Habitual tea consumption is associated with a lower prevalence of kidney stone disease in postmenopausal women

Introduction

Kidney stone disease (KSD) is a global health care issue, and the prevalence has increased in the past decades (Hesse et al., 2003; Scales et al., 2012). The high recurrence rate makes the disease a notable economic burden in many countries (Hyams & Matlaga, 2014; Uribarri, Oh & Carroll, 1989). A nationwide study in Taiwan reported that KSD affects more than 9% of the population (Lee et al., 2002). KSD may cause kidney injury due to obstructive nephropathy, leading to an increased risk of chronic kidney disease (CKD) or dialysis (Shoag et al., 2014). Hence, it is crucial to identify the risk factors for KSD.

Many factors have been reported to be associated with KSD in recent decades, including family history, personal history, cigarette smoking, secondhand smoke exposure, dehydration, hypertension, obesity, diabetes mellitus (DM), metabolic syndrome and diet (Baatiah et al., 2020; Chang et al., 2021; Chen et al., 2021; Lee et al., 2022; Siener, 2021). Male sex is also an important risk factor for KSD, and estrogen has been proposed to be a protective factor (Peerapen & Thongboonkerd, 2019). A large 2022 epidemiological study demonstrated that postmenopausal women had a higher prevalence of KSD, which provides a new perspective on the link between women’s health and kidney stones (Tang et al., 2023). Menopausal women have a large decrease in estrogen and consequently the protective effect of estrogen on stones is lost. Furthermore, postmenopausal women experience changes in bone metabolism, resulting in changes in urine composition. These two factors may explain why postmenopausal women have a higher incidence of KSD (Nih Consensus Development Panel on Osteoporosis Prevention D, Therapy, 2001; Prochaska, Taylor & Curhan, 2018).

Even though menopause in women and KSD are strongly related, few studies focusing have focused on finding ways to reduce kidney stones in postmenopausal women. One of the most widely discussed factors is postmenopausal hormone supplementation, however most studies have shown little protection against KSD (Maalouf et al., 2010; Mattix Kramer et al., 2003; Yu & Yin, 2017). Thus, there is an emerging need to identify protective factors for KSD in postmenopausal women.

Nutrition plays a crucial role in the prevention of KSD. Dietary patterns that include fruits and vegetables can lower the risk of KSD due to their high potassium and magnesium content, which helps inhibit stone formation (Ferraro et al., 2020). A low-sodium diet is also recommended, as high sodium intake can lead to increased calcium excretion in urine, heightening the risk of stones (Tang, Sammartino & Chonchol, 2024). Recent research highlights the beneficial effects of plant-based diets, which not only provide essential nutrients but also reduce the likelihood of KSD by promoting a more alkaline urinary environment (Zayed, Goldfarb & Joshi, 2023). Therefore, optimizing dietary habits is a key strategy in the prevention of kidney stones.

Tea consumption is recognized as a nutritional factor that may help reduce the risk of KSD formation. Previous cohort studies have reported an association between tea consumption and a lower risk of KSD (Barghouthy et al., 2021a; Ferraro et al., 2013). Numerous compounds in tea have demonstrated health-promoting properties, including antioxidant effects, which may provide a protective role against KSD (Barghouthy et al., 2021a; Ferraro et al., 2013). However, these studies have primarily focused on the general population, without specifically addressing postmenopausal women, who are at a higher risk for KSD. Therefore, we hypothesize that habitual tea consumption is associated with a reduced risk of KSD in postmenopausal women.

The present study aims to investigate the association between habitual tea consumption and the risk of KSD in postmenopausal women. Specifically, we seek to determine whether regular consumption of tea can lower the risk of KSD in this high-risk population. By utilizing a large-scale Asian cohort, we aim to provide insights into the potential protective effects of tea consumption against KSD and contribute to the understanding of dietary factors that may mitigate the risk of stone formation in postmenopausal women.

