*Editorial* **The Alcohol Hangover Research Group: Ten Years of Progress in Research on the Causes, Consequences, and Treatment of the Alcohol Hangover**

**Joris C. Verster 1,2,\*, Lizanne Arnoldy 1,2, Sarah Benson 2, Andrew Scholey <sup>2</sup> and Ann-Kathrin Stock 3,4**


Received: 2 November 2020; Accepted: 2 November 2020; Published: 16 November 2020

**Abstract:** The alcohol hangover is defined as the combination of negative mental and physical symptoms, which can be experienced after a single episode of alcohol consumption, starting when blood alcohol concentration (BAC) approaches zero. Here, we present the book "The alcohol hangover: causes, consequences, and treatment", written to celebrate the 10th anniversary of the Alcohol Hangover Research Group (AHRG), summarizing recent advances in the field of alcohol hangover research.

**Keywords:** alcohol; hangover; causes; consequences; treatments

The alcohol hangover is defined as the combination of negative mental and physical symptoms, which can be experienced after a single episode of alcohol consumption, starting when blood alcohol concentration (BAC) approaches zero [1,2]. Despite the fact that the alcohol hangover is the most commonly reported negative consequence of alcohol consumption [3], a relatively small amount of research has been devoted to this topic. The latter is surprising as the alcohol hangover is associated with negative mood, cognitive impairment, and physical effects [4]. Here, we present the book "The alcohol hangover: causes, consequences, and treatment", written to celebrate the 10th anniversary of the Alcohol Hangover Research Group (AHRG).

In 2010, the AHRG was founded to raise the profile of alcohol hangover research [5]. The AHRG scientific meetings aim to bring together active and internationally diverse alcohol hangover researchers to generate discussion on recent developments in hangover research. The objectives of these meetings are to discuss recent findings and future research directions, to raise the profile of alcohol hangover research, and to start new research collaborations. Over the past 10 years, 11 successful AHRG meetings have been held across the world [5–11]. In 2010, the first AHRG meeting was held as a satellite symposium of the Research Society on Alcoholism conference in San Antonio, Texas, USA. Subsequent AHRG meetings were held in Paris in 2010 (France), Utrecht in 2011 (The Netherlands), Wolfville in 2012 (Canada), Keele in 2013 (UK), Bellevue in 2014 (USA), Perth in 2015 (Australia), New Orleans in 2016 (USA), Utrecht in 2017 (The Netherlands), Utrecht in 2018 (The Netherlands), and Wailoaloa Beach, Nadi in 2019 (Fiji). Proceedings of most of the AHRG meetings have been published [5–11].

In the decade since its inception, the AHRG has moved the field forward significantly. The inaugural meeting resulted in the publication of a consensus paper on best practice in hangover research, and an evaluation of the gaps in knowledge that should be addressed by future research [12]. Among the key accomplishments was the development of a definition for the alcohol hangover [1]. In addition, international research collaborations resulted in a significant increase in the number of published articles on the alcohol hangover (see Figure 1).

**Figure 1.** Published articles on the alcohol hangover. Number of publications taken from PubMed (https://pubmed.ncbi.nlm.nih.gov, assessed on 13 October 2020), searching for "alcohol hangover". In 2010 (red bar), the Alcohol Hangover Research Group (AHRG) was founded.

In conjunction with its 10th anniversary, a Special Issue of the Journal of Clinical Medicine on the alcohol hangover was curated by members of the AHRG. After peer-review, twenty-five articles were accepted for the Special Issue, and this collection is combined in this book, entitled "The alcohol hangover: causes, consequences, and treatment".

The first five articles discuss significant methodological advances. In the first article, an update of the definition of the alcohol hangover is discussed [2]. The update of the definition was necessary, as current thinking about the traditional threshold for experiencing hangovers (a BAC of at least 0.11%) had changed. The new consensus, which is discussed in article two, reflects observations that hangovers can be experienced at any BAC [13].

