Table 5. Intake of magnesium, animal protein, potassium, and fluid and the RR of incident kidney stonesa

Quintile 1Quintile 2Quintile 3Quintile 4Quintile 5P for Trend
aFor illustrative purposes, quintile cutpoints and medians for intake of dietary factors were derived from responses to the 1994 dietary questionnaire. However, the period-specific quintile values were used for the 1986 to 2000 analyses. RR are for the risk for stone formation compared with the group that had the lowest intake.
bThe multivariate model includes age; body mass index (six categories); use of thiazide diuretics (yes or no); fluid intake (in quintiles); alcohol use (seven categories); calcium supplement use (four categories); and dietary intake of animal protein, calcium, potassium, sodium, vitamin C, and magnesium (all in quintiles).
Magnesium (mg/d)<314314–354355–394395–450>450
    quintile median (mg/d)287335374419499
    cases437322263246205
    person-years92,46895,35696,34096,28697,250
    age-adjusted RR (95% CI)1.00.72 (0.63–0.83)0.59 (0.51–0.69)0.56 (0.48–0.66)0.47 (0.40–0.56)<0.001
    multivariate RRb (95% CI)1.00.85 (0.73–1.00)0.78 (0.65–0.94)0.80 (0.66–0.97)0.71 (0.56–0.89)0.01
Animal protein (g/d)<4747–5556–6364–74>74
    quintile median (g/d)4052606881
    cases278285314304292
    person-years94,51995,58995,55396,30295,737
    age-adjusted RR (95% CI)1.01.00 (0.85–1.18)1.09 (0.93–1.28)1.04 (0.89–1.23)1.01 (0.86–1.19)0.75
    multivariate RRb (95% CI)1.01.02 (0.86–1.20)1.13 (0.96–1.33)1.10 (0.93–1.30)1.08 (0.91–1.29)0.27
Potassium (mg/d)<29142914–32543255–35693570–3958>3958
    quintile median (mg/d)26713096340537434289
    cases436333288242174
    person-years92,55395,41896,15196,54397,036
    age-adjusted RR (95% CI)1.00.75 (0.65–0.87)0.66 (0.57–0.76)0.56 (0.48–0.66)0.42 (0.35–0.50)<0.001
    multivariate RRb (95% CI)1.00.83 (0.71–0.97)0.77 (0.64–0.91)0.69 (0.56–0.84)0.54 (0.42–0.68)<0.001
Fluid (ml/d)<12631263–16611662–20362037–2517>2517
    quintile median (ml/d)9921474184322512914
    cases349368293254209
    person-years91,65896,00796,18497,20096,651
    age-adjusted RR (95% CI)1.00.98 (0.85–1.14)0.78 (0.67–0.91)0.67 (0.57–0.78)0.53 (0.45–0.63)<0.001
    multivariate RRb (95% CI)1.01.06 (0.91–1.23)0.89 (0.76–1.04)0.80 (0.68–0.95)0.71 (0.59–0.85)<0.001