Citation: Del Arco, A.; Martinez
Aguirre-Betolaza, A.; Malchrowicz-
Mo´sko, E.; Gogojewicz, A.;
Castañeda-Babarro, A. Are
Supplements Consumed by
Middle-Distance Runners
Evidence-Based? A Comparative
Study between Level of Competition
and Sex. Nutrients 2023, 15, 4839.
https://doi.org/10.3390/nu15224839
Academic Editors: Valentín
E. Fernández-Elías and
Olga López Torres
Received: 16 October 2023
Revised: 16 November 2023
Accepted: 17 November 2023
Published: 20 November 2023
Copyright:
© 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
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Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
nutrients
Article
Are Supplements Consumed by Middle-Distance Runners
Evidence-Based? A Comparative Study between Level of
Competition and Sex
Asier Del Arco 1, Aitor Martinez Aguirre-Betolaza 1
, Ewa Malchrowicz-Mo´sko 2
, Anna Gogojewicz 3
and Arkaitz Castañeda-Babarro 1,*
1
Health, Physical Activity and Sports Science Laboratory, Department of Physical Activity and Sports,
Faculty of Education and Sport, University of Deusto, 48007 Bilbao, Spain;
asier.delarco@opendeusto.es (A.D.A.); a.martinezdeaguirre@deusto.es (A.M.A.-B.)
2
Institute of Sport Sciences, Poznan University of Physical Education, 61-871 Pozna´n, Poland;
malchrowicz@awf.poznan.pl
3
Institute of Health Sciences, Poznan University of Physical Education, 61-871 Pozna´n, Poland;
gogojewicz@awf.poznan.pl
*
Correspondence: arkaitz.castaneda@deusto.es
Abstract: Background: Middle-distance running events have special physiological requirements from
a training and competition point of view. Therefore, many athletes choose to take sport supplements
(SS) for different reasons. To date, few studies have been carried out that review supplementation
patterns in middle-distance running. The aim of the present study is to analyze the consumption
of SS in these runners with respect to their level of competition, sex and level of scientiﬁc evidence.
Methods: In this descriptive cross-sectional study, data was collected from 106 middle-distance
runners using a validated questionnaire. Results: Of the total sample, 85.85% responded that they
consumed SS; no statistical difference was found regarding the level of competition or sex of the
athletes. With respect to the level of competition, differences were observed in the total consumption
of SS (p = 0.012), as well as in that of medical supplements (p = 0.005). Differences were observed
between sexes in the consumption of medical supplements (p = 0.002) and group C supplements
(p = 0.029). Conclusions: Higher-level athletes consume SS that have greater scientiﬁc evidence. On
the other hand, although the most commonly consumed SS have evidence for the performance or
health of middle-distance runners, runners should improve both their sources of information and
their places of purchase.
Keywords: middle-distance; supplementation; nutrition; performance; health
1. Introduction
Middle-distance running events are highly complex from a bioenergetic, training and
tactical point of view [1]. The level of energy intensity is in a middle ground between
aerobic and anaerobic metabolism [2], with the aerobic contribution in the 800 m being
between 60 and 75% and slightly higher (77–85%) in the 1500 m [3]. In addition, due
to the type of muscle ﬁbers these athletes have (Mainly IIX and IIA [4]), most middle-
distance runners can reach lactate peaks of >20 mmol/L, leading to muscle pH levels as
low as 6.6 [5]. However, the high speed requirements make both aerobic and anaerobic
metabolism contribute signiﬁcantly during these events [6]. This can be reﬂected in the
distribution of training intensities throughout the season. Middle-distance runners work
a very wide spectrum of training zones, ranging from low-intensity running sessions to
very-high-intensity glycolytic workouts [7]. In this way, elite middle-distance runners
develop aerobic capacities similar to those of long-distance runners, mechanical skills close
to those of sprinters, as well as a highly enhanced anaerobic capacity [1]. Some of these
Nutrients 2023, 15, 4839. https://doi.org/10.3390/nu15224839
https://www.mdpi.com/journal/nutrients
Nutrients 2023, 15, 4839
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characteristics make them adopt different race strategies [8,9]. However, sometimes the
difference between being a medalist or not is minimal [10], and the improvements seen
with some SS are very worthwhile in terms of performance [11].
