Bruno Lapauw

Fat Mass Is Negatively Associated with Cortical Bone Size in Young Healthy Male Siblings

CONTEXT Body weight has been associated with bone mass and bone size through shared genetic determination and environmental influences. Whereas lean mass exerts a positive influence on bone size, the relationship between fat and bone remains unclear. OBJECTIVE The objective of the present study was to investigate the individual influence of fat mass and lean mass on volumetric bone density and size in young healthy male siblings at age of peak bone mass. DESIGN This was a cross-sectional, population-based sibling pair study. PARTICIPANTS A total of 677 men (25-45 yr) were included in this study with 296 independent pairs of brothers. MAIN OUTCOME MEASURES Areal and volumetric bone parameters were determined using dual-energy X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT). Body composition was determined by DXA. Sex steroids, leptin, and adiponectin were determined by immunoassay. RESULTS Total and regional fat mass were found to be inversely associated with areal bone mass and bone size, independent from lean mass (radius periosteal circumference beta: -0.29 +/- 0.04; P < 0.001). Lean mass was positively associated with bone size but inversely with cortical density at both tibia and radius (P < 0.01). The negative association between total fat mass and bone size was independent from sex steroid concentrations. Leptin but not adiponectin was inversely associated with bone size, but this was no longer significant after adjustment for body fat. CONCLUSIONS Increased fat mass is associated with smaller bone size, challenging the view of a high bone mass index as a protective factor for osteoporosis, whereas lean mass was a consistent positive determinant of bone size.

Serum Estradiol Is Associated With Volumetric BMD and Modulates the Impact of Physical Activity on Bone Size at the Age of Peak Bone Mass: A Study in Healthy Male Siblings

This study investigates determinants of peak bone mass (PBM) in healthy men, focusing on effects and interactions of parameters reflecting mechanical loading and sex steroids. Healthy male siblings (n = 677; 25–45 yr) were recruited in a cross‐sectional, population‐based study. Physical activity score was assessed by a self‐reported questionnaire. Cross‐sectional muscle area (CSMA) and bone parameters of radius (4% and 66% site) and tibia (66% site) were assessed using pQCT. Peak torque of biceps and quadriceps muscles was assessed by isokinetic dynamometry. Serum testosterone (T) and estradiol (E2) levels were measured using immunoassays; free hormone fractions were calculated. Relations between indices of bone strength, CSMA, muscle strength, and sex steroids were studied using linear mixed‐effects modeling. Physical activity, CSMA, and muscle strength were positively associated with indices of bone strength, except for volumetric BMD (vBMD). After controlling for age, weight, and height, free E2 levels were positively associated with trabecular and cortical vBMD, negatively associated with endosteal circumference at the radius, and positively associated with cortical vBMD at the tibia. In addition, positive interactions between physical activity and serum E2 concentrations were observed for bone size at the tibia. No associations between free T levels and pQCT bone parameters were found. In this population of healthy men at the age of PBM, parameters reflecting mechanical loading are confirmed as important determinants of bone size. E2, but not T, levels are positively associated with vBMD and modulate the impact of physical activity on bone size at the tibia.

The influence of high-normal testosterone levels on risk-taking in healthy males in a 1-week letrozole administration study

Human studies on the relation between testosterone levels and risk-taking behaviour are scarce. Related functions, like aggression, have been related to higher testosterone levels more consistently, especially in the animal literature. Estradiol affects several neurotransmitter systems that play a role in behaviour regulation. Existing human studies on neurocognitive functions and testosterone levels have largely ignored the interrelatedness of testosterone levels and estradiol levels. Therefore, in this study, the effects of a 1-week combined testosterone and estradiol intervention on risk-taking behaviours were investigated. Twenty-one healthy men, with a normal body mass index, were treated for 7 days with an aromatase inhibitor (letrozole 2.5 mg), resulting in high-normal levels of testosterone and low-normal levels of estradiol, or with a combination of an aromatase inhibitor and estradiol (75 μg/24 h), resulting in low-normal levels of testosterone and high-normal levels of estradiol. A randomized experimenter and participant-blind controlled design was applied. Neurocognitive measures of risk-taking and reward and punishment sensitivity were assessed before starting with the medication and after 7 days of drug administration: Balloon Analogue Risk Task (BART), Game of Dice Task (GDT), and Iowa Gambling Task (IGT). A group by time effect was present for the BART, indicating that the high-normal testosterone group showed an increase in risk-taking on the BART, from the first drug-naive BART performance, to the second BART performance (aromatase inhibitor), whereas such an increase was not present in the low-normal testosterone/high estradiol group. No group by time interactions were present in GDT or IGT performance. These results implicate that testosterone levels in healthy men are associated with increased risk-taking under conditions of unknown probabilities, but not in conditions of known probabilities (GDT) or of strategic decision making (IGT).

