Effect of testosterone therapy on BMD and bone strength in men with low testosterone
STUDY: Snyder PJ, Kopperdahl DL, Stephens-Shields AJ, et al. Effect of Testosterone Treatment on Volumetric Bone Density and Strength in Older Men With Low Testosterone: A Controlled Clinical Trial. JAMA internal medicine. 2017;177(4):471-479.
Osteoporosis is a multifactorial disorder characterized by low bone mass and increased skeletal fragility.1 Osteoporosis and osteoporotic fractures are generally considered to mainly affect older postmenopausal women, but up to 20% of spine (vertebral) fractures and 30% of hip fractures occur in men.2 Osteoporotic fractures in men are associated with substantial morbidity and greater mortality than in women.2 One of the major causes of osteoporosis in men is hypogonadism, which is found in up to 70% of elderly men with hip fractures.2,3
Low bone mineral density is a prevalent and treatable cause of osteoporosis-associated morbidity and mortality in men with hypogonadism.4 Low testosterone levels5 and bone loss6,7, with accompanying reduction in bone strength8 and increase in fractures9, is a common finding in older men. Even among men younger than 50 years who were attending an andrology/infertility clinic, 35% had bone mineral density consistent with osteopenia (borderline osteoporosis) in the spine and/or hip.10 This suggests that it is not age per se but rather low testosterone that contributes to the loss of bone mass and development of osteoporosis.
Here we summarise the results of the Bone Trial of the Testosterone Trials (T-Trials)11, a group of 7 coordinated trials of the effects of testosterone treatment of older men with low testosterone concentrations.12,13 The purpose of the Bone Trial was to determine whether testosterone treatment would improve bone mineral density and estimated bone strength.11
What is known about bone mineral density, osteoporosis and testosterone
Osteoporosis is a silent disorder characterized by reduced bone mass (measured as bone mineral density) and bone strength, predisposing to increased fracture risk.1,14,15 The risk of fracture increases progressively with decreasing bone mineral density.15 Although osteoporosis is more common in women than men, up to 30–40% of all osteoporotic fractures worldwide occur in men.16 Surprisingly, the estimated residual lifetime risk of experiencing an osteoporotic fracture in men over the age of 50 is up to 27%, which is higher than the 12% lifetime risk of developing prostate cancer.17-19 Importantly, the morbidity and mortality consequences of osteoporotic fractures in men are more severe than in women20-23, and men are less likely to return to independent living than women after a hip fracture has occurred.24
Information box: cortical bone versus trabecular bone
Bone in human and other mammal bodies is generally classified into two types:
- Cortical bone, also known as compact bone.
- Trabecular bone, also known as cancellous or spongy bone.
These two types are classified as on the basis of porosity and microstructure. Cortical bone is dense and is found primary in the shaft of long bones and forms the outer shell around trabecular bone.
Trabecular bone is porous and is found at the ends of long bones like the legs (femur) and also in the pelvic bones, ribs, skull, and the vertebrae in spine.
Between 3-11% of men over the age of 50 in the United States have osteoporosis and 31-53% have osteopenia.25 An important risk factor for fractures in men is testosterone deficiency.2,3 Even among men younger than 50 years, those with testosterone levels of 12.1 nmol/L (350 ng/dL) or below had a nearly 4-fold increased risk for osteopenia and 7.6-fold increased risk of osteoporosis.10
The international “Mr Osteoporosis” study showed that both low total testosterone and bioavailable testosterone, but not estradiol or SHBG, are associated with increased falls.26 This confirms the results from the Osteoporotic Fractures in Men Study, which sowed that fall risk was higher in men with total testosterone below 9.3 nmol/L vs. above 20.5 nmol/L (<268 ng/dL vs. >590 ng/dL) and bioavailable testosterone below 1.75 ng/dL vs. above 2.51 ng/dL.27 Remarkably, the effect of testosterone level was independent of poorer physical performance, suggesting that the effect of testosterone on fall risk may be mediated by other testosterone effects.27
Bone mineral density is a strong predictor of fractures in older men and may serve as a useful clinical tool in the evaluation of osteoporosis and fracture risk.28 Most studies show that low testosterone is significantly associated with reduced bone mineral density and increased risk of osteoporotic fractures.29-31 For example, after a follow-up period of up to 13 years, low testosterone was associated with an almost 2-fold increased risk of hip fractures, even after adjustment for major risk factors for fractures (age, weight or bone mineral density, fracture history, smoking status, calcium intake, and SHBG).29 This study concluded that in community-dwelling men older than 60 years, testosterone levels are independently associated with the risk of osteoporotic fracture and its measurement may be a tool to help in the assessment of fracture risk in elderly men.29
In men who are severely hypogonadal, testosterone treatment improves bone mineral density32-34, trabecular bone structure35, and mechanical bone properties.36 Some prior studies of the effect of testosterone treatment on bone in older men have been inconclusive.37-40 The explanation for this is likely inadequate testosterone treatment40, and/or differences in baseline levels of testosterone37 and baseline bone mineral density.41
What this study adds
The Bone Trial was rigorously designed to find out the effects of testosterone therapy on bone mineral density and estimated bone strength.11 211 men 65 years or older with testosterone levels of 9.5 nmol/L (275 ng/dL) or less were divided in two groups and received treatment with either testosterone or placebo for 12 months. Spine and hip volumetric bone mineral density (expressed as cm3) and areal bone mineral density (expressed as cm2) was determined by quantitative computed tomography (qCT) and dual energy x-ray absorptiometry (DEXA), respectively.