Supplements are deﬁned as “A food, food component, nutrient, or nonfood compound
that is purposefully ingested in addition to the habitually-consumed diet with the aim
of achieving a speciﬁc health and/or performance beneﬁt” [11]. Although many athletes
use SS to improve their performance, there are other underlying reasons for their use [12].
According to the Australian Institute of Sport (AIS), supplements are classiﬁed into four
groups using the “ABCD” system [13]. This is based on the latest scientiﬁc evidence for
determining whether a product is safe, permitted and effective in improving performance
or health: (A) supplements with solid scientiﬁc evidence in speciﬁc situations under estab-
lished protocols; (B) components with emerging evidence that should be used in research
or clinical settings; (C) supplements with limited evidence and effects on performance;
(D) prohibited products or those with a high risk of contamination by doping substances.
Regarding middle-distance races, some of the supplements that have shown the most
evidence in improving performance are caffeine [14,15], β-Alanine [16–18] and sodium
bicarbonate [19–21]. However, these SS are not among the most consumed by middle-
distance runners, with the consumption of vitamins, minerals and amino acids being higher
than the previously mentioned ones [22].
Although SS can provide both health and performance beneﬁts, athletes’ knowledge
of them is sometimes limited [23,24]. In the same way, it has been shown that the use of
some SS with less scientiﬁc evidence is greater than those with higher levels of supporting
research [25]. Finally, some of the main motivators for their consumption are unqualiﬁed
individuals, such as friends, teammates or the runners themselves [26–29].
To our knowledge, few studies have been conducted to analyze supplementation
patterns in athletes, and no one exclusively in middle-distance runners. Thus, the objective
of this research is to know the supplementation trends in those athletes with respect to
their level and gender. On the other hand, it aims to assess whether the SS taken by middle-
distance runners are those with the most scientiﬁc evidence, thus reducing the existing gap
in the literature [30].
2. Materials and Methods
2.1. Type of Study
The research was a descriptive and cross-sectional study. The sample was selected
using non-probabilistic, non-injurious and convenience sampling among training groups
and individual middle-distance athletes at the national level.
2.2. Participants and Study Sample
A total of 106 middle-distance runners (800–1500 m) participated, of which 74 were
men and 32 were women (gender assigned at birth). Only two requirements were estab-
lished to participate in the study, which were as follows: (1) be over 18 years of age (legal
age in Spain); (2) be currently performing middle-distance disciplines. The level of the ath-
letes was differentiated by their area of competition, which could be regional (competing at
regional or provincial level), national (competitions in Spain) or international (competitions
at European and World level). Table 1 describes the age, basic anthropometric data and
best performances in middle-distance events of the participants involved in the research.
2.3. Instruments
The questionnaire chosen for this research has been previously used in studies with
the same objectives carried out in other sports [26,31,32]. This one was chosen for two main
reasons; on the one hand, for its contents, structure, applicability and ease of completion
for the athletes. The second reason was the quality of the questionnaire, which was created
by 25 experts from different areas and achieved a 54% methodological validity, being
one of the 57 questionnaires (out of 167) validated to obtain accurate data on supplement
Nutrients 2023, 15, 4839
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consumption [33]. The questionnaire has 4 main parts and a total of 32 questions. The ﬁrst
one asks for personal (e.g., sex), anthropometric (e.g., height, weight) and sociodemographic
(e.g., region of residence) data, with a total of 8 questions. The second, with a total
of 5 questions, covers topics about the sport practice (e.g., years of practice, level of
competition). The third part, with a similar objective, collects information about your best
times in the different middle-distance disciplines or about your training days and number
of competitions and has a total of 8 questions. Finally, the fourth part (11 questions) covers
the area of supplementation, with questions such as: what supplements do they consume,
reason for consumption, and place of purchase. This questionnaire collects data about all
types of supplements, among which we ﬁnd sports foods (e.g., energy bars, sports gels),
medical supplements (e.g., iron, vitamin D, multivitamins) or performance supplements
(e.g., caffeine, creatine, ß-Alanine). These different types of supplements are deﬁned as
sport supplements in the current study. From this last section, different questions related to
diet were eliminated from the original questionnaire because they did not contribute to
the objective of the study and in order to limit the response time. This questionnaire can
be obtained in: Suplementación nutricional en la actividad físico-deportiva: análisis de la
calidad del suplemento proteico consumido [34].