Article three discusses the advantages and limitations of naturalistic study designs and their implementation in alcohol hangover research [14]. In contrast to traditional, controlled clinical trials, hangover research often applies a naturalistic study design in which investigators do not interfere with the drinking session. The article explains why this is important in terms of ecological validity (i.e., a real-life drinking session at a venue of choice, with corresponding behaviors and real-life alcohol consumption levels), and to what extent the naturalistic design has an impact on reliability and validity of study outcomes in comparison to highly controlled clinical trials. Article four discusses the assessment of overall hangover severity [15]. Traditional research has used composite symptom scales to assess hangover severity. The advantage of this approach is that information is gathered about the presence and severity of individual hangover symptoms. However, the research discussed in article four demonstrates that there are several disadvantages to this approach (e.g., the choice of included individual symptoms in a scale determines the overall hangover severity score, which therefore differs between currently used scales). The findings suggest that a one-item hangover severity assessment has advantages over composite symptom scale scores. In the final part of this section, article five discusses the prevalence of hangover resistance according to two methods for calculating estimated

BAC [16]. The findings discussed show that different equations used to calculate estimated BAC yield different outcomes. The latter is an important finding, and future consensus is warranted among AHRG members to ensure harmonization in reporting estimated BAC to allow direct comparisons of research from different groups.

The next two articles discuss the "causes" of alcohol hangover, and articles review the current knowledge on the pathology of the alcohol hangover. Whereas previous reviews on the causes of the alcohol hangover relied heavily on research data from the 1970s by the Finnish group Ylikhari et al., [17–19], the articles in this book provide major advances in the understanding of the pathology of the alcohol hangover. Article six reviews the role of alcohol metabolism in the pathology of the alcohol hangover [20], and article seven presents new data on the inflammatory response to alcohol consumption and its contribution to the alcohol hangover [21]. The data reveal that the rate of ethanol metabolism is an important predictor of next day hangover severity. In addition, the impact of oxidative stress and the balance between free radicals and antioxidants is discussed, as well as the role of acetaldehyde in eliciting an inflammatory response to alcohol (e.g., the release of cytokines), which ultimately elicits the alcohol hangover.

The following six articles discussing a variety of factors ('correlates') that may exacerbate or attenuate hangover symptoms. Article eight presents data on the effect of dietary nutrient intake on alcohol hangover severity [22]. Dietary nutrients are frequently included as ingredients in hangover treatments. Therefore, it is of interest to verify which of these, taken as part of daily diet, are associated with experiencing less severe hangovers. The results indicate that drinkers who consume food rich in zinc and nicotinic acid report less severe hangovers. Both nutrients are involved in the breakdown of ethanol and acetaldehyde, which may explain these findings. Article nine discusses the fact that different drinking levels are associated with experiencing differential levels of hangover severity [23]. The data confirm previous findings that hangover symptom severity is most severe among heavy and chronic drinkers. Article 10 discusses the interesting finding that when individuals experience hangovers more frequently, their severity increases [24]. Contrary to the common notion that drinkers get used to the amount of alcohol they consume and become "immune" to the adverse effects of drinking at this level, this observation suggests that reverse tolerance develops. Article 11 discusses the finding that hangover symptom severity is to some extent determined by the level of pain catastrophizing of drinkers [25]. Reporting higher levels of pain catastrophizing, in particular rumination, was associated with experiencing more severe hangovers. This finding is important, as it may have implications for the percentage of drinkers reporting being hangover resistant, and illustrates that the psychological perception of "what is pain?" and "what is mild, moderate, or severe?" differs between individuals, and thus impacts the reporting of the presence and rating of the severity of hangover symptoms. The latter is important as to date, no objective assessments for alcohol hangover (symptom) severity are available, and researchers have to rely on subjective reporting. Article 12 reviews possible sex differences in the presence and severity of hangover symptoms [26]. In contrast to acute alcohol effects (e.g., greater ratings of subjective intoxication in women), sex differences in the next-day effects of alcohol consumption appear to be limited. Finally, article 13 discusses the impact of mood and subjective intoxication on hangover severity [27]. Whereas baseline mood and mood while drinking had no relevant impact on next-day hangover severity, subjective intoxication (i.e., the level of drunkenness) showed to be a strong determinant of hangover severity.

