Bridging the gap between evidence-based practice and probiotic utilization among US adults: Results from a national survey

INTRODUCTION

Probiotics are live microorganisms that have health benefits to the host if consumed in adequate quantities.^[1] Probiotics either occur naturally in fermented foods, added to food products, or sold as dietary supplements. The most commonly used genera of microorganisms in probiotic-containing products include Lactobacillus, Bifidobacterium, Saccharomyces, Streptococcus, Enterococcus, Escherichia, and Bacillus.^[2,3] Probiotic supplement manufacturers do not have to demonstrate efficacy and safety, because dietary supplements do not require Food and Drug Administration approval before marketing.^[3,4] The dose and purity of the probiotic supplement may vary between brands. For this reason, not all foods and supplements labeled as “probiotics” are proven to have any health benefit to the consumer due to the lack of regulatory oversight.

The mechanism by which probiotics exert health benefits to the host differs among the various strains, species, and genera of microorganisms. Mechanisms of action may include inhibition of growth of pathogenic microorganisms in the gastrointestinal (GI) tract, production of bioactive metabolites such as short-chain fatty acids, reduction of luminal pH in the colon, vitamin synthesis, strengthening the gut barrier, bile salt metabolism, enzymatic activity, and toxin neutralization.^[5,6] Probiotics have been studied for different indications including obesity, irritable bowel syndrome (IBS), and antibiotic-associated diarrhea.^[2,7,8] Research on probiotics has provided frequently conflicting results making it difficult for patients and clinicians to make evidence-based decisions about probiotic use in treating and preventing GI conditions.

Trends in consumer purchasing behavior show that probiotics are among the most widely used supplements. According to data from the Centers for Disease Control and Prevention, as of 2012, the use of pre- and pro-biotics quadrupled since 2007 reaching 3.9 million Americans making it the third most popular non-vitamin and non-mineral dietary supplement.^[9] Prebiotics are non-digestible food ingredients that stimulate the growth of beneficial bacteria in the gut, and will not be included in this study.^[10] Despite its growing utilization by the public, guidelines published by the American Gastroenterological Association (AGA) recommend probiotics in only three circumstances: (1) Prevention of Clostridium difficile infection for adults and children on antibiotic therapy, (2) improvement of symptoms in patients with pouchitis, and (3) prevention of necrotizing enterocolitis in preterm infants <37 weeks gestational age.^[11] The objective of this study was to examine probiotic use, evaluate population knowledge regarding the risks and benefits of probiotics, examine whether pharmacist recommendations are sought before using probiotics, and to identify variables that predict the use of probiotics among US adults.

MATERIALS AND METHODS

RESULTS

In the weighted sample, 51% of respondents were female, 38% were between the ages of 35–59, and 57% of respondents self-identified as non-Hispanic white [Table 2]. Approximately one-third (31%) of survey respondents stated that they currently take or have taken probiotics daily. An additional 29% of respondents said that they would consider future probiotics use [Table 1]. Probiotic formulations selected among survey respondents who either took probiotics in the past, were taking them currently, or considered taking them in the future, included pill (36%), yogurt (43%), or other food or drink (18%) [Figure 1]. Most probiotic users (64%) were using daily probiotics without seeking a medical provider’s recommendation [Table 1]. Good intestinal health (55%), counteracting the negative effects of antibiotics (11%), and weight loss/management (12%) were the most common reasons why respondents took probiotics [Figure 1]. Only 26% of respondents taking probiotics now or in the past reported having a chronic illness [Table 3]. Study respondents were also asked whether they believed daily probiotic use only enhanced health or could also hurt health. The majority (41%) stated that probiotics only enhanced health, while 25% said that they can also hurt health [Table 1]. When the respondents were asked whether they spoke with a pharmacist when visiting a pharmacy, 28% said always, 27% said sometimes, 29% said rarely, and 15% answered never. Only 6% sought pharmacists’ counseling for over-the-counter therapies, including probiotics [Table 1 (suppl)]. There was a weak positive correlation between probiotic use, female sex, age, chronic illness, and white race (P < 0.05) [Table 2 (suppl)]. The full survey questions and answers are shown in [Table 1] in the supplemental material. Predicted probabilities based on the results showed that, controlling for other factors, women were 18% points more likely to report using probiotics than men, and older respondents were less likely to report probiotic use than younger respondents, with the likelihood decreasing by approximately 2.2% points for every 10-year increase in age. White respondents were also about 8 points more likely to report probiotic use than non-white respondents, and individuals with a 4-year college degree were about 6 points more likely to do so than those who did not complete a degree. Further logistical regression analysis was conducted to explore the interaction between race/ethnicity, education level, and having a chronic illness [Table 4]. This analysis included an interaction effect between these three variables (as well as all necessary lower order interactions). The results of this analysis show a significant conditional relationship between chronic illness, education, and white race/ethnicity (z = 1.96 on the three-way interaction, P < 0.05). The largest effects of chronic illness were among more educated non-white respondents. In this group, individuals with a chronic illness were 11% points more likely to report probiotic use than individuals without a chronic illness. This effect did not increase reported probiotic use among more educated white respondents.

