Bone mineral density in Iranian patients : Effects of age , sex , and body mass index

Introduction: Osteoporosis is a multifactorial skeletal disease that is characterized by reduced bone mineral density (BMD). BMD values depend on several factors such as age, sex and age at menopause. The purpose of this study was to determine the prevalence and changes in bone mineral density in Iranian patients. Methods: Three hundred patients were selected through random sampling technique in 2009. BMD was assessed by Norland (Excell) technique at the lumbar and femoral neck. Weight and height were measured through standard methods. A thorough history was taken from each patient. The data was analyzed using SPSS software version 13.0. P-values less than 0.05 were considered statistically significant. Results: From among the 300 studied patients, 86.6% were female. their mean age was 52.7 years. Their average body mass index (BMI) was 28.14 kg/m. Mean T-Score at lumbar spine and femoral neck was −1.07 ± 1.19 and −1.75 ± 1.33 respectively. Mean BMD value at lumbar spine and femoral neck was 0.92 ± 0.19 and 0.77 ± 0.16 respectively. The prevalence of osteoporosis at lumbar spine and femoral neck was 33.7% and 16.7, respectively. There was a significant correlation between age, BMI and BMD values (P-Value < 0.01). Correlation between gender and BMD value at the lumbar spine and femoral neck was not significant. Conclusion: This study shows that ageing and low BMI are risk factors associated with bone loss. it is recommended to measure BMD and implement prevention programs for highrisk people.


INTRODUCTION
Osteoporosis is a multifactorial skeletal disease characterized by reduced bone mineral density (BMD) along with the deterioration of the microarchitectural structure of bone tissue, and a consequent increase in bone fragility and fracture risk [1,2].Osteoporosis is a common disease among the elderly, particularly the post-menopausal women [3][4][5][6][7].BMD values depend on such factors as age, sex and age at menopause [8][9][10].It has been predicted that in 2050, 50% of all hip fractures in the world will be occurring in Asia [11].Osteoporosis is a disease that affects many millions of people around the world.It affects more than 75 million people in the United States, Europe and Japan [12].It is estimated that world's annual incidence of hip fracture will increase from 1.26 million cases in 1990 to 2.6 million by 2025 and to 4.5 million by 2050 [13].Osteoporotic fractures affect the quality of life and are associated with premature mortality [14].
The prevalence of osteoporosis among Iranian women varies from 6 to 34.4 percent in different cities and provinces [15][16][17][18].In the present study, we evaluated the prevalence and correlation of osteoporosis with demographic factors among patients referred to a densitometry center in Gorgan, a city located in North Iran.

MATERIAL & METHODS
From among 3000 patients who were referred to the Azar 5th teaching hospital affiliated to Gorgan University of Medical Sciences, 300 patients were selected through random sampling technique in 2009.The individuals with underlying diseases affecting bone mass such as rheumatoid arthritis, renal and liver failure and any cansers were excluded.BMD was assessed by Norland (Excell) technique at the lumbar and femoral neck.Based on WHO classification, individuals with T-score values higher than −1 were classified as normal, those with T-score between −1 and −2.5 as osteopenic, and those with T-score less than −2.5 as osteoporotic [12].Weight and height were measured through standard methods and BMI was calculated by dividing weight (kilogram) by square height (square meter).A thorough history was taken from each patient.The data was analyzed using SPSS software version 13.0.The descriptive data were presented as frequency, mean and SD, whereas regression, ×2 and T-test were used for further analysis and the comparison of the data.P-values less than 0.05 were considered statistically significant.

RESULTS
From among the 300 studied patients, 260 (86.6%) were female.Their mean age was 52.7 ± 14.42 years, ranging from 21 to 85 years.Their body mass index (BMI) ranged from 16.0 to 45.54 kg/m 2 , with an average of 28.14 (SD = 5.42).Mean BMD value at the lumbar spine and femoral neck was 0.92 ± 0.19 and 0.77 ± 0.16 respectively.According to the T Score values at lumbar spine, 101 patients (33.7%) had osteoporosis and 115 (38.3%) had osteopenia.Furthermore, regarding the values reported at the femoral neck, 50 patients (16.7%) had osteoporosis and 121 others (40.3%) had osteopenia.Mean T-Score at lumbar spine and femoral neck was −1.07 ± 1.19 (−3.78 to 2.25) and −1.75 ± 1.33 (−5.07 to 1.75), respectively.There was a positive and significant correlation between age and BMD values at both lumbar spine (r = 0.32, P-Value < 0.01) and femoral neck (r = 0.42, P-Value < 0.01).There was a significant and positive correlation between BMI values and bone loss at lumbar spine (r = 0.31, P-Value < 0.01); such a significant correlation, however, was not reported at the femoral neck region (r = 0.12, P-Value = 0.11).The prevalence of osteoporosis among women and men at the lumbar spine was 14 and 2.7 percent respectively.28.3 percent of women and 5.3 percent of men had osteoporosis at the femoral neck but correlation between gender and BMD value at the lumbar spine and femoral neck was not significant (Table 1).The correlation between age groups and BMD at both lumbar spine and femoral neck was significant (P-Value < 0.01) (Table 2).

DISCUSSION
In our study, the prevalence of osteoporosis at lumbar spine and femoral neck was 33.7 and 16.7 respectively.Table 3 shows the prevalence of osteoporosis at the LS and FN in different places of the world.The figure ranges from 6.3 in Saudi Arabia to 40.1 percent Korea that is consistent with this study.These discrepancies can be explained based on the differences in race, life style and dietary habits of the people of these countries.In  line with our study, many studies have introduced age as an important factor for bone loss [17][18][19][20][21][22][23][24].Jang et al.
showed that the prevalence of osteoporosis in postmenopausal women increases with age from 30.6% in those aged between 45 and 64 to 68.7 percent in those aged over 75 [25].In our study, there was a positive strong correlation between BMI and bone mineral density in lumbar spine.In other words, each unit increase in BMI values is associated with 0.314 unit increase in bone density.Several studies in the UAE [26], India [27], Japan [28], Netherlands [29], the US [30] and Morocco [31] have considered a positive correlation between BMI and bone mineral density.A Brazilian study reported that body weight is important for gaining and losing body mass, and causes an impact on BMD-age relationship [32].Our results showed that the prevalence of osteoporosis among women was more than men but this correlation was not significant.In some study, on the contrary to our findings, revealed significantly higher prevalence of osteoporosis in women than in men [33][34][35][36] This can be due to the very low number of men compared with women in our study.On the other hand, although hormonal changes in women, especially after menopause, has an important role in osteoporosis, but men should not ignore about BMD changes.

CONCLUSION
The present research indicated the negative effect of age and positive effect of BMI on bone mass.Although, the prevalence of osteoporosis was higher among women, there was no statistically significant difference in this regard.As a result, it is recommended to use risk factors for requesting testing, mainly DXA and implement prevention programs for high-risk people and more attention needs to be paid to men osteoporosis.Future prospective studies are therefore necessary to gather more accurate information in this regard.

Table 1 .
Correlation between BMD and sex.

Table 2 .
Prevalence of osteoporosis and BMD status according to the age groups at both lumbar spine and femoral neck.

Table 3 .
Prevalence of osteoporosis in different places of the world.