Table 1. Characteristics and personal times of the different subjects.
Sex (n)
Category (n)
Age
Height *
Weight *
BMI *
PB 800 m
PB 1500 m
Male
(74)
Regional (29)
22.9 ± 5.7
176.3 ± 8.2
64.8 ± 9.1
18.3 ± 2.0
2:01.74 ± 6.80
4:17.22 ± 16.31
National (43)
24.5 ± 7.6
177.6 ± 6.4
65.1 ± 6.1
18.3 ± 1.4
1:56.42 ± 5.25
4:02.92 ± 16.50
International (2)
20.0 ± 2.8
189.0 ± 5.7
68.5 ± 4.9
18.1 ± 0.8
1:48.38 ± 1.15
3:47.50
Female
(32)
Regional (11)
23.6 ± 8.2
165.0 ± 4.8
52.4 ± 7.0
15.8 ± 1.7
2:26.04 ± 7.04
5:13.66 ± 21.95
National (17)
21.8 ± 3.1
164.8 ± 4.3
52.5 ± 4.1
15.9 ± 1.1
2:15.56 ± 6.55
4:59.61 ± 43.06
International (4)
21.0 ± 2.9
167.5 ± 4.8
55.0 ± 3.2
16.4 ± 0.8
2:05.27 ± 3.84
4:15.23 ± 9.97
Results are expressed as mean ± SD. BMI: body mass index. * Self-reported height and weight. BMI calculated
from self-reported height and weight. PB: personal best. Gender assigned at birth.
2.4. Procedures
For the data collection, the questionnaire was distributed via training groups, known
athletes and social networks. The questionnaire was distributed online so that runners
could complete it remotely, voluntarily and anonymously. The protocol complied with the
provisions of the Declaration of Helsinki for human research and was approved by the
ethical committee of the University of Deusto (ETK-14/23-24) dated 26 October 2023.
2.5. Statistical Analysis
To verify whether the variables had a normal distribution, a Kolmogorov–Smirnov test
was applied, and Levene’s test was used to verify homoscedasticity. The quantitative data
were presented as mean + SD, while the qualitative variables were expressed as percentages
and frequencies. A two-way ANOVA was performed for the sex factor (male–female) and
level of competition (regional, national and international) to analyze the differences in the
total consumption of SS, as well as the SS consumed from the different categories. To assess
sex differences, a t-test for independent variables was performed, while to assess differences
among competition levels, a one-way ANOVA was performed. For those variables in which
signiﬁcant differences were found, the Bonferroni post hoc analysis was used. Regarding
the analysis of the athletes who consumed SS, the reason for consumption, the place where
they obtained them and who advised them to consume them, a chi-square (χ2) test was
used to verify the existence or not of differences between athletes of different sex and level
of competition. As for the SS that were consumed by at least 10% of the sample, a χ2
test was performed to verify possible differences according to sex or level of competition.
The level of statistical signiﬁcance was established as p < 0.05. The statistical analysis was
carried out using the Statistical Package for Social Sciences (SPSS) software v.28.0.0 (IBM,
Armonk, NY, USA) for Windows.
Nutrients 2023, 15, 4839
4 of 11
3. Results
3.1. General Consumption of Sport Supplements
Of the total sample, 85.85% reported consuming supplements, while 15 of the 106 sub-
jects responded that they did not consume any type of sport supplement. Regarding sex,
supplement consumption was higher in men (89.2%) than in women (78.1%), with no
statistical differences between them (p = 0.143). In the analysis of the results by level of
competition, the percentage of autonomous athletes who consumed supplements was
77.5%, in athletes at the national level it was 90.0%, while in athletes who competed at
the international level the consumption was 100%, with no differences between levels
(p = 0.126).
Table 2 shows the supplements consumed according to the different categories es-
tablished by the AIS. With respect to total supplement consumption, differences were
observed at the competitive level between international and regional athletes (p = 0.011).
However, no differences were appreciated based on sex (F = 2.248; p = 0.466), with a total
consumption of 4.8 ± 3.7 and 5.4 ± 5.7 for men and women, respectively. No interactions
were observed between level and sex (F = 0.306; p = 0.737).
Table 2. Descriptive data of the SS consumed according to the different categories deﬁned by the AIS
as a function of sex and level of competition.