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Figure 1:

Survey responses on probiotic utility.

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DISCUSSION

This study found that sex, age, race, and education level were significantly associated with probiotics use. The association between female sex and probiotic use may be explained by increased prevalence of GI disorders, such as IBS and inflammatory bowel disease, in females.^[12] In one study, as many as, 24.3% of females diagnosed with IBS currently use or have used probiotics to manage their symptoms.^[13] In addition, the previous studies showed that in general, women are more likely to use alternative medicines than men, consistent with our findings.^[14,15] In our study, there was a significant decrease in probiotic use with each decade of life. This could be due to marketing targeted to a younger demographic, less knowledge or familiarity with benefits of probiotics in older respondents, or lower acceptance/higher level of mistrust toward probiotics. One study found that older patients were significantly less likely to have heard the word “probiotics” that younger patients.^[16] Correlation of white race and 4-year college degree education level to probiotic use may be explained by this population having higher median disposable income.^[17] There was a weak correlation between probiotic use and having a chronic illness. Survey respondents were not asked which chronic illness, they were diagnosed with limiting the interpretation of this correlation. Respondents with chronic illnesses may be looking for alternative medicines to alleviate their symptoms.^[13] Interaction effects from the logistic regression analyses show the absence of effects in certain respondents, especially in those self-identifying as white and highly educated. While useful, these effects do not answer the question of why suffering from chronic illness does not have a main effect on increasing the likelihood of probiotic use. These interaction effects support a social capital explanation in which certain demographic groups may be more aware of the potential efficacy of probiotics than others. More educated people and whites may be more likely to take probiotics regardless of chronic conditions while others become more informed of the benefits when they have a chronic illness. As such, we did not observe an interaction of indicators of higher social capital with chronic illness, indicating that chronic illness did not make them more likely to take probiotics than they already were. This led to conducting an additional logistical regression to test for interaction effects between race, education, and chronic illness. We found a significant conditional relationship between chronic illness, education, and race in the additional regressions. Among white respondents with the lower levels of education, chronic illness increased the likelihood of reported use of probiotics. The interaction between chronic illness and probiotic use was greatest in more educated, non-white respondents. In general, we observed that chronic illness makes individuals more likely to use probiotics, but only among those not otherwise using them, since majority of patients reported using probiotics for preventive purposes and not for chronic illness. In general, chronic illness makes people who were less likely to take probiotics about as likely as educated white people who do not have chronic illness. This indicates that chronic illness has only a contingent effect on the reported use of probiotics, rather than increasing the likelihood across the board. Our results are similar to some previously reported surveys. A study conducted by Chin-Lee and colleagues (2014) reported similar rates of probiotics use in the US (29.9%); however, they did not find a statistically significant relationship between use of probiotics and other variables such as age, sex, ethnicity, education, or income level.^[18] This could be because their sample size was 162 compared to this study which had 1000 survey respondents. Our study demonstrated lower prevalence of probiotics use when compared to a survey study conducted by Draper et al., which showed that 55% of respondents used probiotics in the 3 months before completing the survey.^[19] In a survey conducted in 2013 by the International Food Information Council Foundation, the top three reasons associated with probiotic use by Americans were maintenance of digestive system health, maintenance of immune system health, and help with weight management which is similar to our findings (International Food Information Council Foundation 2013).^[20] In recently released AGA guidelines, probiotics use is recommended for only three GI conditions: Prevention of C. difficile infection for adults and children on antibiotic therapy, improvement of symptoms in patients with pouchitis, and prevention of necrotizing enterocolitis in pre-term infants <37 weeks gestational age. The recommendations are conditional with differing quality of evidence for each of the three indications. For each of the three conditions, specific probiotic strain or combination of strains is recommended based on extensive review and grading of available evidence.^[11] Moreover, in contrast to the previous 2018 American College of Gastroenterology (ACG) recommendations, which suggested use of probiotics to improve global symptoms of bloating and flatulence in patients with IBS, a recent 2020 ACG update on the management of IBS does not support use of probiotics (conditional recommendation and very low quality of evidence).^[21,22] While there is an abundance of clinical studies and reports on using probiotics for various GI diseases (technical review identified close to 9000), their quality and generalizability were poor in many cases, leading to these limited recommendations.^[23] It is also important to mention that general GI health is not one of the recommended uses; however, majority of respondents in our study utilized probiotics for this non-clinical indication. Respondents reported using a variety of probiotics formulations: Pill (36%), yogurt (43%), or other food/drink (18%). This was an interesting finding since most fermented yogurts contain live probiotic cultures but not at a sufficient level of colony-forming units of bacteria and yeast to be considered a “probiotic,” where there is an implication that the product can alter a disease course. Some yogurts are fortified with adequate cultures to be classified as probiotics, and their benefits have been studied in clinical trials in humans.^[24-27] There is ongoing controversy surrounding probiotic-fortified foods making unsubstantiated claims regarding efficacy.^[28,29] While the cost of probiotic-fortified yogurt appears to be lower than the tablet or capsule, when taking dosing regimen into consideration, cost per day is similar and may even be higher with yogurt.^[30] Among all respondents, 25% indicated that probiotics can hurt their health, with 33% unsure. Lack of concern for safety is one of the reasons probiotics gained such prominence in consumers’ self-prescribed wellness regimens. Due to lack of regulatory status as drugs, probiotic safety has not been studied systematically. One major report prepared by the US agency for health-care research and quality in 2011 identified 11,977 publications and further examined 622 studies that reported any adverse effects tracking. This large-scale evidence-based analysis reported no relative risk increase in the overall incidence of adverse events due to short-term probiotic use (RR 1.00; 95% CI: 0.93, 1.07, P = 0.999). Probiotics also did not increase the risk of GI infections or other adverse reactions, including serious reactions (RR 1.06; 95% CI: 0.97, 1.16; P = 0.201). However, the authors caution that despite abundance of studies on probiotic efficacy, systematic evaluation and reporting of safety and adverse events are subpar to make definitive conclusions on probiotic safety in all patient populations.^[31] Therefore, while majority of available evidence suggests that probiotics are safe, in certain patient populations, such as immunocompromised patients or critically ill patients, risks of bacterial or fungal bloodstream infection or GI ischemia need to be considered.^[32] Our study also found very low utilization of pharmacists for over the counter (OTC) product counseling. A survey conducted by the national council on patient information and education and pfizer showed that 38% of patients were unsure how to select the correct OTC products, with 56% turning to primary care or other providers, as well as pharmacists, for advice on OTC product selection.^[33] Our results show that pharmacists may represent a small proportion of health-care providers giving this advice, despite their knowledge, accessibility, and proximity to products and consumers making OTC or probiotic selection. Underutilization of pharmacists for this task represents an important opportunity for building trusting pharmacist-patient relationships and avoiding unnecessary costs to an individual.

