Effects of a commercial lemonade beverage, potassium citrate, and combination therapy on urinary stone risk parameters in hypocitraturic stone formers: a randomized crossover trial

Introduction

Background

Nephrolithiasis is a common disease with a high lifetime risk of recurrence, and medical prevention is essential to reduce future stone events (1). Hypocitraturia is one of the most common metabolic abnormalities among calcium stone formers, occurring in up to 60% of patients (2). Citrate is a potent endogenous inhibitor of urinary stone formation that binds urinary calcium to form soluble calcium-citrate complexes, thereby reducing the amount of free calcium available to form calcium-containing crystals (3). Thus, citrate can directly inhibit the nucleation, growth, and aggregation of calcium oxalate (CaOx) and calcium phosphate (CaP) crystals (4). Furthermore, citrate raises urinary pH, which increases the solubility of certain stone types such as uric acid (UA) stones (5). Treatment of hypocitraturia with citrate supplementation in the form of potassium citrate (KCit) tablets has been proven to increase urinary pH and citrate levels, resulting in reduced rates of stone formation and recurrence (6-8). However, compliance with KCit use is low due to large pill size, frequent dosing up to two to three times daily, and bothersome gastrointestinal side effects (9). Furthermore, costs can be prohibitive with lack of insurance coverage leading to annual costs up to $5,100 (10). As a result, this has led to interest in alternative therapies for stone prevention, such as lemonade, orange juice, and lime juice, which are rich in citrate and alkali. Lemonade, orange juice, and lime juice have all been shown to increase urinary pH and citrate and may be more palatable and affordable for patients (11-15).

Rationale and knowledge gap

Crystal Light^® (CL) (Kraft Foods, Chicago, IL, USA) lemonade is a low-calorie sugar-free lemonade beverage that has previously been shown to contain a high amount of citrate, the highest of commercially available beverages, based on nuclear medicine spectroscopy studies (16). Unlike traditional lemonade or orange juice, CL is sugar-free and therefore avoids the additional sugar intake associated with these beverages. This may be advantageous because many patients with nephrolithiasis have diabetes or metabolic syndrome, and high dietary sugar intake has been associated with increased urinary calcium excretion, which could potentially attenuate the beneficial effects of increased urinary citrate and urinary pH (13). To our knowledge, no prospective studies have been performed to study how CL affects the urinary stone risk factors such as pH or citrate.

Objective

Therefore, we sought to define the effects of CL on urinary stone risk factors in patients with a history of kidney stone formation and hypocitraturia. The primary objective of this study was to perform a randomized crossover trial comparing 24-hour urine profiles in patients with a history of stones and hypocitraturia at baseline, after 1 week of consuming CL, 1 week of KCit, and 1 week of CL in combination with KCit. We present this article in accordance with the CONSORT reporting checklist (available at https://tau.amegroups.com/article/view/10.21037/tau-2026-0345/rc).

Methods

Study design

After obtaining Institutional Review Board approval of Northwestern University (No. STU00216084), we designed a single-institution prospective, randomized, cross-over trial with the aim of enrolling 8 participants total. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. Informed consent was obtained from all participants. No patients were involved in setting up the research questions or the outcome measures, nor were they involved in developing plans for recruitment, design, or implementation of the study. No patients were asked to advise on interpretation or writing up of results.

We calculated this number based on the assumption that 1 L of CL per day can increase urinary citrate levels by 100 mg/day from a hypothetical mean of 400 mg/day at a power of 0.80 and alpha of 0.05. These assumptions were made based on a prior study by Large et al. (14) investigating participants that consumed 7 days of CL and noted average increases of 155 mg/day of urinary citrate. To account for a possible 20% drop out rate, our plan was to recruit a minimum of 10 participants. Figure 1 shows the CONSORT diagram depicting participant flow through the trial. Participants between the age of 18 to 80 with a history of nephrolithiasis and hypocitraturia, which was defined as citrate on 24-hour urine collection <450 mg/day for men <550 mg/day for women, were deemed eligible to enroll. Patients unwilling to complete 24-hour urine collections, with hyperkalemia, uncontrolled diabetes, chronic kidney disease, adrenal insufficiency, delayed gastric emptying, peptic ulcer disease, distal renal tubular acidosis or medication induced renal tubular acidosis, members of vulnerable patient populations, and those with allergies to ingredients in CL beverage were excluded from this study.