Materials and Methods

Study population

We recruited 11,576 postmenopausal women from the Taiwan Biobank (TWB), a large-scale population-based database. Data on volunteers were collected from 2012 to 2018. Detailed information about the TWB has been reported in previous studies (Chang et al., 2022; Chen et al., 2022; Huang et al., 2022). Participants without available data on habitual tea consumption and obstetric history (n = 92) were excluded, and the remaining 11,484 participants were included in the final analysis (Fig. 1). The participants were divided into two groups according to habitual tea consumption: tea-drinking and non-tea-drinking groups. Written informed consent was collected from all participants, and all investigations followed the Declaration of Helsinki. The Institutional Review Board of Kaohsiung Medical University Hospital (KMUHIRB-E(I)-20210058) approved this study.

Results

Association between habitual tea consumption and KSD in subgroup analysis

To address baseline differences between tea-drinking and non-tea-drinking groups, specifically in smoking status, alcohol use, and physical activity, which differ with p value < 0.001, we conducted a subgroup analysis examining the association between tea consumption and KSD in postmenopausal women (Table 7 and Fig. 2). Among postmenopausal women aged 50 and older (n = 9,720), tea drinkers demonstrated a significantly reduced risk of KSD compared to non-tea drinkers, with an OR of 0.76 (95% CI [0.59–0.95]; p value = 0.018). In nonsmokers (n = 10,875), tea drinking was similarly associated with a significantly lower risk of KSD (OR: 0.80, 95% CI [0.64–0.99]; p value = 0.041), as was the case in nondrinkers (n = 11,159; OR: 0.79, 95% CI [0.63–0.98]; p value = 0.029). In addition, coffee drinkers (n = 4,419) who consumed tea had a significantly reduced risk of KSD (OR: 0.63, 95% CI [0.45–0.88]; p value = 0.007), as did married individuals (n = 10,976; OR: 0.79, 95% CI [0.64–0.98]; p value = 0.026). These findings suggest a lower prevalence of KSD among tea drinkers in specific subgroups, particularly older women, nonsmokers, nondrinkers, coffee drinkers, and married women, supporting the hypothesis that tea consumption itself may play a role in reducing KSD risk.

Table 7:

Subgroup analysis: the association between tea consumption and kidney stone disease in postmenopausal women.

Subgroup	Odds ratio (95% CI)*	p value
Age
<50 (n = 1,764)	0.91 [0.54 to 1.52]	0.717
≧50 (n = 9,720)	0.76 [0.59 to 0.95]	0.018
BMI
<25 (n = 7,699)	0.78 [0.59 to 1.04]	0.086
≧25 (n = 3,807)	0.77 [0.56 to 1.06]	0.112
Smoking
Yes (n = 609)	0.62 [0.29 to 1.31]	0.207
No (n = 10,875)	0.80 [0.64 to 0.99]	0.041
Drinking
Yes (n = 325)	0.53 [0.20 to 1.45]	0.400
No (n = 11,159)	0.79 [0.63 to 0.98]	0.029
Physical activity
Yes (n = 6,664)	0.79 [0.59 to 1.03]	0.083
No (n = 4,820)	0.78 [0.57 to 1.07]	0.128
Coffee
Yes (n = 4,419)	0.63 [0.45 to 0.88]	0.007
No (n = 7,065)	0.94 [0.71 to 1.23]	0.629
Married
Yes (n = 10,976)	0.79 [0.64 to 0.98]	0.026
No (n = 508)	0.27 [0.06 to 1.28]	0.098
All	0.78 [0.63 to 0.96]	0.021

DOI: 10.7717/peerj.18639/table-7

Notes:

CI, Confidence interval.

* Multivariable analysis adjusts for body mass index, smoke status, physical activity, hormone therapy use, history of hypertension, dyslipidemia, diabetes mellitus and chronic kidney disease.

Discussion

In this cross-sectional study of a population-based database in Taiwan, habitual tea drinking was significantly associated with a reduction in the prevalence of KSD in postmenopausal women. We also found that daily tea consumption of two cups or more was associated with an almost 30% decreased risk of KSD after adjusting for covariates. Among the different types of tea, semi- or non-fermented tea was more effective in reducing the risk of KSD. To the best of our knowledge, this is the first large-scale study to demonstrate a possible effect of tea consumption on the development of KSD in postmenopausal women.