Variable
Sex
Level of Competition
M
F
R
N
I
Total
Mean ± SD
Mean ± SD
Mean ± SD
Mean ± SD
Mean ± SD
Med
IQ
Mean ± SD
Med
IQ
Total SS
4.8 ± 3.7
5.4 ± 5.7
4.0 ± 3.8
5.1 ± 3.7
9.5 ± 9.6
6.0
26
5.0 ± 4.4
5.0
27
Group A
Sports food
1.1 ± 1.0
1.0 ± 1.2
1.0 ± 1.1
1.1 ± 1.0
1.2 ± 1.5
0.5
3
1.1 ± 1.1
1.0
4
Medical supplement
0.4 ± 0.6
0.8 ± 0.9
0.3 ± 0.5
0.6 ± 0.8
1.3 ± 1.0
1.0
3
0.52 ± 0.7
0.0
3
Performance supplement
1.0 ± 1.1
0.9 ± 1.1
0.8 ± 1.1
1.0 ± 1.9
1.7 ± 1.6
1.5
4
1.0 ± 1.1
1.0
4
Total Group A
2.5 ± 1.9
2.7 ± 2.4
2.1 ± 2.0
2.7 ± 1.9
4.2 ± 3.7
3.0
10
2.5 ± 2.1
2.0
10
Group B
0.5 ± 0.7
0.5 ± 0.7
0.5 ± 0.6
0.5 ± 0.7
1.2 ± 1.2
1.0
3
0.5 ± 0.7
0.0
3
Group C
0.5 ± 0.6
0.3 ± 0.4
0.3 ± 0.6
0.5 ± 0.6
0.4 ± 0.6
0.5
1
0.4 ± 0.6
0.0
2
AIS: Australian Institute of Sport; SS: sport supplements; SD: standard deviation; M: male; F: female; R: regional;
N: national; I: international; Group A: supplements with solid scientiﬁc evidence in speciﬁc situations under
established protocols; Group B: components with emerging evidence that should be used in research or clinical
settings; Group C: supplements with limited evidence and effects on performance; gender assigned at birth.
For Group A, no differences were observed between sexes or levels or for the sex–
level interaction for the sports food, performance supplement or total intake. However,
differences were observed for the group of medical supplements between competition
levels (international athletes, p = 0.004 vs. regional and p = 0.037 vs. national athletes),
with consumption being higher as the level of the athletes increased. Likewise, differences
between sexes were noted in this group (F = 3.797; p = 0.002), with higher consumption
in women than in men (0.4 ± 0.6 vs. 0.8 ± 0.9). Table 3 describes the differences between
supplement consumption according to level of competition, sex and the interaction between
both. Regarding Group B, no differences were observed between sexes (F = 1.591; F = 0.860),
levels of competition (F = 2.656; p = 0.075) or the interaction between sex and level of
competition (F = 0.279; p = 0.860). Finally, for group C supplement consumption, differences
were observed with respect to sex (F = 13.297; p = 0.029), with 0.5 ± 0.6 vs. 0.3 ± 0.4 for
males and females, respectively. However, no differences were seen between levels or for
the sex–level-of-competition interaction.
3.2. Most-Consumed Supplements by Competitive Level and Sex
Table 4 shows those supplements that were consumed by more than 10% of the sample.
The most-consumed supplements were caffeine (37%), followed by energy bars and sport
drinks (34% for both) and creatine (31.1%). With respect to sex, differences were only
observed for iron consumption (p < 0.001), with higher consumption in women than in
men (17.6% vs. 56.3%). Differences between levels were observed for recovery shakes
Nutrients 2023, 15, 4839
5 of 11
(83.3% vs. 20% vs. 7.5%, p < 0.001; for international, national and regional athletes) and
vitamin D (50.0% vs. 18.3% vs. 10.0%, p = 0.047; for international, national and regional
athletes). The most-consumed supplements in the sport food subgroup for women were
sport drinks (34%), contrary to men where the use of sports bars was a little bit higher
(36.5%). Regarding medical supplements, iron was the main supplement for both sexes
(17.6 vs. 56.3 for male and female).
Table 3. ANOVA of the SS consumed according to the different categories deﬁned by the AIS as a
function of sex, level of competition and their interaction.
