Globally, kidney stones are a common urological issue, characterized by high rates of incidence and recurrence, which heavily impact public health systems in many nations (1). About 10% of men and 7% of women in the U.S. will encounter kidney stones over the course of their lifetime (2). In China, kidney stone prevalence is also rising, with rates of 7%−9% observed in economically developed eastern regions (3). Although the direct mortality rate of kidney stones is low, severe complications such as urinary tract infections and kidney damage can be fatal (4). Furthermore, the recurrent nature of kidney stones imposes substantial medical costs, including diagnostics, surgical treatments, and long-term medication (5, 6). Evidence suggests that annual U.S. healthcare expenses for kidney stones top $2 billion, creating a notable strain on healthcare systems (7). As a result, a clear understanding of the causes and contributors to kidney stones is critical for preventing the disease.

Moderate exercise has a protective effect against kidney stones (8). However, since the physiological pathways triggered by VPA and moderate exercise are significantly different (9), the impact on kidney stones cannot be simply understood as the effect of exercise on stones. Vigorous physical activity (VPA) is typically defined as physical activity that significantly elevates heart and respiratory rates, often reaching 70%−85% or more of maximum heart rate. VPA is widely endorsed for its various health benefits (10). Research shows that regular VPA can improve cardiovascular function, increase cardiac output, and enhance circulation, helping reduce the risks of heart disease, hypertension, and stroke (11). Additionally, VPA significantly boosts energy expenditure, promoting fat burning, which supports body fat reduction and healthy weight maintenance (12). VPA has also been associated with improved insulin sensitivity, reducing the risk of insulin resistance (13). VPA can further alleviate symptoms of depression and anxiety, enhancing mental health (14), VPA also contributes to enhancing muscle strength and bone health (15). Despite these benefits, VPA carries certain potential drawbacks and risks. For individuals lacking conditioning, VPA may cause significant increases in heart rate and blood pressure, potentially leading to arrhythmia or even sudden cardiac arrest (16). Overloading the body with VPA, without proper warm-up or recovery, may result in common injuries, such as muscle strains, sprains, and joint pain (17, 18). Although VPA helps reduce stress and anxiety, excessive VPA may increase psychological stress (19). Thus, it is important to understand how VPA affects specific diseases to better guide exercise recommendations.

A considerable amount of research has explored the link between physical activity and kidney stones. Many studies have indicated that physical activity may protect against kidney stones (8, 20–22), while a sedentary lifestyle has been identified as a risk factor (23). Given the dual effects of VPA, focusing solely on whether physical activity affects kidney stones may be insufficient. Previous studies have not directly investigated the possible influence of VPA on the formation of urinary stones. Considering this, the study aims to evaluate the relationship of daily VPA time to kidney stones prevalence in U.S. adults, with data from NHANES.

In this observational study, we observed a significant association between prolonged vigorous physical activity (VPA) duration and increased kidney stone prevalence after adjusting for confounders. Specifically, when daily VPA exceeded 240 min, each additional minute was linked to a 0.3% rise in prevalence, plateauing near 360 min. This pattern corresponded with increased urine specific gravity during extended VPA, suggesting dehydration may contribute to risk. These findings highlight the importance of targeted moisture strategies for high-exposure groups (e.g., athletes): clinicians should advise proactive moisture, before, during, and after prolonged VPA to mitigate urine concentration. Mechanistic confirmation requires further research: we propose longitudinal cohorts tracking VPA exposure against dynamic urine composition changes (calcium, citrate, pH), followed by randomized controlled trials (RCTs) testing moisture interventions on stone incidence in high-risk populations. While moisture remains, a practical precaution based on our data, definitive causal pathways warrant verification through these studies.

The association between physical activity and kidney stones has been a topic of much discussion. Liu et al., using data from the UK Biobank, found that physical activity was negatively associated with kidney stone disease (KSD) risk, irrespective of genetic predisposition (27). A non-linear relationship between physical activity and KSD was observed in The study by Feng et al. found that KSD prevalence decreased as physical activity rose, before leveling out at a certain threshold (20). Using NHANES data, Li et al. showed that in individuals who did not engage in vigorous recreational activity, increased sedentary time was associated with a higher prevalence of kidney stones (23). While some studies suggest physical activity protects against KSD, others have found no meaningful correlation. A cohort study of 215,133 participants observed no evident link between physical activity and KSD after accounting for various confounding factors (22). Similarly, Patrick et al.'s systematic review, which included 17,511 patients, found inconclusive evidence on the relationship of physical activity to KSD (28). In contrast, our study found that prolonged VPA was not protective against kidney stone.

It was associated with an increased risk. Li et al.'s research also suggested that after reaching a certain intensity and duration of exercise, kidney stone prevalence does not continue to decrease, consistent with our findings. Our study addresses a research gap by specifically examining the impact of vigorous physical activity on kidney stone prevalence.

