Is the Caffeine in Coffee an Issue for Those with GERD?

Stephanie Matthews

NTR 402

Introduction:

Coffee is considered to be, globally, the one of the most consumed beverage (Samoggia,

& Riedel, 2019). It is a universal drink for consumers to enjoy for social purposes, health

benefits, and overall effects (Samoggia, & Riedel, 2019). Studies have demonstrated positive

effects of coffee on certain diseases such as liver disease, Parkinson’s disease, type II diabetes,

and certain types of cancer (Barthel, Wiegand, Scharl, Scharl, Frei, Vavricka, Biedermann,

2015). Coffee contains niacin, magnesium, and potassium (Nieber, 2017). Antioxidants, anti-

inflammatory, antifibrotic, and anticancer effects are due to being composed of thousands of

bioactive compounds (Poole, Kennedy, Roderick, Fallowfield, Hayes, Parkes, 2017). These

compounds are produced through the Maillard reaction because the roasting of the beans happen

during high temperatures (Nieber, 2017). Selfridge provided some of the key compound classes

include caffeine, chlorgenic acids, melanoidins, trigonelline, and diterpenes, as described below

on Table-1 (Selfridge, 2016). According to Samoggia and Riedel, coffee contains more

antioxidants needed per day than fruits, vegetables, as well as green and black teas (Samoggia

&Riedel). Thus research is gearing towards calling coffee a functional food due to its bioactive

properties and the way it can promote health (Samoggia &Riedel).

Table-1:

Table 1: Major compound classes in coffee and their characteristics1

Compound Class Qualities/Mechanisms Putative Physiologic Effects

Chlorgenic acids

Powerful antioxidants in vitro; may modulate cell-signaling pathways, increasing phase II enzyme activity; effects may be due more to metabolites and catabolites than to original compounds in coffee

Anticarcinogenic; antithrombotic; anti-inflammatory; enhanced endothelial function; altered glucose metabolism; antimicrobial

MelanoidinsProduced by roasting process; behave as dietary fiber: largely indigestible and fermented in gut

Antioxidant; metal chelating; antimicrobial; anticariogenic; modulate colonic microflora; antihypertensive; antiglycative

Caffeine

Concentration in coffee beverages varies significantly; rapidly absorbed in the gut and distributed to all tissues; adenosine receptor antagonist (stimulates release of dopamine); synergistic interactions with epinephrine and norepinephrine; may protect cell membranes against oxidative stress

Increases metabolic rate and energy expenditure; increases lipid oxidation and lipolysis; increased heart rate and blood pressure; CNS stimulation enhances alertness, perception, memory consolidation, may cause sleeplessness; possible reduced fetal growth at higher levels of intake

Trigonelline

Absorption starts in stomach; pass through body to be excreted in urine without substantial phase II metabolism; regulates key enzymes of glucose and lipid metabolism

Hypoglycemic; neuroprotective; anti-invasive; estrogenic; antimicrobial

Diterpenes (cafestol and kahweol)

Abundant in boiled and unfiltered coffees, absent in filtered coffees; fatty acyl esters; may induce phase II detoxifying enzymes

Raise serum cholesterol; chemopreventive; enhance defense against oxidative damage

Table-1: (Selfridge, 2016). Coffee contains different compounds that affect the body in positive ways. These classes aid in reduced risk for heart disease, type II diabetes, Parkinson’s disease, and certain cancers. (Selfridg, 2017). It also aids in attentiveness thus most drinking coffee for its caffeine content (Samoggia & Riedel, 2019).

Caffeine is one of the most prominent components of coffee as well as 5-caffeoylquinic

acid, cafestol, kahweol, and adenosine (Nieber, 2017). It can also be found in additional food

items such as chocolate, tea, and energy drinks (Nieber, 2017). When comparing caffeine content

to other items, coffee contains approximately 65-120mg of caffeine per cup of normal coffee

(Neiber, 2017). People drink coffee due to the stimulating effects, such as keeping one awake

(Nieber, 2017). The respiratory system is affected by the caffeine consumed which the central

nervous system controls (Welsh, Pan, Belik, 2015). It is also known to affect smooth muscle and

the gastrointestinal system (Welsh et al., 2015).

Figure-1: The key compound classes found in coffee and their chemical structure.