Figure 1 CONSORT diagram.

The study consisted of three 1-week long regimens over five weeks total, assigned using a simple random scheme via computer generated random sequence by research study investigators. Of the six possible sequences, 2 were repeated for patients 7 and 8. Allocation sequence was concealed from both investigators and patients both before and during randomization. However, no parties were blinded to the allocation after randomization. Patients were recruited from a single tertiary level hospital urology clinic in the United States. Phase 1 was the CL-only phase, which consisted of consuming 1 L of CL, a commercially available sugar-free lemon flavor beverage, daily for 7 days total (mixed according to manufacturer’s instructions-1 packet into 2 quarts of water). This provides approximately 117 mEq of citrate per day based on prior data (16). A 24-hour urine collection was then collected on day 7, and there was a one-week washout period prior to initiating the second phase. Phase 2 was the KCit-only phase, which consisted of 1 week of consuming 15 mEq of KCit daily. A 24-hour urine collection was completed on day 7 followed by a one-week washout period. Finally, phase 3 involved a combination of consuming 500 mL of CL and 10 mEq of KCit daily for 7 days. A 24-hour urine collection was completed on day 7 of phase 3. All urine collections were performed as send out tests by Litholink (Laboratory Corporation of America, Itasca, IL, USA). Figure 2 depicts a sample patient regimen illustrating the experimental flow of each phase. On the last day of each phase, an email survey was sent out to each participant to elicit if they were compliant with the regimen and if they had experienced any side effects such as nausea, vomiting, diarrhea, constipation, heartburn, dizziness, or other.

Figure 2 Sample of experimental flow.

Patients were prescribed 5 mEq tablets of KCit covered through their individual insurance coverage. CL sugar-free lemonade packets were provided by the study team and given to the patient to ensure consistency and decrease potential for variation in CL varieties and quantities consumed. Participants were provided detailed instructions on what to take during each assigned phase and were reminded to intake at least 2 L of fluid daily. Participants were not required to adhere to a specific diet but were instructed to maintain a low sodium diet (<2,300 mg/day) with moderate meat intake (12 oz/day). Three 24-hour Litholink urine collections were provided by the Urology Department to participants free of charge. To increase recruitment interest, a $100 gift card incentive was provided to all participants who completed this study.

Justification of doses and regimen

Although KCit is usually titrated up to 0.5 mEq/kg × the patient’s weight, in our metabolic stone clinic, we typically start at 10 mEq of KCit as patients can have significant side effects e.g., gastrointestinal distress even with these lower dosages. Therefore, we chose to prescribe a dose of 15 mEq/day for the KCit only phase and 10 mEq/day of KCit + 500 mL of CL in an effort to prevent any side effects. We chose 1 L and 500 cc as the study beverage volumes and 1 week duration as our study period based on a recent trial which compared low-calorie orange juice and CL lemonade where 1L of each beverage per day was administered without adverse effects (14).

Statistical analysis

Survey and Litholink data were collected and stored electronically in secure REDCap database through our institution. The 24-hour urine collection values were compared to baseline and the difference in various relevant Litholink parameters were calculated. The Litholink urine panel analyzes calcium, magnesium, creatinine, oxalate, citrate, UA, urea nitrogen, ammonium, and phosphorus using colorimetric assays, sodium, potassium, chloride using ion-selective electrode devices, pH using potentiometry, and sulfate using turbidimetric assay. Urinary supersaturation (SS) indices for CaOx, CaP, and UA are calculated from the measured urine chemistries using the EQUIL-2 algorithm (17).

