Osteoporosis is a systemic bone disease influenced by both bone mass in early adulthood and the subsequent rate of bone loss (1). Bone mineral density (BMD) is a key determinant of osteoporosis (2). A 10% increase in peak bone mass (PBM) has been reported to reduce the risk of fracture later in life by 50% (3). Individuals in middle age and the elderly face a heightened risk of osteoporosis, given the accelerated bone loss associated with aging (1). In a 2021 study, P-L Xiao et al. conducted a comprehensive review of the global prevalence of osteoporosis. The findings revealed a 30.5% prevalence of osteoporosis in individuals aged 50 and above worldwide (4). Notably, in China, the prevalence of osteoporosis among those aged 60 to 69 was reported to be 35.2%, while among those aged 80 and above, the prevalence rate of osteoporosis is as high as 53.9% (5). Therefore, osteoporosis in the elderly population in China warrants serious attention to prevent its progression to bone damage, underscoring the urgency of addressing this issue to prevent bone damage and alleviate associated medical burdens on families and society.

BMD and the development and progression of osteoporosis are influenced by Genetics, endocrinology, machinery, lifestyle, and more (6–10). Among various lifestyle factors, diet is considered the most modifiable risk factor (11). Hence, the elderly population needs to take intervention measures about increasing or preventing a decrease in BMD to prevent osteoporosis. For instance, calcium and vitamin D, in the form of calcium phosphate, play a vital role in the bone mineral matrix, contributing significantly to bone strength (12). Dairy products, being rich in calcium and protein, have the potential to lower parathyroid hormone (PTH) levels, thereby positively impacting bone remodeling (13–17). Despite the established beneficial effects of specific nutrients and foods on bone health, some studies overlook the intricate relationships and interactions among different dietary components. People eat meals consisting of a variety of foods with complex combinations of nutrients (18). And some nutrients (such as potassium and magnesium) are highly correlated, making it difficult to examine their separate effects (19). In addition, the effect of a single nutrient may not be detected because its effect is too small (20). Therefore, it is essential to explore the potential connections between dietary patterns and bone health.

Since 2002, research on the association between dietary patterns and skeletal health has been a focal point in public health (21–25). Osteoporosis is a major clinical problem in elderly people (26), yet despite growing recognition of dietary patterns' importance for their bone health, few studies have used principal component analysis to examine this association in elderly populations across diverse regions, with inconsistent results (27–30). Among these, the impact of the Mediterranean diet on bone density (BMD) has garnered significant attention. The Mediterranean diet is characterized by the extensive consumption of unrefined grains, fruits, vegetables, beans, and olive oil (9). Most studies have shown that adherence to MD was associated with a higher BMD (31–33). While some cohort studies suggest that the Mediterranean diet may have no effect or even adverse effects on bone health (34–37), further research on dietary patterns is necessary.

In our study, we conducted a cross-sectional investigation in Qingdao, China, using principal component analysis to explore the correlation between dietary patterns and bone mineral density (BMD), along with body composition. Through this study, we aim to identify specific dietary patterns that could help mitigate the risk of osteoporosis in the elderly population of Qingdao, China, providing a foundation for targeted dietary interventions in osteoporosis prevention.

Osteoporosis, a systemic skeletal disease characterized by a decrease in bone mass and the destruction of bone microstructure, has become a global public health problem. In this study, the prevalence of osteoporosis among the elderly aged 60 and above was 11.95%. This figure is comparable to the prevalence of 13.4% among people aged 50 and above reported by Zeng et al. based on a national multi-center study (38). It is worth noting that a meta-analysis from China showed that the prevalence of osteoporosis among the elderly reached 18.9% (39). Previous studies have indicated that the prevalence of osteoporosis is higher among Asian elderly people (40). In a systematic review that included multiple studies, it was found that the prevalence rates of osteoporosis in Asia, Europe, and the United States were 24.3%, 16.7%, and 11.5%, respectively (41). The differences in prevalence rates among different study cohorts suggest that dietary patterns may be an important influencing factor. The characteristic of high intake of high-quality proteins such as legumes in the population of this study may be an important reason why the prevalence rate in this population is lower than the domestic average level. The Mediterranean diet pattern, which is popular in the United States, is beneficial to bone health (42). The Mediterranean diet is characterized by being rich in fruits, vegetables, whole grains, and fish, and it advocates the intake of nutrients with anti-inflammatory effects, such as dietary fiber, omega-3 fatty acids, monounsaturated fatty acids (MUFA), and polyphenols in olive oil (OO). These nutrients may have a positive impact on reducing the process of bone resorption and muscle wasting (43, 44). However, the deficiency of vitamins and dietary deficiencies such as calcium among the Asian population may contribute to the relatively high prevalence of osteoporosis among Asians (45).