Body composition and metabolic parameters are associated with variation in thyroid hormone levels among euthyroid young men.

OBJECTIVE Thyroid disorders affect metabolism and body composition. Existing literature has been conflicting on whether this is also the case for thyroid hormone levels within the euthyroid range. Therefore, we have investigated the relationship between thyroid hormone concentrations and body composition together with metabolic parameters in a population of healthy euthyroid men. METHODS Healthy male siblings (n=941, 25-45 years, median BMI 24.6) were recruited in a cross-sectional, population-based study; a history or treatment of thyroid disease and thyroid autoimmunity were exclusion criteria. Body composition and muscle cross-sectional area were assessed by dual-energy X-ray absorptiometry and peripheral quantitative computed tomography. Total (triiodothyronine (T(3); TT(3)) thyroxine and (T(4); TT(4))) and free thyroid hormones (FT(3) and FT(4)), TSH, and reverse T(3) (rT(3)) and thyroid-binding globulin (TBG) were determined using immunoassays. RESULTS BMI was positively associated with (F)T(3) (P<0.0001). Whole body fat mass displayed positive associations with TT(3) and with (F)T(4) and TBG (P≤0.0006). Positive associations were further observed between leptin and (F)T(3), TT(4), and TBG (P≤0.0002). Inverse associations between lean mass and muscle cross-sectional area and (F)T(3), (F)T(4), and TBG were observed (P≤0.0003). Higher levels of (F)T(3) and TBG were associated with lower insulin sensitivity, assessed by homeostatic model assessment of insulin resistance (IR; P≤0.0001). No associations between TSH and body composition or metabolic parameters were seen. CONCLUSION We show that a less favorable body composition (with higher fat and lower muscle mass and accompanying higher leptin concentrations) and IR are associated with higher thyroid hormone levels in healthy young men with well characterized euthyroidism.

Body composition, volumetric and areal bone parameters in male-to-female transsexual persons

CONTEXT Male-to-female (M-->F) transsexual persons undergo extreme changes in gonadal hormone concentrations, both by pharmacological and surgical interventions. Given the importance of sex steroids for developing and maintaining bone mass, bone health is a matter of concern in daily management of these patients. OBJECTIVE To provide data on bone metabolism, geometry and volumetric bone mineral density in M-->F transsexual persons. DESIGN/SETTING/PARTICIPANTS Twenty-three M-->F transsexual persons, recruited from our gender dysphoria clinic and at least 3 yrs after sex reassignment surgery, together with 46 healthy age- and height-matched control men were included in this cross-sectional study. MAIN OUTCOME MEASURES Body composition, areal and volumetric bone parameters determined using DXA and peripheral quantitative computed tomography. Hormone levels and markers of bone metabolism assessed using immunoassays. Peak torque of biceps and quadriceps muscles and grip strength assessed using an isokinetic and hand dynamometer, respectively. RESULTS M-->F transsexual persons presented lower total and regional muscle mass and lower muscle strength as compared to controls (all P<0.001). In addition, they had higher total and regional fat mass (P<0.010) and a lower level of sports-related activity index (P<0.010). Bone mineral content and areal density (aBMD) of the lumbar spine, total hip and distal radius, as well as trabecular vBMD of the distal radius was lower as compared to controls (P<0.010). At cortical sites, no differences in cortical vBMD were observed, whereas M-->F transsexual persons were characterized by smaller cortical bone size at both the radius and tibia (P<0.010). Lower levels of biochemical markers of bone formation and resorption (P<0.010) suggested decreased bone turnover. CONCLUSION M-->F transsexual persons have less lean mass and muscle strength, and higher fat mass. In addition, they present lower trabecular vBMD and aBMD at the lumbar spine, total hip and distal radius, and smaller cortical bone size as compared to matched controls. Both the lower level of sports-related physical activity as well testosterone deprivation could contribute to these findings. These results indicate that bone health should be a parameter of interest in the long-term follow-up care for M-->F transsexual persons.

