly shown that excess cortisol suppresses bone formation while increasing bone breakdown. Animal studies, including experiments involving cortisone administration, demonstrate dramatic reductions in bone density when cortisol levels remain chronically elevated.

In many ways, osteoporosis can be viewed as a disease of prolonged stress physiology.

The Vitamin D Connection

When vitamin D levels fall, the body compensates by increasing production of parathyroid hormone. As discussed earlier, chronically elevated PTH can accelerate bone loss.

Low vitamin D status is also associated with higher cortisol and prolactin levels, creating a hormonal environment that may further compromise skeletal health.

Vitamin D deficiency becomes increasingly common with age, particularly among individuals who spend limited time outdoors. One study observed that vitamin D levels are low in the majority of reported hip fracture cases and suggested that declining vitamin D status may significantly contribute to age-related bone loss.

Because vitamin D helps the body absorb calcium efficiently, deficiency may force the body to withdraw calcium from the skeleton in order to maintain normal blood calcium levels.

Regular sunlight exposure, vitamin D-rich foods, and appropriate supplementation when necessary can all help support healthy vitamin D status. Many clinicians consider blood levels of 25-hydroxyvitamin D between 50 and 70 ng/mL to be supportive of optimal calcium absorption and bone health.

Magnesium: The Forgotten Bone Mineral

When osteoporosis is discussed, calcium tends to receive all the attention.

Yet magnesium may be just as important. Magnesium participates in hundreds of enzymatic reactions throughout the body and plays a critical role in calcium regulation. Without sufficient magnesium, calcium cannot be properly utilized.

Researchers have found that magnesium deficiency contributes to osteoporosis through several pathways. It directly affects bone formation and mineralization while also influencing parathyroid hormone activity and promoting chronic low-grade inflammation.

Inadequate magnesium intake has become increasingly common due to soil depletion, food processing, and dietary changes.

Multiple studies have found that magnesium supplementation can improve bone density and reduce fracture risk, particularly in older women. Rather than focusing exclusively on calcium intake, maintaining adequate magnesium levels may be one of the most effective strategies for supporting skeletal health.

The Role of Progesterone and Pregnenolone

Hormones are often discussed in the context of fertility and reproduction, but they also play a major role in maintaining healthy bones.

One hormone that receives surprisingly little attention in osteoporosis discussions is progesterone.

Progesterone directly stimulates osteoblasts—the cells responsible for building new bone. While estrogen has historically received most of the attention in bone research, progesterone appears to play an important role in promoting bone formation itself.

During perimenopause, progesterone levels often decline years before menopause occurs. Ovulation becomes less consistent, resulting in lower progesterone production. This may contribute to the accelerated bone loss commonly observed during this stage of life.

A woman may therefore begin losing bone density long before she reaches menopause.

Pregnenolone may also be important. Often referred to as the "mother hormone," pregnenolone serves as a precursor to progesterone and numerous other steroid hormones.

Research suggests that pregnenolone may help maintain bone density and support healthy bone remodeling by promoting hormonal balance. Some studies have even reported improvements in osteoporosis markers following pregnenolone administration.

Taken together, declining progesterone and pregnenolone levels may represent an underappreciated aspect of age-related bone loss.

Protein: An Overlooked Building Block

Approximately one-third of bone is composed of a protein matrix, primarily collagen, that provides flexibility and structural integrity.

Without adequate protein, the body cannot effectively build or maintain strong bones.

Higher protein intake has consistently been associated with improved bone strength, better calcium absorption, and reduced fracture risk. Yet many older adults consume less protein as they age, potentially accelerating bone loss.

Historical evidence raises interesting questions about whether osteoporosis is truly an inevitable consequence of aging.

Researchers examining the skeletons of Huguenots, 16th-century Europeans known for their traditional lifestyle, found remarkably little difference in bone density between postmenopausal women and younger women. While multiple factors likely contributed to this observation, their nutrient-dense diet, rich in animal protein, may have played an important role.

The Estrogen Debate

For decades, estrogen was promoted as one of the primary treatments for preventing osteoporosis.

One reason was that women receiving estrogen therapy often retained more calcium than they excreted. Researchers interpreted this as evidence that estrogen was helping move calcium into bone.

However, some endocrinologists questioned this conclusion.

Retaining calcium does not necessarily reveal where that calcium is going. While some may be deposited into bone, calcium can also accumulate in soft tissues throughout the body, including arteries, kidneys, breast tissue, and other organs.

This distinction is important because calcium accumulation outside the skeleton may contribute to tissue dysfunction and degeneration. So we want to make sure calcium is retained, but in the right places! 

A Bone Promoting Ecosystem

Osteoporosis is often presented as a simple calcium deficiency, but the reality is far more complex.

Bone health is influenced by stress hormones, vitamin D status, magnesium levels, protein intake, hormonal balance, sunlight exposure, inflammation, and overall metabolic health.

Bones reflect what is happening throughout the body. Supporting healthy bones therefore requires a broader perspective, one that looks beyond calcium alone and considers the many interconnected systems that determine whether the body is breaking down bone or building it.