Roasting, temperature, bean type, brew setting, and caffeine content play a role in how

coffee reacts with the body as well as shape the chemical components within each cup (Poole et

al., 2017). Poole et al stated “An individual’s genotype and gut microbiome will then determine

the bioavailability and type of coffee metabolites to which that individual is exposed,” (Poole et

al, 2017). This states that the bacteria in an individual’s gut will determine how the coffee is

metabolized in its current composition. This can be crucial for people who have developed issues

related to gastroesophageal reflux disease (GERD).

GERD is caused from the lower esophageal sphincter relaxing allowing stomach acid to

proceed up the esophagus causing a burning or heartburn like sensation (McCulloch, 2016).

Approximately 20% of the U.S population is affected by GERD (McCulloch, 2016). This

number is on the rise due to the current obesity epidemic among adults and children (McCulloch,

2016). According to Kurbo et al, GERD is prominent in Western culture, approximately ¼ of the

population experiences symptoms such as heart burn and acid reflux each month (Kurbo et al,

2014). Additional symptoms include, dysphasia, chest pain, nausea, or cough in one’s voice

(Kurbo et al, 2014). It can affect the quality of one’s life because GERD can lead to other

problems such as Barrett’s esophagus and esophagitis leading to asthma, lung disease, and other

respiratory issues (Castillo, Otero, Trespalacios, 2015). Castillo et al states the gold standard of

pharmaceuticals for treating GERD are proton pump inhibitors (Castillo et al., 2014). These

medications reduce the amount of hydrochloric acid produced reducing symptoms however these

proton pump inhibitors can come with side effects (Kurbo et al., 2014). Risks include the

reduced absorption of calcium which increases the probability of bone fractures as well as food

borne illness (Kurbo et al., 2014). The National Institutes of Health and the American College of

Gastroenterology have stated some ways patients can reduce their GERD symptoms (Kurbo et

al., 2014). Dietary intake would involve less consumption of chocolate, coffee, tea, acidic

products such as tomatoes and citrus foods (Kurbo et al, 2014). Alcohol, consuming large

portions as well as lifestyle factors like exercising, losing weight, and stop smoking (Kurbo et

al., 2014). The research is controversial on which dietary items effect symptoms for GERD.

According to Rao and Fuller, the pH of coffee might not have as great of an effect on symptoms

compared to caffeine (Rao & Fuller, 2018). The purpose of this paper is to evaluate the effects of

caffeine on gastroesophageal reflux disease.

Effects of Brewing and Acidity: Does Cold Brew Coffee Have More Health Benefits?

Cold brew coffee has become increasingly popular in the United States since 2011, and

had an increase in sales from 2011-2016 by 580% (Rao & Fuller, 2018). It presents as more

beneficial because the coffee doesn’t have a bitter taste and has a smoother mouthfeel compared

to regular hot coffee (Rao & Fuller, 2018). The bitterness in coffee is caused by the chlorogenic

acids, caffeine, and other phenolic compounds such as caffeoylquinic acids, which are the

antioxidants present (Fuller & Rao, 2017). Rao and Fuller have also mentioned online articles

claiming that there isn’t as much acidity in cold brew as well as not as much caffeine and more

antioxidants when compared to hot coffee (Rao & Fuller, 2018). Cold brew is produced over an

extended period of time compared to hot coffee. It is made using lower temperatures, 20-25°C,

for approximately 8-24 hours (Fuller & Rao, 2017). Commercial producers of cold brew have

claimed the longer steeping times have reduced acidity being easier for those with

gastrointestinal diseases to consume (Rao & Fuller, 2018).

In 2017, Fuller and Rao studied the correlation between time, roasting, and temperature

on caffeine and chlorogenic acid amounts in cold brew. There were four types of coffee

including two roasting temperatures, medium and dark, and two bean sizes, medium and course

(Fuller & Rao, 2017). The particle size was determined by ASTM Cl136/C136M-14 Standard

Test Method for Sieve Analysis for Fine and Course Aggregates (Fuller & Rao, 2017). The cold

brew was prepared using an article of The New York Times and brewed at room temperature

while the hot brew was prepped the same way however was heated to 98°C and sat for six

minutes (Fuller & Rao, 2017). Caffeine and 3- chlorogenic acid (3-CGA) have been evaluated

through liquid chromatography system (Fuller & Rao, 2017). The results pertaining to the grain

size and kinetics of the coffee demonstrates the importance of the intragranular and intergranular

pore space (Fuller & Rao, 2017). The intragranular space is the space between each pore of

coffee while the intergranular space is considered to be each grain of coffee (Fuller & Rao,

2017).