Eleven subsequent articles discuss various aspects of cognitive, psychomotor, and physical performance during the hangover state ('consequences'). Article 14 describes the results of a study that assessed cognitive functioning and mood, applying a naturalistic study design [28]. The study demonstrates that participants can be tested at home using mobile technology to collect data. This methodology has clear advantages for participants (they do not have to come to the research center) and logistics for researchers (no lab space needed). Article 15 describes an investigation in which participants were approached on premise after consuming alcohol [29]. Both objective (breathalyzer) and subjective assessments (interview) of alcohol consumption and intoxication were

made, and subjects were invited to complete online assessments of hangover severity and cognitive performance the next morning. Articles 14 and 15 demonstrate the utility of mobile/online assessments for hangover research. Future direct comparisons should investigate if validity and reliability of at home testing are equal to that of testing in controlled laboratory environments. Driving a car is one of the common daily activities that are potentially dangerous, as the use of alcohol can significantly impair driving performance and increase the chances of having an accident. Numerous studies have demonstrated that driving a car or bicycle while intoxicated is unsafe [30,31]. Previous research has also shown that simulated highway driving whilst experiencing a hangover is significantly impaired [32]. Despite this knowledge, a substantial number of both private and professional drivers continue to drive a car while experiencing a hangover [33]. Article 16 discusses the impact of alcohol hangover on simulated driving performance during a "commute to work" [34]. The study also revealed that during a relatively short drive, driving performance was significantly impaired while hungover. Driving is also a clear example of multitasking. In article 17, Benson et al. investigate alcohol hangover effects on another behavior, which can be translated to everyday workload, namely multitasking [35]. A hangover was associated with worse mood (reduced alertness and contentment, and increased anxiety and mental fatigue), and poorer multitasking performance, with greater effort needed to complete the tasks compared to the non-hangover condition. Interestingly, stress reactivity was not differentially affected by the hangover. The effects of alcohol hangover on executive functions are discussed in article 18. The investigation by Gunn et al. found that the alcohol hangover impairs core executive function processes that are important for everyday behaviors, such as decision-making and planning [36].

Affected daily behaviors and cognitive functioning during the hangover may ultimately be related to impaired information processing during the hangover. Three articles from Stock and colleagues investigated this in more detail. In article 19, they demonstrate that the alcohol hangover differentially modulates the processing of relevant and irrelevant information [37], and article 20 discusses findings showing that the alcohol hangover slightly impairs response selection but not response inhibition [38]. Finally, article 21 shows that the alcohol hangover does not alter the application of model-based and model-free learning strategies [39]. Together, these three articles provide further insights into the nature of slowed and impaired information processing during a hangover.

Whereas much research is devoted to cognitive aspects of the alcohol hangover, our understanding of the effects on physical state and sports performance has been limited. In article 22, Devenney et al. [40] report on physical activity level assessments comparing hangover and alcohol-free days. Using mobile technology, the continuous assessments of activity levels showed that during hangover subjects performed at lower activity levels, and vigorous activities were absent. Additionally, the assessments revealed that sleep quality was significantly poorer after the evening of alcohol consumption. Article 23 discusses the results of a study investigating the effects of alcohol consumption and hangover on endurance performance. Subjects on holiday walking the 18 km Samariá Gorge on the island of Crete in Greece were surveyed before and after they completed the walk. The analysis revealed that a variety of factors may predict walking performance and effort required to perform the walk, ranging from baseline physical state, immune fitness, to past night sleep quality, and also alcohol consumption and hangover severity [41].

Two articles discuss the outcomes of recent clinical trials that evaluated potential new hangover treatments. Despite a clear demand from drinkers who experience hangovers [42], currently there are no hangover treatments where the effectiveness has been demonstrated in independent double-blind, placebo-controlled clinical trials [43–45]. The increasing knowledge on the pathology of the alcohol hangover has resulted in focusing treatment development on products that aim to reduce the inflammatory response to alcohol and/or to enhance alcohol metabolism. In article 24, results of a pilot study are presented examining the effectiveness of SJP-005, a combination product of naproxen and fexofenadine, aiming to prevent hangovers by reducing the inflammatory response to alcohol consumption [46]. In article 25, the effects of Rapid Recovery are discussed—a hangover treatment aiming to reduce oxidative stress—and thereby preventing hangovers or reducing their severity [47].

Taken together, "The alcohol hangover: causes, consequences, and treatment" provides a comprehensive overview of current insights and research into many aspects of the alcohol hangover. The book highlights the advances in the field over the past decade, fueled by successful collaborations of researchers of the Alcohol Hangover Research Group and others investigating the interesting yet sometimes puzzling phenomenon of the alcohol hangover.

