Abdulkadir ¥Unal, 
Emel Gur, 
Ahmet Arvas, 
Ayten Erginel, 
Mujgan AlikasifoÃglu and 
¥Ozdemir <Ilter

From the Unit of Social Pediatrics, Department of Pediatrics, Cerrahpasa Medical Faculty, Instanbul University, Istanbul.
Reprint requests: Dr. Emel Gur, CaferaÃga Mah. Miralay Nazim Sok. No: 13 Daire: 1, Kadik¥oy / Istanbul

Manuscript received: August 18, 1999; 
Initial review completed: October 8, 1999; 
Revision accepted: November 3, 1999.

Objective: To determine values of bone density of Turkish infants under one year of age. Design: Cross sectional. Methods: This study included 1, 2, 4, 6, 9 and 12 months old 164 male and female healthy infants who were evaluated by dual energy X-ray absorbtiometry. Results: The values for each age were computed. There was no significant difference between boys and girls. A significant relationship was found between bone mineral density, bone mineral content, total body calcium and calcium/body surface, and age, height, body weight, head circumference and body surface area. Multiple regression analysis showed that body mineral density was affected by weight, height, head circumference and body mass index. Body mineral content and total calcium content were affected by weight and height. Conclusion: The results will serve as reference values for healthy 1-12 months old Turkish infants.

Key words: Bone density, Dual energy X-ray absorbtiometry.

Bone mineralization is a complex process in which adequate nutrition, balance of hormones and a number of growth factors play various roles. A defect in any of these factors may lead to congenital and acquired diseases of bone mineralization. Race, gender, geo-graphic conditions, seasonal variations, muscle activity and indulgence in sports are other factors that effect bone mineralization(1-3). Correlation between body parameters and bone mineralization have been reported in a number of studies(4-6), but there are controversial results regarding the effect of race and gender in mineralization process. There are reports indicating higher bone mineral density values in black and male kids comparing to whites and females (2,3,7-9), but some reports have found no differences in relation to race and gender (10-13).

Bone density can be evaluated by invasive (bone biopsy) and non-invasive methods such as radiography, quantitative computerized tomography, neutron activation, single photon absorbtiometry (SPA), dual photon absorb-tiometry (DPA) and dual X-ray absorbtiometry (DXA). The novel noninvasive method is DXA which has lower radiation dose (under 3 mRem), higher accuracy and precision, and shorter scanning time. DXA is the most appro-priate method for evaluating the bone mineral density (BMD) in children (1,5,6,10,11,14,15).

The objectives of this study were to determine values of bone density of Turkish infants under one year old; to evaluate the relationship between gender and bone mineral measurements; and to evaluate the correlation between body parameters and age, and bone mineralization.

The study was conducted between August 1995 and August 1996. One hundred and sixty four healthy children born at term with a birth weight above 2500 g were evaluated. They had no maternal problem that may effect fetal growth and were completely healthy. All infants were given 400 IU vitamin D and 0.25 mg flour daily but not supplementary calcium and phosphorus. After weight, height and head circumference records were taken, and physical examination completed, the infants were sent to Istanbul University, Cerrahpasa Medical Faculty Bone Dansitometer Measurement Center. The bone density of naked infants were measured at supine and knee-flexed position using LUNAR Corp DPX-L equipment and by DXA method in which an X-ray tube is used as the radiation source. During the measurement, the infant was supine, and the physiological lumbar scoliosis was flattened. The system scans the lumber spine in the rectilinear way. The X-ray tube pulses alternatively at two different voltages, and the instrument has an internal reference system that compensates for drifts in measurements. The dose received by the subject is less than 5 mRem.

DXA method was used to determine bone mineral content (BMC), BMD and total body calcium content (total Ca) of the subjects. Body area was determined from height and weight by using the height/weight standard chart. Calcium/body area values were calculated.

Student ‘t’ test, Chi-square test, correlation and multiple regression analysis methods were used for determining the relation between BMD, BMC, total body calcium and total body calcium/body area values, and body weight, height and head circumference.

Seventy five per cent of the subjects were girls and 25% boys. The mean (± SD) age for girls and boys was 4.46 ± 3.38 months (range 1-12 months) and 4.31 ± 3.2 months (range 1-12 months), respectively (p >0.05). In this study, 79.8% of the patients consumed only breast milk, 6.1% formula, and 14.1% both breast milk and formula in their first four to six months of life. Supplementation of other foods began at three months in 2.9%, four months in 76.5% and 5 or 6 months in 20.6% of the cases. The mean birth weight was 3319 ± 380 g in males, and 3296 ± 377 g in females. The mean gestational age was 39.3 (range 37-41) weeks in males and 39.4 (range 37-41) weeks in females. Only two cases had height measure-ments under 3rd percentile. In others, weight, height and head circumference measurements were above the 3rd percentile. A comparison of body weight, height and head circumference percentiles among girls and boys revealed no significant difference in weight (p >0.05) but showed a significant difference in height and head circumference (p = 0.0002 and p = 0.0001, respectively).

Table I shows bone mineral density (total BMD, spinal BMD, total BMC, total body calcium, calcium/body surface area) according to age and sex. These values were statistically comparable between males and females.

A significant relationship was found between body weight, length, head circum-ference, body surface area and age and total BMD, total BMC, total body calcium and calcium/body surface. The total BMC and total BMD ratio showed a high correlation using anthropometric measurements (Table II). The correlations between various indicators of bone density are shown in Table III.