While nutrition and bone health have long been focal points in public health, studies exploring the relationship between dietary patterns and osteoporosis in the elderly remain limited, and research focusing on rural regions of China is notably scarce. Our study analyzed the dietary patterns of elderly residents in a rural area of Qingdao, China. We found that a high-protein dietary pattern is significantly associated with a reduced risk of osteoporosis and demonstrates a positive correlation with T-scores, a key indicator of bone mineral density. These findings are largely consistent with previous research. Several studies have reported a positive correlation between bone mineral density (BMD) and protein intake (46, 47). A cross-sectional study found that low protein intake may increase the risk of osteoporosis in adults over 45 years of age (48), while other Animal studies have also linked low protein consumption to decreased bone mass (49, 50). Moreover, a systematic review found that a relatively high intake of protein from low-fat or skimmed dairy products in the population is associated with an improvement in bone health status (51). Dietary protein intake was reported to be associated with bone density in in a prospective cohort study of 2,160 people (52). In contrast, a meta-analysis of the U.S. population showed that a higher protein intake had no statistically significant beneficial effect on bone mineral density (BMD) (53). The BMD of the lumbar spine was only slightly improved, and there was no impact on the BMD of the total hip, the BMD of the femoral neck, or bone markers (54).

Dietary protein intake can have a direct positive influence on bone structure and function. A protein-rich diet contributes to sustaining the functionality of the skeletal system and body muscles, reducing the risk of complications associated with osteoporosis (55). There are some mechanisms as follows: firstly, the extracellular matrix of bone is mainly composed of collagen, and its major component, type I collagen, plays an important role in maintaining the structural integrity of the collagen network in bone. Protein is involved in collagen synthesis (56–58). Importantly, collagen determines the amount of mineral deposition. Thus, the capacity of bone to resist mechanical forces and fractures depends not only on the quantity of bone tissue (mineralization) but also its quality (organization of the collagen framework) (59, 60). Secondly, many hormones, kinases, and growth factors involved in bone formation, such as TGF-β and BMP, are composed of proteins (61, 62). For instance, BMP (bone morphogenetic protein) can induce bone and cartilage formation. Some cytokines, such as RUNX2 and SOX9, function downstream of BMP, which have a positive effect on bone health (63). Studies have found that IGF-1, which is widely concerned at present, is related to protein intake (64). For instance, IGF-1 (insulin-like growth factor-1) plays a crucial role in bone remodeling, influencing osteoblast differentiation, proliferation, and the function of osteoclasts, thereby affecting bone mineralization (65). Thirdly, the study found that the interaction between protein metabolism and gut microbiota has a special regulatory mechanism for bone health. The gut microbiota generates short-chain fatty acids (such as acetic acid and propionic acid) through the metabolism of proteins, regulating the process of bone remodeling. There is an association between changes in the microbiota structure (such as an increase in Bacteroidetes and a decrease in Firmicutes) and the improvement of bone metabolism (66–70). These mechanisms echo the Spearman results of the analysis on body composition and t-score, indicating that components with significant differences in different factor score levels of high-protein dietary patterns are correlated with T-scores. Additionally, the RCS analysis of body composition and T-score reveals that body composition indices such as protein, muscle, total water, and inorganic salts all show a positive correlation with T-score before reaching a certain threshold, with no discernible trend beyond this threshold. Last, further insights obtained through body composition testing in our study unveiled that in a high-protein dietary pattern, key body composition indicators such as protein content, skeletal muscle, and muscle mass demonstrated an increasing trend with rising intake. These changes in body composition mainly reflect changes in protein in the body. The reason may be that high protein intake can stimulate the availability of amino acids in the whole body and thus increase protein synthesis so that the digested and absorbed amino acids stimulate muscle protein formation (71). In summary, it can be seen that a high-protein diet has certain benefits for bones.

