Association of Bone Metabolism with Fatty Liver Disease in the Elderly in Japan: A Community-based Study

Abstract

Objective With the aging of society, both osteoporosis and fatty liver disease (FLD) are becoming important issues. However, the relationship between osteoporosis and FLD remains controversial. We investigated the association between bone metabolism and FLD in a Japanese community in a cross-sectional study. Methods A total of 1,020 participants were enrolled in a health survey. FLD was diagnosed by ultrasonography. Bone metabolism was evaluated based on bone mineral density (BMD), which was assessed using dual-energy X-ray absorptiometry, and with the bone formation index (total type I procollagen N-terminal propeptide/bone-alkaline phosphatase ratio; P1NP/BAP ratio) and the bone resorption index (crosslinked N-telopeptide of type I collagen/tartrate-resistant acid phosphatase-5b ratio; NTx/TRACP-5b ratio) calculated from serum bone turnover markers. Results The BMD (percentage of the young adult mean) was the same level in both male and female participants with and without FLD. Both men and women showed an age-dependent decrease in their bone formation index and bone resorption index values. Men of ≥70 years of age and women of 60-69 years of age with FLD had significantly lower bone formation index values and higher bone resorption index values. However, similar findings were not seen in women of ≥70 years of age. Conclusion Although the BMD levels were the same, regardless of the presence or absence of FLD, elderly participants with FLD showed decreased bone formation and increased bone resorption, with sex differences. Because our results suggest that FLD in elderly individuals is detrimental for bone metabolism, and that it leads to bone loss and osteoporosis, further studies using a cohort population are warranted.

Keywords: bone formation index; bone mineral density; bone resorption index; bone turnover markers; fatty liver disease.

Figure 1.

Bone mineral density (BMD) in men and women. Regardless of the presence or absence of fatty liver, BMD decreased in an age-dependent manner in both men (A) and women (B). Women over approximately 50 years of age showed a remarkable decrease in BMD (B).

Figure 2.

Bone formation index and bone resorption index values in men. Bone formation index and bone resorption index values decreased in an age-dependent manner in men, regardless of the presence of FLD [bone formation index: all participants, r=-0.399; participants without FLD, r=-0.429; participants with FLD, r=-0.332 (all p<0.001); bone resorption index, all participants: r=-0.285 and p<0.001, participants without FLD: r=-0.317 and p<0.001, participants with FLD: r=-0.246 and p=0.008] (A, B). Among men of ≥70 years of age, lower bone formation index values were observed in participants with fatty liver in comparison to those without fatty liver (C). Among men of 40-59 and ≥70 years of age, higher bone resorption index values were observed in participants with fatty liver in comparison to those without fatty liver (D). The numbers in parentheses indicate the number of participants. *p<0.05. **p<0.01. FLD: fatty liver disease

Figure 3.

Bone formation index and bone resorption index values in women. Bone formation index values decreased in an age-dependent manner in women without FLD. However, there was no correlation between the bone formation index and age in women with FLD [all participants, r=-0.272 (p<0.001); participants without FLD, r=-0.301 (p<0.001); participants with FLD, r=-0.081 (p=0.381)] (A). Bone resorption index values decreased in an age-dependent manner in women [all participants, r=-0.570; participants without FLD, r=-0.601; participants with FLD, r=-0.412 (all p<0.001)] (B). Among women of 20-39 and 60-69 years of age, lower bone formation index values were observed in the participants with FLD in comparison to those without FLD (C). Among women of 50-69 years of age, higher bone resorption index values were observed in participants with FLD in comparison to those without FLD (D). The numbers in parentheses indicate the number of participants. *p<0.05. FLD: fatty liver disease