Abstract

Aim

Osteoporosis can occur in individuals with liver disease, and its development is thought to be influenced by the activity of the underlying hepatic disorder, as noted in previous studies. This study aimed to investigate the influence of the degree of liver steatosis, an important indicator of non-alcoholic fatty liver disease (NAFLD) severity, on bone mineral density (BMD).

Methods

Between August 2022 and July 2023, this cross-sectional study enrolled patients aged 50 to 90 years who were followed at an osteoporosis clinic and had a diagnosis of NAFLD confirmed by ultrasonography (US). Based on abdominal ultrasound findings, patients were classified into four groups reflecting the degree of liver steatosis. The groups were compared with respect to T-scores and BMD at the total spine, femur, and femoral neck, measured by dual-energy X-ray absorptiometry.

Results

Of the 792 patients assessed for eligibility, 248 met the inclusion criteria. The participants had a mean age of 65.1±11.2 years, and 97.6% (n=242) were female. The mean body mass index was 27.31±4.58 kg/m². Significant between-group differences were detected for lumbar total T-scores. A significant difference was identified in the lumbar spine T-score evaluation between the grade 3 and grade 0 groups in abdominal US imaging.

Conclusion

Because NAFLD and osteoporosis share several risk factors and involve chronic inflammation, NAFLD is considered a potential risk factor for bone loss. The findings of our study demonstrate that the risk of low BMD in the lumbar spine is elevated, particularly in advanced stages of liver steatosis.

Introduction

Non-alcoholic fatty liver disease (NAFLD) represents a continuum of chronic liver disorders encompassing simple steatosis, non-alcoholic steatohepatitis, fibrosis, cirrhosis, and ultimately hepatocellular carcinoma (HCC) (1). Non-alcoholic fatty liver disease, a metabolic disorder of the liver, is increasingly prevalent and is estimated to affect approximately 25% of the global population. It is estimated that 3.5 million new cases are diagnosed annually (2). Non-alcoholic fatty liver disease is the most common chronic liver condition globally and imposes a significant health and economic burden (3). Recently, the terminology has been updated to metabolic dysfunction-associated fatty liver disease and subsequently to metabolic dysfunction-associated steatotic liver disease (MASLD), following the Delphi consensus statement. This revision reflects recognition that metabolic disorders—including abdominal obesity, type 2 diabetes, dyslipidemia, insulin resistance, and cardiovascular disease—are commonly associated with NAFLD (4).

Osteoporosis is a common systemic condition characterized by decreased bone mass and deterioration of bone microarchitecture. According to the World Health Organization, it affects approximately 6.3% of men aged 50 years or older and 21.2% of women aged 50 years or older worldwide. Additionally, it is estimated that approximately 37 million fragility fractures occur annually among individuals older than 55 years, corresponding to approximately 70 fractures per minute globally (5). A substantial body of research has highlighted the causal relationship between NAFLD and osteoporosis (1). These two diseases share similar risk factors, including older age, obesity, type 2 diabetes mellitus, and a sedentary lifestyle (6). The prevalence of osteoporosis is higher in patients with chronic liver disease than in people without liver disease, with figures ranging from 10% to 40% (7). Studies have shown that the prevalence of osteoporotic fractures is 2.5 times as high in individuals with NAFLD as in those without the condition (8). Substantial evidence from the literature substantiates the presence of osteoporosis in individuals with chronic liver disease. Nevertheless, no study has yet evaluated the impact of disease severity on osteoporosis.

In our study, we hypothesized that bone mineral density (BMD) would be lower in patients with a high degree of hepatic steatosis. The purpose of this study was to evaluate how different levels of liver steatosis affect BMD in patients with NAFLD. Consequently, this study will facilitate the incorporation of liver stenosis as a risk factor into osteoporosis clinical practice.

Materials and Methods

Compliance with Ethical Standards

The study received approval from the Ethics Committee of the University of Health Sciences Türkiye, Sisli Hamidiye Etfal Training and Research Hospital, (approval number: 4061, date: 29.08.2023). Informed consent was obtained from all participants during their initial outpatient visit. The research was conducted in accordance with the Declaration of Helsinki and adhered to the Strengthening the Reporting of Observational Studies in Epidemiolog guidelines for observational studies.

