Bone and mineral density in obese children

INTRODUCTION

Childhood obesity has emerged as a significant global public health challenge, with the prevalence of overweight and obesity among children and adolescents increasing by nearly 47% worldwide between 1980 and 2013.^[1] High-income countries initially bore the most significant burden, although middle- and low-income nations have also shown sharp increases.^[2] By 2022, the World Health Organisation reported that more than 390 million individuals aged 5–19 were overweight or obese, rising from 8% in 1990 to about 20% in 2022, with obesity alone increasing from 2% to 8%.^[3] Recent data from 2021 indicate that this trend continues into young adulthood.^[4] In India, the prevalence has similarly escalated – from approximately 5% in 2013 to over 12% for overweight and 8% for obesity in recent meta-analyses.^[5] Regional studies and United Nations Children’s Fund data further highlight a striking rise, particularly among urban and higher-income groups, with adolescent overweight and obesity rates increasing by over 100% in girls and nearly 300% in boys.^[5] Collectively, these findings underscore a significant and ongoing rise in childhood and adolescent obesity globally and in India.^[6]

Childhood obesity is associated with multiple comorbidities, including diabetes mellitus, coronary artery disease, musculoskeletal problems and increased mortality. Obese children have a higher risk of fractures requiring surgery, with a 1.7-fold increased risk and greater prevalence of complications such as wound infection and post-operative issues.^[7] Bone health is influenced by genetics, diet, physical activity, hormonal status and body composition, with the maximum accrual of bone mass occurring during childhood and adolescence. Body mass index (BMI) and weight are important predictors of osteoporotic fractures.

The relationship between obesity and bone mineral density (BMD) remains a topic of debate. Studies in Indian children have reported lower BMD in obese children, whereas several international studies show higher BMD in obese or overweight children compared to normal-weight peers. Despite extensive global research, data on the effect of obesity on bone health in Indian children are limited. Therefore, this study aimed to assess BMD in obese children aged 5–12 years and compare it with age- and sex-matched normal-weight peers to guide early preventive strategies against osteoporosis and fractures.

MATERIAL AND METHODS

This was a case–control study conducted at a tertiary care hospital in Northern India. Children aged 5–12 years with a BMI >27 kg/m², an adult equivalent according to the 2015 growth charts of the Indian Academy of Paediatrics, were enrolled as cases after obtaining consent. Children with syndromic obesity, chronic diseases (rheumatological, endocrine, renal or musculoskeletal disorders) or those using medications affecting bone and mineral metabolism (such as steroids, anticonvulsants, calcium and Vitamin D supplements in the last 6 months) were excluded. Age- and sex-matched normal-weight healthy children attending the vaccination or growth clinic of the institute were enrolled as controls.

Demographic data were collected for all participants at enrolment. Anthropometric measurements were performed in the growth laboratory of the institute using standardised instruments and techniques. Measurements were taken by the same observer, with a precision of ±50 g for weight and 1 mm for height. Pubertal staging was assessed according to Tanner criteria.

Total body less head (TBLH) and regional BMD were evaluated using a whole-body dual-energy X-ray absorptiometry (DEXA) unit and the Hologic Discovery A. Additional parameters, including bone mineral area (BMA), bone mineral content (BMC), total body mass, lean body mass, fat mass, trunk fat mass and fat percentage were also estimated using the whole-body DEXA scan. Participants were positioned supine on the DEXA couch with their hands pronated and their feet inverted, with the toes touching, and the mid-sagittal plane aligned with the couch’s midline. The default whole-body DEXA scan mode was used for all measurements.

The study was conducted after obtaining ethical clearance from the Institute’s Ethics Committee. Statistical analyses were performed using the Statistical Package for the Social Sciences for Windows (version 23.0, IBM Corp., Armonk, NY). Comparisons of means were done using Student’s t-test or Mann–Whitney test for normally and non-normally distributed variables, respectively. Correlations were assessed using Pearson or Spearman correlation coefficients for normally and non-normally distributed variables, respectively. Associations between body composition and bone parameters were evaluated using multiple regression analysis, adjusted for age, sex, weight, height and pubertal stage.

RESULTS

We enrolled 60 obese children (42 males) and 26 healthy controls (17 males) who were age- and sex-matched. About 30% of cases and 50% of controls were from rural areas and the rest from urban areas. The majority of cases belonged to the lower middle (40%) and upper lower (40%) socioeconomic classes, whereas the majority of controls belonged to the upper lower socio-economic class (61.5%). The anthropometric parameters are described in Table 1.

TBLH BMD, lumbar spine and pelvis BMD were higher in obese than in normal-weight healthy children. BMA of the lumbar spine and pelvis were lower in obese children than in healthy controls; however, BMA of the whole body was higher in obese children. The BMC of the whole body was higher in obese children than in normal-weight children; however, there was no statistically significant difference in the BMC of the lumbar spine and pelvis between cases and controls [Figure 1].

