Association between physical activity and kidney stones based on dose–response analyses using restricted cubic splines

Background This study aimed to determine whether there is a dose–response relationship between physical activity and the self-reported prevalence of kidney stone, based on a restricted cubic splines (RCS) method. Methods This study analyzed 8931 adults aged ≥20 years who had participated in the National Health and Nutrition Examination Survey (NHANES) during 2013–16. Kidney stones and physical activity were defined using a standard questionnaire, and metabolic equivalents (MET) were used to quantify the physical activity level. Logistic regression was used to assess the association between physical activity and the risk of kidney stones, and the dose–response relationship was explored using RCS. Results Kidney stones were present in 10.3% of the analyzed individuals: 11.5% of males and 9.2% of females. After adjusting for potential confounders, compared with the first quartile (Q1) of MET, the odds ratios (ORs) of kidney stones for those with Q2, Q3 and Q4 of MET were 0.72 [95% confidence interval (CI)=0.59–0.87], 0.77 (95% CI = 0.63–0.93) and 0.63 (95% CI = 0.51–0.78), respectively (all P < 0.01). The RCS regression showed that physical activity was related to kidney stones in a non-linear manner (P for non-linearity = 0.0100). The prevalence of kidney stones decreasing as physical activity increased, reaching a plateau for physical activity at approximately 2480 MET-min week−1 (OR = 0.75, 95% CI = 0.63–0.91). Conclusions Physical activity is inversely associated with the prevalence of kidney stones, and the dose–response relationship has a plateau, after which the prevalence of kidney stones does not change with the increase of physical activity.