Study Design 

Patients followed at the osteoporosis outpatient clinic of our hospital between August 2022 and July 2023 were screened in this cross-sectional study. Throughout the study period, 792 patients followed at our osteoporosis clinic were assessed for eligibility. Inclusion criteria required that participants be aged 50-90 years, be either men or postmenopausal women, and have undergone abdominal ultrasonography (US) within six months of their dual-energy X-ray absorptiometry (DXA) assessments. Furthermore, they were required to have US-defined NAFLD and a diagnosis of NAFLD by a gastroenterologist at our hospital. Individuals with any disease that would impair liver function (e.g., hemochromatosis, HCC, cirrhosis), a history of malignancy, or a history of surgery and biopsy of the liver, bile ducts, or intestines were excluded from this study.

Patients meeting the inclusion criteria underwent abdominal US to assess the degree of hepatic steatosis, on the basis of which they were assigned to one of four groups. The grading of steatosis was as follows: Grade 0 (absent)—normal liver echotexture; Grade 1 (mild)—slight, diffuse increase in echogenicity with clear visualization of the diaphragm and portal vein walls; Grade 2 (moderate)—moderate echogenicity elevation with partial blurring of the diaphragm and portal vein walls; and Grade 3 (severe)—pronounced echogenicity increase, with poor or absent visualization of the diaphragm, portal vein wall, and posterior right hepatic lobe (9). Demographic and clinical data, including age, sex, height, weight, body mass index (BMI), and comorbid conditions, were retrieved from the hospital records. Laboratory assessments included albumin, aspartate aminotransferase (AST), alanine aminotransferase (ALT), gamma-glutamyl transferase, alkaline phosphatase, phosphorus, calcium, 25-hydroxyvitamin D, and international normalized ratio.
Bone mineral density and T-scores for the lumbar spine (L1-L4 and L2-L4), femoral neck, and total femur were determined using DXA.

Statistical Analysis

Descriptive statistics included the mean, standard deviation, median, minimum, maximum, frequencies, and proportions. The Kolmogorov–Smirnov test was employed to assess the distribution of variables. The homogeneity of variances was evaluated using the Bartlett’s test; since the variances were homogeneous, the Analysis of Variance F-test p-value was used. Subsequent between-group comparisons were conducted using the Bonferroni correction for post-hoc analyses. Statistical analyses were conducted using Jamovi (The Jamovi Project, 2024; Version 2.5) (Computer software), retrieved from https://www.jamovi.org, Sydney, Australia.

Results

Of 792 patients screened according to the study criteria, 248 were included in the study (Figure 1). Participants had a mean age of 65.1±11.2 years, and 242 (97.6%) were female. Their mean BMI was 27.31±4.58 kg/m². The remaining demographic and clinical features are provided in Table 1.

Abdominal US scores were used to divide patients into four groups, which were then compared with total lumbar spine, femoral neck, and total femur T-scores. A Statistically significant difference was identified between the groups for lumbar total T-scores (p=0.027). Nevertheless, no significant differences were observed between the groups for femoral neck and total femur T-scores (p=0.073 and p=0.088, respectively) (Table 2). To ascertain the stages at which this statistically significant difference occurred, a post-hoc comparison was conducted using the Bonferroni correction. Consequently, it was determined that the notable difference was between Grade 0 and Grade 3 (p=0.46). There was no significant difference among the remaining groups (p=0.995, p=0.436) (Table 3).

All patients were evaluated, without grouping, for potential correlations between AST, ALT, and CRP levels and T-scores of the total lumbar spine, femoral neck, and total femur, as well as BMD values. Nevertheless, no statistically significant correlation was identified (p>0.05).

Discussion

The findings of our investigation demonstrated that the presence of advanced liver steatosis is associated with a reduction in BMD in the lumbar spine in patients diagnosed with NAFLD. Chen et al. (10) reported that individuals with moderate-to-severe NAFLD had an increased risk of osteoporosis, whereas no significant association was observed in patients with mild NAFLD. In a cohort study by Shen et al. (11), patients with NAFLD had an increased risk of both osteoporosis and osteopenia. Additionally, a correlation was identified between the increase in fibrosis markers and the decrease in BMD. In a cross-sectional study of postmenopausal women, Lee et al. (12) found that NAFLD patients had reduced BMD, particularly at the lumbar spine and femoral neck, whereas no significant decrease was observed in the total femur. According to Moon et al. (13), postmenopausal women diagnosed with NAFLD exhibited reduced BMD at the lower lumbar spine, whereas this association was not observed among premenopausal women. In the current study, both male and postmenopausal female participants were assessed. The analysis revealed that lumbar spine BMD varied with the degree of hepatic steatosis. In contrast, BMD values at the total femur and femoral neck showed no statistically significant differences. Xie et al. (14) demonstrated a positive association between BMD and the presence of advanced fibrosis or cirrhosis. Furthermore, an independent negative correlation between NAFLD and BMD was observed in individuals aged 20-59 years.