Previous large-scale studies have reported that tea consumption was associated with an 8~11% lower risk of KSD (Barghouthy et al., 2021a; Curhan et al., 1998; Ferraro et al., 2013). The caffeine in tea has a diuretic effect, and it was shown to reduce calcium oxalate (CaOx) crystal adhesion on the surface of renal epithelial cells in an in vitro study (Peerapen & Thongboonkerd, 2018). Tea consumption has been associated with additional water intake. Moreover, the presence of antioxidant components may have a protective effect against stone formation (Itoh et al., 2005). Even though tea is known to contain oxalates, the amount of which is determined by the duration of infusion and type of tea, there is no evidence of oxalate-dependent stones in daily green tea drinkers (Rode et al., 2019). In female, the prevalence of KSD increases with age (Scales et al., 2012). In particular, postmenopausal status is associated with a higher risk of developing KSD, which may be due to differences in urine composition compared to premenopausal women (Prochaska, Taylor & Curhan, 2018). Shu et al. (2019) reported that tea consumption in middle-aged women was associated with a lower risk of KSD, predominantly driven by green tea, which is a non-fermented type of tea. However, they did not state whether their population included postmenopausal women. In the present study, we enrolled more than 11,000 postmenopausal women and collected sufficient clinical information to allow us to adjust for potential cofounders. The large sample size and detailed characteristics allowed us to investigate the relationship between tea consumption and the incidence of KSD.

In a previous meta-analysis, dose–response information was found in three studies (Dai et al., 2013; Ferraro et al., 2013; Goldfarb et al., 2005), and a daily intake of around 250 mL was found to be a cut-off level for the protective effect of tea consumption. Considered as a continuous variable, dose-dependent tea consumption (each 110 mL/day increase) has been associated with a reduction in the risk of KSD (Xu et al., 2015). Another study of 13,842 Taiwanese patients revealed that daily tea consumption of ≥240 mL (two cups) and ≥20 cup-years was related to a lower risk of KSD (Chen et al., 2019). Our results are compatible to previous studies of daily tea consumption. Taken together, these findings suggest that clinicians could inform postmenopausal women to drink two or more cups of tea per day to prevent the development of KSD.

Interestingly, we found that drinking semi- and non-fermented tea decreased the odds of KSD. Two longitudinal studies also found a decreased risk of developing KSD in people who drank non-fermented tea (Barghouthy et al., 2021a; Shu et al., 2019). Aside from additional water intake and the diuretic effects of caffeine, antioxidant compounds may play an important role in effect of non-fermented tea and in particular catechins (Henning et al., 2004; Itoh et al., 2005; Kanlaya & Thongboonkerd, 2019). In an animal model, the catechin epigallocatechin gallate was shown to have an inhibitory effect on urinary stone formation (Jeong et al., 2006). A Korean study reported that non-fermented tea contains higher concentrations of catechins than fully fermented tea (Jin, Jin & Row, 2006). This finding is consistent with our study, where semi- or non-fermented tea was associated with a decreased incidence of KSD. Regarding fermented tea, the small number of events in the fully-fermented tea group, only 16 cases of KSD, limits the ability to reach statistical significance. More research is needed to explore the role of fermented tea.

Postmenopausal status has been associated with a higher risk of developing KSD, and surgical menopause has been associated with a relatively higher risk than natural menopause (Prochaska, Taylor & Curhan, 2018). In an animal model, increased oxidative stress was detected in ovariectomized animals (Muthusami et al., 2005). Oxidative stress due to reactive oxygen species can cause oxidative damage to cells, and oxidative stress and CaOx crystallization have been strongly associated with KSD (Chaiyarit & Thongboonkerd, 2020; Khan, 2013; Li et al., 2021). Even though tea consumption can decrease oxidative stress, it had a limited effect in the women with surgical menopause in the present study, which may be related to higher oxidative stress. Hence, aside from drinking tea, high antioxidative dietary supplements for women with surgical menopause are suggested.

In our subgroup analyses, we demonstrated that the protective effect of habitual tea consumption was more pronounced in specific subgroups, particularly among older women (aged 50 and above), non-smokers, non-drinkers, coffee drinkers, and married women. This sensitivity analysis strengthens our conclusion that tea consumption is significantly associated with a reduced risk of KSD in postmenopausal women. These findings offer valuable insights into the lifestyle factors that may influence KSD risk and can serve as a foundation for further research in this area.

