To our knowledge, this is the first study that has used the MR approach to investigate the causal relationship between SLE and osteoporosis. Our results provide valuable insights into the association between these two complex diseases and may have significant implications for their prevention and treatment strategies.
First, it is essential to recognize that both SLE and osteoporosis are multifactorial diseases influenced by a multitude of genetic and environmental factors. Consequently, it is challenging to establish a clear causal relationship using conventional observational studies, which can be impacted by confounding and reverse causation. MR analysis offers a robust alternative by using genetic instruments as proxies for the exposure of interest, thereby minimizing biases and providing a more reliable assessment of causality[16].
The results of our MR analysis provide evidence for a potential causal relationship between SLE and an increased risk of osteoporosis. This supports the notion that the autoimmune-mediated inflammation characteristic of SLE may have a direct impact on bone metabolism and remodeling processes, potentially leading to the development of osteoporosis. Several possible biological mechanisms may underlie this causative relationship. One possible explanation for the link between SLE and osteoporosis is that chronic inflammation, a hallmark of SLE, can lead to bone loss[22]. Inflammation can activate bone-resorbing cytokines, which stimulate the activity of osteoclasts (cells that break down bone tissue) and inhibit the activity of osteoblasts (cells that build new bone tissue). This results in a net loss of bone mass over time, leading to a higher risk of osteoporosis. Several studies have reported that individuals with SLE have higher inflammatory cytokine levels than healthy controls, supporting this theory[22, 23]. Another potential mechanism is the use of corticosteroids in the management of SLE[24]. Corticosteroids are frequently used to control inflammation in SLE patients, but long-term use of these drugs increases the risk of osteoporosis[25]. Corticosteroids can interfere with the normal balance of bone remodeling, leading to decreased bone formation and increased bone resorption[26]. Moreover, renal involvement in SLE might contribute to secondary hyperparathyroidism, increased osteoclastic bone resorption, and reduced synthesis of 1,25(OH)2D, ultimately leading to a reduction in bone mass[27–31]. Lastly, limitations in physical activity and sunlight exposure among SLE patients could lead to reduced bone mineral density. These are all important mechanisms underlying the link between SLE and osteoporosis[32, 33]. However, more research is needed to elucidate the complex interactions among these factors and to develop more effective strategies for managing and preventing osteoporosis in SLE patients.
Given the potential causality between SLE and osteoporosis identified here, it is imperative that clinicians and researchers be aware of this connection. Early identification of osteoporosis risk in SLE patients allows healthcare providers to monitor and implement preventive measures against the development of this condition[34, 35]. Preventative measures, such as promoting adequate calcium and vitamin D intake[36], encouraging regular weight-bearing exercise, and considering the use of bone-protecting medications, such as bisphosphonates and denosumab[37], may be crucial in mitigating the increased risk of osteoporosis in SLE patients[38].
Despite the strengths of MR analysis, some limitations should be acknowledged. First, potential pleiotropy, or the influence of genetic variants on multiple traits, may affect the validity of the causal association identified. Second, the extent to which our findings may be generalizable across diverse populations is unclear. As the genetic predisposition to SLE and osteoporosis may vary by race, ethnicity, and genetic background, replication in diverse cohorts is essential to determine the generalizability and robustness of our findings. Future MR studies incorporating more diverse populations are needed to validate these associations.
In conclusion, our MR analysis provides evidence supporting a potential causal relationship between SLE and osteoporosis. Our findings highlight the need for increased awareness regarding the potential risk of osteoporosis among SLE patients and recommend monitoring bone health as a part of routine SLE management. Further studies should refine genetic instruments, explore potential pleiotropic effects, and validate the findings in diverse populations.