The role of androgens for bone health in elderly men is unclear. We show that free testosterone within the normal range is a predictor of BMD at predominantly cortical bone sites and of previous osteoporosis-related fractures in elderly Swedish men.Introduction: Osteoporosis-related fractures constitute a major health concern not only in women but also in men. Previous studies have clearly shown that serum levels of estradiol are associated with BMD, whereas more conflicting data have been presented regarding the predictive value of testosterone (T) for bone health in elderly men. The aim of this study was to investigate if serum levels of T are associated with BMD and/or prevalent fractures in a large cohort of elderly men. Materials and Methods:In the Swedish part of the MrOS study (n ‫ס‬ 2908; average age, 75.4 years), bone parameters were measured using DXA, and prevalent fractures were recorded using standardized questionnaires and by vertebral X-ray analyses. Serum levels of total T, total estradiol (E2), and sex hormone-binding globulin (SHBG) were measured by radioimmunoassay, and free T (FT) and free E2 (FE2) were derived from the mass action equations. Height, weight, age, physical activity, smoking habits, and calcium intake were included together with FT and FE2 in regression models for BMD. Results: FT was an independent positive predictor of BMD in total body, total hip, femur trochanter, and arm but not in the lumbar spine. The highest independent predictive value of FT was found in the arm and the hip (with a relatively high content of cortical bone). FE2 was an independent predictor of BMD at all bone sites studied, and the highest predictive value was seen for lumbar spine (with relatively high content of trabecular bone) BMD. FT but not FE2 was a positive predictor of total body bone area and BMC. FT levels below the median were independent predictors of prevalent osteoporosis-related fractures (OR, 1.56; 95% CI, 1.14-2.14; p < 0.01) and X-ray-verified vertebral fractures (OR, 2.00; 95% CI, 1.34-2.86; p < 0.001). The predictive value of FT for prevalent fractures was not affected by adjustment for BMD. Conclusions: These findings show that variation of FT within the normal range is an independent but modest predictor of BMD at predominantly cortical bone sites and of previous osteoporosis-related fractures in elderly men. Our data indicate that not only estrogens but also androgens are of importance for bone health in elderly men. Longitudinal studies investigating the predictive value of T for fracture risk in elderly men are required.

Testosterone concentrations in men are associated with cardiovascular morbidity, osteoporosis, and mortality and are affected by age, smoking, and obesity. Because of serum testosterone's high heritability, we performed a meta-analysis of genome-wide association data in 8,938 men from seven cohorts and followed up the genome-wide significant findings in one in silico (n = 871) and two de novo replication cohorts (n = 4,620) to identify genetic loci significantly associated with serum testosterone concentration in men. All these loci were also associated with low serum testosterone concentration defined as <300 ng/dl. Two single-nucleotide polymorphisms at the sex hormone-binding globulin (SHBG) locus (17p13-p12) were identified as independently associated with serum testosterone concentration (rs12150660, p = 1.2×10−41 and rs6258, p = 2.3×10−22). Subjects with ≥3 risk alleles of these variants had 6.5-fold higher risk of having low serum testosterone than subjects with no risk allele. The rs5934505 polymorphism near FAM9B on the X chromosome was also associated with testosterone concentrations (p = 5.6×10−16). The rs6258 polymorphism in exon 4 of SHBG affected SHBG's affinity for binding testosterone and the measured free testosterone fraction (p<0.01). Genetic variants in the SHBG locus and on the X chromosome are associated with a substantial variation in testosterone concentrations and increased risk of low testosterone. rs6258 is the first reported SHBG polymorphism, which affects testosterone binding to SHBG and the free testosterone fraction and could therefore influence the calculation of free testosterone using law-of-mass-action equation.

Few genome-wide association studies (GWAS) account for environmental exposures, like smoking, potentially impacting the overall trait variance when investigating the genetic contribution to obesity-related traits. Here, we use GWAS data from 51,080 current smokers and 190,178 nonsmokers (87% European descent) to identify loci influencing BMI and central adiposity, measured as waist circumference and waist-to-hip ratio both adjusted for BMI. We identify 23 novel genetic loci, and 9 loci with convincing evidence of gene-smoking interaction (GxSMK) on obesity-related traits. We show consistent direction of effect for all identified loci and significance for 18 novel and for 5 interaction loci in an independent study sample. These loci highlight novel biological functions, including response to oxidative stress, addictive behaviour, and regulatory functions emphasizing the importance of accounting for environment in genetic analyses. Our results suggest that tobacco smoking may alter the genetic susceptibility to overall adiposity and body fat distribution.

Androgens may regulate the male skeleton either directly by stimulation of the androgen receptor (AR) or indirectly by aromatization of androgens into estrogens and, thereafter, by stimulation of the estrogen receptors (ERs). To directly compare the effect of ER activation on bone in vivo with the effect of AR activation, 9-month-old orchidectomized wild-type and ER-inactivated mice were treated with the nonaromatizable androgen 5␣-dihydrotestosterone, 17␤-estradiol, or vehicle. Both ER␣ and AR but not ER␤ activation preserved the amount of trabecular bone. ER␣ activation resulted both in a preserved thickness and number of trabeculae. In contrast, AR activation exclusively preserved the number of trabeculae, whereas the thickness of the trabeculae was unaffected. Furthermore, the effects of 17␤-estradiol could not be mediated by the AR, and the effects of 5␣-dihydrotestosterone were increased rather than decreased in ER-inactivated mice. ER␣, but not AR or ER␤, activation resulted in preserved thickness, volumetric density, and mechanical strength of the cortical bone. ER␣ activation increased serum levels of insulin-like growth factor I, which were positively correlated with all the cortical and trabecular bone parameters that were specifically preserved by ER␣ activation but not by AR activation, suggesting that insulin-like growth factor I might mediate these effects of ER␣ activation. Thus, the in vivo bone-sparing effect of ER␣ activation is distinct from the bone-sparing effect of AR activation in adult male mice. Because these two pathways are clearly distinct from each other, one may speculate that a combined treatment of selective ER modulators and selective AR modulators might be beneficial in the treatment of osteoporosis. S ex steroids are important not only for the maintenance of the female skeleton, but also for the male skeleton. The relative contribution of androgens versus estrogens in the regulation of the male skeleton is unclear. Testosterone replacement therapy increases bone mineral density (BMD) in hypogonadal men (1), but several clinical studies indicate that BMD is correlated more to serum levels of estradiol than to serum levels of testosterone in males (2-4). A previous clinical study, which directly compared estrogen versus testosterone effects on bone, showed that estrogens play the dominant role in the regulation of bone resorption markers, whereas both estrogens and testosterone contribute to the maintenance of markers for bone formation (5).The effects of testosterone can be exerted either directly by means of the androgen receptor (AR) or indirectly by aromatization to estrogens and further by estrogen receptor (ER)␣ and͞or ER␤. All three sex steroid receptors are expressed both in growth-plate cartilage and in bone (6-11). Functional studies using sex steroid receptor-inactivated animal models have demonstrated that ER␣ but not ER␤ is important for the regulation of appendicular longitudinal skeletal growth in male mice (12-14), and a recent report indicates that AR-inactivate...