Effect of Carbohydrate-Electrolyte Sports Beverages on Urinary Stone Risk Factors

Results 

For the final analysis group A consisted of 12 normal subjects (mean ± SD age 36.3 ± 10.6 years) and group B included 12 hypercalciuric stone formers (mean ± SD age 38.8 ± 7.7 years). Statistically significant changes in serum levels of sodium, potassium and BUN occurred with Gatorade consumption but did not appear to be clinically significant as the results remained within the range of normal serum levels (table 1). Evaluation of changes in urinary risk factors after Gatorade consumption revealed no statistically significant difference between normal subjects and stone formers. However, both groups showed intragroup variation in urinary pH (p = 0.006), urinary chloride (p = 0.044), urinary sodium (p = 0.008), urinary potassium (p = 0.035) and urinary uric acid (p = 0.019). Among normal subjects and stone formers Gatorade consumption significantly increased mean urinary pH (group A 6.17 vs 6.58, group B 6.42 vs 7.08) and mean urinary chloride (group A 108 vs 132 mEq/24 hours, group B 87 vs 138 mEq/24 hours) compared to baseline (table 2, fig. 1). When Gatorade consumption was compared to water consumption mean urinary sodium (group A 158 vs 102 mEq/24 hours, group B 170 vs 149 mEq/24 hours) and mean urinary potassium levels (group A 50 vs 43 mEq/24 hours, group B 57 vs 49 mEq/24 hours) increased significantly in both groups (fig. 2). Urinary uric acid supersaturation decreased after consumption of Gatorade compared to baseline (group A 1.7 vs 0.6, group B 0.85 vs 0.22) while urinary volume, calcium and citrate did not change when comparing Gatorade consumption to water and baseline (fig. 3).

Table 1. Serum parameters

		Mean ± SD Baseline	Mean ± SD Gatorade Consumption	Mean ± SD Water Consumption	p Value
	Serum glucose:
	Group A	70.2±13.6	80.3±25.1	74.0±13.1
	Group B	83.3±20.4	79.8±12.8	73.5±15.8
	Serum sodium:*				0.027 (visitbygroup)
	Group A	142.3±1.7	141.1±1.3	141.5±2.0
	Group B	141.0±1.8	141.8±1.5	141.6±1.6
	Serum potassium:†				0.005 (group)
	Group A	4.3±0.3	4.2±0.3	4.4±0.3
	Group B	4.03±0.41	3.88±0.33	3.96±0.35
	Serum chloride:
	Group A	103.6±2.4	102.4±2.9	103.4±3.1
	Group B	100.8±3.0	101.5±3.2	101.0±3.0
	Serum BUN:‡				0.003 (visit)
	Group A	13.5±3.7	11.8±3.1	12.0±3.9
	Group B	14.0±3.6	10.9±3.0	15.0±5.1
	Serum creatinine:
	Group A	1.0±0.2	1.0±0.2	0.93±0.2
	Group B	0.9±0.2	0.8±0.1	0.9±0.2
	Serum calcium:
	Group A	9.2±0.3	9.2±0.3	9.2±0.3
	Group B	9.3±0.2	9.2±0.3	9.2±0.2