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Figure 1:

Comparison of TBLH BMD, total BMC and BMA among obese and normal weight children

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Total lean mass, total body fat percentage, truncal fat mass and total fat mass were higher in obese children. Lean indices – lean/height² and appendicular lean/height² were also higher in obese children. The differences in the total BMD and BMC persisted after adjusting for age, sex, sexual maturity rating (SMR) staging and height. However, there was no statistically significant difference in total BMA between obese and normal weight children after adjusting for age, sex, SMR staging and height [Table 2].

We assessed the correlation of bone health parameters with anthropometric parameters. TBLH, BMD and BMC were found to be positively correlated with height, weight and waist circumference. Body mass, total body fat and truncal body fat had a positive influence on whole-body as well as regional BMC and BMD. Age, male sex and puberty had a positive impact on bone health parameters, while residence and socioeconomic status had no significant association with BMD or BMC [Table 3].

We assessed the influence of lean mass and total fat mass on TBLH BMD and BMC after adjusting for age, sex, weight, height and SMR staging. A 1-kg gain in fat mass decreased the TBLH BMD by 0.004 ± 0.002 g/cm² and increased whole body BMC, BMA by 8 g and 14 cm², respectively. A one-kilogram increase in lean mass improved TBLH-BMD, BMC and BMA by 0.003 kg/cm², 6.1 g and 4.84 cm², respectively. [Table 4 and Figure 2] show the correlation of fat mass, lean mass, with TBLH BMD, whole body BMC in obese and normal weight children.

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Figure 2:

Scatter diagram showing relation between lean mass, fat mass with TBLH BMD and BMC parameters in obese and normal children

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DISCUSSION

Childhood and adolescence represent the period of maximum bone mass accrual, with approximately 80% of this growth determined by genetic factors and 20% by environmental influences. Optimising these environmental determinants remains a significant challenge, particularly because the roles of body weight and adiposity – once considered protective – have recently been called into question. Given the rising prevalence of childhood obesity and uncertainty about its impact on skeletal health, we conducted this study to assess the effect of obesity and fat mass on bone health in young Indian children.

In our cohort, mean BMC, BMA and BMD values were lower than those reported in most previous studies, likely reflecting the younger age and prepubertal status of our participants. Pubertal progression has a significant impact on bone accrual, as surges in growth hormone, insulin-like growth factor 1 and sex steroids stimulate bone formation and mineralisation.^[8,9] Khadilkar et al. reported higher total body BMD (0.969 ± 0.010 g/cm² in obese boys and 0.959 ± 0.009 g/cm² in obese girls) than our findings, which can be attributed to their inclusion of older and more mature children.^[10] Similarly, Jeddi et al. (Iran) observed BMD values of 0.93–0.99 g/cm² in adolescents aged 9–18 years, reinforcing the role of age and pubertal maturation in bone accrual.^[11]

Unlike Khadilkar et al., who found lower BMC and BMD in obese Indian children after adjustment for confounders, our study demonstrated higher TBLH-BMD, BMC and BMA in obese participants, even after adjusting for age, sex, SMR stage and height.^[10] This aligns with multiple international reports from the United States, France, China and Spain, showing a positive association between adiposity and bone mass, with increments in BMD ranging from 0.04 to 0.08 g/cm².^[12-15]

Among Indian children, Marwaha et al. (2017) reported that lean mass was the strongest predictor of total and regional BMC (r² = 0.83–0.88), while fat mass had a weaker but still positive correlation.^[11,16,17] Similar findings by Zhang et al. (2024, China) showed that fat-free mass exerted the most protective effect on bone. In contrast, truncal fat displayed a mild positive association that reversed at higher BMI levels.^[18] Emeriau et al. further clarified that fat mass independently exerted a negative effect on BMC after adjusting for lean mass and height, emphasising that muscle-derived mechanical forces, rather than adiposity itself, primarily drive bone accrual.^[19]

Our cohort showed only a modest increase in BMC among obese children (83 g higher than normal weight), which is much lower than the differences reported elsewhere (246– 800 g).^{[11,15,20-22]} This may reflect our participants’ younger age, prepubertal stage and lower lean mass indices, as well as ethnic skeletal differences. South Asian children generally exhibit smaller body frames and lower Vitamin D levels, which contribute to lower absolute BMD measures. Unlike previous reports suggesting lower bone density in urban children, we found no significant difference in bone density by residence, possibly reflecting improved physical activity and sunlight exposure in our population.^[23,24]

Anthropometric indices such as BMI and waist circumference were positively associated with TBLH-BMD and regional bone parameters, consistent with Ferrer et al. (2021), and Jeddi et al., which described a nonlinear relationship – moderate BMI increases enhanced BMD, while excessive adiposity provided no additional benefit.^[11,25] In our cohort, absolute fat mass correlated positively with BMC and BMD, but total body fat percentage did not, mirroring findings by Gállego Suárez et al. (2017) and Ferrer et al.^[25,26] This supports the notion that relative adiposity without proportional lean mass does not improve bone mineralisation.

