Physiological Benefits and Performance of Sea Water Ingestion for Athletes in Endurance Events: A Systematic Review

urance events, athletes have limited access to uid intake, such as ultra- endurance running. For this reason, it is necessary to establish an adequate hydration strategy for this type of long-duration sporting event. Indeed, it seems that the intake of seawater is a suitable hydration alternative to improve post-exercise recovery in this type of endurance event. This seawater is characterized by being a deep natural mineral water of moderate mineralization, which is usually extracted from a depth of about 700 m. Therefore, the aim of this systematic review is to evaluate

sporting event. Indeed, it seems that the intake of seawater is a suitable hydration alternative to improve post-exercise recovery in this type of endurance event. This seawater is characterized by being a deep natural mineral water of moderate mineralization, which is usually extracted from a depth of about 700 m. Therefore, the aim of this systematic review is to evaluate the ef cacy of seawater consumption in both performance and post-exercise recovery in long-duration sport events. A systematic and comprehensive literature search was performed in PubMed, Scopus, and Web of Science in September 2022. Initially, 8 out of 558 articles met the inclusion criteria. Among these eight studies, six were randomized clinical trials, and two were observational studies (one cross-sectional and one prospective study in well-conditioned student athletes). The results showed that deep sea water consumption accelerated the recovery of aerobic capacity and leg muscle capacity on running performance. In addition, the lactate production after the running exercise in seawater was signi cantly lower than in pure water. In conclusion, the present review demonstrates that seawater consumption could signi cantly improve the capacity of recovery after exercise. Keywords:exercise physiology; endurance exercise; sweating; hydration 1. Introduction Nowadays, endurance sporting events are experiencing an increase in popularity, especially during the summer season [1]. This situation would be de ned as a hostile environment where the body is subjected to a prolonged and demanding effort, resulting in a state of dehydration within minutes [2]. Indeed, in triathlon events, in the swimming and running stages, due to their dynamic nature, uid intake is limited [3]. For this reason, an ef cient hydration strategy must be established [4]. This is to avoid a signi cant negative impact on both aerobic performance [5] and athlete health [6] due to progressive dehydration combined with hyperthermia [7]. In addition, the amount of uid consumed and its composition should be carefully considered. Indeed, the excessive consumption of liquids without the necessary composition can induce a state of hyponatremia [8] and Nutrients2022,14, 4609.

[6] due to progressive dehydration combined with hyperthermia [7]. In addition, the amount of uid consumed and its composition should be carefully considered. Indeed, the excessive consumption of liquids without the necessary composition can induce a state of hyponatremia [8] and Nutrients2022,14, 4609.

Nutrients2022,14, 4609 2 of 15 rehydration with an electrolyte-enriched drink may reduce susceptibility to sudden painful involuntary contractions [9]. Therefore, both the volume of the rehydration uid and its composition are critical for maintaining whole body uid homeostasis. Currently, a hydration alternative that is gaining popularity in the sports community is the intake of deep seawater (DSW) [10]. This seawater is characterized by being a deep natural mineral water of moderate mineralization, which is usually extracted from a depth of about 700 m [11]. This is because deep-ocean mineral water contains components that could complement and increase human recovery following an exhaustive physical challenge [12]. Although water is suf cient to rehydrate after short-term acute effort, in the case of endurance events, it may be insuf cient and should be supplemented with the consump- tion of some type of meal that restores the loss of electrolytes. Indeed, such long-duration events generate large sweat losses, which induce signi cant salt elimination. Therefore, a rehydration program should be undertaken to restore electrolyte losses, leading to ad- equate recovery [13]. Stasiule et al. [11] reported that ingestion of deep mineral water could accelerate the recovery of aerobic capacity and leg muscle power compared with the ingestion of water alone [11]. In addition, it has been shown that desalinated ocean mineral water, taken from 662 m below sea level, can substantially accelerate the recovery of aerobic capacity and lower-body muscle power after a prolonged bout of dehydrating exercise [12]. DSW is mainly characterized by a high percentage of minerals such as magnesium (Mg). Indeed, Mg de ciency may potentiate exercise-induced muscle damage and stress, as well as exacerbate in ammation through an increase in the secretion of pro-in ammatory cy- tokines [14–16]. However, the evidence for the bene cial effects of DSW is still limited. This is because it has not been thoroughly evaluated in endurance sports, such as the triathlon, with the compounding factor that it has limited access to liquids. Several studies have shown that a marked state of mild to moderate hypohydration occurs during ultramarathon running competitions [17–20]. This might be

