1. Introduction
Appropriate use of dietary supplements is encouraged as a self-care procedure. However, it has been reported that patients use dietary supplements, including various herbal products, for the treatment of their diseases [
1,
2]. The use of dietary supplements has been reported among patients diagnosed with eye disease, high plasma cholesterol levels, arthritis, and cancer [
3]. It appears that this situation may be the result of a flood of internet misinformation about health—including claims of therapeutic effects of dietary supplements [
4,
5,
6].
The use of dietary supplements for therapeutic purposes may result not only in missed opportunities for appropriate treatments but also in the exacerbation of disease. Moreover, in the case of patients taking pharmaceuticals, interactions between dietary supplements and medicines may occur during digestion, absorption, distribution, and metabolism, with consequent risks to health. Cytochromes P450 (CYP) are a major source of variability in drug-metabolized enzymes and mainly exist in the liver and other tissues. In humans, CYP1, 2, and 3 families are responsible for the drug metabolism in clinical use. The most expressed forms are CYP3A4, CYP2C9, CYP2C8, and CYP2E1 in the liver [
7]. In this regard, CYPs are an important target for interactions between dietary supplements and medicines. For example, it is well known that vitamin K interferes with the anti-coagulant effects of warfarin [
8]. However, vitamin K is not the only food component that interacts with warfarin, which is mainly metabolized by CYP1A2, CYP2C8, CYP2C9, CYP2C19, and CYP3A4 in the liver; food components that affect these CYPs also affect the efficacy of warfarin [
8]. As with warfarin, there have been many reports of adverse interactions with other medicines induced by the consumption of various foods and herbs as supplements [
9,
10,
11]. In addition, it has been reported that certain herbs can themselves cause liver dysfunction [
12]. In light of these findings, attention must be paid to the use of dietary supplements by patients.
However, it is also known that dietary supplements, especially vitamins, minerals, and amino acids, are helpful to support nutritional conditions in elderly people [
13] and cancer patients [
14,
15]. Such individuals cannot obtain enough nutrients from a regular diet because of decreased appetite, polypharmacy, dementia, frailty, poor dentition, or swallowing difficulties [
16]. In addition, prescribed medications may interfere with micronutrient absorption and induce nutritional insufficiencies [
17]. When treating and curing individuals affected by disease, it is important that good nutritional conditions are maintained [
18,
19]. However, even vitamins, minerals, and amino acids can be harmful when taken excessively or when they interact negatively with medicines. For this reason, consultations with healthcare professionals, such as physicians or pharmacists, are important when determining the appropriate use of dietary supplements. However, researchers have found that most patients use dietary supplements without consulting their physicians or pharmacists [
1,
2,
20,
21] and that physicians and pharmacists do not always ask their patients about their use of dietary supplements [
20,
22]. Communication between healthcare professionals and patients is therefore important for the prevention of adverse events caused by inappropriate use of dietary supplements.
In this study, an internet survey was conducted to learn more about the motives, attitudes, and beliefs of patients regarding their usage of dietary supplements for disease treatment and how they perceived their situation regarding consultation with health professionals about their supplement usage.
4. Discussion
This study surveyed awareness of dietary supplement use and consultation status among patients who used dietary supplements for the therapeutic treatment of their disease. The prevalence of dietary supplement use varied across diseases, ranging from 7.7% in cancer to 28.2% in menopausal disorder and from 57.1% in liver disease to 75.1% in rheumatoid arthritis, according to patients who were satisfied with the efficacy of dietary supplements. Furthermore, one-third of patients concomitantly used medicines to treat the diseases that they also used dietary supplements for, and they wished to continue using dietary supplements even after they were provided with risk information about the interaction between dietary supplements and medicines. Despite this, most of them preferred face-to-face consultations with physicians or pharmacists.
