Normative bone mineral density z-scores for Canadians aged 16 to 24 years: the Canadian Multicenter Osteoporosis Study

Abstract

The objectives of the study were to develop bone mineral density (BMD) reference norms and BMD Z-scores at various skeletal sites, to determine whether prior fracture and/or asthma were related to BMD, and to assess possible geographic variation of BMD among Canadian youth aged 16-24 yr. Z-Scores were defined as the number of standard deviations from the mean BMD of a healthy population of the same age, race, and sex. Z-Scores were calculated using the reference sample defined as Canadian Caucasian participants without asthma or prior fracture. Reference standards were created for lumbar spine (L1-L4), femoral neck, total hip, and greater trochanter, by each year of age (16-24 yr), and by sex. The Z-score norms were developed for groups noted earlier. Mean Z-scores between the asthma or fracture subgroups compared with the mean Z-scores in the reference sample were not different. There were minor differences in mean BMD across different Canadian geographic regions. This study provides age, sex, and skeletal site-specific Caucasian reference norms and formulae for the calculation of BMD Z-scores for Canadian youth aged 16-24 yr. This information will be valuable to help to identify individuals with clinically meaningful low BMD.

Fig. 1

Mean bone mineral density (BMD) by sex, age, and skeletal site in study sample. (A) Youth female—mean BMD by age and skeletal site; (B) youth male—mean BMD by age and skeletal site.

Fig. 2

Comparison of the mean Z-scores by sex and skeletal site in subgroups with asthma and fracture. The dashed line represents the values of the reference sample. (A) Female lumbar spine bone mineral density (BMD); (B) male lumbar spine BMD; (C) female total-hip BMD; (D) male total-hip BMD.

Fig. 3

Mean Z-scores (95% confidence intervals) by center and skeletal site. (A) Female lumbar spine bone mineral density (BMD); (B) male lumbar spine BMD; (C) female total-hip BMD; (D) male total-hip BMD.VR, Vancouver; CA, Calgary; SK, Saskatoon; HA, Hamilton; TO, Toronto; KN, Kingston; QC, Quebec City; HX, Halifax; ST, St. John’s. The dashed line represents the values of the reference sample.

Fig. 4

Comparison of mean BMD by sex and skeletal site between CaMos youth cohort and that of the United States. (A) Comparison of TH BMD by age and sex: CaMos and data of Bachrach et al; (B) comparison of FN BMD by age and sex: CaMos and data of Bachrach et al; (C) comparison of TH, FN, and TR BMD: CaMos 20–24 yr and NHANES III 20–29 yr. BMD, bone mineral density; TH, total hip; FN, femoral neck; TR, trochanter; NHANES III, National Health and Nutrition Examination Survey.