Analyzing 3-CGA, results suggest that this compound reacts with roasting temperature

(Fuller & Rao, 2017). An increase in temperature caused the chlorogenic acid concentration to

decrease (Fuller & Rao, 2017). When comparing 3-CGA to caffeine, the results may differ.

Caffeine is not as soluble at room temperature and also isn’t as sensitive to roasting temperature

(Fuller & Rao, 2017). Observing the roast type, the caffeine content was high and similar in both

samples even though the medium grain size sample displayed a higher dose of caffeine it was

classified as being statistically insignificant (Fuller & Rao, 2017). When evaluating time, the

longer the cold brew was brewed, 400 minutes, the samples resembled higher caffeine content

(Fuller & Rao, 2017). Figure-2 demonstrated the comparison of cold brew and hot brew

concentrations as well as pH. The pH of the coffee in this study ranged from 5.40-5.63 however

no correlation could be determined with acidity and brewing methods (Fuller & Rao, 2017).

Coffee Sample (Roast - Grind)

3-CGA Concentration (mg/L)

Caffeine Concentration (mg/L)

pH

Cold Brew Method

Hot Brew Method

Cold Brew Method

Hot Brew Method

Cold Brew Method

Hot Brew Method

Medium - Medium

510 ± 20

510 ± 30

1180 ± 90

1040 ± 70

5.54 ± 0.02

5.41 ± 0.02

Medium - Coarse

520 ± 40

460 ± 40

1230 ± 60 970 ± 70 5.40 ± 

0.01 5.35 ± 0.03

Dark - Medium

390 ± 10

430 ± 30

1080 ± 70

1060 ± 70

5.53 ± 0.01

5.61 ± 0.02

Dark - Coarse

360 ± 20

340 ± 10 990 ± 30 840 ± 10 5.41 ± 

0.02 5.48 ± 0.02

Figure-2: Brew time varied from 6 minutes for hot brew to 1400 minutes for cold brew and the caffeine concentration and 3-CGA were close in numbers in addition to pH. (mean ± 95% CI, n=6) (Fuller & Rao, 2017).

In 2018, Rao and Fuller analyzed the acidity and antioxidant concentrations within cold

brew coffee (Rao & Fuller, 2018). The coffee used in this study was from five different regions,

Brazillian, Ethiopian-Ardi, Ethiopian-Yirgz, Myanmar, Columbia, and Mexico (Rao & Fuller,

2018). The beans were already ground, and were a light-to-medium roast (Rao & Fuller, 2018).

The pH values of the hot coffee ranged from 4.85-5.10 and the cold brew samples ranged from

4.96 to 5.13 (Rao & Fuller, 2018). For the hot brew, the Brazilian coffee has the lowest

concentration of caffeolyquinic acid yet the highest pH, 5.10±0.02, while the Ethiopian-Ardi

blend was the least acidic, 4.85±0.09, but has the highest concentration of the caffeolyquinic acid

(Rao & Fuller, 2018). For cold brew the Ethiaopian-Yirgz has the highest pH while Myanmar

has the lowest (Rao & Fuller, 2018). Research also showed that titratable acids played a role in

acidity in hot brewed coffee however in Rao and Fuller’s research they found a weak correlation

between acidity and the amount of titratable acids (Rao & Fuller, 2018). Similar to hot brew,

cold brew had no correlation between titratable acids and pH as well as an insignificant relation

between caffeolyquinic acid and pH.

Their research suggested that hot brew coffee had a higher concentration of CQA present

when compared to cold brew. However the correlation coefficient was less than 0.5 which means

the acidity and pH have a weak relationship (Rao & Fuller, 2018). The antioxidant activity and

CQA have a strong relationship in the cold brew coffee, correlation coefficient of 0.82, when

compared to hot coffee, correlation coefficient of 0.22 ( Rao & Fuller, 2018). It can be said that

the hot coffee had a weaker correlation with antioxidant activity and CQA could be due to

temperature (Rao & Fuller, 2018). However, when comparing hot brew and cold brew, hot brew

has more antioxidant properties because it extracts more non-deprotonated acids (Rao & Fuller,

2018). More research needs to be done to fully understand cold-brew and its relationship with

GERD (Rao & Fuller, 2018).