Variable
Sex
Level of
Competition
Sex–Level-of-Competition (Mean ± SD)
F
p
F
p
R
N
I
F
p
M
F
M
F
M
F
Total SS
2.248
0.466
4.582
0.012 #
4.0 ± 3.6
3.9 ± 4.5
5.1 ± 3.4
5.2 ± 4.5
7.5 ± 9.1
10.5 ± 11.1
0.306
0.737
Group A
Sports food
1.330
0.726
0.102
0.903
1.1 ± 1.1
0.8 ± 1.1
1.1 ± 0.9
1.1 ± 1.4
1.5 ± 2.1
1.0 ± 1.4
0.270
0.764
Medical supplement
3.797
0.002 *
5.693
0.005 #$
0.24 ± 0.4
0.6 ± 0.7
0.5 ± 0.7
0.8 ± 0.9
0.5 ± 0.7
1.8 ± 1.0
1.138
0.325
Performance supplement
0.014
0.592
2.167
0.120
0.8 ± 1.1
0.6 ± 1.3
1.1 ± 1.1
0.8 ± 0.7
1.5 ± 2.1
1.8 ± 1.7
0.162
0.850
Total group A
0.671
0.560
3.066
0.051
2.1 ± 2.0
2.0 ± 2.3
2.7 ± 1.8
2.8 ± 2.1
3.5 ± 4.9
4.5 ± 3.7
0.163
0.849
Group B
1.591
0.860
2.656
0.075
0.5 ± 0.7
0.5 ± 0.5
0.5 ± 0.8
0.4 ± 0.5
1.0 ± 1.4
1.3 ± 1.3
0.279
0.757
Group C
13.297
0.029 *
1.884
0.157
0.3 ± 0.7
0.1 ± 0.3
0.6 ± 0.6
0.3 ± 0.5
0.5 ± 0.7
0.5 ± 0.6
0.151
0.860
AIS: Australian Institute of Sport; SS: sport supplements; SD: standard deviation; M: male; F: female; R: regional;
N: national; I: international; Group A: supplements with solid scientiﬁc evidence in speciﬁc situations under
established protocols; Group B: components with emerging evidence that should be used in research or clinical
settings; Group C: supplements with limited evidence and effects on performance; gender assigned at birth. *
Statistical difference at p < 0.05 between male and female. # Statistical difference at p < 0.05 between regional and
international athletes. $ Statistical difference at p < 0.05 between national and international athletes.
Table 4. Distribution (%) of the most-consumed supplements (>10%) as a function of sex and level of
competition according to the categories deﬁned by the AIS.
Category
Supplement
Name
Total (%)
Sex (%)
Level of Competition (%)
M
F
p
R
N
I
p
Group A
Sports foods
Sport bars
34.0
36.5
28.1
0.273
30.0
38.3
16.7
0.451
Sport drinks
34.0
33.8
34.4
0.561
27.5
38.3
33.3
0.533
Sports gel
21.7
21.6
21.9
0.582
22.5
21.7
16.7
0.949
Whey protein
30.2
29.7
31.3
0.525
25.0
31.7
50.0
0.429
Recovery shakes
18.9
20.3
15.6
0.394
7.5
20.0
83.3
<0.001 *
Medical supplements
Iron
29.2
17.6
56.3
<0.001 *
22.5
30.0
66.7
0.084
Vitamin D
17.0
14.9
21.9
0.269
10.0
18.3
50.0
0.047 *
Performance supplements
β-Alanine
20.8
20.3
21.9
0.521
12.5
23.3
50.0
0.081
Caffeine
37.7
36.5
40.6
0.424
35.0
36.7
66.7
0.318
Creatine
31.1
36.5
18.8
0.054
20.0
38.3
33.3
0.151
Group B
Vit C
19.8
20.3
18.8
0.542
17.5
20.0
33.3
0.662
Group C
BCAA
10.4
12.2
6.3
0.295
10.0
10.0
16.7
0.873
Glutamine
11.3
12.2
9.4
0.482
5.0
15.0
16.7
0.276
AIS: Australian Institute of Sport; M: male; F: female; R: regional; N: national; I: international; Group A: sup-
plements with solid scientiﬁc evidence in speciﬁc situations under established protocols; Group B: components
with emerging evidence that should be used in research or clinical settings; Group C: supplements with limited
evidence and effects on performance; gender assigned at birth. * Statistical difference at p < 0.05.