Thyroid hormone status within the physiological range affects bone mass and density in healthy men at the age of peak bone mass

CONTEXT The hormonal factors involved in the regulation of peak bone mass (PBM) in men have not been fully investigated. Apart from gonadal steroids and somatotropic hormones, thyroid hormones are known to affect bone maturation and homeostasis and are additional candidate determinants of adult bone mass. OBJECTIVE We aimed to investigate between-subject physiological variation in free and total thyroid hormone concentrations, TSH, and thyroid binding globulin (TBG) in relation to parameters of bone mass, geometry, and mineral density in healthy men at the age of PBM. DESIGN AND SETTING We recruited 677 healthy male siblings aged 25-45 years in a cross-sectional, population-based study. Areal and volumetric bone parameters were determined using dual-energy x-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT). Total and free thyroid hormones, TBG, and TSH were determined using immunoassays. RESULTS Free and total thyroid hormone concentrations were inversely associated with bone mineral density (BMD) and bone mineral content (BMC) at the hip and total body (free triiodothyronine (FT(3)), total T(3) (TT(3)), and total T(4) (TT(4))) and at the spine (FT(3)). TBG was negatively associated with BMC and areal BMD at all sites. At the radius, cortical bone area was inversely associated with TT(3), TT(4), and TBG, and trabecular bone density was inversely associated with free thyroxine, TT(4), and TBG. We observed inverse associations between cortical bone area at the mid-tibia and FT(3), TT(3), TT(4), and TBG. No associations between TSH and DXA or pQCT measurements were found. CONCLUSION In healthy men at the age of PBM, between-subject variation in thyroid hormone concentrations affects bone density, with higher levels of FT(3), TT(3), TT(4), and TBG being associated with less favorable bone density and content.

Early smoking is associated with peak bone mass and prevalent fractures in young, healthy men

Smoking is associated with lower areal bone mineral density (aBMD) and higher fracture risk, although most evidence has been derived from studies in elderly subjects. This study investigates smoking habits in relation to areal and volumetric bone parameters and fracture prevalence in young, healthy males at peak bone mass. Healthy male siblings (n = 677) at the age of peak bone mass (25 to 45 years) were recruited in a cross‐sectional population‐based study. Trabecular and cortical bone parameters of the radius and cortical bone parameters of the tibia were assessed using peripheral quantitative computed tomography (pQCT). Areal bone mass was determined using dual energy X‐ray absorptiometry (DXA). Sex steroids and bone markers were determined using immunoassays. Prevalent fractures and smoking habits were assessed using questionnaires. Self‐reported fractures were more prevalent in the current and early smokers than in the never smokers (p < .05), with a fracture prevalence odds ratio for early smokers of 1.96 (95% confidence interval 1.18–3.24) after adjustment for age, weight, educational level, and alcohol use and exclusion of childhood fractures. Current smoking was associated with a larger endosteal circumference (β = 0.027 ± 0.009, p = .016) and a decreased cortical thickness (β = −0.034 ± 0.01, p = .020) at the tibia. In particular, early smokers (≤16 years) had a high fracture risk and lower areal BMD, together with a lower cortical bone area at the tibia and lower trabecular and cortical bone density at the radius. An interaction between free estradiol and current smoking was observed in statistical models predicting cortical area and thickness (β = 0.29 ± 0.11, p = .01). In conclusion, smoking at a young age is associated with unfavorable bone geometry and density and is associated with increased fracture prevalence, providing arguments for a disturbed acquisition of peak bone mass during puberty by smoking, possibly owing to an interaction with sex steroid action.