evidence for the bene cial effects of DSW is still limited. This is because it has not been thoroughly evaluated in endurance sports, such as the triathlon, with the compounding factor that it has limited access to liquids. Several studies have shown that a marked state of mild to moderate hypohydration occurs during ultramarathon running competitions [17–20]. This might be because not enough uid was ingested to compensate for sweat losses during exercise [21]. When combined with hyperthermia, this can cause cardiovascular instability, such as reduced plasma volume, cardiac lling, and stroke volume [7,22]. Consequently, dehydration may induce a stress response and, thus, suppress immune function [23–25], and even increase exercise-induced in ammatory responses [26]. Dehydration, in particular, can cause a sys- temic response of cytokine production and an imbalance between pro-in ammatory and anti-in ammatory cytokines in the system [23], which could negatively interfere with the regeneration of damaged tissue after exercise [22]. Therefore, it would be interesting to report how DSW consumption alters the in am- matory response and the muscular damage induced by exercise and its relationships with post-exercise recovery. In summary, the authors of this systematic review are interested in nding out if DSW consumption could provide an adequate hydration alternative, which could improve performance and recovery periods post-exercise. Therefore, the main pur- pose of the present systematic review was to evaluate the ef cacy of a hydration strategy using DSW consumption, mainly in endurance events. 2. Materials and Methods 2.1. Search Strategy Based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [27], this systematic review was conducted. An exhaustive bibli- ographic search was conducted in three databases (Web of Science, PubMed, and Sco- pus), from 1 January 2000 to 31 July 2022. As there has been no systematic review of seawater consumption in endurance events, we have set the starting year as 2000 in order to identify as many studies from the last 22 years as possible. A search strat- egy for Web of Science, PubMed, and Scopus is shown in Table. This systematic re- view was listed on the PROSPERO

2022. As there has been no systematic review of seawater consumption in endurance events, we have set the starting year as 2000 in order to identify as many studies from the last 22 years as possible. A search strat- egy for Web of Science, PubMed, and Scopus is shown in Table. This systematic re- view was listed on the PROSPERO (International prospective register of systematic re- views) website on 9 July 2022, with the following record CRD42022341587. Available

Nutrients2022,14, 4609 3 of 15 from: (accessed on 30 August 2022). Table 1.Search strategy in databases. Database Search Strategy Limits Filters Web of Science (ALL (deep sea water AND endurance exercise OR deep-sea water AND sweating OR deep-sea water AND sweating OR deep sea mineral water AND endurance exercise OR deep sea mineral water AND sweating OR deep sea mineral water AND hydration)) Publication date, 2000–2022, English language, Article, Search strategy (Topic) 54 items ltered PubMed (Deep sea water OR deep sea mineral water) AND (endurance exercise OR sweating OR hydration) Publication date, 1 January 2000–31 July 2022, Humans, Adults: 18–50 years, English language, Search strategy (All Fields) 97 items ltered Scopus TITLE-ABS-KEY (deep AND sea AND water AND hydration) OR (deep AND sea AND water AND hydration AND endurance AND exercise) OR (deep AND sea AND water AND hydration AND endurance AND exercise AND barrier) OR (deep AND sea AND water AND hydration AND endurance AND exercise) AND LANGUAGE (English) AND (PUBYEAR > 2000) Publication date, 2000–2022, English language, Article or review, Search strategy (TITLE-ABS-KEY) 407 items ltered 2.2. Criteria Used for Selection In the selection process, the following criteria were used: (i) English-written articles; (ii) databases derived from Web of Science, PubMed, and Scopus; (iii) human studies; (iv) original articles: clinical trials; randomized controlled trials (RCTs); quasi-experimental studies; long-term, prospective, and cross-sectional studies; (v) articles published between January 2000 and July 2022. Exclusion criteria included: (i) studies that included persons suffering from pathologies; (ii) studies that included children under the age of 18 and older adults (+50 years); (iii) studies that included supplements or dietary interventions; (iv) case studies, case reports, letters to the editor, systematic reviews and meta-analyses, and narrative reviews. Training subjects were not restricted in terms of their body composition. Following the removal of duplicates, eligibility was determined by reading the title and abstract, and if still potentially eligible, by reading the full text. 2.3. Reliability and Extraction of Data Three independent reviewers conducted the search (Jerânimo Aragân-Vela, Olivia Gonz¡lez-Acevedo, and Julio Plaza-Diaz). The authors read the titles and abstracts of all the articles that