For performance supplements, differences were observed with caffeine and creatine
being the most consumed for men (36.5%) and only caffeine for women (40.6%). Finally,
for group C, both BCAA and glutamine were the most-consumed ones for males (12.2%),
but not for females (glutamine = 9.4%). As for the level of the athlete, the most-consumed
supplements for international athletes were recovery shakes (83.3%), followed by iron and
caffeine (66.7%). The national-level athletes’ most-consumed supplements were creatine,
sports bars and sport drinks (38.3%), while caffeine was the most-consumed one by regional
athletes (35%).
Nutrients 2023, 15, 4839
6 of 11
3.3. Information about the Place of Purchase, Recommendations and Consumption Patterns
Most athletes took supplements on training and competition days (39.62%). The daily
consumption of supplements was 26.42%, followed by training (14.15%) and competition
(11.32%). No differences were observed between genders (p = 0.106) as opposed to between
categories for daily consumption (p = <0.00). Thus, 33.3% of the international athletes
consumed it daily, while only 18.3% or 7.5% did so in the case of national and regional ones.
In analyzing the moment of consumption, most of the sample used them after (56.60%)
or before (50.94%) practicing exercise, followed by during training (20.75%). Only a small
percentage responded that it was taken during the holiday period (1.89%) or indifferently
(7.55%). No differences were observed for levels but between levels for pre- and post-
training consumption (p = 0.007), which varied according to the level of competition (33%
vs. 20% vs. 25% for international, national and regional athletes, respectively).
The principal objective of consumption was to improve performance (70.75%), fol-
lowed by taking care of their health (35.85%) and palliating dietary deﬁcits (16.98%). Finally,
of the 106 middle-distance runners, only 6.60% consumed them for health problems or
necessity (3.77%). In this area, no differences were observed between sexes (p = 0.564) or
levels of competition (p = 0.086). The primary place of purchase was the internet (51.89%),
followed by specialized stores (26.42%) or a pharmacy (24.54%). Other minority sources of
purchase were herbalists (12.26%), sports monitors (3.77%), friends (1.89%) or parapharma-
cies (0.94%), with no statistically signiﬁcant differences (p = 0.082 and p = 0.545 for gender
and level). Finally, those who encouraged the use of SS were mainly coaches (37.74%),
followed by dieticians–nutritionists (26.42%), teammates (21.70%) or physicians (16.04%).
There were other people and sources that recommended its use such as friends and the
internet (8.49%) or social network proﬁles (4.72%). Likewise, there were no differences
between levels (p = 0.919) or genders (p = 0.410).
4. Discussion
The main objective of this study was to analyze the supplementation patterns in
middle-distance runners, as well as the differences between genders and level of compe-
tition. The results indicate that the main differences between levels are observed both in
total consumption and in the intake of medical supplements, with these being greater as
the level of the athlete increases. Similarly, differences between levels were also observed
in the consumption of medical supplements, as well as in pre- and post-training intake.
This indicates that, although most athletes place emphasis on performance enhancement
via supplementation, higher-level athletes also use these aids to maintain a better state of
health and recover between sessions.
Of the total sample, 85.85% responded that they consumed SS, which was higher
than the consumption in other disciplines such as fencing or sailing [26,35], but lower
than in sports such as rowing, trail running or tennis (100%, 93.8% and 88.6%, respec-
tively) [25,29,31]. No differences were noted for sexes or competition levels, in line with
recent research [25,35]. Comparing the data obtained with a sample of athletes from dif-
ferent disciplines, the consumption of SS in middle-distance runners is higher (85% vs.
77%) [36]. Although there have been previous attempts to investigate supplementation
patterns in athletes [22], one contained a limited sample while the other had only a few
supplements [33,37] and no one has conducted it exclusively in middle-distance athletes.
Therefore, this is the ﬁrst to do so using a representative sample of middle-distance event
participants and a broad list of SS.
With respect to total SS consumption, there were differences between international
and regional athletes, which had been previously noted in all types of sportsmen and
women [33]. With respect to the different groups established by the AIS according to
the level of evidence [13], in group A, no differences were observed between levels and
genders, contrary to other recent studies [32,35,38]. However, differences between levels
were close to being statistically signiﬁcant (p = 0.051). Within the subgroups that exist in
group A, only differences in medical supplements are observed for gender, which may be
Nutrients 2023, 15, 4839
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primarily due to the higher consumption of iron among women compared to men (56.3%
vs. 17.6%). For the level of competition, differences were also observed in this subgroup,
being higher as the level increased. These two ﬁndings are contrary to the results from
other sports, where no differences have been observed for this subgroup between athlete
levels or genders [26,29,35,39].
