Osteoporosis is a systemic skeletal disorder defined by diminished bone mineral density (BMD) and microarchitectural degradation of bone tissue (1–3). With the advanced aging of the population, osteoporosis has emerged as the most prevalent bone metabolic disorder (4). Almost 14.1 million individuals aged 50 and older suffer from osteoporosis in the United States (US), and the incidence rate exhibits a steady increase (5–7). Osteoporosis can result in higher fragility of the bone and an elevated fracture risk, which impacts almost all skeletal sites due to the systemic nature of the disease (1, 3, 8, 9). Traditionally, hip and vertebral fractures have been regarded as prototypical osteoporotic fractures (1). However, a far greater incidence of osteoporotic fractures has been observed at all other sites (i.e., excluding the hip and vertebrae) (10). The consequences of osteoporotic fractures include serious complications, reduced quality of life, elevated disabilities, and raised death rates (11). Moreover, osteoporosis and its associated fractures impose an enormous financial burden on patients, their families, and society (12–14). Therefore, preventing osteoporosis is vital.

Diet has a vital role in modifying the risk of osteoporosis and contributing to its prevention (15). Water is an important nutrient in the diet and is connected with several physiological functions, such as metabolism, modulation of body temperature, transportation of nutrients, and elimination of waste products (16–18). There are various sources of water consumed in daily life, including tea, coffee, sugar-sweetened beverages, and plain water. The source of water consumed is important for bone health. Huang et al. discovered that consuming tea provided a protective effect against osteoporosis, especially in women and middle-aged adults (19). Xu et al. (20) reported that regular moderate consumption of coffee may provide protection against osteoporosis between older US adults and those in middle age. Notably, a systematic review and meta-analysis comprising 26 publications exhibited that the intake of beverages that were sweetened by sugar was negatively related to BMD in adults (21). Nevertheless, few investigations have focused on the connection between plain water intake (PWI) and osteoporosis risk.

Therefore, this cross-sectional study was performed to determine the link between PWI and osteoporosis risk among older US adults and those in middle age.

In this cross-sectional study with 6,686 participants, the three distinct models indicated that individuals in the greatest PWI tertile had a significantly decreased risk of osteoporosis in contrast to those in the lowest tertile. After adjusting for all covariates, a higher PWI was linked to a decreased risk of osteoporosis. Subgroup analyses exhibited that this trend remained consistent across different population settings. Furthermore, smooth curve fitting and threshold effect analysis indicated that when PWI was less than 1,220 mL/day, a greater PWI was connected with a diminished osteoporosis risk, although an increase in PWI did not further significantly reduce osteoporosis risk when PWI was more than 1,220 mL/day. Notably, 4,953 participants (74.08% of the sample) reported a PWI of less than 1,220 mL/day. Many older US adults and those in middle age may ignore the importance of PWI. Therefore, our investigation is of high significance in the field of public health.

Dietary nutrients are essential for life and serve as the foundation for numerous metabolic processes. A diet rich in balanced nutrients is acknowledged as a preventive measure against osteoporosis, and the impact of nutrition on bone health has garnered growing interest (24). Many dietary nutrients, especially dietary micronutrients, including calcium, vitamin C, iron, potassium, magnesium, phosphorus, and vitamin D, may be strongly associated with osteoporosis (25–32). For example, Lee et al. (33) reported that bone mass might be improved by increasing calcium consumption and maintaining a high dietary calcium/phosphorus ratio. Liu et al. (27) reported that moderate rises in iron consumption were linked with a diminished osteoporosis risk in females. In addition, protein is necessary to maintain bone health and lower daily protein consumption may be connected with a greater risk of osteoporosis (34–36). A cross-sectional study of 4,707 participants revealed that elderly people and those in middle age in the US have an increased risk of osteoporosis when their daily dietary protein consumption is reduced (37). Importantly, fatty acids are one of the components of fat, and consuming fatty acids could be good for bone health (38–40). Fang et al. (38) reported that saturated, monounsaturated, and polyunsaturated fatty acids intake was positively connected with overall BMD among people aged 20 to 59 years. Notably, a cross-sectional study of 4,447 participants revealed that increased carbohydrate consumption was linked to decreased BMD (41). Recently, dietary fiber has been found to have potential benefits for bone health (42–44). Zhang et al. (44) conducted a cross-sectional study with 2,829 individuals and revealed that postmenopausal females with a dietary ratio of carbohydrate/fiber greater than 17.09 have a greater osteoporosis risk, while increased dietary fiber consumption is connected with a diminished risk of osteoporosis. Water is the richest nutrient in the diet, and plain water is the most affordable and accessible source of water consumed in daily life. Nevertheless, the link between PWI and osteoporosis risk has rarely been investigated.