terms of their body composition. Following the removal of duplicates, eligibility was determined by reading the title and abstract, and if still potentially eligible, by reading the full text. 2.3. Reliability and Extraction of Data Three independent reviewers conducted the search (Jerânimo Aragân-Vela, Olivia Gonz¡lez-Acevedo, and Julio Plaza-Diaz). The authors read the titles and abstracts of all the articles that were retrieved. In order to resolve disagreements regarding eligibility, a meet- ing was held. As part of the analysis of each included study, the following information was collected: the rst author, the publication year, the type of study, the objective, the number of subjects, gender, age, when the information was available, type of exercise, how the exercise was performed, biochemical markers of fatigue, the in ammatory response, the variables in sports performance (exercise recovery periods, mainly in endurance events), and the main conclusions and ndings of DSW consumption. Based on the type of study (low, medium, or high intensity, or long-duration exercise interventions, and humans that consumed DSW), the selected articles were categorized. A review of the results of the studies that met the selection criteria for their recovery was conducted.

Nutrients2022,14, 4609 4 of 15 2.4. Evaluation of the Validity and Reliability of the Evidence We assessed the risk of bias using the Joanna Briggs Institute's Critical Appraisal Tool for Systematic Reviews developed by the Joanna Briggs Institute, Adelaide, Australia [28]. To summarize, this tool contains four speci c checklists for different types of studies (i.e., cross-sectional, quasi-experimental, cohort, and RCTs studies). For each of them, there are four possible answers: “yes” (criterion met) and “no” (criterion not met). There were eight items for cross-sectional studies, nine items for quasi-experimental, and thirteen items for RCTs. Based on the above criteria, the studies are considered as “low-quality” evidence when 49% of the items are classi ed as “yes” (criterion met). As a result, articles are considered “medium-quality” evidence if 50–74% of the items are scored as “yes” and “high-quality” evidence when 75% of the items are scored as “yes”. The total percentage excludes the answers “not applicable” and “not clear” [29–31]. Each of the three reviewers assessed the quality of the studies separately. For the purpose of resolving possible differences between the reviewers, a consensus meeting was organized. 3. Results A ow chart illustrating the selection of reporting elements for systematic reviews is depicted in Figure. The three databases assessed contained a total of 558 studies. Based on the title and abstract and duplicates, 195 studies were excluded, and 23 studies were excluded for being outside the scope of the review. The eligibility of 22 studies was assessed. Based on the exclusion criteria, eight studies were included in the analysis. There were six RCTs, and two observational studies (one cross-sectional and one well-conditioned student-athletes study).Nutrients 2022, 14, x FOR PEER REVIEW 4 of 16 A review of the results of the studies that met the selection criteria for their recovery was conducted. 2.4. Evaluation of the Validity and Reliability of the Evidence We assessed the risk of bias using the Joanna Briggs Institute’s Critical Appraisal Tool for Systematic Reviews developed by the Joanna Briggs Institute, Adelaide, Australia [28]. To summarize, this tool contains four specific checklists for different types of studies

