Your bones are at their strongest in your early to mid-twenties, and from there, a slow and steady decline begins. How quickly you lose bone depends on your sex, hormone levels, diet, and activity level, but everyone experiences some degree of bone loss with age. Understanding what’s happening inside your skeleton at each stage of life can help you protect your bones for as long as possible.
When Bones Reach Their Peak
Bones aren’t static. Throughout childhood and adolescence, your body builds bone faster than it breaks it down, resulting in a net gain of bone mass year after year. This process reaches its ceiling in early adulthood. Women typically hit peak bone density around age 22, while men reach theirs closer to age 27. The difference matters: the more bone you build before that peak, the larger the “reserve” you carry into the decades of gradual loss that follow.
After peak bone mass, the balance tips. Your body continues breaking down old bone and replacing it with new bone (a process called remodeling), but the replacement side of the equation slowly falls behind. For most of your thirties and forties, the loss is subtle, often less than 1% per year. The real trouble starts when hormonal shifts accelerate the process.
What Changes Inside the Bone
Two types of cells control bone remodeling. One type builds new bone, and the other dissolves old bone. In young, healthy adults, these two crews work in rough balance. As you age, the cells responsible for building bone become less effective. The stem cells that would normally develop into bone-building cells increasingly turn into fat cells instead. Meanwhile, the cells that dissolve bone remain active or even ramp up, creating a growing imbalance.
This isn’t just a slowdown in construction. Aging also increases the production of reactive oxygen species (molecules that damage cells), which directly harm bone-building cells and suppress new bone formation. At the same time, your body’s ability to clear out old, dysfunctional cells declines, and the resulting low-grade inflammation further tips the balance toward bone loss.
The protein framework of bone changes too. Bone isn’t just mineral; roughly a third of its structure is collagen, a flexible protein that gives bone some ability to bend under stress rather than snap. With age, the cross-links between collagen fibers become more rigid. This makes bones stiffer and less able to absorb impact, increasing fracture risk even in people whose bone density scans look reasonable.
How Hormones Drive Bone Loss
Estrogen is the single most important hormone for bone maintenance in both women and men. It slows the rate of bone remodeling and keeps the balance between bone building and bone breakdown roughly even. When estrogen drops, that balance collapses.
For women, menopause is the turning point. In the first five to seven years after menopause, bone loss accelerates to 1 to 5% per year, a dramatic jump from the gradual decline of earlier decades. This rapid phase is why osteoporosis is far more common in women: by the time the loss slows again, a significant portion of bone density may already be gone.
Men lose bone more gradually, but they’re not immune. Testosterone declines slowly with age, and low testosterone is clearly linked to lower bone density and higher fracture risk. Interestingly, though, research from the large multinational MrOS study found that estrogen levels (men produce small amounts too) are actually a stronger predictor of fracture risk in older men than testosterone itself. Men with low levels of both hormones face the greatest risk overall.
Structural Changes You Can’t See on a Scale
Bone loss doesn’t happen uniformly. The interior of your bones has a spongy, honeycomb-like structure called trabecular bone, which provides much of the skeleton’s shock absorption. This interior network is especially vulnerable to aging. The number of these tiny supporting struts decreases steadily from middle age onward, and as individual struts disappear, the remaining ones can’t compensate. The outer shell of bone (cortical bone) thins too, but the loss of the internal scaffolding is what makes bones most vulnerable to the compression fractures common in the spine and the breaks that follow a fall.
Your Gut Absorbs Less Calcium Over Time
Even if you eat the same diet at 70 that you did at 40, your bones get less benefit from it. Calcium absorption in the intestines declines significantly with age. Research measuring absorption efficiency in adults found a clear downward trend as people got older, and by age 65 and beyond, the gut loses its ability to ramp up absorption when dietary calcium is low. Younger adults can partially compensate for a low-calcium diet by absorbing a higher percentage of what they eat. Older adults largely cannot.
The reason traces back to vitamin D. Your kidneys convert vitamin D into its active form, which is what actually drives calcium absorption in the gut. In both older adults and people with osteoporosis, levels of this active form are significantly lower, even when their baseline vitamin D levels appear normal. This means the problem isn’t always a lack of vitamin D in the diet; it’s that the body can no longer activate it as efficiently.
The National Institute of Arthritis and Musculoskeletal and Skin Diseases recommends that adults over 70 get at least 800 IU of vitamin D daily, along with adequate calcium. Because absorption is less efficient, getting enough through food or supplements becomes more important with each passing decade, not less.
How Bone Density Is Measured
Bone density scans use a low-dose X-ray to measure the mineral content of your bones, typically at the hip and spine. The result is reported as a T-score, which compares your bone density to that of a healthy 30-year-old of the same sex. A T-score of negative 1 or higher is considered healthy. Between negative 1 and negative 2.5 indicates osteopenia, a stage of moderate bone loss that raises your fracture risk but hasn’t yet crossed into osteoporosis. A T-score of negative 2.5 or lower indicates osteoporosis.
These thresholds matter because bone loss is painless. Most people have no idea their bones are thinning until they break one from a minor fall or even from bending over. Screening is generally recommended for all women over 65 and for men over 70, though people with risk factors (early menopause, low body weight, long-term steroid use, smoking) may benefit from earlier testing.
What Actually Protects Aging Bones
Resistance training is one of the most effective tools for maintaining bone density as you age. A meta-analysis of studies in older adults found that regular resistance exercise produced a small but meaningful increase in bone density at the hip (0.64%) and spine (0.62%). Those numbers may sound modest, but in the context of aging, where the default trajectory is steady loss, even holding steady or gaining slightly represents a real shift in fracture risk over time. The benefits held regardless of how long the training program lasted.
Weight-bearing aerobic exercise (walking, jogging, dancing, stair climbing) also helps by stimulating bone through impact. The combination of resistance and weight-bearing exercise is more effective than either alone. Swimming and cycling, while excellent for cardiovascular health, don’t load the skeleton enough to significantly benefit bone density.
Nutrition plays an equally critical role. Because calcium absorption declines with age, consistent intake through dairy, leafy greens, fortified foods, or supplements helps ensure the raw material for bone maintenance is available. Vitamin D supports that absorption, and adequate protein provides the building blocks for the collagen matrix that gives bone its flexibility. Smoking accelerates bone loss, and heavy alcohol use interferes with bone-building cell activity, so avoiding both offers meaningful protection.
The earlier you start these habits, the better. Building a higher peak bone mass in your twenties gives you more to work with later. But even starting resistance training or improving your diet in your sixties or seventies can slow the rate of loss and reduce fracture risk. Bone responds to the demands placed on it at every age.