Am J Respir Crit Care Med Vol 165. pp 708–712, 2002DOI: 10.1164/rccm.2102115Internet address: www.atsjournals.org

Decreased serum cortisol levels have been proposed to contribute tonocturnal airway obstruction. We investigated whether endoge-nous cortisol levels are lower, and also whether the 24-h cortisolvariation is greater, in children with asthma than in control sub-jects and assessed the relationship between serum cortisol and noc-turnal airflow limitation in children with asthma. Cortisol and FEV

1

were measured every 4 h over 24 h; blood eosinophils, airway re-sponsiveness to methacholine and adenosine 5

�

-monophosphate(AMP) were measured at 0400 and 1600. Children with asthma hadlower cortisol levels than did control subjects; at midnight the dif-ference was significant. Subjects with nocturnal asthma (24-h FEV

1

variation

�

15%) had significantly lower cortisol levels than did con-trol subjects at 0000, 0800, and 1200. A higher mean 24-h cortisollevel in subjects with asthma was associated with a significantlyhigher FEV

1

as a percentage of the predicted value (FEV

1

%pred)at 0400, 0800, and 2000, yet not in control subjects. Higher 24-h cor-tisol variation was associated with lower FEV

1

%pred at all timepoints in both control subjects and subjects with nonnocturnalasthma. There was no significant association between the level orvariation of cortisol and PD

20

methacholine (provocative dose ofmethacholine causing a 20% fall in FEV

1

), PD

20

AMP, or eosino-phils. Our data suggest that lower cortisol levels contribute to bothoverall lower levels of FEV

1

especially at night. This may be due toa lack of suppression of airway inflammation.

Keywords:

asthma; children; endogenous serum cortisol; FEV

1

Nocturnal cough, wheeze, and chest tightness interfere at leastonce a week with sleep in almost 50% of children with asthma(1). These symptoms result from overnight airflow limitation,as a consequence of an exaggeration of the normal circadianrhythm in airway caliber. The pathogenesis of nocturnal air-way obstruction is still unclear and several mechanisms havebeen proposed. Possible causes include increased parasympa-thetic tone (2, 3), and increased airway inflammation associ-ated with enhanced bronchoconstrictor mediator release (3–9).Decreased serum cortisol levels have also been suggested as afactor in the pathogenesis of nocturnal airway obstruction inadult asthma (10–12). Cortisol, a glucocorticoid produced byadrenal glands, shows a circadian rhythm with its peak atabout 0800 h and its nadir at about midnight. These low corti-sol levels at night precede the nocturnal fall in FEV

1

and mayresult in less suppression of airway inflammation with subse-quent increased airflow limitation (13).

Increased airway responsiveness, which is predominantlycaused by airway inflammation, is another phenomenon un-derlying nocturnal airflow limitation (5, 14). Airway hyperre-sponsiveness can be measured with various stimuli. Histamineand methacholine challenges cause airway obstruction mainly

by their direct action on receptors of airway smooth muscles,whereas a stimulus such as adenosine 5

�

-monophosphate (AMP)is thought to act primarily on inflammatory cells. The latterstimulus thereby initiates processes that indirectly lead tosmooth muscle contraction (14). A relationship between se-rum cortisol levels and increased airway responsiveness can beexpected if either overall circadian cortisol levels are lower orif low cortisol levels, specifically at night, result in less sup-pression of airway inflammation.

The aim of this study was to determine whether endoge-nous serum cortisol levels are lower and/or the variation in en-dogenous 24-h serum cortisol levels is greater in children withasthma compared with normal control subjects. In addition,we assessed the relationship between serum cortisol levels andairway obstruction and hyperresponsiveness in children withasthma. Therefore, we measured serum cortisol and FEV

1

atsix time points over a 24-h period, blood eosinophils at 0400and 1600, and airway responsiveness to methacholine andAMP at 0400 and 1600.