The primary outcome was difference in urinary citrate from baseline to intervention. Secondary outcomes analyzed included the differences in urine volume, urinary calcium, oxalate, sodium, pH, UA, SS CaOx, SS CaP, and SS UA. These values were compared with one another with Kruskal-Wallis rank sum tests. Linear mixed-effects models were then performed adjusting for treatment period and sequence, with participant included as a random effect. Pairwise comparisons were performed using estimated marginal means with Tukey adjustment for multiple comparisons. Statistical significance was defined by a P value of <0.05. Statistical analyses were performed using R version 4.1.1 (R Foundation for Statistical Computing, Vienna, Austria). All participants were included in the analysis.

Results

A total of 11 participants were recruited for the study, and 8 were consented and enrolled from April 2022 to March 2023. Three participants were excluded-one had a medical emergency prior to enrollment, one declined due to lack of insurance coverage for KCit, and one declined to participate (Figure 1). No participants were on any concomitant kidney stone prevention drugs at time of study. The mean age of participants was 59.75 years old; 7 participants of the 8 were women, and all were Caucasian. Table 1 displays the average 24-hour urine parameters for all participants based on regimen. The CL regimen had the highest mean urine volume (2.6 L/day; baseline: 2.07 L/day), urine citrate (484 mg/day, baseline: 235 mg/day), and urine pH (6.5; baseline 6.06).

Table 2 displays the median and mean differences between the subject’s 24-hour urine parameters between each phase of the study. Both the CL and combination CL + KCit regimens led to increases in urinary volume, but the CL regimen led to the greatest increases in urinary volume. The KCit regimen did not lead to any changes in urinary volume (CL: 0.53 L vs. KCit: −0.08 L vs. CL + KCit: 0.21 L, P=0.5). The CL and combination regimen had greater increases in median urinary citrate than KCit alone (CL: 172 vs. KCit: 68 vs. CL + KCit: 173, P=0.8). However, these differences did not reach statistical significance. In terms of urinary pH, the CL regimen led to a median increase in pH of 0.42 compared to 0.25 with CL + KCit and 0.18 with KCit (P=0.6). There were similar increases in SS CaP in all groups (CL: 0.2 vs. KCit: 0.08 vs. CL + KCit: 0.22, P>0.9). The SS CaOx decreased by 0.15 in the CL regimen and by 1.39 in the KCit regimen but showed slight increases in the CL + KCit regimen (0.47, P>0.9). Figure 3 displays the plots of differences in urinary stone risk factors from baseline in CL, KCit, and CL + KCit regimens.

Figure 3 Plots of differences in urinary stone risk factors from baseline in Crystal Light^®, potassium citrate, and combination (Combo) groups. Mean is depicted by red point. CaOx, calcium oxalate; CaP, calcium phosphate; SS, supersaturation.

Table 3 showcases results of the linear mixed-effects models, and Table 4 displays pairwise comparisons between each individual regimen. Most urinary parameters showed no statistically significant differences between treatments after Tukey adjustment. However, SS UA was significantly lower following CL compared with KCit (mean difference −0.49, P=0.002). The CL + KCit treatment also resulted in lower SS UA compared with KCit (mean difference 0.44, P=0.019). Urinary pH showed a trend towards significance for KCit vs. CL + KCit (P=0.066), but it did not reach the threshold after adjustment.

Based on the participant survey responses at the end of each week, the CL only regimen was well tolerated with no patients reporting any adverse symptoms. One out of 8 participants (12.5%) reported compliance with the regimen as “most of the time” instead of “all of the time”. The CL + KCit regimen was poorly tolerated with 50% (4/8) of participants reporting symptoms that week. Two patients (25%) reported having diarrhea, 1 nausea (12.5%), and 1 constipation (12.5%). In the KCit regimen, two patients (25%) reported symptoms—one had cramping and another reported constipation. All patients reported 100% compliance while on the KCit and CL + KCit regimens.