The widespread use of complementary and alternative medicines (CAMs) by cancer patients, mainly in the form of herbal medicines and dietary supplements, has been previously reported [
14,
23,
24,
25,
26]. However, in the present study, only 7.7% of cancer patients used dietary supplements. One of the reasons for this discrepancy might be the small number of cancer patients in this survey in the first place, and it may be that these individuals were not serious cancer patients because they participated in an internet questionnaire survey. It has been reported that CAM utilization tends to be higher among patients in advanced cancer stages [
27]. Therefore, it is conceivable that the utilization rate of dietary supplements was unusually low in this study. Second, Agaricus blazei mushroom had been the most popular ingredient for CAM in Japan, but the use of Agaricus blazei supplements has induced severe hepatic dysfunction in cancer patients [
28], and the Ministry of Health, Labour and Welfare has issued a warning to this effect. Because this was also picked up by the media, this might have affected cancer patients’ perceptions of dietary supplements. However, details of the types and stages of their cancers were not asked. Further research is needed to clarify the actual use of dietary supplements by cancer patients, considering their types and stages.
The highest prevalence of dietary supplement use was among menopausal disorder patients, with a total of 28.2%. In a previous survey on the use of supplements claiming female-hormone-like effects, treatment for menopausal symptoms was the most common purpose for which these products were used [
29]. Phytoestrogens (e.g., soy isoflavones, daidzein, red clover isoflavones, and flaxseed extract) are plant-derived compounds that have a similar structure to estradiol and affinity to the estrogen receptor [
30]. Phytoestrogen-containing supplements are therefore sold with the claim that they have female hormone-like effects and thus improve symptoms of menopausal disorder. In addition, Japanese people are familiar with soy products, such as tofu, miso, and natto [
31,
32]. It is thought that this circumstance may lower barriers to the use of soy supplements for menopausal disorders.
The internet was the most common source of information for patients seeking to begin the use of dietary supplements for the therapeutic treatment of their diseases. It has been reported that cancer patients gained information about CAM via the internet and SNS (Facebook) [
26]. At present, to claim therapeutic effects on food labeling and advertisements is illegal in Japan; nevertheless, many such claims for supplements are made on websites without scientific evidence. It is conceivable that people believe such claims and purchase dietary supplements as a result, even though these products actually have no curative effect. In addition, it has been reported that more than half of the health-related information provided by healthcare professionals on Twitter was false [
33]. In addition, the media provides commercials and advertisements for dietary supplements that healthcare professionals recommend, and some of them might be misleading. This situation might be a reason that healthcare professionals could be the motive for dietary supplement use for therapeutic purposes in this study. Misinformation on the website was highlighted during the COVID-19 pandemic and was termed an “infodemic” by the World Health Organization [
34]. Fake news related to COVID-19 prevention (e.g., consumption of salty water, bleach, or garlic for prevention of coronavirus infection) was compounded by low levels of awareness, knowledge, and health literacy; in this regard, SNS (especially Twitter) was found to be the major platform of dissemination [
35].
One of the important findings in this study is that more than half of patients felt that dietary supplements produced therapeutic effects against their diseases, even when the supplements had no such effects. The placebo effect seems to be the main reason why patients reported therapeutic effects of dietary supplements [
36,
37]. They also believed that dietary supplements were safe. Such perceptions might have encouraged them to continue with the use of dietary supplements and medicines, even after they were provided with risk information about the interaction between dietary supplements and medicines. Despite this, patients in this survey still wished to consult with physicians and pharmacists on a face-to-face basis. More consultation with healthcare professionals could improve this situation. However, knowledge about dietary supplements amongst such professionals is inadequate, and healthcare professionals lack confidence in consulting about dietary supplements [
38,
39]. Indeed, 14.5% of respondents in our survey began to use dietary supplements for therapeutic purposes after receiving recommendations from healthcare professionals. Even though some dietary supplements, especially vitamin/mineral supplements, might be helpful for nutritional treatments in patients, the use of dietary supplements for therapeutic purposes is not recommended. Better education about dietary supplements is needed for healthcare professionals.
There are some limitations to this study. First, patients’ status, whether they were inpatients or outpatients, was not asked. This might affect the prevalence and purpose of dietary supplement use [
1]. However, the majority of participants in our actual survey were patients with dyslipidemia, hypertension, mental disorders, and diabetes mellitus, so it is supposed that most patients were outpatients. Second, there was no question about the clinical efficacy of dietary supplement use. Even though patients reported satisfaction with the efficacy of their dietary supplements, most of them did not declare their supplement usage to their physicians or pharmacists, and it was unclear whether dietary supplements were actually effective for therapeutic purposes. Communication between healthcare professionals and patients is important for the appropriate use of dietary supplements. Lastly, because this survey was conducted via the internet, caution should be exercised in generalizing the results, especially with respect to older generations.