There were several limitations to this study. The survey relied on respondents’ self-report, which makes the questions vulnerable to variable interpretation by the survey respondents. Like all surveys, there is the possibility of nonresponse bias. Our sample, while representative of all the dimensions we set out to measure, may differ from the general population. All respondents who said that they did/do take probiotics daily also reported having health insurance [Table 3]. In 2020, 28 million (8.6%) of Americans did not have health insurance; therefore, these results may not be generalizable.^[34] In addition, there were 100 respondents who selected “other reasons” to the question about the reason for probiotic use and there was no follow-up question to elaborate on this response. Their reason for use is unknown and could not be analyzed. The survey also did not ask respondents about the type of chronic illness, they had which is a limitation. In addition, it is unknown whether respondents who answered “yes” to consuming yogurt bought regular yogurt or probiotic-fortified yogurt. Furthermore, this survey was conducted in 2019 and respondent behavior may have changed since then. The results of this study do not reflect potential changes in consumer behavior that were brought on by the coronavirus disease 2019 pandemic.

CONCLUSION

Probiotics are marketed as beneficial for gut health; however, evidence-based indications for their use are limited. This study shows that some US adults are using probiotics for reasons where their benefit is unconfirmed. Pharmacists can play an important role in educating patients about probiotic benefits and curtail potentially unnecessary use of these products.