The Effect of Caffeine on Rats:

Caffeine is one of the most common drugs consumed (Welsh, Pan, Belik, 2015). Studies

have shown that caffeine has affected the smooth muscle in the gastrointestinal tract in adult rats

(Welsh et al, 2015). Newborn rats are given caffeine within the first few days of life to analyze

how their bodies process. This study determined how long the caffeine traveled through the

gastrointestinal tract and how it effects the lower esophageal sphincter and motor function

(Welsh et al., 2015).

There were two samples given to the rats, the group that received carbachol, experiment,

or were held in the contracted state with muscarinic agonist, the control group (Welsh et al.,

2015). The evaluation between the two groups stated that the LES relaxed due to caffeine, by

30% in the experimental and 50% in the control which is statistically significant (Welsh et al,

2015). Welsh et al, studied the affect caffeine had on muscle tone. Their conclusions were

statistically significant, P < 0.01, because caffeine reduced the rate of contraction within the

large intestine as well as increasing gastric emptying (Welsh et al, 2015). When the newborns

were also compared to adult rats, it was found that caffeine had the same affect in regards to

lowering the LES pressure and gastric emptying (Welsh et al, 2015). In conclusion, it can be

found that caffeine has a relaxation effect on the gastrointestinal tract in rats and it has been

known that caffeine can affect humans. The correlation between the LES pressure and caffeine

needs to be further studies in humans (Welsh et al, 2015).

The Role of Caffeine on Reflux:

There is research to conclude that acid reflux is caused by highly acidic foods. Doctors

have recommended steering clear of certain foods such as tomatoes, citrus, fatty foods, soft

drinks, chocolate, mint/peppermint, spicy foods, and coffee (Castillo et al, 2015). Lifestyle

factors also alleviate symptoms such as exercise, not laying down right after eating, eating right

before bed, and smoking (Castillo et al, 2015). Castillo et al, reviewed the effects dietary and

lifestyle factors had on individuals with GERD.

In their review, Castillo et al included 20 articles that fit their criteria for their research.

They rated the articles for how much evidence there was to back up the claims as well as the

effect of the studies (Castillo et al, 2015). Studies have shown that those who consumed coffee

experienced symptoms related to GERD, such as heartburn (Castillo et al, 2015). When

evaluating if other food items were involved, the only significance between coffee and the LES

pressure was when food was consumed at the same time (Castillo et al, 2015). When comparing

consumption of coffee with other countries, a Norwegian study found a positive effect of those

who experienced GERD symptoms when seven cups of coffee were consumed compared to

those with less, OR: 0.6, 95% CI: 0.4-0.7 (Castillo et al, 2015). When looking at a study done in

Japan, there was a correlation between GERD and coffee consumption (Castillo et al, 2015).

Castillo et al, reviewed how decaffeinated coffee effects GERD (Castillo et al, 2015). When

compared to decaffeinated tea the results didn’t reproduce the same thing which gave the authors

the speculation that other factors were also included (Castillo et al, 2015). The conclusion is

there is not sufficient evident to prove that coffee does not cause GERD symptoms (Castillo et

al, 2015).

A Japanese study reviewed the effects of coffee on gastroesophageal reflux disease and

ulcers (Shimamoto et al, 2013). In this study, 8,103 people were evaluated to see if there was a

correlation. They included factors such as age, gender, BMI, smoking, drinking alcohol, H.

pylori, coffee consumption, and pepsinogen I/pepsinogen II ratio and excluded those taking

medication that reduced stomach acid, such as proton pump inhibitors, gastric bypass, and a

history H. pylori infection (Shimamoto et al, 2013). Shimamoto did a cohort study to evaluate

their research (Shimamoto et al, 2013). The authors broke GERD into four segments, gastric

ulcer, duodenal ulcerm reflux esophagitis, and non-erosive reflux disease (Shimamoto et al,

2013). A positive relationship between H pylori infection and GERD was present, as well as the

male gender, high BMI, smoking, drinking alcohol, and pepsinogen I and II (Shimamoto et al,

2013).There was a statistically insignificant attempt to associate GERD and coffee when using a

multivariate analysis (Shimamoto et al, 2013). Figure-3 shows the relationship between GERD

symptoms and other lifestyle factors. There was no positive correlation between GERD and

coffee consumption.

Figure-3- The relationship between coffee and GERD symptoms are shown to be insignificant related to the number of cups of coffee consumed. 1-2 cups/day OD: 0.93 95% CI: (0.79-1.08) and ≥ 3 cups/day OD: 0.93 95% CI: (0.79-1.10). The p-value for consuming 1 or more cups per day was greater than 0.05 (Shimamoto et al, 2013).