Despite numerous supporting studies, the risk of osteoporosis in individuals with NAFLD remains a subject of debate within the scientific community. In their retrospective cohort analysis, Sung et al. (15) found that the presence of NAFLD was not significantly associated with the occurrence of osteoporosis. It is plausible that the observed discrepancy arises from the larger representation of mild NAFLD cases and the comparatively brief observation period of two years. In a meta-analysis conducted by Vachliotis et al. (6), numerous studies reported no association between NAFLD and osteoporosis. Nevertheless, it is imperative to acknowledge that these studies were conducted in heterogeneous groups. Consequently, it is not possible to reach a definitive conclusion. Furthermore, although some studies have not identified a correlation between NAFLD and BMD, elevated serum ALT levels have been linked to reduced BMD (16-18). It has been demonstrated that increases in ALT levels serve as indicators of liver damage in advanced chronic liver disease. This finding provides further evidence to support the hypothesis that a reduction in BMD may occur in the context of advanced steatosis. However, the present study did not identify a correlation between ALT levels and BMD.

The pathophysiology of osteoporosis in chronic liver diseases is complex. The mechanism underlying the development of NAFLD involves increased osteoclastic activity, modulated via the receptor activator of nuclear factor κB ligand (RANKL)/RANK–osteoprotegerin (OPG) pathway. Receptor activator of nuclear factor κB ligand, via its receptor, RANK, stimulates osteoclastogenesis; in contrast, OPG, a second RANKL receptor that acts as a decoy, restrains osteoclastogenesis and inhibits bone loss by binding RANKL, thereby preventing the RANK-RANKL cascade. In chronic liver diseases, the concentration of soluble RANKL in the extracellular matrix increases, thereby accelerating bone turnover. Despite the increase in OPG production to promote hemostasis and elevate the OPG/RANKL ratio, this increase is not sufficient. Furthermore, chronic liver diseases are characterized by sustained inflammatory processes. Proinflammatory cytokines, including interleukin-1, interleukin-6, and tumor necrosis factor-α (TNF-α) when produced, cause bone resorption in two ways: directly by increasing osteoclast activity and indirectly by increasing RANKL production. Furthermore, TNF-α has been demonstrated to enhance osteoclastogenesis via colony-stimulating factor-1 receptor gene expression, a mechanism that operates independently of the RANKL pathway (19). Furthermore, the synthesis of select hepatokines, including fibroblast growth factor-21 and insulin-like growth factor-binding protein-1, is elevated during the pathogenesis of NAFLD. These can cause bone loss via two distinct mechanisms: first, through the action of RANKL, and second, through binding to integrin-beta. Fibroblast growth factor-21 suppresses the maturation of bone marrow–derived mesenchymal stem cells into osteoblasts through interaction with the peroxisome proliferator-activated receptor-γ (6).

The term “NAFLD” has been modified to reflect its association with metabolic disorders, including obesity. This enabled the establishment of an association between NAFLD and osteoporosis, the most severe metabolic bone disease. Previously, it was postulated that elevated BMI was associated with increased BMD. It was argued that osteocytes are active in response to mechanical loading, particularly in relation to weight, and that bone formation is enhanced as a result (20). Nevertheless, a considerable body of recent research has demonstrated that fracture risk is elevated in individuals with obesity even when BMD is within the normal or high range (21). In particular, low muscle mass in obesity reduces the mechanical load applied to bone, thereby increasing the risk of falls in sarcopenic obesity. Metabolically unhealthy obesity, often accompanied by reduced muscle mass, is an important determinant of osteoporosis and fracture susceptibility.
In a comprehensive review, Khanmohammadi and Kuchay (22) reported that individuals with MASLD have an increased risk of low BMD and fractures. Nevertheless, it was underscored that additional research is imperative, particularly for this recently designated disease with evolving diagnostic criteria.

Study Limitations

The main limitation of this research is the relatively small sample size. In the present study, NAFLD diagnosis and grading were performed using US, whereas neither elastography nor liver biopsy was used. The study population included only postmenopausal patients and male patients; premenopausal patients were excluded. Despite these limitations, our study can be considered the first to reveal the effect of liver steatosis on osteoporosis. Further research is required to assess this issue in greater depth.

Conclusion

This study demonstrated that patients with NAFLD showing advanced grades of hepatic steatosis tend to have reduced BMD, particularly at the lumbar spine. These observations imply that increasing steatosis severity may play a role in bone deterioration, underscoring the need to recognize NAFLD as a possible contributing factor in osteoporosis management.