Testosterone plays a direct role in maintaining bone density in both men and women, though the relationship is more complex than most people realize. Much of testosterone’s bone-protective effect actually comes from its conversion into estrogen inside the body. When testosterone levels drop significantly, bone loss accelerates, but raising testosterone back up doesn’t always translate into fewer fractures.
How Testosterone Keeps Bones Strong
Your bones are constantly being broken down and rebuilt in a process called remodeling. Specialized cells tear down old bone tissue while others lay down fresh material. Testosterone supports the building side of this equation and helps restrain the breakdown side. But here’s what surprises most people: testosterone doesn’t do this entirely on its own.
A large portion of testosterone’s benefit to bone comes after an enzyme called aromatase converts it into estradiol, a form of estrogen. In men, about 85% of the estradiol circulating in the blood originates from this conversion. That estradiol is what primarily slows bone breakdown. Estrogen actually has a greater effect than testosterone itself in preventing bone resorption in men. So when testosterone drops, estradiol drops with it, and bones lose a key layer of protection.
Testosterone also contributes independently. It stimulates the cells that build new bone and helps maintain the outer shell (cortical bone) that gives bones their structural strength. The combined effect of testosterone acting directly on bone plus its conversion to estradiol creates a two-pronged system. Losing one side weakens the whole structure.
What Happens When Testosterone Drops
Low testosterone, clinically called hypogonadism, sets off a chain reaction. Less testosterone means less raw material for estradiol production, which means the cells that break down bone face less resistance. Over time, bones become thinner and more porous. This is why hypogonadism is listed as a risk factor for osteoporosis in men, alongside more commonly recognized risks like long-term steroid use or smoking.
Current screening guidelines from the Endocrine Society recommend bone density testing (a DXA scan) for all men aged 70 and older, and for men between 50 and 69 who have risk factors like hypogonadism, chronic lung disease, thyroid disorders, heavy alcohol use, or prolonged use of certain medications. If you’ve been told your testosterone is low, your doctor may want to check your bone density earlier than the general population would typically be screened.
Testosterone’s Role in Women’s Bones
Testosterone isn’t just relevant to men’s bone health. Postmenopausal women produce much smaller amounts of testosterone, and those levels still matter. A population-based analysis of middle-aged postmenopausal women found a clear positive relationship between testosterone levels and bone density in the lumbar spine, but only up to a point. Below about 30 ng/dL, every increase in testosterone was associated with meaningful gains in bone density. Above that threshold, the benefit flattened out and additional testosterone made little difference.
This suggests that for postmenopausal women with very low testosterone, even modest increases could support bone health. The effect was strongest in the spine, which is one of the most fracture-prone areas after menopause.
Does Testosterone Therapy Improve Bone Density?
Testosterone replacement does appear to increase bone density on a scan. In men with documented testosterone deficiency, measurable improvements in bone density show up after about six months of treatment and continue for at least three years. The gains are modest but consistent. One study of men who started testosterone therapy found an average gain of about 0.62% per year in the lumbar spine and 0.25% per year in the hip over a follow-up period of roughly seven and a half years.
Those numbers are small in any single year but meaningful when compounded over time, particularly for someone starting from a deficit. The spine tends to respond more robustly than the hip, likely because spinal vertebrae contain more of the spongy interior bone that is most metabolically active.
Better Density Doesn’t Mean Fewer Fractures
Here’s the most important nuance: improving a number on a bone density scan is not the same as preventing a broken bone. A large trial published in the New England Journal of Medicine followed over 5,200 middle-aged and older men with hypogonadism for a median of about three years. The men who received testosterone treatment did not have fewer fractures than those who received a placebo. In fact, the fracture rate was numerically higher in the testosterone group: 3.5% experienced a clinical fracture compared to 2.46% in the placebo group.
This was true across all fracture types measured, not just one specific location. The finding doesn’t necessarily mean testosterone causes fractures, but it does make clear that testosterone therapy alone should not be relied upon as a fracture prevention strategy. Bone density is only one piece of the fracture puzzle. Factors like balance, muscle coordination, bone microstructure, and fall risk all play roles that a DXA scan doesn’t capture.
What This Means Practically
If you have low testosterone and are concerned about your bones, the relationship is real but layered. Low testosterone genuinely weakens bones over time, largely by starving the body of the estradiol it needs to keep bone breakdown in check. Testosterone therapy can partially reverse the density loss, with changes appearing on scans within six months. But density gains are gradual, on the order of less than 1% per year, and they haven’t been shown to translate into fewer actual fractures in clinical trials.
Weight-bearing exercise, adequate calcium and vitamin D intake, and fall prevention remain the foundation of bone health regardless of hormone status. Testosterone’s role is best understood as one contributing factor in a system with many moving parts, not a standalone solution.