Table 2. Urinary parameters

		Mean ± SD Baseline	Mean ± SD Gatorade Consumption	Mean ± SD Water Consumption	p Value (visit)
	Urinary creatinine (gm/24 hrs):
	Group A	1.46±0.46	1.48±0.81	1.20±0.40
	Group B	1.45±0.5	1.40±0.53	1.51±0.60
	Urinary vol (l/24 hrs):
	Group A	1.64±1.00	2.03±0.71	2.15±1.04
	Group B	2.26±0.71	2.44±0.71	2.31±0.48
	Urinary pH:				0.006
	Group A	6.17±0.33	6.58±0.26	6.21±0.31
	Group B	6.42±0.79	7.08±0.76	6.33±0.49
	Urinary osmolality (mOsm/kg):
	Group A	554.1±264.2	403.1±218.8	371.6±245.6
	Group B	335.0±187.7	308.4±76.2	345.2±143.8
	Urinary NH3 (mg/24 hrs):				0.005
	Group A	567.9±161.0	440.7±148.7	535.7±149.2
	Group B	604.7±239.6	503.2±203.7	685.1±258.8
	Urinary calcium (mg/24 hrs):
	Group A	166.1±88.9	167.2±127.9	136.9±118.7
	Group B	223.0±75.4	201.9±90.4	246.8±121.6
	Urinary citrate (mg/24 hrs):
	Group A	605.6±301.5	657.8±377.7	480.2±312.8
	Group B	534.7±186.2	564.7±272.8	579.2±289.5
	Urinary chloride (mEq/24 hrs):				0.044
	Group A	108.2±50.2	132.2±66.1	92.4±26.2
	Group B	87.1±39.5	137.8±65.9	125.2±59.2
	Urinary magnesium (mg/24 hrs):
	Group A	82.7±32.2	76.9±48.8	72.0±66.8
	Group B	100.2±22.5	81.4±42.7	99.4±47.2
	Urinary oxalate (mg/24 hrs):
	Group A	15.6±5.1	18.9±8.9	15.6±4.9
	Group B	15.0±3.6	21.6±15.2	19.7±6.1
	Urinary phosphate (mg/24 hrs):
	Group A	849.5±322.8	793.2±371.6	641.2±189.8
	Group B	894.1±383.0	941.6±328.8	966.8±345.8
	Urinary potassium (mEq/24 hrs):				0.035
	Group A	52.4±20.5	49.8±29.3	43.0±16.4
	Group B	60.5±22.4	56.7±34.1	48.5±19.7
	Urinary sodium (mEq/24 hrs):				0.008
	Group A	120.9±54.5	158.5±66.6	102.6±25.5
	Group B	107.4±32.2	170.3±73.3	148.7±68.3
	Urinary sulfide (mmol/24 hrs):
	Group A	18.4±7.9	16.1±11.5	14.1±6.0
	Group B	20.8±10.9	17.8±8.0	25.2±17.8
	Urinary urate (mg/24 hrs):
	Group A	493.7±151.6	457.7±178.6	413.2±162.3
	Group B	539.2±174.1	470.7±186.2	508.3±211.3
	Urinary brushite (relative supersaturation):
	Group A	0.2±0.2	0.2±0.3	0.1±0.1
	Group B	0.2±0.2	0.2±0.1	0.2±0.1
	Urinary calcium oxalate (relative supersaturation):
	Group A	1.9±1.3	1.6±1.2	1.3±1.1
	Group B	1.4±0.6	1.4±0.6	1.7±0.9
	Urinary struvite (relative supersaturation):				0.040
	Group A	0.03±0.06	0.04±0.07	0.01±0.03
	Group B	0.06±0.12	0.08±0.12	0.03±0.08
	Urinary uric acid (relative supersaturation):				0.019
	Group A	1.70±1.70	0.61±0.60	0.90±1.04
	Group B	0.85±0.82	0.22±0.27	0.67±0.70

View Large Image Download to PowerPoint

Figure 1. Increase in mean urinary pH (A) and mean urinary chloride (B) in both groups after consumption of Gatorade compared to baseline.

View Large Image Download to PowerPoint

Figure 2. Increase in mean urinary sodium (A) and mean urinary potassium (B) in both groups after consumption of Gatorade compared to consumption of water.

View Large Image Download to PowerPoint

Figure 3. Decrease in mean urinary uric acid supersaturation in both groups after consumption of Gatorade compared to baseline.

Discussion 

Although numerous intrinsic and extrinsic factors influence the formation of kidney stones, low urinary volume and dehydration have a predominant role. Low urinary volume is the most commonly encountered abnormality among stone formers and, not surprisingly, urine volume exceeding 2 l daily significantly decreases the risk of stone disease, likely through the presumed dilutional effect of increased urine volume on lithogenic factors.1 Thus, populations exposed to high ambient temperatures, high degrees of physical activity and insufficient hydration have a high incidence and prevalence of urolithiasis.4 An increase in fluid intake is the primary modality for the prevention of urolithiasis, and the most important therapeutic measure regardless of stone composition or stone formation etiology.3, 5, 6

Recent epidemiological and short-term studies of urinary composition in response to dietary changes have analyzed the effects of specific beverages on the risk of stone formation in the general population.7, 8, 9 For example citrus beverages, particularly lemon juice, orange juice and lemonade, have been associated with decreased urinary lithogenicity. The high levels of citrate found in orange and lemon juice alkalinize the urine, stimulate calcium reabsorption and inhibit calcium crystal growth aggregation.9 The protective nature of beverages high in citrate may also be due to a reduction in urinary calcium excretion.10 However, due to the different amounts of potentially lithogenic substances found in many of the beverages examined, studies have yielded highly variable results.

Many beverages have proven controversial with regard to their lithogenic effect. McHarg et al reported that cranberry juice has antilithogenic properties in that consumption resulted in a decrease in oxalate excretion, a decrease in relative supersaturation of calcium oxalate and a resultant increase in urinary citrate.11 Conversely Gettman et al reported mixed effects on urinary stone risk factors after consumption of cranberry juice.12 In their study cranberry juice increased urinary calcium and oxalate levels, decreased pH levels but did not alter urinary citrate levels. Cranberry concentrate tablets were also shown to increase the risk of stone formation by increasing urinary oxalate levels.13 Similar debate surrounds the effect of grapefruit juice. Curhan et al reported epidemiological data derived from the Nurses' Health Study I and II, and the Health Professionals Follow-Up Study that suggest grapefruit juice was associated with increased lithogenicity related to increased urinary oxalate levels.8, 9 While Goldfarb and Asplin noted an increase in urinary citrate and oxalate content with grapefruit juice consumption, they did not demonstrate any clinically significant changes related to lithogenicity.10

Paradoxically coffee and tea were protective against stone formation despite containing high levels of oxalates.7 Carbonated beverages, a staple of the American diet, have been associated with an increased risk of stone formation due in large part to increased levels of urinary oxalates.14 However, recently presented data from Abbott and Goodman demonstrated that cola does not increase urinary stone risk factors.15

In a recent large prospective analysis of 3 cohorts, The Nurses' Health Study I and II, and the Health Professionals Follow-Up Study, Taylor and Curhan reported an independent association between increased risk of incident kidney stones and fructose intake, but no association with the intake of nonfructose carbohydrates.16 The mechanisms underlying the relation between stone risk and fructose consumption remain unknown, but may be secondary to resultant hypercalciuria, hyperoxaluria, decreased urinary pH and increased urinary uric acid.