Dietary protein intake not only affects bone structure and function but also plays a crucial role in calcium balance. Notably, studies have shown that excessive protein consumption increases urinary calcium excretion, which may negatively affect bone integrity. A series of carefully controlled metabolic balance studies have shown that a high-protein diet is harmful to bone health because the metabolic acidity from protein catabolism can lead to an increase in urinary calcium excretion (72, 73). In addition, many studies have indicated that for the elderly population, increasing the dietary calcium intake level may not necessarily result in a clinically significant reduction in the risk of fractures, nor is it easy to achieve a sustained improvement in bone density (74, 75). Our findings are consistent with these studies, suggesting that a high-protein dietary pattern at the Q3 level may represent an optimal intake range for supporting bone health. The lack of additional benefit and potential adverse effects at the Q4 level supports the hypothesis of a non-linear dose-response relationship, where excessive protein intake may disrupt calcium balance and counteract bone protection.

Notably, the dietary patterns of rural elderly individuals exhibit unique characteristics. A study on the elderly in rural areas of Northeast China shows that due to the relatively limited food resources in rural areas, the dietary structure of the elderly is relatively simple, and they mostly take grains and vegetables grown at home as the staple food (76). Furthermore, the consumption proportions of fruits, dairy products, and vegetables have reached the recommended value rather low. Existing research data indicate that the intake of the above-mentioned food categories by Chinese residents is seriously insufficient (77, 78). In contrast, the dietary patterns of the elderly in cities are more diverse. A survey targeting the elderly population in cities shows that the abundant food supply in cities makes the elderly have more diverse food choices (79–81). In terms of protein intake, in addition to obtaining protein from traditional sources such as meat and eggs, urban elderly people also choose various sources such as soy products and dairy products, with a relatively high proportion of high-quality protein (82). In terms of calcium intake, urban elderly people consume dairy products such as milk, cheese and yogurt, as well as calcium-rich foods like soy products and seafood. Their intake content is relatively higher than that of rural elderly people, which is helpful for maintaining bone health (82). Numerous studies have shown that a healthy dietary pattern is beneficial to bone health. A healthy dietary pattern rich in vegetables, fruits, and high protein can help reduce the risk of fractures (83–86). Although rural elderly people have an adequate intake of vegetables, they do not consume enough high-quality protein, while some urban people have their bone health affected by poor dietary patterns. Therefore, it is necessary to further study the correlation between dietary patterns and bone health in rural populations.

This study focuses on rural elderly individuals, a population often overlooked in previous studies, particularly within China. Given the rural population's unique economic conditions, dietary habits, and limited nutritional knowledge, exploring their dietary patterns and bone health provides valuable insights into potential urban-rural differences. The use of quantitative ultrasound to obtain T-scores enhances the reliability of osteoporosis diagnosis. Moreover, applying dietary pattern analysis moves beyond the limitations of single-nutrient studies, reflecting overall dietary behaviors more realistically and improving the practical relevance of our findings. However, the cross-sectional design prevents causal inference, and unmeasured confounders such as vitamin D levels and calcium intake may affect the results. Additionally, the study's geographic limitation to Jiaozhou, Qingdao, may restrict generalizability to other regions. Further longitudinal and multicenter studies are needed to validate these findings.

Principal component analysis identified four distinct dietary patterns. Among these, one pattern characterized by elevated consumption of legumes, white meat, seafood, and non-fried potatoes was significantly associated with improved bone health. However, additional large-scale, population-based studies are required to confirm these associations and evaluate their generalizability.