Treatment with testosterone undecanoate injection increases BMD and improves bone structure in men with low testosterone
Hypogonadism (also known as testosterone deficiency or low testosterone) is a significant risk factor for low bone mineral density (BMD) and osteoporosis.1, 2 Low levels of testosterone or estradiol are associated with higher prevalence of osteoporosis at baseline and greater loss of BMD over time.3 In men with hypogonadism, which is found in up to 70% of elderly men with hip fractures,4, 5 low BMD is a prevalent and treatable cause of osteoporosis-associated morbidity and mortality.1
Randomized controlled trials 6, 7 as well as long-term real-world evidence studies 8, 9 have provided evidence for the importance of testosterone for bone health in men, showing that testosterone therapy increases BMD and estimated bone strength.
Here we summarise the results of the Testosterone for Bone (T4Bone) trial, a sub-study of the Testosterone for Diabetes Mellitus trial (T4DM) trial https://www.nebido.com/hcp/testosterone-for-diabetes-prevention , which investigated the effects of testosterone treatment on BMD and bone microarchitecture.10
What is known about hypogonadism, testosterone therapy and bone density
Previous RCTs have shown that testosterone therapy significantly increases both areal BMD (measured dual-energy X-ray absorptiometry, DEXA) 6 and volumetric BMD (measured by quantitative computed tomography, QCT).7 In the longest duration RCT to date, testosterone therapy in older men with low testosterone levels increased spine and hip BMD over 36 months.6 This study is notable for doing serial measurements of BMD every 6 months, showing that the largest increase in both spine and hip BMD occurred between month 24 and month 36, underscoring the importance of long-term testosterone therapy. Furthermore, low BMD was not an inclusion criterion, suggesting that long-term testosterone therapy can prevent development of testosterone in older men with low testosterone levels.6 The Bone Trial of the Testosterone Trials (T-Trials) showed that testosterone treatment for 1 year in older men with low testosterone significantly increased volumetric BMD and estimated bone strength.7 For more information about this study, see “Effect of testosterone therapy on BMD and bone strength in men with low testosterone”
Bone strength is determined not only by BMD, but also by bone microarchitecture (structure).11 In clinical practice, evaluation of bone status and diagnosis of osteopenia and osteoporosis is done using DEXA, which only measures BMD. However, the majority of fractures occur in individuals not diagnosed with osteoporosis by BMD testing and/or in those with few clinical risk factors, and thus low fracture probability by FRAX (Fracture Risk Assessment Tool).12 Therefore, interventions for prevention and treatment of osteoporosis should be evaluated for their effect on both BMD and bone microarchitecture.
The T-Trials used the QCT technique, which lacks sufficient resolution to provide information about bone microstructure.7 In order to accurately elucidate microarchitecture of cortical and trabecular bone, high resolution-peripheral quantitative CT (HR-pQCT) is required.13 No previous RCTs have examined the effect of testosterone treatment on bone microarchitecture, measured by HR-pQCT.
What this study adds
The T4Bone trial was designed to examine the effect of testosterone treatment on bone microarchitecture using the HR-pQCT technique. Men with low testosterone levels (<14 nmol/L or 403 ng/dL) and abdominal obesity (waist size 95 cm or higher), age 50 years and older, were recruited from 6 Australian centers. All men participated in a community-based lifestyle program and were randomized to receive either testosterone undecanoate injection or placebo injection for 2 years. Primary endpoint was cortical volumetric BMD at the tibia, measured using HR-pQCT in 177 men. Secondary endpoints included other HR-pQCT parameters and bone remodelling markers. Areal BMD (aBMD) was measured by DEXA in 601 men (five centers). Treatment effect was reported as before-after changes between groups and analysed as mean adjusted differences at 12 and 24 months.
Over 24 months, testosterone treatment, compared to placebo, significantly increased tibial cortical vBMD by 3.1%, radial cortical vBMD by 2.9%, total tibial vBMD by 1.3%, and total radial vBMD by 1.8%. Testosterone also significantly increased cortical area and thickness at both sites. Effects on trabecular microarchitecture were minor.