Little is known about the influence of carbohydrate-electrolyte sport beverages such as Gatorade on stone formation but based on their varying composition increased and decreased urine lithogenicity could be expected. While the content of citrate would be expected to increase urine citrate excretion and urine pH, and provide protection against calcium and uric acid stones, the sodium content of sports beverages promoted as useful for rehydration in athletes might be associated with increases in urine calcium excretion.16 However, since these beverages are low in oxalate forming compounds and are designed to facilitate rehydration, they may be protective in nature. According to the Gatorade Sports Science Institute the 4 key components of carbohydrate-electrolyte sports beverages that promote rehydration are 1) electrolyte composition (5% RDA sodium and 1% RDA potassium in an 8 oz serving), 2) beverage flavor, 3) optimal carbohydrate composition (6% carbohydrate solution) to assure rapid fluid delivery and carbohydrate use, and 4) maximal fluid osmolality which facilitates gastrointestinal absorption as quickly as water (see Appendix).17 The composition of Gatorade also includes citric acid and sodium citrate, components that increase the alkali load and ultimately cause an increase in urinary citrate and pH levels.

Regardless of their hydrating capabilities anecdotal reports of carbohydrate-electrolyte sports beverages promoting lithogenesis exist but have yet to be documented in the literature. The putative lithogenic effect may stem from the high sodium content of these beverages (with an 8 ounce serving accounting for 5% of the RDA of sodium), and the undefined contribution of high fructose corn syrups to nephrolithiasis. Goodman et al recently reported that ingestion of Propel®, a carbohydrate sports drink with more citrate and a higher pH than Gatorade, significantly increased mean urinary citrate excretion and pH compared to water with no significant difference in the excretion of sodium and calcium.18 The varying carbohydrate composition among carbohydrate-electrolyte beverages makes it difficult to extrapolate our results with Gatorade, which contains a 6% carbohydrate mixture of glucose, sucrose and fructose, to those of other beverages.

Carbohydrate-electrolyte sports beverages such as Gatorade have become staples in the American diet. Specifically Gatorade commands 80% of the market share of sports drinks in the United States.17 Gross retail of Gatorade surpassed $3 billion in the United States in 2004 with 142 bottles sold in the United States each second.19 Although Gatorade and other carbohydrate-electrolyte sports beverages were initially developed for rehydration of athletes during extreme exercise, the average American now consumes this beverage regardless of athletic prowess or metabolic state. The popularity of this class of beverages underscores the importance of identifying the effect of Gatorade on urinary stone risk factors.

Evaluation of changes in urinary risk factors after Gatorade consumption revealed no statistically significant difference between normal subjects and stone formers. However, both groups demonstrated statistically significant intragroup variation in urinary pH, urinary chloride, urinary sodium, urinary potassium and urinary uric acid. Gatorade consumption compared with baseline levels and water consumption had no effect on urinary volume, calcium and citrate levels.

Gatorade consumption produced changes in a subset of urinary risk factors. For example, it caused statistically significant differences in the serum levels of sodium, potassium and BUN. However, these values did not appear to be clinically significant because the results remained within respective normal ranges. The increase in mean urinary pH after consumption of Gatorade compared to baseline could be related to the observation of a nonstatistically significant increase in urinary citrate levels. This observation could imply a protective effect in the consumption of Gatorade. The increase in urinary sodium and chloride compared to water consumption and baseline levels is not surprising given the high sodium load (50% RDA) that each subject ingested. However, the values were well within the normal range for urinary parameters and did not appear to be clinically significant. It is also important to note that urinary calcium did not increase after Gatorade consumption even with the increased sodium load. Finally the decrease in urinary uric acid observed after consumption of Gatorade compared to baseline should be noted as another parameter that may be protective against stone formation.

However, caution must be advised in the routine consumption of beverages containing high levels of sodium, fructose and carbohydrate as there may be other deleterious health effects. Furthermore, we are not advocating the consumption of these types of beverages rather than water as a means of stone prevention. We are merely highlighting the effects of this beverage type on urinary stone risk factors because they are common in the Western diet.

Conclusions 

Compared to the consumption of water and baseline, Gatorade consumption increased mean urinary sodium and mean urinary chloride levels. However, the results were within normal limits. The change in these parameters did not appear to be clinically significant because urinary calcium was unchanged. Overall Gatorade consumption does not increase or decrease urinary stone risk factors, and may be protective when considering pH and mean urinary uric acid levels.