Relatively little is known about the bone health of ethnic groups within the UK and data are largely restricted to women. The aim of this study was to investigate ethnic differences in areal bone mineral density aBMDvolumetric bone mineral density vBMDbone geometry and strength in UK men.
Adjustments were made for age, weight and height. Black men had higher aBMD at the whole body, total hip and femoral neck compared to White and South Asian men independent of body size adjustments, with no differences between the latter two groups. White men had longer hip axis lengths than both Black and South Asian men.
At the tibia and radius diaphysis, Black men had larger bones with thicker cortices and greater bending strength than the other groups. There were fewer differences between White and South Asian men.
At the diaphysis, after size-correction, South Asian men had similar sized bones but thinner cortices than White men; measures of strength were not broadly reduced in the South Asian men.
Combining pQCT and DXA measurements has given insight into differences in bone phenotype Black and asian men men from different ethnic backgrounds.
"Black and asian men" such differences is important in understanding the aetiology of male osteoporosis. Osteoporosis is an important health problem through its association with age-related fractures and consequent morbidity and mortality.
There are important differences in the occurrence of age related fractures between different regions and populations, which are likely due to variation in bone strength and, or trauma — particularly fall risk. However, there are few data concerning bone mass and strength, and the underlying determinants of fracture risk in UK ethnic minority groups, with no data in men. Conversely South Asian women were reported to have a lower lumbar spine and femoral neck aBMD compared to White European women, however, after correcting for skeletal size the differences at the lumbar spine were attenuated .
These Black and asian men illustrate the limitations of DXA when describing population differences  where body size and habitus differ. Using peripheral quantitative computed tomography pQCT has advantages because it measures volumetric BMD vBMDcortical and trabecular compartments separately and provides information also about other structural parameters which contribute to bone strength.
There are limited data comparing pQCT measurements in different ethnic Thus, it is possible that bones of pre-menopausal
Black and asian men Asian women may be efficiently adapted to a lower BMC as a result of a different distribution of bone mineral within the periosteal envelope, thereby preserving bone strength . Whether these findings are similar in men remains unknown. We investigated also whether any observed differences could Black and asian men explained by body weight and height.
The men subsequently attended a follow-up assessment of identical measurements a median of 4. The results reported here are from the follow-up assessment.
Black and asian men by participants' self-report with 3 of 4
Black and asian men being of identical ethnic origin. "Black and asian men" for these ethnic groups was through a combination of approaches including advertising in community centers and through local media targeted at the relevant ethnic groups.
At their clinic visit, participants completed an interviewer-assisted questionnaire which included questions to determine their Physical Activity in the Elderly PASE score . Smoking status was assessed by asking whether participants had ever smoked at least cigarettes or been a regular pipe or cigar smoker. Those answering yes to any of the questions Black and asian men considered as ever smokers. Ethical approval for the study was obtained in accordance with the local ethics review board in Manchester.
All participants provided written informed consent. Body mass index BMI was calculated as weight in kilograms kg divided by the square of height m. Measurements of aBMD at the whole body, total hip, femoral neck and lumbar spine L1—4 were obtained; the non-dominant proximal femur was scanned. Hip axis length HALwhole body Black and asian men mass and lean mass were also measured.
All scans were reported by an experienced musculoskeletal radiologist JEA. Standard manufacturer QA and QC procedures were followed using manufacturer Hologic provided phantoms. All measurements were made in the non-dominant limb. Forearm length was defined as the distance from the styloid process of the ulna to the olecranon. Leg length was defined as the distance from the most proximal edge of the medial malleolus to the intercondylar eminence.
The scan sites were determined using a "Black and asian men" scout view of the distal radius or tibia and the reference line was placed to "Black and asian men" the lateral border of the endplate. Medullary area mm 2was calculated by total area minus cortical area.
Black and asian men and SSI are measures of bending and torsional strength at the diaphysis and have been related to fracture load .
Where significant motion artefact was detected, scans were excluded. Manufacturer's standard QA and QC procedures were followed using manufacturer supplied phantoms. Differences in descriptive characteristics were assessed using one-way analysis of variance with a Bonferroni multiple-comparison test. Differences in smoking status were assessed using a chi squared test. To investigate the ethnic differences in DXA and pQCT parameters, we performed linear regression analyses, with bone parameters as the dependent variable and ethnicity as the independent variable, with adjustments made for age, weight and height.
We used the fitted regression lines to perform pairwise comparisons between ethnic groups, correcting for multiple comparisons using the Bonferroni method. All analyses were performed in Stata, Version Three hundred and forty three participants were included in the analyses, White, 44 Black and 64 South Asian men.
White men were older than the Black and South Asian men. South Asian men were shorter than White "Black and asian men" Compared to Black and White men, total lean mass was lower in South Asian men, with no significant difference in total Black and asian men mass between groups.
Whole body fat mass to lean mass ratio was higher in South Asian men compared to White
Black and asian men Black men. The percentage of subjects who were ever smokers was lower in South Asian compared to White men. Black men had higher aBMD at the whole body, total hip and Black and asian men neck than White men.
These differences persisted after adjustment for age, weight and height Table 2. There were no significant differences in cortical or trabecular vBMD at the radius following adjustments Table 3.