Polymorphisms of the SHBG gene contribute to the interindividual variation of sex steroid hormone blood levels in young, middle-aged and elderly men

Objective  In men there is a large interindividual variation of SHBG levels and consequently of testosterone (T) and E2 levels. Family and twin studies suggested a strong genetic contribution, besides metabolic and hormonal influences. The aim of this study was to examine the influence of a missense mutation in exon 8 (Asp327Asn) and a (TAAAA)n‐repeat in the promoter region of the SHBG gene, on SHBG and sex steroid serum concentrations in a population of healthy men.

Short-term aromatase inhibition: effects on glucose metabolism and serum leptin levels in young and elderly men.

OBJECTIVE To assess and compare the effects of short-term aromatase inhibition on glucose metabolism, lipid profile, and adipocytokine levels in young and elderly men. DESIGN AND METHODS Ten elderly and nine young healthy men were randomized to receive letrozole 2.5 mg daily or placebo for 28 days in a crossover design. RESULTS Both in young and elderly men, active treatment significantly increased serum testosterone (+128 and +99%, respectively) and decreased estradiol levels (-41 and -62%, respectively). Fasting glucose and insulin levels decreased in young men after active intervention (-7 and -37%, respectively) compared with placebo. Leptin levels fell markedly in both age groups (-24 and -25%, respectively), while adiponectin levels were not affected by the intervention. Lipid profile was slightly impaired in both groups, with increasing low density lipoprotein-cholesterol levels (+14%) in the younger age group and 10% lower levels of APOA1 in the elderly. A decline in IGF1 levels (-15%) was observed in the younger age group. No changes in weight or body mass index were observed in either young or old men. CONCLUSIONS Short-term aromatase inhibition appears to affect glucose metabolism in young men, and lipid metabolism, including leptin secretion, in young and elderly men. Furthermore, the short period of exposure suggests that these changes might be mediated by direct effects of sex steroids rather than by changes in body composition.

Prevalent fractures are related to cortical bone geometry in young healthy men at age of peak bone mass

Low areal bone mass is a risk factor for fractures in men. Limited data are available on fractures and bone geometry in men, and the relation with sex steroids is incompletely understood. We investigated prevalent fractures in relation to peak bone mass, bone geometry, and sex steroids in healthy young men. Healthy male siblings (n = 677) at the age of peak bone mass (25 to 45 years) were recruited in a cross‐sectional population‐based study. Trabecular and cortical bone parameters of the radius and cortical bone parameters of the tibia were assessed using peripheral quantitative computed tomography (pQCT). Areal bone mineral density (aBMD) was determined using dual‐energy X‐ray absorptiometry (DXA). Sex steroids were determined using immunoassays, and fracture prevalence was assessed using questionnaires. Fractures in young men were associated with a longer limb length, shorter trunk, lower trabecular BMD, smaller cortical bone area, and smaller cortical thickness (p < .005) but not with bone‐size‐adjusted volumetic BMD (vBMD). With decreasing cortical thickness [odds ratio (OR) 1.4/SD, p ≤ .001] and decreasing cortical area (OR 1.5/SD, p ≤ .001), fracture odds ratios increased. No association between sex steroid concentrations and prevalent fractures was observed. Childhood fractures (≤15 years) were associated with a thinner bone cortex (−5%, p ≤ .005) and smaller periosteal size (−3%, p ≤ .005). Fractures occurring later than 15 years of age were associated with a thinner bone cortex (−3%, p ≤ .05) and larger endosteal circumference (+3%, p ≤ .05) without differences in periosteal bone size. In conclusion, prevalent fractures in healthy young men are associated with unfavorable bone geometry and not with cortical vBMD when adjusting for bone size. Moreover, the data suggest different mechanisms of childhood fractures and fractures during adult life.