ARTICLE
Auteur(s) : Gloria
Grases1, JA Pérez-Castelló1, P
Sanchis2, A Casero1, J Perelló2, B
Isern2, E Rigo1, F Grases2
1University of Balearic Islands, Dept. Applied
Pedagogy and Educational Psychology, Palma of Mallorca, Spain
2University of Balearic Islands, University Institute of
Health Sciences Research (IUNICS), Palma of Mallorca, Spain
Stress is related to well established biomarkers such as cortisol
[1-4] and aldosterone. The increase in intracellular cortisol with
respect to aldosterone in renal cells prevents the aldosterone
effect, since these two hormones compete for the same
mineralcorticoid receptor [5-7]. The aldosterone suppression
induces an increase in urinary calcium since this hormone increases
renal calcium reabsorption by calcium channels [8].Anxiety is
associated with an increase in catecholamines [9-11] which is
responsible for an increase in magnesium urinary excretion and a
decrease in its plasmatic concentrations [12-16]. In fact, Mg
reduction increased anxiety-related behaviour in mice [17].Several
studies have demonstrated that the daily activity of scholars
causes significative stress [18-21] and this could be related to a
great number of psychosomatic disorders [22, 23]. Chronic stress
was found to reduce the endothelial function, which may also be
associated with an intracellular magnesium level decrease in humans
[24].Scientific studies (Chemistry, Physics, Mathematics) are
highly demanding and need a huge continuous effort from students.
The aim of this paper was to evaluate the stress and anxiety of the
students in basal conditions and during exams through validated
stress and anxiety questionnaires. In addition, the correlation
between the data obtained and biochemical markers such as calcium
and magnesium would be established.
Material and methods
Thirty-five volunteers (12 males and 23 females aged 18 to 20
years) in the first level of university chemistry studies (Faculty
of Sciences of the University of Balearic Islands) were selected.
Written informed consent was obtained from all volunteers. The
study was divided into two parts. The first one corresponded to
basal conditions and was developed at the beginning of the academic
course (beginning of November) and the second during exams in the
middle of the academic course (end of January). In all cases stress
and anxiety questionnaires and urine analysis were performed.
Stress and anxiety questionnaires
Validated stress and anxiety questionnaires were used. STAI (State
Treats Anxiety Inventory) questionnaire [25] was used to evaluate
state (STAIE) and trait (STAIR) anxiety. PSQ (Perceived Stress
Questionnaire) [26] was used also to assess recent (stress) and
general (stressr) stress. Both questionnaires have satisfactory
validity properties [25, 26]. Internal consistency was 0.83 - 0.92
for the STAI [25] and 0.87 for the state and 0.9 for the trait PSQ
[26]. The correlations between scales are shown in table 1(
Table 1 ).
Table 1 Correlations between scales [26].
|
General PSQ
|
Recent PSQ
|
|
State anxiety (STAI) (n = 80)
|
0.22
|
0.28
|
|
Trait anxiety (STAI) (n = 80)
|
0.65
|
0.69
|
Analysis of urinary samples
Urine was analyzed in basal conditions and during exams. All
subjects were on a free diet at the time of urine collection and
none of them was undergoing pharmacological treatment.
Twenty-four-hour urine was collected in sterile flasks containing
thymol as a preservative. The volume was recorded and the samples
were stored at -20°C until assayed. Two-hour urine collection was
performed next day, after 24-hour urine collection and after
overnight fasting, and the pH was immediately measured with a glass
electrode (Crison pH-meter). Calcium, magnesium and phosphorus were
determined in both samples by atomic emission spectrometry using an
inductively coupled plasma (ICP Optima 5300DV) and creatinine by
Sigma kit (ref. 557).
Statistics
Values in the tables are expressed as mean ± SE. The Student t-test
for paired-values was used to assess differences of means.
Conventional Windows software was used for statistical analysis. A
value of p < 0.05 was considered significant.
Results
Questionnaire results are summarized in table 2( Table 2 ). The only significant differences were
observed in state anxiety as shown by STAI questionnaire in basal
conditions (39.7 ± 4.3) and during exams (72.6 ± 3.5). No
significant differences appeared between the stress questionnaires.
Urine sample analysis results are reported in tables 3 and
4( Table 3 )( Table
4 ). There were no significant differences in diuresis, pH,
calcium and creatinine concentrations and excretion in 24h urine
when basal values (urine collected in November) were compared with
values obtained during exams (urine collected in January).
Nevertheless, a significant magnesium and phosphate (phosphorus)
increase were noticed in 24h urine collected during exams (94 ±
8 mg/L Mg, 929 ± 82 mg/L P) as compared with basal values
(72 ± 5 mg/L Mg, 686 ± 42 mg/L P). No significant
differences were observed between the 2h urinary parameters
(diuresis, pH, Mg, P, creatinine) in both groups, except for
calcium excretion and concentrations.