Testosterone treatment resulted in significantly greater increases than placebo in spine trabecular volumetric bone mineral density (7.5% vs 0.8%; treatment effect, 6.8%) and estimated strength of spine trabecular bone (10.8% vs 2.4%; treatment effect, 8.5%). The estimated strength increases were greater in trabecular than cortical bone and greater in the spine than hip. There were also increases in volumetric bone mineral density at other locations; spine cortical bone (+2.9%), spine whole bone (4.2%), hip whole bone (+1.8%), hip trabecular bone (+1%), hip cortical bone (+1%), and DEXA measured (areal) spine bone mineral density (+1.2%).
Figure 1: Effect of testosterone therapy for 1 year on volumetric bone mineral density.
Figure 2: Effect of testosterone therapy for 1 year on estimated bone strength.
It was concluded that testosterone treatment for 1 year in older men with low testosterone significantly increases volumetric bone mineral density and estimated bone strength, more in trabecular than cortical bone and more in the spine than hip.
Osteoporosis is underdiagnosed and undertreated, and imposes a considerable economic burden on the health system.42 Effective strategies for the prevention and management of this disease are needed.42 The Bone Trial presented here shows unequivocally that testosterone therapy for 1 year significantly increases volumetric bone mineral density and estimated bone strength, especially in the spine and trabecular bone. This is remarkable considering that the full effect of testosterone on bone mineral density takes at least 24 months, and probably even longer to achieve.32,43 Thus, had the study continued for a longer time-period, even greater improvements would likely have been seen. While to date there are no studies on the effect of testosterone therapy and fracture incidence, both lower areal bone mineral density and volumetric bone mineral density are associated with increased fracture incidence.44 Hence, the increase in volumetric bone mineral density and to a lesser degree areal bone mineral density the Bone Trial suggests that testosterone therapy may reduce fracture risk.
Comparison with previous studies
Several previous longer-term studies have investigated the effect of testosterone therapy on bone mineral density. Testosterone treatment for 24 months significantly increased bone mineral density in the spine and total hip by 7.4% (from 0.93 to 1.00 cm2) and 3.8% (from 0.96 to 0.99 cm2), respectively.35 Another study showed that testosterone therapy for 36 months significantly increased spine bone mineral density by 18% (from 0.891 to 1.053 cm2) and femoral bone mineral density by 17% (from 0.847 to 0.989 cm2).45 The improvement in bone mineral density was directly related to the elevation in testosterone levels. In the non-treated group there was a decrease in both spine and femoral bone mineral density.45 Notably, the increase in spine and femur bone mineral density with testosterone therapy for 36 months is larger than that seen with medications specifically approved to treat osteoporosis, which increase spine and hip bone mineral density by only 4% to 13.5% and 2% to 6.5%, respectively.46 It has been predicted that treatments that increase spine bone mineral density by 8% can reduce fracture risk by 54%.47
The longest-term studies to date reported effects of testosterone therapy on T-scores. The T-score is defined as the difference between a patient’s bone mineral density and that of a young normal population.48 Minus values indicate that bone mineral density is below average, and plus values indicate that bone mineral density is above average.
