The effects of sex steroids and some elements of lifestyle on the normal variation of bone mineral content in younger versus older healthy Polish males

The aim of the study was to evaluate the independent 'net' effects of hormonal variables (estradiol, free testosterone and dehydroepiandrosterone sulfate (DHEAS) levels) and lifestyle variables (alcohol consumption, coffee drinking, cigarette smoking, physical activity and muscle strength) on trabecular, cortical and total bone mineral content (BMC) in a group of 236 healthy males, aged 22-67 years. The men were occupationally active inhabitants of the city of Wroclaw, Lower Silesia, Poland. Trabecular, cortical and total bone mineral content, at the distal radius of the non-dominant hand, were assessed by peripheral quantitative computed tomography (pQCT) using the Stratec 960 apparatus. Sex steroids levels were measured using standard immunoassays. Data on lifestyle variables (alcohol consumption, cigarette smoking, coffee drinking and physical activity) were obtained through a questionnaire. Hand-grip strength of the dominant hand was assessed using a standard dynamometer. All statistical analyses were made separately in two subgroups, younger males (aged 22-39 years) and older males (aged 40 years and over). The impact of a particular independent variable on BMC and the extent of determination on BMC by the complex of chosen variables were evaluated using a path analysis. In younger males, the effects of physical activity and muscle strength were the most important among all the factors that influenced BMC, as they contributed to 16.2%, 16.9% and 16.5% of the variability of trabecular, cortical and total BMC, respectively. Taking into consideration cigarette smoking, alcohol and coffee drinking together, the coefficients of determination of the variability in trabecular, cortical and total BMC were 10.6%, 11.3% and 16.1%, respectively. The variances in trabecular, cortical and total BMC levels were determined in only 5.8%, 11.5% and 13.0% by sex steroids, respectively. The influence of free testosterone on trabecular BMC was greater compared with that of dehydroepiandrosterone sulfate (DHEAS) and estradiol; for cortical BMC, the impacts of estradiol and DHEAS were similar and greater than that of free testosterone, and the variability of total BMC was affected mainly by estradiol. In contrast, in older men the effects of physical activity and muscular strength were the least important among all the complexes of independent variables, as they contributed to 4.5%, 7.8% and 7.0% of the variability in trabecular, cortical and total BMC, respectively. Taking into consideration the influences of cigarette smoking, alcohol and coffee drinking, the coefficients of determination of the variability in trabecular, cortical and total BMC were 16.5%, 14.8% and 17.4%, respectively. Among the older men, the variances in trabecular, cortical and total BMC were determined in only 9.4%, 6.3% and 13.6% by sex steroid levels, respectively. The influence of DHEAS on trabecular BMC was greater when compared with that of estradiol and free testosterone, whereas the variability of both cortical and total BMC in older men was affected mainly by estradiol. It is quite striking that, in younger healthy subjects, both physical activity and muscle strength contributed to a greater extent to BMC variance when compared with sex steroids levels, whereas, in older men, physical activity and muscular strength were less important than androgen- estrogen activity in determining the variability of BMC. This may suggest that the tropic effect of mechanical force influences bone structure mainly in younger men; probably male bone tissue becomes less prone to mechanical stimuli during aging. It is astonishing that both in younger and older men the coefficients of determination of physical activity and muscle strength were the highest for cortical BMC, which would indicate the greatest response of that part of the bone tissue to mechanical force. It is worth noting that the coefficients of determination of the complex of lifestyle factors (alcohol consumption, cigarette smoking and coffee drinking) were higher in older men compared to younger Polish males. This can be explained by the longer exposure of male bone to environmental influences (ethanol, nicotine, caffeine) during a lifetime. Our study revealed that all the evaluated variables were related to the variability in BMC in healthy Polish men, but the coefficients of determination differed depending on the age of the examined subject and on the BMC of a particular bone component. This suggests that the responsiveness of male bone tissue to environmental factors changes with age, and that these effects vary significantly between particular parts of the male bone structure.