#### **Funding:** This research received no external funding.

**Acknowledgments:** This Special Issue and forthcoming book was composed to celebrate the 10th anniversary of the Alcohol Hangover Research Group. We wish to thank all members of the AHRG for their support and input.

**Conflicts of Interest:** S.B. has received funding from Red Bull GmbH, Kemin Foods, Sanofi Aventis, Phoenix Pharmaceutical and GlaxoSmithKline. Over the past 36 months, A.S. has held research grants from Abbott Nutrition, Arla Foods, Bayer, BioRevive, DuPont, Fonterra, Kemin Foods, Nestlé, Nutricia-Danone, Verdure Sciences. He has acted as a consultant/expert advisor to Bayer, Danone, Naturex, Nestlé, Pfizer, Sanofi, Sen-Jam Pharmaceutical, and has received travel/hospitality/speaker fees from Bayer, Sanofi and Verdure Sciences. Over the past 36 months, J.C.V. has held grants from Janssen and Sequential Medicine, and acted as a consultant/expert advisor to More Labs, Red Bull, Sen-Jam Pharmaceutical, Toast!, Tomo, and ZBiotics. A.K.S. has received funding from the Daimler and Benz Foundation. L.A. has no conflicts of interest to declare.

#### **References**


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© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

### *Communication* **Updating the Definition of the Alcohol Hangover**

#### **Joris C. Verster 1,2,3, Andrew Scholey 3, Aurora J. A. E. van de Loo 1,2, Sarah Benson <sup>3</sup> and Ann-Kathrin Stock 4,\***


Received: 26 February 2020; Accepted: 14 March 2020; Published: 18 March 2020

**Abstract:** In 2016, the Alcohol Hangover Research Group defined the alcohol hangover as "the combination of mental and physical symptoms experienced the day after a single episode of heavy drinking, starting when blood alcohol concentration (BAC) approaches zero". In the light of new findings and evidence, we carefully reviewed the different components of that definition. Several studies demonstrated that alcohol hangovers are not limited to heavy drinking occasions. Instead, data from both student and non-student samples revealed that at a group level, alcohol hangover may occur at much lower BAC levels than previously thought. Regression analysis further revealed that for individual drinkers, the occurrence of hangovers is more likely when subjects consume more alcohol than they usually do. However, hangovers may also occur at a drinker's usual BAC, and in some cases even at lower BAC (e.g. in case of illness). We also carefully reviewed and modified other parts of the definition. Finally, hangovers are not necessarily limited to the 'next day'. They can start at any time of day or night, whenever BAC approaches zero after a single dinking occasion. This may also be on the same day as the drinking occasion (e.g. when drinking in, or until the morning and subsequently having a hangover in the afternoon or evening). To better reflect the new insights and sharpen the description of the concept, we hereby propose to update the definition of the alcohol hangover as follows: "The alcohol hangover refers to the combination of negative mental and physical symptoms which can be experienced after a single episode of alcohol consumption, starting when blood alcohol concentration (BAC) approaches zero", and recommend to use this new definition in future hangover research.

**Keywords:** alcohol; hangover; definition

#### **1. Introduction**

In 2016, the Alcohol Hangover Research Group defined the alcohol hangover as "the combination of mental and physical symptoms experienced the day after a single episode of heavy drinking, starting when blood alcohol concentration (BAC) approaches zero" [1]. The development of this definition was a welcome and necessary addition to the substance abuse and addiction research field. Since then, ongoing research has generated new insights and there have been continuous discussions among researchers about how to further improve the definition of the alcohol hangover. Updating the current definition is necessary to describe the alcohol hangover more precisely against the background of new findings in the field. These specifications address recently discussed issues and further remove ambiguity from the previous wording.

#### **2. Heavy Drinking**

The most important discussion pertains to the amount of alcohol consumption that is required to elicit a hangover. Given this discussion, there is controversy about the word 'heavy' in the definition of alcohol hangover. First, the word 'heavy' is unspecific, as it does not define what exact amount of alcohol should actually be consumed to elicit a hangover. Second, it suggests that hangovers occur only when large amounts of alcohol are consumed. However, the Alcohol Hangover Research Group recently reached a consensus to abandon the criterion that a BAC of 0.11% or higher is needed to provoke a hangover [2]. This conclusion was drawn based on an increasing body of evidence showing that drinkers also report hangovers at BACs that are much lower than both the suggested threshold of 0.11%, as well as the binge drinking threshold of 0.08% issued by the National Institute on Alcohol Abuse and Alcoholism (NIAAA) [3].

