Abstract
BACKGROUND AND OBJECTIVES: Diet is an important contributor to kidney stone formation, but there are limited data regarding long-term changes in dietary factors after a kidney stone. DESIGN, SETTING, PARTICIPANTS & MEASUREMENTS: We analyzed data from three longitudinal cohorts, the Health Professionals Follow-Up Study and Nurses' Health Study I and II, comparing changes in dietary factors in participants with and without kidney stones during follow-up. The daily intake of dietary calcium, supplemental calcium, animal protein, caffeine, fructose, potassium, sodium, oxalate, phytate, vitamin D, vitamin C, sugar-sweetened beverages, fluids, net endogenous acid production, and Dietary Approaches to Stop Hypertension score were assessed by repeat food frequency questionnaires and computed as absolute differences; a difference-in-differences approach was used to account for temporal changes using data from participants without kidney stones from the same calendar period. RESULTS: Included were 184,398 participants with no history of kidney stones, 7095 of whom became confirmed stone formers. Several intakes changed significantly over time in stone formers, with some showing a relative increase up to 8 years later, including caffeine (difference in differences, 8.8 mg/d; 95% confidence interval [95% CI], 3.4 to 14.1), potassium (23.4 mg/d; 95% CI, 4.6 to 42.3), phytate (12.1 mg/d; 95% CI, 2.5 to 21.7), sodium (43.1 mg/d; 95% CI, 19.8 to 66.5), and fluids (47.1 ml/d; 95% CI, 22.7 to 71.5). Other dietary factors showed a significant decrease, such as oxalate (-7.3 mg/d; 95% CI, -11.4 to -3.2), vitamin C (-34.2 mg/d; 95% CI, -48.8 to -19.6), and vitamin D (-18.0 IU/d; 95% CI, -27.9 to -8.0). A significant reduction was observed in sugar-sweetened beverages intake of -0.5 (95% CI, -0.8 to -0.3) and -1.4 (95% CI, -1.8 to -1.0) servings per week and supplemental calcium of -105.1 (95% CI, -135.4 to -74.7) and -69.4 (95% CI, -95.4 to -43.4) mg/d for women from Nurses' Health Study I and II, respectively. Animal protein, dietary calcium, fructose intake, Dietary Approaches to Stop Hypertension score, and net endogenous acid production did not change significantly over time. CONCLUSIONS: After the first episode of a kidney stone, mild and inconsistent changes were observed concerning dietary factors associated with kidney stone formation.