In a study population of hypogonadal patients with various diseases - including Klinefelter’s syndrome, Crohn’s disease, alcohol abuse, Hodgkin’s lymphoma, kidney transplant, and undescended testis – who were all diagnosed with osteoporosis at baseline, testosterone therapy for 6 years increased T-scores by +1.5 points.49 This reclassified the patients from osteoporosis to osteopenia, and reduced the calculated fracture risk by 50%.49 Another long-term study investigated hypogonadal men with aging associated low testosterone, who were treated with testosterone for up to 8 years.50 It was found that T-scores of vertebral and femoral bone mineral density increased significantly, which led to a marked decrease in the incidence of osteopenia in the spine and femoral neck.50 These two studies show that the increases in bone mineral density with long-term testosterone therapy are meaningful and that benefits are seen in all hypogonadal men, regardless of whether low testosterone is caused by disease or associated with aging. The Bone Trial of the TTrials is the largest randomized clinical trial showing that testosterone therapy confers significant bone benefits in men with low testosterone associated with aging, and refutes previous ideas that testosterone therapy should be limited to hypogonadism caused by rare diseases.51
It should be pointed out that estrogen modulators, such as clomiphene citrate, and aromatase inhibitors – which are sometimes prescribed off label to increase testosterone levels in men with low testosterone who are concerned about fertility - decrease bone mineral density.10
Effect of testosterone therapy on bone in dieting obese men
Considering that diet-induced weight loss leads to a reduction in bone mineral density, it is notable that testosterone therapy in middle-age dieting obese men mitigates the detrimental effects of caloric restriction on bone health.52 It was suggested that even during caloric restriction, testosterone treatment may lead to a temporary increase in bone formation and a sustained reduction in bone resorption.
Effect of testosterone therapy in men with osteoporotic fractures and normal testosterone levels
Most studies on the effects of testosterone therapy on bone mineral density have been conducted in men with low testosterone. However, one notable study showed that testosterone therapy also significantly increases bone mineral density in men with idiopathic vertebral fractures (i.e. fractures not associated with hypogonadism-related low bone mineral density).54 The subjects in this study were men aged 34-73 years, with vertebral crush fractures and back pain. Their mean baseline testosterone level was 19.4 nmol/L (560 ng/dL), which is typically not considered low. Testosterone therapy for 6 months elevated testosterone to 29 nmol/L (836 ng/dL). Bone mineral density in the spine increased by 5% from 0.799 g/cm2 to 0.839 g/cm2,54 which could be estimated to lead to a 30% reduction in fracture risk.55 In contrast, there were no significant changes in bone mineral density at the femoral neck, trochanter, and total hip, likely due to the relatively short treatment duration of only 6 months. Interestingly, age was not predictive of response to treatment.54 The increase in spine bone mineral density was accompanied by significant favorable reductions in diastolic blood pressure (-4.7 mmHg), serum triglyceride (-0.405 mmol/L), and total cholesterol (-0.27 mmol/L). A small elevation in blood thickness (hematocrit) was seen at 3 months which then plateaued and stayed within normal range. There was no change in glucose levels, serum electrolytes, hepatic or renal function.54,56 It was concluded that testosterone is a promising treatment for men with idiopathic osteoporosis.56 This study is particularly interesting because it shows significant bone mineral density benefit in men who do not have low testosterone and who therefore would not receive testosterone treatment in general routine clinical practice. The potential benefits of testosterone therapy on bone health – regardless of baseline testosterone status – merits further study.
Association of bone mineral density with atherosclerosis, cardiovascular disease and mortality
Atherosclerosis and osteoporosis have traditionally been viewed as separate pathological conditions, however accumulating data show interesting associations between bone mineral density, atherosclerosis, cardiovascular disease and mortality.57-60 A meta-analysis showed that lower trabecular volumetric bone mineral density at baseline was found to predict long-term mortality after adjusting for demographics, hip size, health behaviors, chronic conditions, and history of bone fractures.59 It is particularly interesting to note in the Bone Trial that the greatest improvement with testosterone therapy was seen in trabecular volumetric bone mineral density.11
Several mechanisms have been suggested to explain the relationship between low bone mineral density and cardiovascular disease.61,62 A well known risk factor for both low bone mineral density and cardiovascular disease in men is low testosterone levels.61-63 In previous editorials we have summarised research about low testosterone and risk of cardiovascular disease, as well as the beneficial effects of testosterone therapy on cardiovascular health:
Testosterone Therapy and Cardiovascular Risk - Advances and Controversies
Testosterone treatment is not associated with risk of adverse cardiovascular events – RHYME study
Low Testosterone is Associated with Elevated Cardiovascular Disease Biomarkers
Effective testosterone treatment reduces incidence of atrial fibrillation
The Bone Trial unequivocally shows significant benefits of testosterone therapy on bone mineral density and estimates bone strength in older men with aging related low testosterone. This study adds to the evidence base showing that testosterone has significant osteoanabolic effects, which supports the use of testosterone therapy in men with low bone mineral density. Data from other studies suggest that men with low bone mineral density may benefit even if their baseline testosterone level is higher than what is normally considered low testosterone.