Discussion

Key findings

Hypocitraturia is a frequently noted metabolic abnormality that increases risk of kidney stone formation (2). Traditionally, it is treated with citrate supplementation in the form of oral KCit pills (6-8). However, compliance with this medication has been poor due to several factors including the size of the pills, frequent dosing up to two to three times daily, gastrointestinal side effects, and lack of insurance coverage leading to affordability issues (9,10). Indeed, one study utilizing national drug codes, found rates of adherence within the first 6 months of initiating citrate medications was only 13.4% (18). In this limited study of active stone formers, CL consumption in hypocitraturic stone formers resulted in increases in urine citrate, volume, and pH, although not statistically significant. On pairwise comparison, CL showed significantly greater decreases in SS UA compared to KCit. Therapy appeared to be safe, feasible, and well tolerated with no reported adverse effects.

Strengths and limitations

Our study has several limitations-the most notable being the small sample size given the proof-of-concept nature of this study making it underpowered to detect significant differences. However, our study design of a prospective, randomized, cross-over trial is a methodologic strength of the study, where the patients serve as internal controls. Unfortunately, accrual for the trial was difficult given the multiple weeks of commitment and testing phases required. Thus, it took over 1.5 years of recruitment to enroll the necessary 8 patients. While we provided all participants with the same CL sugar-free lemon beverage packets to prevent discrepancy, compliance with intake and all side-effects was self-reported, which could lead to variation. In addition, 1 L of CL theoretically provides more citrate than 15 mEq of KCit, which could introduce bias in the results. That said, it is unclear if the total amount of citrate in CL is fully absorbed into the body compared to KCit. Artificial sweeteners and additives in CL could also potentially interact with absorption and limit efficacy. Further studies investigating differentiating doses of CL and KCit will be necessary to confirm these findings.

Comparison with similar research

Because of the difficulties associated with KCit usage, an interest in alternative therapies that may be more tolerable and less cost prohibitive has emerged. Citrus juice therapy has garnered significant interest given the high content of natural citrate and alkali in citrus fruits that are easy to consume and generally well-tolerated. Several studies have analyzed the citric acid content in various juice formulations, ranging from fresh-squeezed to from-concentrate, powdered mixes, and commercially-available mixed beverages (16,19). Lemonade therapy (LT) was the original beverage that sparked interest in juice-based therapy when Seltzer et al. (12) studied consumption of 2 L of daily lemonade consumption (4 oz of lemon juice mixed with 2 L of water) and found that after six days of therapy, citrate levels on 24-hour urine collection increased from 142 to 346 mg. Based on these findings, Kang and colleagues (11) performed a retrospective study comparing 11 patients on lemonade therapy to 11 control patients on 20 mEq of KCit twice daily and found that both groups had significant increases in their urinary citrate levels from baseline (LT: 383 mg/day; KCit: 482 mg/day). LT group participants also had a decrease in stone formation from 1.00 to 0.13 stones per year. Similar studies have been replicated in grapefruit, orange, and lime juice consumption (13-15,20-22). Grapefruit juice has been shown to contain citrate concentrations higher than lemon juice (16). However, it has also been shown to significantly increased urinary oxalate levels leading to it being a risk factor for stone formation (21). Orange juice similarly has been shown to increase urinary oxalate levels while not producing changes in urinary calcium levels (13). In addition, the high sugar (calciuric effect) and ascorbic acid content in orange juice has made it a less attractive alternative therapy (14). Finally, lime juice has increased in popularity as an alternative to lemon juice in countries where lemons are less prevalent. Studies have shown varying efficacy in altering urinary stone risk parameters in comparison to KCit (15,22).