In summary, the possible protective effects of tea consumption against stone formation in postmenopausal women include additional water intake, the diuretic effects of caffeine, and the presence of antioxidant components (Barghouthy et al., 2021a). In addition, differences in urine composition compared to premenopausal women may be associated with a higher risk of developing of KSD (Prochaska, Taylor & Curhan, 2018). Metabolic syndrome has also been reported to be more prevalent in postmenopausal women than in premenopausal women (Park et al., 2003), and metabolic syndrome has been strongly associated with an increased risk of KSD (Chang et al., 2021). Several mechanisms have been proposed for the effect of green tea, including decreased absorption of lipids and activated AMP-activated protein kinase, thereby reducing metabolic syndrome parameters (Yang et al., 2016). This may be another explanation for the association between tea consumption and a lower incidence of KSD in postmenopausal women.

This is the first large-scale longitudinal population-based study to report a strong association between habitual tea drinking and a reduction in the prevalence of KSD in postmenopausal women. Despite these strengths, there are also some limitations to the current study. First, self-reported KSD is the major limitation, even though the participants answered the questions during follow-up interviews to ensure consistency of the responses. KSD in the participants could have been confirmed with computed tomography to reduce bias. In addition, previous similar studies have used self-reported KSD questionnaires (Shoag et al., 2019; West et al., 2008). Second, we did not measure the maximum amount of tea consumption that effectively prevent the development of KSD, because some people may experience side effects related to the caffeine and tannin contents. Third, it is common to distinguish different types of tea according to how the tea leaf is fermented, and to use the classification of fully, semi- and non-fermented tea. However, there are still subtle different in each fermented group, based on the tea tree and place of origin. Fourth, we did not discuss women with early menopause, which seems to be another subgroup. Early menopause can occur naturally or be induced by some medical treatments such as surgery or chemotherapy. Fifth, we lacked information about stone types, but CaOx stones account for the majority of KSD in the Taiwanese population, followed by calcium phosphate, and uric acid stones (Chou et al., 2007). Sixth, we acknowledge that a limitation of our study is our focus solely on postmenopausal women, which restricts its applicability to a broader population. However, evidence from at least 14 studies, including one meta-analysis, indicates the protective effects of tea consumption on kidney stone risk in men and premenopausal women (Barghouthy et al., 2021b). Our aim was to provide new insights into this specific population rather than reiterate findings from groups where this topic has already been explored. By concentrating on postmenopausal women, our study seeks to address the unique factors that may influence kidney stone disease risk in this higher-risk group. Seventh, as this is a cross-sectional analysis, we only assessed the presence of KSD at the time of enrollment. The questionnaire asked whether participants had ever been diagnosed with KSD but did not specify whether the diagnosis occurred during pre- or post-menopause. Furthermore, as a cross-sectional study, we cannot establish causality and can only report associations. To address this, we conducted sensitivity analyses across different subgroups to provide a more precise understanding of the effects of tea consumption on KSD. Finally, a limitation of this study is the overlap in the postmenopausal women cohort with our previous publication (Tang et al., 2023). However, the two studies have distinctly different focuses and objectives. The previous study explored the association between menopause (pre- vs. post-menopausal) and KSD in a cohort of 17,460 women, assessing the impact of menopause on KSD risk. In contrast, the current study focuses solely on postmenopausal women (11,484 women) and investigates the relationship between habitual tea consumption and the prevalence of KSD. The target variables, population subgroups, and research questions are different. Despite the overlapping dataset, the hypotheses and findings in this study are novel and provide valuable insights into tea consumption and KSD risk, which were not explored in our previous work.

Conclusions

In conclusion, our study highlights that habitual tea consumption may be linked to a lower prevalence of KSD among postmenopausal women. With a significant reduction in risk observed among those who regularly consume tea, our findings underscore the potential protective role of tea in this vulnerable population. Given the increasing incidence of KSD in postmenopausal women, it is crucial to further investigate the underlying mechanisms by which tea may exert its protective effects. Future research should focus on elucidating the specific compounds in tea that contribute to this reduction in risk, as well as conducting longitudinal studies to confirm these associations and explore the optimal amount and type of tea for kidney health.

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