Table 2 Anxiety and stress questionnaires texts results
under basal conditions and during exams (n = 35).
|
Condition
|
Questionnaire
|
|
stress
|
stressr
|
STAIE
|
STAIR
|
|
Basal conditions
|
0.40 ± 0.01
|
0.38 ± 0.01
|
39.7 ± 4.3
|
43.9 ± 4.9
|
|
During exams
|
0.39 ± 0.01
|
0.40 ± 0.02
|
72.6 ± 3.5*
|
49.4 ± 4.7
|
Table 3 Urinary biomarkers determined in 24h urine
under basal conditions and during exams (n = 35).
|
Urinary parameter
|
Basal conditions
|
During exams
|
|
Volume (mL)
|
1318 ± 88
|
1213 ± 74
|
|
pH
|
6.3 ± 0.1
|
6.4 ± 0.1
|
|
[Calcium] (mg/L)
|
131 ± 11
|
145 ± 12
|
|
Calcium excretion (mg)
|
155 ± 10
|
173 ± 19
|
|
[Magnesium] (mg/L)
|
72 ± 5
|
94 ± 8*
|
|
Magnesium excretion (mg)
|
84 ± 4
|
121 ± 19
|
|
[Phosphorus] (mg/L)
|
686 ± 42
|
929 ± 82*
|
|
Phosphorus excretion (mg)
|
808 ± 44
|
1180 ± 156*
|
|
[Creatinine] (mg/L)
|
915 ± 89
|
1002 ± 82
|
Table 4 Urinary biomarkers determined in 2h urine under
basal conditions and during exams (n = 35).
|
Urinary parameter
|
Basal conditions
|
During exams
|
|
Volume (mL)
|
105 ± 9
|
89 ± 10
|
|
pH
|
5.9 ± 0.1
|
5.8 ± 0.1
|
|
[Calcium] (mg/L)
|
149 ± 14
|
115 ± 10 *
|
|
Calcium excretion (mg)
|
15 ± 2
|
9 ± 1*
|
|
[Magnesium] (mg/L)
|
84 ± 7
|
72 ± 4
|
|
Magnesium excretion (mg)
|
8 ± 1
|
6 ± 1
|
|
[Phosphorus] (mg/L)
|
793 ± 87
|
750 ± 72
|
|
Phosphorus excretion (mg)
|
72 ± 10
|
69 ± 13
|
|
[Creatinine] (mg/L)
|
1562 ± 182
|
1507 ± 141
|
Discussion
The present results showed that the evaluated students did not
experiment a stress increase during exams but suffered a
significant anxiety increase. It is interesting to observe that the
psychological findings agree with urinary biomarkers studied. It is
known that anxiety is related to partial magnesium decrease
associated with an increase in urinary magnesium excretion [12-17].
This might be partially attributed to the plasmatic glucose
decrease caused by anxiety that leads to catecholamine secretion in
order to restore glucose levels. These hormones are implicated in
hypomagnesemia [9-11]. Also, an increase in aldosterone secretion
might be able to explain the findings of this paper, as aldosterone
leads to an increased renal excretion of magnesium [27-29].
The noticeable increase in muscular tension linked to anxiety
consumes an important amount of energy that is partially due to the
ATP-ADP transformation. A high increase in urinary phosphate
excretion [30-32] also contributes to the magnesium reduction.
Indeed, magnesium has been proposed for treatment in different
anxiety disorders [33-38].
Stress correlates with a urinary calcium increase resulting from
cortisol liberation [39, 40]. Cortisol blocks the calcium tubular
reabsorption mediated by aldosterone, and as a consequence
increases calcium urinary excretion [5-8]. Moreover, aldosterone
causes an increase in renal magnesium excretion. In the present
paper, we did not observe changes in stress and no correlatively
significant increases were detected in urinary calcium
concentration or excretion.
It must be pointed out that no differences were observed in
urinary concentrations and excretion of magnesium and phosphate
(phosphorus) when the first urine of the morning was studied (2h
urine). This can be linked to the relaxation induced by sleep that
must be accompanied by a decrease in anxiety.
Conclusion
The present results showed that the evaluated university science
students did not experience stress increase as a consequence of
exams but suffered a significant increase in anxiety. This was
associated to a urinary magnesium excretion increase responsible
for partial magnesium depletion.
Acknowledgements
P.S. expresses her appreciation to the Spanish Ministry of
Education, Culture and Sport for a fellowship of the FPU program.
Also, B.I. expresses his appreciation to the Conselleria
d’Innovació i Energia del Govern de les Illes Balears for a
fellowship. This work was supported by the Conselleria d’Innovació
i Energia del Govern de les Illes Balears (Grant PROIB-2002GC1-04)
and by the project BQU 2003-01659 of the Spanish Ministry of
Science and Technology.
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