For example, Verster et al. [4] found that non-student subjects (*N* = 176) who consumed a mean (SD) of 3.0 (1.8) alcoholic drinks (10 g ethanol each) reported considerable next-morning hangover severity, i.e., a mean (SD) overall hangover severity score of 4.6 (2.4) on a 0–10 scale. Despite this, their peak estimated BAC was 0.03%. In another student sample, Kruisselbrink et al. [5] found significant hangover symptoms in subjects having consumed as few as two beers, with a mean maximum BAC of 0.036%. These observations are neither consistent with 'heavy drinking' in the definition of the alcohol hangover, nor with the binge drinking threshold suggested by the NIAAA. Surveys completed by large student samples from Canada (*N* = 5540) and The Netherlands (*N* = 6002) further confirmed that alcohol hangovers are reported across all BAC levels [6,7]. Thus, hangovers may occur at any reasonable BAC level, and are not limited to 'heavy' drinking only. Given this, we need to modify the current definition of the alcohol hangover and omit the referral to heavy drinking.

#### **3. The Concept of Alcohol Hangover Versus Risk Factors and Possible Causes**

When developing a definition, it is vital to accurately describe the concept (i.e., alcohol hangover). Furthermore, a proper definition of a phenomenon should not contain potential risk factors for its occurrence. There are many risk factors for hangover including, but not limited to, the amount of consumed alcohol (compared to normal), peak BAC, congener content of drinks, smoking, activities during drinking (e.g. dancing or sitting in a bar), or the emotional state during drinking. While these risk factors are of course important to investigate and mention in relation to alcohol hangover, they should not be included in a definition of the concept itself, as the observation/diagnosis of a condition should be separate from the risk/likelihood that it will occur. It is however important to still refer to 'alcohol consumption' in the definition of alcohol hangover as this behavior is mandatory to elicit the condition (rather than a mere risk factor).

Evaluating hangover experiences from individual drinkers has shown that developing a useful, short, and accurate description of the relevant amount of alcohol intake to elicit a hangover is not straightforward. First of all, the presence and severity of alcohol hangovers may vary from day to day [8], even when the same amount of alcohol is consumed and the same BAC is reached. In line with this, regression analyses revealed that neither the amount of consumed alcohol, nor BAC, were strong predictors of hangover severity [2]. Instead, the relative increase in alcohol consumption, as compared to what subjects normally consume on a typical drinking occasion, was the best predictor of overall hangover severity [2]. Thus, the chances of having a hangover are significantly increased when drinking more alcohol than usual, whatever the usual amount consumed. However, including the phrase 'relatively elevated amounts of alcohol consumption' into the definition would exclude a substantial amount of drinkers who also experience hangovers, but do not fulfill this criterion. For example, there are drinkers who almost always experience a hangover, also when only drinking their usual amount of alcohol. One of the many potential reasons for this could be deficient metabolization of alcohol and/or its metabolite acetaldehyde in the liver. Genetic variation in alleles for alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH), which are the enzymes necessary for metabolizing ethanol into acetaldehyde and further into acetate, may account for this. Twin studies showed that heritability of this genetic variation is related to about 45% of the reported hangover severity [9,10]. In this context, in populations of Asian descent, subjects with ALDH2\*2 alleles, i.e., those who breakdown acetaldehyde more slowly, usually report significantly worse hangovers [11,12], and are more likely to experience hangovers at lower alcohol consumption levels than others. In such hangover-sensitive drinkers, the amount of alcohol does not need to be elevated to elicit a hangover. Aside from this, hangovers may also occur when drinking less alcohol than usual on a given occasion. This might for example be the case if subjects experience illness or reduced immune fitness [13,14], or in case of elevated negative mood while drinking [15,16]. It is hence challenging to encompass the different scenarios that may result in a hangover in a modified definition, without making it very lengthy. We therefore propose to substitute 'heavy drinking' with 'alcohol consumption' without any further reference to the amount consumed. Further, to more accurately reflect the day-to-day variability in the likelihood of developing a hangover despite more or less equal circumstances [8], we further propose to change 'experienced' into 'which can be experienced'. This also acknowledges the fact that about 10% to 20% of drinkers report not having a hangover, even after consuming large amounts of alcohol [6,7].

