In our study, we analysed the clinical data of 520 patients aged ≥ 65 years. We found that osteoporotic patients showed significantly decreased BMI and decreased TG levels in comparison with normal bone mass patients. The number of patients diagnosed with osteoporosis is increasing annually and previous studies have shown that many factors contribute to osteoporosis, including age, gender, BMI, and levels of Ca, P, ALB, ALP, AST, ALT, TG, TC, HDL and LDL.
Previous studies reported that many factors contribute to osteoporosis. In our studies, we found that age, gender, ALP and TG were independent factor for osteoporosis. Bone mass declined with age. In line with our study, many studies showed increased age contributing to bone mass loss. Based on this, we classified the groups according to the age. In our study, female patients in the 65–79 and ≥ 80 year age groups presented lower T-scores than male patients. In accordance with our results, men have higher peak BMD and higher BMD at a later age than women[21, 22]. Significant differences were observed in the levels of Ca, P, ALB, ALP, TC, HDL and LDL between men and women in the 65–79 year age group. These results indicate that men and women present differences in many factors for osteoporosis. Cui et al. supported our results in their analysis of 1035 men and 3953 women where they also showed significant differences in BMI and T-score, as well as in levels of TG, TC, high-densitylipoprotein cholesterol (HDL-C), and low-densitylipoprotein cholesterol (LDL-C) between men and women .
Previous studies have described the correlation between lipid profiles, BMI, and BMD[7, 23]. In our study, we found that male and female osteoporotic patients showed significantly decreased BMI in the groups aged 65–79 and ≥ 80 years. Similarly, many studies have reported an association between BMI and BMD. Alay et al. investigated 452 postmenopausal women inan outpatient clinic between 2012 and 2015, and observed decreased BMI related to lower BMD. In their study, Fawzy et al. analysed 101 men and womenand found that a declinein BMI was associated with lower BMD. Moreover, BMI is a weight-change profile. These results suggest that weight loss is associated with bone loss. Moreover, our study demonstrated that male and female osteoporotic patients presented obviously decreased levels of TG in the groups aged 65–79 years and ≥ 80 years. In addition, male and female osteoporotic patients also showed obviously decreased levels of TC in the groups aged 65–79 years. Our study findings were in agreement with those of Cui et al. who showed that BMI and TG levels were significantly lower in patients with osteoporosis than in those with normal BMD. However, there was no significant difference in the TC levels . They also described an association between osteoporosis and levels of HDL, LDL, TG, and TC; however, we did not find any significant differences in the levels of HDL and LDL between the two groups in our study. In a meta-analysis, Chen et al. selected ten publications and investigated the relationship between lipid profiles (HLD, LDL, TG, and TC) and osteoporosis in postmenopausal women, and found significantly higher levels of HDL and TC in postmenopausal osteoporosis patients than in the normal BMD group. Although they did not show any significant difference in TG levels, postmenopausal osteoporosis patients presented a lower level of TG. Alay et al. did not observe significant differences in the levels of HDL, LDL, TG, and TC. However, Bijelic et al. evaluated lipid profiles and BMI in 100 postmenopausal osteoporotic and normal BMD patients. They proved that osteoporosis in postmenopausal patients was associated with the levels of LDL, TC, and TG. Contrary to our results, they showed an increased level of TG in osteoporotic patients than in those with a normal BMD. The reason might be that, in their study, there were 72 overweight patients in the osteoporosis group and 54 overweight patients in the normal BMD group. BMI and TG were showed independent factors for osteoporosisin in our study. Osteoporotic male and female patients aged 65–79 and ≥ 80 years had lower BMI and decreased TG levels compared with patients of normal bone mass. Moreover, we also observed a positive correlation between BMI and TG levels in the groups of male and female patients aged 65–79 and ≥ 80 years. These results suggest that weight loss is related to the decreased TG levels, which might contribute to bone loss.
It has been reported that lipids may be a predisposing factor for osteoporosis and are associated with bone fragility, and TG metabolism is considered to be correlated with bone metabolism. Ando et al. investigated serum TG levels and N-telopeptide of type I collagen (uNTx) – a bone resorption marker – levels in 113 Japanese middle-aged and elderly women, and found that patients with lower serum TG levels had higher uNTx levels, indicating that low serum TG levels might affect osteoclast activity, leading to bone loss. Moreover, Dragojevic et al. performed a gene expression study by analysing bone tissue in 50 patients with osteoporosis and 62 controls. They reported that osteoporosis patients had lower osteoblastogenesis, higher osteoclastogenesis, and lower TG metabolism than controls. These results indicate an association between TG metabolism and bone metabolism. However, the underlying mechanism between TG metabolism and bone metabolism remains unclear, and more studies should be performed in the future.
In addition, we did not observe significant differences in other factors for osteoporosis, such as levels of Ca, P, AST, ALT and ALB between the osteoporosis and control groups in our study. Serum levels of Ca and P were normal in postmenopausal women with or without osteoporosis. This may be because osteoporosis leads to lower bone mineralisation, rather than to changes in the ratio of bone mineral to organic matrix. In previous studies, nutrition was reported to be related to osteoporosis, and serum levels of ALB were lower in patients with osteoporosis [31, 32]. By analysing the serum ALB of 15539 individuals, hypoalbuminemia (serum ALB less than 3.5 g/dL) was found to be associated with osteoporosis. Similarly, our study showed that serum levels of ALB were more than 35g/L in normal bone mass patients and osteoporotic patients. This might be the reason that serum ALB is not a factor for diagnosing osteoporosis in our study. AST and ALT were liver enzymes, and they were reported the association with osteoporosis. In agreement with our study, Do et al. selected 7160 subjects to analyze the association between liver enzymes and BMD in Koreans. They did not show the differences in AST and ALT with femur BMD. The reason might be that we did not select patients with liver diseases. In our study, ALP was an independent factor for osteoporosis, and osteoporotic female patients aged ≥ 80 years showed significantly increased ALP levels. Serum levels of ALP are considered an important method for the diagnosis of some bone diseases, including osteomalacia and Paget’s disease. Increased serum ALP levels in postmenopausal women was reported by high bone turnover. Serum levels of ALP > 129 U/L are helpful for diagnosing osteoporosis in men[34, 35].
This is a single-center retrospective study with a small sample size. Further multicenter and prospective studies, with larger samples, are needed to prove the association between TG metabolism and bone metabolism.
In conclusion, osteoporotic patients showed significantly decreased BMI and TG levels in comparison with normal bone mass patients in our study. These results indicate an association between TG metabolism and bone metabolism and provide a new method for the treatment of osteoporosis.