Advanced imaging studies such as high-resolutuion peripheral quantitative computed tomography (HR-pQCT) have demonstrated that although obese children may show higher volumetric BMD, they can have reduced cortical thickness and altered trabecular structure, explaining their higher fracture risk despite elevated areal BMD.^[27]

Integrating evidence from multiple studies, it appears that moderate adiposity and greater lean mass facilitate bone accrual, whereas excessive truncal fat may compromise bone quality. Ethnic and developmental differences should always be taken into account when comparing paediatric bone data. Our results contribute to this growing body of literature, demonstrating that in younger Indian children, obesity is associated with mild yet significant increases in bone mineral parameters, although the magnitude of change is smaller than that observed in older or Western cohorts.

In our study, the total body fat percentage was negatively correlated with lumbar spine BMC and BMA, but showed no significant association with lumbar BMD. Conversely, Jeddi et al. (Iran, n = 24) reported a weak positive correlation between total body fat (r = 0.18, P < 0.001) and trunk fat (r = 0.19, P < 0.001) with lumbar BMD – differences likely due to sample size, ethnicity and body composition patterns.^[11] In our participants, fat percentage negatively affected lumbar BMC but was positively associated with total body BMC and pelvic BMD, suggesting regional variation in bone response to adiposity.^[14,28-30]

These findings parallel those of Khadilkar et al. (2016, Pune, n = 245), who reported lower total body BMC/BMD in obese children after adjusting for confounding factors.^[10] In contrast, we observed higher BMC and BMA in obese children, likely due to younger age and earlier-stage obesity. Similarly, Ferrer et al. (2021, Spain, n = 553) found that BMC and BMD increased with body weight but decreased with waist circumference, underscoring that central fat has an adverse effect on bone mass.^[25] Our finding that trunk fat did not correlate with lumbar BMD aligns with Ferrer’s conclusion that waist circumference is inversely related to axial bone indices.

The positive association between fat mass index and BMD in our study also mirrors the findings of Zhang et al. (2021, China), who demonstrated that fat-free mass (b = 0.04, P < 0.001) was the strongest predictor of BMD, while truncal fat had only a mild effect that reversed with higher BMI.^[31] Marwaha et al. (2017) likewise observed that lean mass correlated more strongly with BMC (r² = 0.83–0.88) than fat mass (r² = 0.77–0.78).^[16] Emeriau et al. confirmed that fat mass exerted a negative indirect effect on total BMC after controlling for lean mass, while lean body mass index (b = 0.48, P < 0.001) remained the primary determinant.^[19]

The complex relationship between fat and bone was also underscored by Gállego Suárez et al. (2017)^[26] and Wang et al. (2021),^[32] who used NHANES data. Both studies found non-linear associations: moderate BMI levels correlated with higher BMD, but extreme adiposity failed to confer further benefit.^[26,32] Franceschi et al. (2022) similarly noted that obese children can show higher cortical BMD but thinner cortices, explaining their increased fracture susceptibility.^[33]

Mechanistically, the stronger relationship between lean mass and bone parameters in our study reinforces the concept of mechanical loading as a key determinant of bone strength. Muscle contractions generate skeletal strain that stimulates osteoblast activity and bone remodelling. While hormonal factors such as oestrogen, insulin and leptin may partly explain fat-bone correlations (Rinonapoli et al., 2021, IJMS), the pro-inflammatory adipokine milieu in obesity can counteract these benefits.^[34]

The limited sample size and lack of detailed data regarding diet, calcium and Vitamin D intake, sunlight exposure and physical activity represent key limitations of our study. These shortcomings underscore the importance of future research utilising larger cohorts and more comprehensive assessment methods to understand the factors affecting bone health in young children fully.

In summary, our results and existing evidence suggest that moderate adiposity may aid bone accrual through both mechanical and hormonal mechanisms; however, lean mass remains the dominant and consistent determinant of paediatric bone mineral status. The heterogeneity of fat-bone associations across populations highlights the importance of considering ethnicity, puberty and fat distribution. Large, longitudinal, multi-ethnic studies employing Peripheral quantitative computed tomography (pQCT) and HR-pQCT are needed to elucidate further how fat and muscle interact to shape skeletal development during growth.

CONCLUSION

Bone health in children is dependent on a multitude of factors such as nutrition, physical activity, weight and pubertal hormones. Body fat has shown variable association with bone health parameters, and further insight is needed to reveal the actual relationship. Maintaining a balance of critical weight to maintain good bone health is like walking on a tightrope, and tilting the balance towards obesity may do more metabolic harm than the benefit.