In our study, vigorous activity appeared as a risk factor for kidney stones, likely due to multiple mechanisms. First, exercise-induced sweating and fluid loss may cause dehydration, leading to urine concentration and supersaturation of stone-forming substances, calcium oxalate and uric acid, for instance, may then deposit in the kidneys (29–31). Additionally, electrolyte imbalances from sweat loss could disrupt calcium metabolism, raising calcium ion concentration in urine and increasing the risk of calcium oxalate stones (31). Acidic metabolic by-products that accumulate during intense exercise may further acidify urine, promote the deposition of uric acid and calcium oxalate and thereby increasing kidney stone risk (32). Furthermore, vigorous exercise accelerates metabolism, increasing uric acid production, especially under dehydrated conditions that favor urate crystal formation (30). Based on these observations, we hypothesized that VPA may lead to urine concentration, with stone-forming substances reaching supersaturation and depositing in the kidneys, thus elevating kidney stone risk. To explore this hypothesis, we analyzed the relationship between daily VPA time and urine specific gravity. As depicted in Supplementary Table S1 and Supplementary Figure S1, after adjusting for various confounders, we found that vigorous exercise was associated with an increase in urine specific gravity (β = 0.07, 95% CI from 0.002 to 0.12, P = 0.00495), especially when VPA time exceeded 170 min, aligning with the K-value calculated using a two-segment linear regression model. Notably, when daily VPA time exceeded 360 min, the prevalence of kidney stones no longer increased, investigating the underlying mechanisms may be valuable. In the initial stages of exercise, sweating induces dehydration, electrolyte loss, elevated uric acid levels, and urine acidification, all of which collectively elevate the risk of kidney stone formation; however, as exercise continues (e.g., reaching 360 min), the body initiates a series of adaptive responses to mitigate this risk. These include: (1) activation of AMPK to inhibit xanthine oxidase activity, thereby reducing uric acid production; (2) enhanced activity of antioxidant enzymes such as superoxide dismutase (SOD) (33) and glutathione peroxidase (GPx), alleviating renal tubular damage; (3) restoration of urine dilution through rehydration and the antidiuretic hormone (ADH) escape mechanism; and (4) increased urinary citrate excretion, promoting calcium chelation and inhibiting crystal formation (34). Together, these mechanisms facilitate rehydration, restore electrolyte balance, regulate uric acid metabolism, and enhance acid-base buffering, ultimately enabling the body to progressively reduce the likelihood of kidney stone formation during prolonged exercise (35).

There are several strengths in our study. First, it is based on NHANES data, which is a nationally representative dataset obtained through standardized protocols. We performed all analyses using appropriate NHANES sampling weights, ensuring our findings reflect the broader population. We also controlled for a variety of confounding factors to ensure the robustness of our conclusions, and the large sample size allowed for detailed subgroup analyses. Moreover, based on available information, this study assesses the effect of daily VPA on kidney stone risk, clearly defining the type of exercise. Our results offer valuable insights for those in physically demanding occupations or recreational activities, with implications for kidney stone management. Despite the insights provided by this study, there are limitations. Primarily, because it is based on the NHANES database, we cannot establish causality for daily VPA time and kidney stone prevalence. Additionally, as NHANES data represents only the U.S. population, the generalizability of our findings may be limited. The self-reported nature of both the exposure and outcome variables introduces potential for recall and self-report biases, which could lead to the omission of asymptomatic kidney stone cases. We acknowledge the absence of important confounders [e.g., diet (36), dietary supplement intake (37), oxalate intake, genetics (38), occupation (39), climate (40)] due to data limitations. Reverse causality is also a possibility. These are now explicitly listed as limitations, and we propose future cohort studies and Mendelian randomization to further clarify causal relationships. Additionally, variations in moisture reporting between participants with and without kidney stones could introduce reporting bias. Specifically, those with a history of kidney stones may report higher moisture, which may account for the lack of a significant positive correlation between daily VPA time and kidney stone prevalence in our subgroup analysis of moisture. Although VPA itself can lead to short-term dehydration, which is a known theoretical risk factor for kidney stone formation, in real-world settings—particularly when individuals maintain adequate fluid regulation—the net effect of VPA on kidney stone risk tends to be neutral or even beneficial. This is primarily because sufficient water intake plays a decisive role in urine dilution, effectively mitigating the concentration of urine caused by intense physical activity (41). In populations with low or no fluid intake, the duration of VPA may be limited (since prolonged exercise without hydration can lead to severe consequences), and previous findings suggest that short-term vigorous activities—such as swimming—may even have protective effects (42). While it is true that VPA can lead to dehydration, the key factor is the individual's hydration habits during and after exercise. If exercisers—especially those who engage in regular, health-conscious physical activity—actively replenish fluids during and after workouts, they can effectively reverse the temporary urine concentration caused by exercise. Overall, adequate total moisture intake is one of the most effective strategies for preventing kidney stones (43).

Our analysis demonstrates that, in this observational study, longer durations of VPA are linked to a higher prevalence of kidney stones after accounting for potential confounders. Specifically, we observed that kidney stone prevalence increased with rising daily VPA time. When daily VPA time exceeded 240 min, each additional minute of VPA was associated with a 0.3% increase in kidney stone prevalence, reaching a plateau around 360 min. This observed association may be related to the concurrent increase in urine specific gravity seen with prolonged VPA. Given these findings, maintaining adequate moisture during periods of VPA could be a prudent practical measure.