Testosterone treatment also significantly increased aBMD at the lumbar spine (+3.3%), the hip (+1.9%) and femoral neck (+1.7%) (figure 1). This was accompanied by a significant reduction in bone remodeling markers, C-terminal type I collagen telopeptide (CTX) and procollagen type 1 N-terminal propeptide (P1NP).
Figure 1: DEXA measured increase in BMD of the spine, hip and femoral neck in men receiving testosterone treatment, over and beyond the changes seen in men receiving placebo.10
Data from: Ng Tang Fui M, Hoermann R, Bracken K, et al. Effect of Testosterone treatment on bone microarchitecture and BMD in men: a two-year RCT. J Clin Endocrinol Metab. Mar 8 2021
It was concluded that testosterone treatment for 2 years in men older than 50 years with prediabetes or early diabetes improves bone microarchitecture as measured by HR-pQCT at both the tibia and the radius. This effect is predominantly due to increases in cortical, rather than trabecular, bone. Consistent with the findings in bone microarchitecture, testosterone treatment reduces bone remodeling, and increases aBMD at lumbar spine and femur. This is the first RCT to address the effect of testosterone treatment on bone microarchitecture; however, the implications for fracture risk reduction require further studies.
Safety measures were reassuring; there were no significant between-group differences in the change of systolic or diastolic blood pressure, or alanine transferase. As expected, compared to placebo, testosterone treated men had elevations in hematocrit by 4% (see below) and PSA by 0.3 ng/mL, which remained within the normal range in most men.
The T4Bone trial is the first randomized controlled trial to examined the effect of testosterone treatment on bone microarchitecture, measured by HR-pQCT.10 The finding that uninterrupted testosterone treatment for 2 years significantly improves both BMD (spine and hip) and bone structure in men with low testosterone levels suggests that testosterone treatment could prevent bone deterioration and possibly reduce risk of fractures.
Interestingly, the magnitude of improvement (effect size) in the T4Bone trial,10 ranging from 1.3% to 3.1% for total and cortical vBMD, is similar to that seen with osteoporosis drug treatments, which over 12 to 24 months have been shown to result in effect sizes on HR-pQCT indices ranging from 0.3% to 3.8% using alendronate 14, 15, denosumab 14 or zoledronic acid.16 While testosterone therapy is not an approved treatment of osteoporosis and should not be used as such, the results of the T4Bone trial highlight its clinical importance for men with hypogonadism who are at risk of bone fragility and fractures.
Consistent with improvement in bone structure, the T4Bone trial also found that testosterone treatment resulted in a reduction in bone remodeling markers (CTX and P1NP). This confirms findings from a previous RCT, in which men with obesity and low testosterone levels were put on a diet for weight loss.17 Compared to the placebo group, men receiving testosterone treatment had reduced CTX and P1NP, suggesting a favourable effect on bone mass and/or structure even during a diet,17 a condition that is associated with loss of BMD.18
The T4Bone trial 10 and T-trial bone study 7 both showed that testosterone therapy increases volumetric BMD, albeit using different measurement techniques. Testosterone treatment increased spine BMD (measured by DEXA in both studies) by +3.3% in the T4Bone trial 10 and +1.2% in the T-trials bone study.7 The T4Bone trial 10 also found a significant increase in BMD at the total hip (+1.9%) and femoral neck (+1.7%). The greater effect in the T4Bone trial is likely due to the longer duration of treatment (2 years in the T4Bone trial vs. 1 year in the T-Trials bone study). The use of testosterone injection vs. testosterone gel could possibly also contribute to the greater improvement in BMD, as have been shown previously for muscle outcomes.19
The T4Bone trial provides high quality evidence that treatment duration is essential for achievement of significant improvements in bone parameters with testosterone therapy. Long-term real-world evidence studies have shown that BMD continues to progressively improve for up to 8 years with uninterrupted testosterone therapy 8, 9 However, testosterone undecanoate injection (Nebido®) is not approved to be used a treatment for osteoporosis, and such use would therefore be off-label. Bayer does not recommend use for non-approved indications. Nevertheless, due to the high prevalence of hypogonadism in men with osteoporosis (27-58%),20 measuring testosterone levels in these men is warranted.21 If the diagnosis of hypogonadism is made, which requires the presence of low testosterone levels combined with symptoms/signs, men with osteoporosis can obtain additional bone health benefits.