studies that met the selection criteria for their recovery was conducted. 2.4. Evaluation of the Validity and Reliability of the Evidence We assessed the risk of bias using the Joanna Briggs Institute’s Critical Appraisal Tool for Systematic Reviews developed by the Joanna Briggs Institute, Adelaide, Australia [28]. To summarize, this tool contains four specific checklists for different types of studies (i.e., cross-sectional, quasi-experimental, cohort, and RCTs studies). For each of them, there are four possible answers: “yes” (criterion met) and “no” (criterion not met). There were eight items for cross-sectional studies, nine items for quasi-experimental, and thirteen items for RCTs. Based on the above criteria, the studies are considered as “low-quality” evidence when ≤49% of the items are classified as “yes” (criterion met). As a result, articles are considered “medium-quality” evidence if 50–74% of the items are scored as “yes” and “high-quality” evidence when ≥75% of the items are scored as “yes”. The total percentage excludes the answers “not applicable” and “not clear” [29–31]. Each of the three reviewers assessed the quality of the studies separately. For the purpose of resolving possible differences between the reviewers, a consensus meeting was organized. 3. Results A flow chart illustrating the selection of reporting elements for systematic reviews is depicted in Figure 1. The three databases assessed contained a total of 558 studies. Based on the title and abstract and duplicates, 195 studies were excluded, and 23 studies were excluded for being outside the scope of the review. The eligibility of 22 studies was assessed. Based on the exclusion criteria, eight studies were included in the analysis. There were six RCTs, and two observational studies (one cross-sectional and one well- conditioned student-athletes study). Figure 1. Flow chart systematic review [27]. Figure 1.Flow chart systematic review [27]. The quality of the selected studies is summarized in Table. All studies were designed as a high-quality study according to the checklist from Joanna Briggs Institute's criterium. Tables

systematic review [27]. The quality of the selected studies is summarized in Table. All studies were designed as a high-quality study according to the checklist from Joanna Briggs Institute's criterium. Tables

Nutrients2022,14, 4609 5 of 15 According to the information provided above, it appears that the majority of the studies are RCTs. Table 2. Checklist from Joanna Briggs Institute's criterium according to kind of study, percentage of criterium reached, and quality level of evidence.Criteriums According to Kind of Study Authors 1 2 3 4 5 6 7 8 9 10 11 12 13 Percentage Reached Quality Level Hou et al., 2013 [12] 1 1 1 1 1 1 1 1 1 1 1 1 1 100% HQ Stasiule et al., 2014 [11] 1 1 1 1 0 0 1 1 1 1 1 1 1 85% HQ Keen et al., 2016 [10] 1 0 1 1 1 0 1 1 75% HQ Wei et al., 2017 [32] 0 1 1 1 1 1 1 1 1 1 1 1 1 92% HQ P²rez-Turpin et al., 2017 [33] 0 1 1 0 0 1 1 1 1 1 1 1 1 77% HQ Harris et al., 2019 [34] 1 1 1 1 1 1 1 1 1 1 1 1 1 100% HQ Higgins et al., 2019 [35] 1 1 1 1 1 1 1 1 1 1 1 1 0 92% HQ Gonz¡lez Acevedo et al., 2022 [36] 0 1 0 1 1 1 1 1 1 1 1 0 1 76% HQ HQ: high quality. The values 1 and 0 indicate whether the item was achieved or not, respectively. 3.1. Selected Studies Our selected investigations used different forms of DSW, and we divided the results according to that, starting with DOM, followed by deep mineral water (DMW), and seawater. 3.1.1. Deep-Ocean Mineral Water In response to exercise and heat, the body becomes dehydrated and the osmolality of extracellular uid increases, which results in decreases in exercise performance and poor thermoregulation. It has been demonstrated in previous studies that DOM can promote the recovery of exercise performance following exercise [34]. This study evaluated the effects of DOM on recovery from a fatiguing exercise con- ducted at 30 C using a randomized, double-blind, placebo-controlled crossover design. During the fatiguing exercise protocol, aerobic

The review assesses seawater as a hydration strategy for athletes in endurance sports.