Multiple regression analysis showed that BMD were related to body weight (p = 0.0001), height (p = 0.0018) and BMI (p = 0.0002) and head circumference (p = 0.04646). There was no significance relation between BMD and age and sex (p >0.05, p >0.05, respectively). BMC and total calcium content were significantly related to body weight (p = 0.0001), height (p = 0.0001) and BMI (p = 0.0002).

Table I: Observed Total BMD, Spinal BMD, Total BMC, Total Body Ca and Ca/body Surface Area.       

Values depict means ± SDs.
Figures in parentheses represent ranges.

Table II: Summary of Correlations

Values represent correlation coefficients (r). All correlations were statistically significant (p <0.0001).

Table III: Correlation Between Various Indicators of Bone Density

Values represent correlation coefficients (r). All correlations were statistically significant (p <0.0001).

Bone mineralization is a complex process affected by race, gender and environmental conditions and in which nutrition (protein for osteid production, vitamin D for calcification, calcium, phosphorus), hormonal homeostasis (thyroid, gonadal and pituitary hormones) and other growth factors play a role. A defect in this process may lead to congenital or acquired diseases that go along with bone mineralization disorders in children and adults(2,16,17).

Direct radiological investigations, quantita-tive CT, SPA, DPA and lately DXA methods have been used for the determination of osteopenia(18). DXA is the best method due to it’s short measurement duration, low radiation dose and (less than 5mRAM) and its sensi-tivity. It is also the most suitable method for the measurement of bone density in children(6,11,14).

Somatic growth is very fast during the first year of life. Optimum environmental condition and adequate nutrition are important factors that effect growth in this period. The recommended daily vitamin D requirement of an infant is 400 IU because of low vitamin D content of breast milk (20-40 IU/L)(18). Greer et al.(19) showed that at 6 months BMC values were lower in infants fed only breast milk without vitamin D supplementation as compared to the infants taking vitamin D. However, the BMC values didn’t differ between two groups in measure-ments carried out at 12th month. A possible explanation for this may be the introduction of high calcium containing cow milk into the diet of the infants after six months. But in some studies it has been found that bone mineralization level is similar in supplementary mineral containing formula fed infants and breast-fed infants(20,21). Reports suggest that increase in milk consumption during childhood and adolescence may lead to decrease in traumatic bone fractures(22), may prevent mineral loss caused by breastfeeding(23) and may diminish menopausal osteopenia(24). In our study BMD, BMC, total body calcium values obtained from healthy male and female infants at 1, 2, 4, 6, 9 and 12 months of their life were positively correlated with age, weight, length, head circumference and body surface area. BMC showed higher correlation as compared to other parameters. Various publica-tions have reported similar results(5,6,12, 13,24). In our study the total BMD increased by a mean of 25% at 12 months as compared to one month. Spinal BMD increase was near to that level (mean 26.5%). The increase in total BMC, total calcium and calcium/body surface area values were more significant (2-2.7 times) than spinal BMD increase.

In our study, bone density measurements were not significantly different between genders. Other workers also reported no differ-ence between males and females but pointed out that peak bone density is reached earlier in females because of earlier puberty(11,23). However, some other investigators(3,7,9) have reported lower mineral content in females.

In previous studies it has been reported that, although there is no significant difference at the newborn period, bone density of older children and adults is higher in black than whites and osteoporosis is less frequent in blacks as compared to whites(2,8,25). This indicates that there is no difference between two races regarding in utero mineralization(13). A study carried out in infants from England and Gambia has revealed that BMC values were different in each country at birth and 30th month, being higher in English children(26). Our results are higher as compared to the spinal BMD values obtained from 22 healthy children in France(6). Our results (spinal BMD in 1 year males - 0.535 ± 0.03 and females - 0.523 ± 0.05) are higher also from another study from France (0.446 ± 0.048 g/cm2)(11).

Bone density differences between races and nations may stem from yet unkown reasons other than genetical and environmental factors. Further studies are needed to answer this question. Previous reports have pointed out spinal BMD and total BMC as the reference measurement parameters. In addition to these, we have obtained total BMD and total calcium values. Total BMD is an important measure-ment paremeter in severe osteopenia where bone metabolism gets diffusely affected. In the literature the reference values were not given separately for each month group in infants between 0-12 months. Since growth is very rapid in the first year of life, it is important to know the reference values for each month. The results of our study may serve as a reference value for Turkish infants under 1 year of age.

We observed significant correlation between total BMD and spinal BMD (r = 0.58, p <0.0001). In severe problems where the bones are affected diffusely except for severe osteopenia, spinal BMD measurement may be done instead of total BMD measurement and may provide reliable information about bone density. This approach should be preferred because of less radiation exposure, shorter scanning duration and low cost.

In conclusion, determination of BMD accurately in children is important for the evaluation of metabolic bone diseases (rickets, malabsorption and malnutrition, cholestatic syndromes, various renal and endocrine disorders). Our results revealed no difference between genders and may serve as reference value for Turkish infants under 1 year old. We feel that similar studies should be carried out for older children.

Contributors: EG coordinated the study (particularly its design) and drafted the paper; she will act as the guarantor for the paper. AU and MA participated in the data collection and also helped in drafting the paper. AA, AE and OI helped in interpretation of the data and drafting the paper.

Funding: None.
Competing interests: None stated.

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