#### **4. Alcohol Hangover Symptoms**

The definition refers to a 'combination of mental and physical symptoms'. Hangover symptoms are generally perceived to be negative, but the original wording does not specify whether these symptoms are expected to be negative or positive. Therefore, we suggest to modify this as a 'combination of negative mental and physical symptoms'. In line with previous discussions [1], hangover symptoms are not listed as part of the definition. Symptoms vary between drinkers and between drinking occasions, even when same amounts of alcohol are consumed [8,17]. Including specific symptoms instead of the general description 'combination of negative mental and physical symptoms' would thus significantly limit the applicability of the definition.

#### **5. Timing of Drinking**

The previous definition states that hangover is 'experienced the day after ... ', which was included to clearly differentiate the intoxication phase from the hangover phase. In the vast majority of cases, the hangover starts when waking up after an afternoon, evening, or night of drinking, followed by a period of sleep. Yet, this definition would not properly match cases where an individual drinks past midnight, in the morning, or during the day [18]. For example, a UK study revealed that almost 20% of all 'drinking occasions' took place before 5:00 p.m. [19]. In these instances, drinkers may experience a hangover in the afternoon or evening of the same day. We therefore decided to omit the next day criterion and changed the definition to 'experienced after'.

#### **6. Di**ff**erentiating between Alcohol Hangover and Withdrawal**

The definition refers to 'a single episode ... '. This was included to differentiate hangovers in social drinkers from withdrawal symptoms experienced by individuals with alcohol use disorders (i.e., alcoholism), who tend to not only engage in alcohol binges but also maintain a rather steady baseline level of alcohol consumption with continuous drinking for several days, or even longer. This leads to extensive homeostatic adaptations in the regulation of many vital parameters as well as neuroadaptive processes [20], which foster the development of alcohol tolerance. These counter-regulatory mechanisms require clinical treatment as they may cause life-threatening complications when the BAC approaches zero. In contrast to individuals with alcohol use disorder, social drinkers lack such extensive tolerance, as they do by definition not engage in such continuous drinking. Given the functional differences in the symptom-associated drinking patterns as well as the underlying physiological mechanisms, we therefore decided not to alter this part of the definition.

#### **7. Di**ff**erentiating between Alcohol Hangover and Intoxication**

The definition states that hangover is 'starting when blood alcohol concentration (BAC) approaches zero'. This is crucial in order to clearly distinguish between alcohol intoxication and alcohol hangover on the basis of timing. We did therefore not alter this part of the definition.

#### **8. Conclusions**

We hereby propose to update the definition of alcohol hangover as follows: "The alcohol hangover refers to the combination of negative mental and physical symptoms which can be experienced after a single episode of alcohol consumption, starting when blood alcohol concentration (BAC) approaches zero".

**Author Contributions:** Conceptualization, J.C.V., A.S., A.-K.S. writing—original draft preparation, J.C.V.; writing—review and editing, J.C.V., A.S., A.-K.S., A.J.A.E.v.d.L. and S.B. All authors have read and agreed to the published version of the manuscript.

**Conflicts of Interest:** S.B. has received funding from Red Bull GmbH, Kemin Foods, Sanofi Aventis, Phoenix Pharmaceutical and GlaxoSmithKline. Over the past 36 months, A.S. has held research grants from Abbott Nutrition, Arla Foods, Bayer, BioRevive, DuPont, Kemin Foods, Nestlé, Nutricia-Danone, Verdure Sciences. He has acted as a consultant/expert advisor to Bayer, Danone, Naturex, Nestlé, Pfizer, Sanofi, Sen-Jam Pharmaceutical, and has received travel/hospitality/speaker fees Bayer, Sanofi and Verdure Sciences. Over the past 36 months, J.C.V. has held grants from the Dutch Ministry of Infrastructure and the Environment, Janssen, Nutricia, and Sequential, and acted as a consultant/expert advisor to Clinilabs, Morelabs, Red Bull, Sen-Jam Pharmaceutical, Toast!, and ZBiotics. A.K.S. has received funding from Daimler and Benz.A.J.A.E.V.D.L. has no conflicts of interest to declare.

#### **References**


© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

#### *Communication*