Regarding group B, which includes SS with emerging evidence but in need of future
research, no differences are observed for level and gender, in line with the results in other
sports [25,26,29,35,39]. Finally, in group C (supplements with insufﬁcient scientiﬁc evidence
to support its use), differences were noted between sexes, in line with some [25], but not all,
recent evidence [26,35,39]. This could be due to the athlete’s knowledge, which is worse as
the level of competition decreases [40].
Taking into account the days of sport practice when they usually take the SS, 39.62%
responded that they take them during training and competition, followed by daily consump-
tion and solely on training days, at 26.42% and 14.15%, respectively. Although the main
sporting day is similar to that of other sports such as mountain running or rowing [25,29,39],
the second and third causes differ between sports. This could be due to differences in the
physiological demands of each event, as well as the average duration and energetic require-
ments of training sessions. Differences were noted in daily consumption between levels of
competition, indicating that the main difference between higher- and lower-level athletes
was the use of medical supplements on a daily basis. On the other hand, the majority of
middle-distance athletes take SS after (56.60%) or before sports practice (50.94%), while
a lower percentage take them during sports practice. The duration of middle-distance
sessions rarely surpasses 90–120 min [7], while other sports training sessions usually exceed
this time, in which they will need to provide higher nutrition and hydration [25]. Here
too, differences between levels are observed for pre- and post-consumption, demonstrating
how top-level runners place greater importance on preparing for training or recovering
for an upcoming workout. In analyzing the reasons for its consumption, the main one is
to improve their performance (70.75%), followed by health care (35.85%) and to palliate a
dietary deﬁcit (16.98%), similar to other sport disciplines [26,29,31,32,35,36].
Concerning the person who motivated the consumption of SS, the main motivator
was the coach (37.74%), followed by dietitians–nutritionists (26.42%), which showed a
worse advisor in the case of middle-distance runners compared to other sports [25,39].
The next advisors were teammates, followed by physicians, indicating the existence of
other sports modalities with a worse source of support [26,35]. In this sense, dietitians–
nutritionists are the most appropriate when choosing one supplement or another regardless
of the level of scientiﬁc evidence [26,41,42]. Finally, most athletes purchased SS on the
internet (51.89%), followed by specialized stores (26.42%) and pharmacies (24.53%). In
this sense, both pharmacy and internet products may contain quantities different from
those advertised or contaminated substances, which may also put the athletes at risk of
unintended doping [43], so athletes tend to go to specialized stores in order to avoid these
problems [12,42].
Finally, with regard to the most-consumed SS, we can appreciate caffeine in the ﬁrst
place. Caffeine is a natural stimulant for the central nervous system, possesses various
suggested beneﬁts for enhancing performance and is one of the supplements with the
highest scientiﬁc evidence supporting its use [15]. These advantages encompass enhanced
neuromuscular functionality and a decrease in fatigue and perceived effort levels during
physical exertion, among others [44]. The following most-consumed SS were sport drinks
(formulated to provide a balanced combination of carbohydrates and liquids, facilitating
athletes in rehydrating and replenishing energy simultaneously during and after their
workout) and sport bars (created as a portable source of carbohydrates, helping meeting
carbohydrate intake goals) [13], which also belong to Group A, such as caffeine. These
two supplements help mainly in carbohydrate replenishment post or during training or
to reach the recommended daily intake of carbohydrates, which can be up to 70% of the
total diet or around 6–12 CHO · kg−1 · BW · day−1. In this sense, carbohydrate intake both
Nutrients 2023, 15, 4839
8 of 11
during [45] and immediately after [46] exercise limits fatigue and improves performance in
the following training sessions.
The next most-consumed supplement was isolated protein, with considerable scientiﬁc
evidence supporting its use [13], which appears necessary both for the recovery and repair
of damaged myoﬁbrillar proteins and to optimize mitochondrial and possibly sarcoplasmic
protein synthesis [47]. However, this seems unnecessary in most cases, since athletes
tend to consume more protein than any high recommendation [47]. Continuing with
the SS that can provide more beneﬁts among those consumed by more than 10% of the
sample, we ﬁnd iron or β-Alanine. Iron plays a fundamental role in the transport of oxygen
and a high prevalence of anemia has been observed among middle-distance runners [22].