Comparing Tea to Coffee: Is Tea a Safer Option?

Tea is a widely popular beverage especially in Asian cultures (Cao et al, 2018). It has

been shown to have benefits such as anti-aging properties and reduced risk of diabetes (Cao et al,

2018). Green tea has also been shown in studies to reduce the risk of metabolic syndrome and

obesity (Wei et al, 2019). While it has benefits, tea also contributes to the GERD symptoms

similar to coffee however research is controversial due to various studies showing positive and

negative correlations (Cao et al, 2018).

A meta-analysis was done on the Asian population to evaluate the association between

tea and GERD (Cao et al, 2018). Cao et al used 23 studies in their analysis that were eligible and

majority were from East Asian populations (Cao et al., 2018) Europe, Middle East, North

American, and South Asian studies were also included (Cao et al, 2018). Of their findings, cross-

sectional studies, case-control, and cohort studies were evaluated in their final results (Cao et al,

2018). Cao et al, finally concluded that the tea and GERD relationship were statistically

insignificant, OR 1.12, 95% CI 0.98-1.27, (Cao et al, 2018). A meta-regression was then

conducted to test the variability in their research (Cao et al, 2018). This showed that there was an

increased risk of GERD in East Asian culture. When compared to Middle East there was a

decreased risk and this could be due to the high consumption of tea in East Asia however, there

are other factors that need to be factored in such as genetics and other lifestyle habits that can

influence one’s risk (Cao et al, 2018). When comparing the cross-sectional studies to the cohort

and case-control the results vary as there was a positive correlation with cross-sectional but none

with case-control and cohort (Cao et al, 2018). The final outcome came to the conclusion that

GERD and tea consumption is insignificant (Cao et al, 2018).

A cross-sectional study was done to evaluate the effects coffee and tea had on GERD and

erosive esophagus when sugar and milk were added (Wei et al, 2019). Participants were asked to

complete a reflux disease questionnaire and any questions with missing answers were excluded

from the experiment (Wei et al, 2019). Coffee or tea was consumed for minimum of four days

per week for three months and in this study, heavy coffee drinking was considered consuming at

least two cups per day (Wei et al, 2019). The questionnaires asked about symptoms, how often,

as well as confounding factors such as age, gender, BMI, hyperlipidemia history, type II

diabetes, H. Pylori and hypertension (Wei et al, 2019). Lifestyle factors such as smoking,

drinking alcohol, and use of aspirin and non-steroidal anti-inflammatory drugs were asked (Wei

et al, 2019).

The total number of participants of the study was 1837 (Wei et al, 2019). Out of this

population, 65% drank coffee and within that percentage 15.5% were considered heavy coffee

drinkers (Wei et al, 2019). Out of the total 1837 participants, 44.9% added milk to their coffee

and 28.4% added sugar (Wei et al, 2019). In comparison to tea, 22.6% of the population were

heavy tea drinkers and 4% added sugar (Wei et al, 2019). Their study found that men were

heavier tea drinkers, smokers, drank more alcohol, used aspirin, had hypertension, H. pylori

infection, erosive esophagus and hyperlipidemia when compared to women (Wei et al., 2019).

Men were less likely to add milk to their coffee (Wei et al, 2019). For tea drinkers and heavy tea

drinkers P < 0.001, sugar with tea P =0.277, coffee drinkers P = 0.380, heavy coffee drinkers P =

2.56, milk with coffee P= 0.032, sugar with coffee P= 0.074, and GERD p = 0.700 (Wei et al,

2019). Researchers found BMI to be correlated with GERD symptoms however Wei et al found

no significance between drinking coffee or tea and adding milk or sugar to reflux (Wei et al,

2019).

Conclusion:

It can be stated that the correlation between coffee and GERD are not statistically

significant. This can indicate coffee is safe to drink for those diagnosed with GERD. As it

showed in the research by Castillo et al, GERD is more associated with the foods that are also

consumed with drinking coffee not so much the caffeine that is present (Castillo et al, 2015).

While other foods have an impact, lifestyle factors such as obesity and genetics have a greater

role on GERD symptoms than coffee (Castillo et al, 2015).