Adequate PWI is crucial for proper body function (45, 46). Prior investigations have discovered the connection between PWI and a variety of diseases or metabolic disorders (47–53). For instance, Li et al. (47) conducted a cross-sectional study of 5,882 individuals and reported that PWI was inversely linked to the risk of periodontitis in those in middle age and older adults in the US. Another cross-sectional study of 16,434 individuals demonstrated that a greater PWI was independently linked with less afresh diagnosed nonalcoholic fatty liver disease in men but not in females (48). Furthermore, Pan et al. (49) performed a 5-year cohort study of 3,200 participants and discovered that a PWI over 4 cups a day was connected with a decreased risk of developing new-onset overweight for people with normal body weight. Most importantly, Lee et al. (50) drew conclusions from a cross-sectional study of 112,250 participants that there was a significant connection between lower PWI and increased risk of self-reported depression or suicidality. This research revealed that, among older US adults and those in middle age, a greater PWI was connected with a moderately diminished risk of osteoporosis. Managing PWI may decrease the osteoporosis risk.

To explain the connection between PWI and osteoporosis risk, we propose several potential mechanisms. Initially, a greater PWI was related to healthier dietary patterns described by greater intake of vegetables, fruits, and dairy products with low and reduced fat (54, 55). Thus, plain water is considered a possible dietary component that could improve dietary micronutrient profiles (56). Dietary micronutrients, including iron, phosphorus, magnesium, calcium, vitamin C, potassium, and vitamin D, may be closely related to osteoporosis. Therefore, a greater PWI may protect bone health through healthier dietary patterns associated with moderately increased intake of certain dietary micronutrients. Second, people with greater PWI were more likely to reduce their sugar-sweetened beverages intake (57). A high intake of sugar-sweetened beverages may reduce BMD (58). As a result, PWI may enhance bone health by decreasing sugar-sweetened beverages consumption. In addition, there were variations in the gut microbiota between people who drank more water and those who consumed less water (59). The gut microbiota can participate in preserving bone balance and protecting against osteoporosis development (60). Consequently, greater PWI may help individuals maintain their bone health through changes in the gut microbiota. Finally, increased daily PWI was shown to decrease the blood urea nitrogen concentration and inhibit the decrease in the estimated glomerular filtration rate (61). The osteoporosis risk was elevated in individuals with a decreased estimated glomerular filtration rate (62). Therefore, a greater PWI may help preserve bone health by inhibiting a reduction in the estimated glomerular filtration rate. Notably, these mechanisms are speculative, and we intend to conduct more research in the future to verify the underlying mechanism(s).

In our study, the ORs between PWI and risk of osteoporosis for all subgroups were < 1. Notably, the association between PWI and osteoporosis risk was significant (p < 0.05) in certain subgroups such as post-menopausal female, Non-Hispanic White, or Non-Hispanic Black, whereas it was not significant (p > 0.05) in male, non-menopausal female, or any other races. However, larger p-values should not be interpreted as indicating no association or no effect: absence of evidence is not evidence of absence (63, 64). In addition, Hodzic-Santor et al. (65) reported that studies with smaller samples are more likely to have larger p-values, and studies with larger samples are more likely to have smaller p-values. The small number of participants in certain subgroups is a possible reason why the association was not significant.

Our investigation has multiple strengths. First, this study is the first investigation of the correlation between PWI and osteoporosis risk in elderly individuals and those who are middle age in the US. Second, we utilized nationally representative data, which greatly increased the sample size. Third, to ensure the reliability of our outcomes, we adjusted for confounders as much as possible. Finally, we enhanced the robustness of the data analysis by treating each 500 mL/day PWI as a unit and dividing participants into three PWI tertile groups. However, several limitations exist in our study. First, participants could be from different parts of the US, where the chemical composition of the soil, and therefore the water varies. Second, due to data source restrictions, we failed to additionally validate the outcomes using additional NHANES cycles. Third, the 24-h PWI of each participant was determined based on interviews, which may have led to recall bias. Finally, owing to the cross-sectional nature of this study, a causative association between PWI and osteoporosis risk could not be determined. Additional prospective and experimental investigation is necessary in the future to validate the causal link between PWI and osteoporosis risk and to elucidate the underlying processes.

The findings of our study suggested that among middle-aged and elderly people in the US, a greater PWI was connected with a moderately lower osteoporosis risk. Managing PWI might diminish osteoporosis risk.