A small decrease in hemoglobin content (subclinical anemia) leads to a signiﬁcant decrease
in oxygen transport capacity and, therefore, a decrease in performance [48]. Thus, it is
important to monitor these variables on a recurring basis in order to supplement if necessary.
On the other hand, β-Alanine acts as an intracellular buffer by increasing the concentration
of muscular carnosine [49]. Since high-intensity exercise (usually performed by middle-
distance runners both in training and competition [7]) increases the amount of hydrogen
ions and lowers the intracellular pH from 7.0 to 6.6, supplementation with β-Alanine
may improve the ability to withstand this drop, limiting muscular fatigue. However, the
determination of whether supplementation enhances performance in elite middle-distance
athletes is challenging due to insufﬁcient data and non-performance-related tests [47].
Despite this, considering the absence of side effects and potential performance beneﬁts,
individual athletes and their support teams may want to try β-Alanine supplementation to
assess its effectiveness for them [1]. Finally, it is important to note the very low percentage
of athletes using inorganic nitrates or beetroot juice as SS (6.60%). This supplementation
seems to improve performance via the bioavailability of nitric oxide, improving exercise
efﬁciency (decreased O2 cost at the same absolute workload) [50]. However, this low use
may be due to variability in the response to its supplementation [1] or decreased effects as
the physiological capabilities of the athletes increase [50].
It is important to mention that, although a large part of the SS consumed by middle-
distance runners in this study belong to group A, it is also observed that there is still a
fairly large consumption of supplements with little or no scientiﬁc evidence (groups B and
C). This has also been observed in other sports, so it is important that athletes use reliable
sources of information when deciding which supplements to consume [25,51]. In addition,
the present research has several limitations. First of all, the sample is larger than that of
other studies with the same population, but a greater participation of international athletes
is necessary. In addition, it was the athletes themselves who responded retrospectively to
the consumption of SS, which could lead to errors in the number or type of supplements.
Therefore, it is necessary to compare and have the support of different federations or
institutions worldwide to check if the consumption is similar depending on the competitive
level or gender.
5. Conclusions
Supplement consumption in middle-distance running is similar to that in other sports.
The main differences between levels are seen in the total supplement consumption and in
the consumption of medical supplements, as well as in daily or pre- and post-exercise con-
sumption, with these being higher as the level of competition increases. On the other hand,
the differences between sexes are found in the consumption of both medical supplements
and supplements with limited evidence. Middle-distance runners should improve both
their sources of information and places of purchase in order to avoid supplements with
low scientiﬁc evidence or contaminated/fraudulent products.
Author Contributions: Conceptualization, A.D.A. and A.C.-B.; Methodology, A.D.A., A.M.A.-B. and
E.M.-M.; Software, A.M.A.-B.; Formal Analysis, A.D.A., A.M.A.-B. and A.G.; Investigation, A.D.A.
and A.M.A.-B., Data Curation, A.D.A. Writing—Original Draft Preparation, A.D.A.; Writing—Review
Nutrients 2023, 15, 4839
9 of 11
& Editing, A.M.A.-B., E.M.-M., A.G. and A.C.-B.; Supervision; A.C.-B. Project Administration; A.C.-B.
All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Informed Consent Statement: Informed consent was obtained from all subjects involved in the
study. The protocol complied with the provisions of the Declaration of Helsinki for human research
and was approved by the ethical committee of the University of Deusto (ETK-14/23-24) dated 26
October 2023.
Data Availability Statement: Data of the article are available in the tables of this paper or on request
from the corresponding author.
Acknowledgments: Asier del Arco gives thanks for the distribution of the questionnaire and ded-
icates the article to the memory of Carlos and Angel Basas, for their contributions to the world of
athletics at the national and world levels.
Conﬂicts of Interest: The authors of the present article declare no conﬂict of interest.
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Are Supplements Consumed by Middle-Distance Runners Evidence-Based? A Comparative Study between Level of Competition and Sex.
Del Arco, Asier,Martinez Aguirre-Betolaza, Aitor,Malchrowicz-Mośko, Ewa,Gogojewicz, Anna,Castañeda-Babarro, Arkaitz