Coffee contains many biochemical antioxidants that are beneficial for one’s health. It has

been studied to be reduce the risk of cardiovascular disease, Parkinson’s disease, and certain

cancers (Selfridge, 2016). The type of coffee being consumed, such as cold brew or hot brew,

showed no association with GERD despite claims that have been made. Adding sugar or milk to

coffee will not increase reflux symptoms and tea also showed no correlation with GERD.

Consuming 3-4 cups of coffee, hot brew or cold brew per day is safe for GERD patients

References:

Barthel, C., Wiegand, S., Scharl, S., Scharl, M., Frei, P., Vavricka, S. R., ...Biedermann, L. (2015). Patients' perceptions on the impact of coffee consumption in inflammatory bowel disease: friend or foe? - a patient survey. Nutrition Journal, 14(1). Retrieved from https://nutritionj.biomedcentral.com/articles/10.1186/s12937-015-0070-8. Retrieval Date November 1, 2019

Cao, H., Huang, X., Zhi, X., Han, C., Li, L., & Li, Y. (2019). Association between tea consumption and gastroesophageal reflux disease: A meta-analysis. Medicine, 98(4), Retrieved from: https://insights.ovid.com/crossref?an=00005792-201901250-00034 Retrieval Date November 1, 2019

Castillo, Roger, Otero, William, & Trespalacios, Alba. (2015). Evidence Based Review of the Impact of Treatments of Gastroesophageal Reflux Disease. Revista Colombiana de Gastroenterologia, 30(4), 431-446.

Fuller, M., Rao, N.Z. (2017) The Effect of Time, Roasting Temperature, and Grind Size on Caffeine and Chlorogenic Acid Concentrations in Cold Brew Coffee. Sci Rep 7, 17979 (2017) Retrieved from: https://www.nature.com/articles/s41598-017-18247-4#Abs1

Kubo, A., Block, G., Jr, Quesenberry,C. P., Buffler, P., & Corley, D. A. (2014, August 14). Dietary guideline adherence for gastroesophageal reflux disease. Retrieved from https://bmcgastroenterol.biomedcentral.com/articles/10.1186/1471-230X-14-144 Retrieval Date: November 1, 2019

McCulloch, M. (2016, April). Dietary relief from GERD: tame the flames of gastroesophageal reflux disease naturally, with dietary and lifestyle changes. Environmental Nutrition, 39(4), 4.

Nieber, Karen. (2017) “The Impact of Coffee on Health.” Planta Medica, vol. 83, no. 16, 2017, pp. 1256–1263.

Poole, R., Kennedy, O. J., Roderick, P., Fallowfield, J. A., Hayes, P. C., & Parkes, J. (2017). Coffee consumption and health: umbrella review of meta-analyses of multiple health outcomes. BMJ (Clinical research ed.), Retrieved from https://www.bmj.com/content/359/bmj.j5024 Retrieval Date: November 1, 2019

Rao, N. Z., & Fuller, M. (2018). Acidity and Antioxidant Activity of Cold Brew Coffee. Scientific reports, 8(1), Retrieved from https://www.nature.com/articles/s41598-018-34392-w . Retrieval Date: October 30, 2019

Samoggia, A., & Riedel, B. (2019). Consumers' Perceptions of Coffee Health Benefits and Motives for Coffee Consumption and Purchasing. Nutrients, 11(3). Retrieved from: https://www.mdpi.com/2072-6643/11/3/653/htm . Retrieval Date: October 30, 2019

Selfridge, N. J. (2016). The effects of coffee consumption on health outcomes. Integrative Medicine Alert, 19(6) Retrieved from https://www.reliasmedia.com/articles/137936-the-effects-of-coffee-consumption-on-health-outcomes . Retrieval Date: October 19, 2019

Shimamoto T, Yamamichi N, Kodashima S, Takahashi Y, Fujishiro M, et al. (2013) No Association of Coffee Consumption with Gastric Ulcer, Duodenal Ulcer, Reflux Esophagitis, and Non-Erosive Reflux Disease: A Cross-Sectional Study of 8,013 Healthy Subjects in Japan. PLOS ONE 8(6): e65996. Retrieved from: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0065996 . Retrieval Date: October 31, 2019

Wei, T. Y., Hsueh, P. H., Wen, S. H., Chen, C. L., & Wang, C. C. (2019). The role of tea and coffee in the development of gastroesophageal reflux disease. Ci ji yi xue za zhi = Tzu-chi medical journal, 31(3), Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6559035/?report=classic . Retrieval Date: November 1, 2019