At the diaphysis of the radius, Black men had thicker cortices and greater cortical area. There were no significant differences in aBMD between "Black and asian men" and South Asians except at the whole body; this difference was attenuated and became nonsignificant after adjustment for age, height and weight Table 2.
Black and asian men Asians had smaller CSA at the metaphysis and diaphysis of the radius, following adjustment, differences at the diaphysis were attenuated Table 3. South Asians had smaller cortical area and consequently thinner cortices at the diaphysis of the radius and tibia, however, Black and asian men and CSMI were similar to White at both sites following adjustments; SSI was lower in South Asian men at the tibia yet similar at the radius compared to White men Table 3Table 4.
South Asian men had lower aBMD at the whole body, total hip, femoral neck and lumbar spine; the difference at the lumbar spine was attenuated following adjustments Table 2.
In this study, for the first time, we describe the ethnic differences in BMD, bone geometry and bone bending and torsional strength in UK men. Black men had higher aBMD compared to White and South Asian men, and these differences were independent of weight and height, in contrast "Black and asian men" in aBMD between White and South Asian men were attenuated by correcting for body size.
Rather, the geometry of bone Black and asian men between the groups and mostly at the diaphyseal sites, and hip axis length was longer in White men. At the radius and tibia diaphysis, Black men had more cortical bone within a slightly larger "Black and asian men" envelope and consequently greater bending strength than the other two groups.
For the same size and body weight, South Asian men had similar sized bones compared to White and Black men at the diaphysis but had thinner cortices.
Patterns were similar in the radius and tibia. Taken together these observations suggest that there are other factors than aBMD which contribute to the differences in fracture risk between the two groups . The same group extended these findings by showing that the highest prevalence of fracture was in White American men and the lowest was observed in Black Afro-Caribbean men . Larger bones containing greater cortical area have been associated with greater bone bending strength as estimated by CSMI .
Our data are consistent with previous findings with Black men having larger bones, thicker cortices and greater CSMI compared to White and South Asian men. Additionally White men had longer Black and asian men axis lengths than both Black and South Asian men, which has also Black and asian men shown to be a risk factor for fracture .
Our findings that after adjustment for covariates, there were no differences in aBMD between White and South Asian men is consistent with data in young women were observed differences in hip and lumbar spine aBMD between White and South Asian women were explained by body size . Furthermore, The Oslo Health Study showed no differences in distal or ultra-distal Black and asian men aBMD between South Asian and White Norwegian men and women independent of height adjustments, though interestingly, mineral apparent density BMAD was shown to be greater in South Asian than in Norwegian men and women .
In contrast to these findings comparing aBMD differences, we report differences in bone geometry in South Asian compared to White men. South Asian men had smaller CSA at the tibia compared to White men, these differences were attenuated after adjustments were made for age, weight and height. Lower cortical vBMD at the diaphysis of the tibia in White men may indicate increased cortical porosity and bone turnover in this group which may in part contribute to higher fracture risk; greater porosity may be related to the differences in age between the groups but the difference was robust to age-adjustments .
Our findings are similar to those reported in young British women, where South Asians had significantly thinner cortices but similar bone size and strength "Black and asian men" the diaphysis when compared to White European women .
Parallel to data in young women, a recent study in older UK women showed that following adjustments for BMI, South Asians had smaller bones and cortical area, with lower bone mineral content at the diaphyseal radius compared to White European women . Further, a Finnish study showed that South Asian women had lower cortical vBMD and area at the diaphyseal radius, and smaller bones when compared to White Finnish women .
Black and asian men have been shown to predict fracture load in laboratory testing . The findings of lower SSI in Black men were surprising. These measures are derived parameters and are heavily based on cross-sectional area which is only one component of bone strength.
The most plausible explanation for this finding is that the measurement of SSI is not fully robust to differing bone shape, distribution and density and therefore this parameter may be limited in comparisons between populations where bone shape may differ. There are several potential limitations in this study. Ancestral
Black and asian men were self-reported and it is possible that this may have resulted in misclassification; we attempted to limit this however, by ensuring that 3 out of 4 grandparents were Black and asian men the same ethnic origin.
The concept of ethnicity embraces also cultural and environmental differences, however, this was beyond the scope of this study. The focus in this study was on looking at ethnic differences in bone parameters. There was some evidence that levels of physical activity and smoking varied between the groups of men which may have contributed to the observed differences. The number of men in the Black and South Asian groups was relatively small and so caution is required in interpreting the results.
Further adequately powered studies are needed to explore in more detail our findings and the role of lifestyle and other factors which contribute to observed ethnic differences in bone health in these groups. It should
Black and asian men be stated that this is a cross-sectional study so we were unable to study antecedents of the observed ethnic differences in the bone outcomes. We do not have data on fracture so we cannot draw causal associations between bone health and fracture.
In conclusion, this study demonstrated that Black men have higher aBMD compared to White and South Asian men, with no differences between the latter two groups.
These differences are reflected in the greater bone strength in Black men. South Asian men had thinner cortices at the radius and tibia, however, bone strength appeared to be maintained as there were Black and asian men differences in CSMI when compared to White men. These data indicate the necessity to understand the underlying ethnic differences in bone shape, mineralization and distribution to ultimately decrease the burden of male osteoporosis. The views expressed in this publication are those of the author s and not necessarily those of the NHS, the National Institute for Health Research or the Department of Health.
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