CL lemonade is a low-calorie sugar-free powdered beverage that has been shown to have high concentrations of citrate on nuclear magnetic resonance spectroscopy of 38.39 mmol/L, the highest of all commercially available beverages based on a study by Haleblian et al. (16) Similarly, a study by Large et al. (14) comparing various beverages including orange juice to CL found that CL contained on average approximately 30.4 mmol/L of citrate (using ion chromatography). The authors found that patients that consumed 7 days of CL beverage had average increases of 155 mg/day of urinary citrate, 196 mL of urinary volume, and +0.25 for urinary pH (14). Currently, there are no studies in the literature comparing usage of CL to the gold-standard treatment, KCit. In this study, we sought to compare the two treatments to see if CL was effective in improving urinary stone risk parameters, alone or in combination with KCit, compared to KCit alone. While all patients were counseled to intake at least 2 liters of fluids daily during all regimens, we noted that patients had increases in median urinary volume during the CL and CL + KCit phases but a slight decrease while taking the KCit regimen. This could perhaps be due to the fact that CL itself contains water and helps motivate participants to intake more fluid. Similar to prior studies, we found that CL consumption led to increases in urinary pH of +0.42 and decreases in SS CaOx of −0.15 from baseline while being very well tolerated with no participants reporting adverse side effects on the CL regimen. Both the CL and CL + KCit regimens also led to increases in urinary citrate of 172 and 173 mg/day, respectively. However, these differences did not reach statistical significance possibly due to the small sample size.

More recently, over the counter (OTC) citrate supplementation has grown in popularity with a variety of formulations in the form of tablets, powdered drink mixes, instant coffee, and gummies. Several brands of OTC citrate supplements have been shown to have high citrate concentration levels up to 63.9 mEq and have good efficacy increasing citrate and urinary pH levels (23,24). These alternative supplements can potentially be more cost-effective than prescription KCit tablets (25). However, there are no studies comparing the efficacy of these OTC citrate supplements against KCit for stone prevention. In addition, these products are more difficult to obtain that CL and often have to be purchased through online sources, whereas CL can be easily obtained at majority of grocery stores and drugstores in the United States.

Explanation of findings

Our study represents a real-world experience, where patients were provided with general stone prevention dietary advice and were not prescribed a strict diet. Characteristics such as age, sex, and other medical co-morbidities are potential confounders that could affect stone formation risk. Given the small participant size and difficulty with accrual, we did not exclude patients based on these characteristics. Nevertheless, our trial design allows for patients to serve as their own controls, which limits the confounding effects of these characteristics on our results. Overall, our study findings are unique and show that CL is well tolerated and can improve stone risk parameters.

Implications and actions needed

Future multi-institutional studies are necessary comparing CL to other commercially available citrate supplement alternatives to determine if these alternative therapies can reduce stone recurrence. In addition, studies comparing varying doses of KCit to CL are also needed to determine if there is truly a potential for substitution.

Conclusions

In this limited study in active stone formers, low-calorie sugar-free citrate-containing lemon beverage consumption in hypocitraturic stone formers was well tolerated with no reported adverse effects.

Acknowledgments

The abstract for this paper has been published in “Abstracts of the 40^th World Congress of Endourology: WCE 2023”, Journal of Endourology, 2023.

Footnote

Reporting Checklist: The authors have completed the CONSORT reporting checklist. Available at https://tau.amegroups.com/article/view/10.21037/tau-2026-0345/rc

Trial Protocol: Available at https://tau.amegroups.com/article/view/10.21037/tau-2026-0345/tp

Data Sharing Statement: Available at https://tau.amegroups.com/article/view/10.21037/tau-2026-0345/dss

Peer Review File: Available at https://tau.amegroups.com/article/view/10.21037/tau-2026-0345/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tau.amegroups.com/article/view/10.21037/tau-2026-0345/coif). A.E.K. is a consultant for Wolf, Storz, and Boston Scientific. A.P. received payment for invited talk by Storz. M.S.L. is a consultant for Boston Scientific, and Richard Wolf Medical Instruments Corporation; and is on the data monitoring committee for Butterfly. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Institutional Review Board of Northwestern University (approval No. STU00216084). Informed consent was obtained from all participants.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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