METHODS

Subjects with Asthma

We studied 28 children with stable asthma, aged 7 to 16 yr, recruitedat the pediatric outpatient clinic of the University Hospital of Gronin-gen (Groningen, The Netherlands). All children had a history of epi-sodic wheezing on exposure to allergens or nonallergic stimuli. In ad-dition to the clinical diagnosis of asthma, the other inclusion criteriawere as follows: allergy for at least one aeroallergen determined by apositive specific immunoglobulin E (IgE) response to house dustmite, cat, dog, grasses, and trees, and an increased level of total serumIgE (Kabi Pharmacia, Woerden, The Netherlands). All children hadan increased airway responsiveness to histamine (PC

20

histamine [pro-vocative concentration of histamine causing a 20% fall in FEV

1

]

�

8mg/ml) and used inhaled corticosteroids as maintenance medicationbefore the study. Patients entered the study after they had stopped in-haled corticosteroid for 2 wk, and long-acting

�

2

agonists for 5 d be-fore the onset of the study. Short-acting

�

2

agonists were withheld for8 h before the study. No oral corticosteroids were used for at least2 mo before the study.

Subjects without Asthma

Eighteen age-matched healthy control subjects were studied. Selec-tion criteria were as follows: (

1

) no history of asthma symptoms, ei-ther for the child or for the family in the first line, (

2

) normal totaleosinophil count (0.0–0.4

�

10

9

/L), (

3

) no demonstrated allergy foraeroallergens, (

4

) a normal level of total serum IgE (

�

50 KU/L for 7–10 yr,

�

100 KU/L for

�

10 yr), and (

5

) no increased airway respon-siveness to histamine (PC

20

histamine

�

16 mg/ml).Informed consent was obtained from all children and their par-

ents. The study was approved by the Medical Ethical Committee ofthe University Hospital of Groningen.

Study Design

We used FEV

1

variation (highest minus lowest FEV

1

value divided bythe mean FEV

1

value) for classification of asthmatic children with andwithout nocturnal worsening of asthma. The group of asthmatic chil-dren with a variation in FEV

1

�

15% was defined to have nocturnalworsening of asthma. The mean daily dose of inhaled corticosteroids

they used before the study was 420

g for the children with and 380

gfor those without nocturnal worsening of their asthma.

(

Received in original form February 27, 2001; accepted in final form December 6, 2001

)

Supported by the Dutch Asthma Foundation (grant 94.115) and by StichtingAstma Bestrijding.

Correspondence and requests for reprints should be addressed to A. M. Landstra,M.D., Department of Pediatrics, Rijnstate Hospital, P.O. box 9555, 6800 TA Arn-hem, The Netherlands. E-mail: amlandstra@hetnet.nl

Role of Serum Cortisol Levels in Children with Asthma

ANNEKE M. LANDSTRA, DIRKJE S. POSTMA, H. MARIKE BOEZEN, and WIM M. C. Van AALDEREN

Department of Pediatrics, Rijnstate Hospital, Arnhem; Department of Pulmonology, University Hospital, Groningen; Department of Epidemiology, University of Groningen, Groningen; and Department of Pediatric Pulmonology, Emma Children’s Hospital AMC, Amsterdam, The Netherlands

Landstra, Postma, Boezen,

et al.

: Serum Cortisol Levels in Children 709

Children arrived at the hospital at 1930 and remained until 1700the next day. An intravenous line was placed to take blood samples.The intravenous line was kept open with a continuous infusion of0.9% saline with a portable CADD

pump (Graseby Medical BV,Rosmalen, The Netherlands). Children were awakened 10 min beforethe measurements at 0000 and 0400. Bedtime was between 2100 and2200. The children with asthma attended the hospital a second day forthe AMP inhalation challenge at 1600 and 0400, 24 h after the lastmeasurement of the first day.

Measurements

Serum cortisol was measured by a chemiluminescence immunoassaymethod (University Hospital Groningen) every 4 h over a 24-h period,starting at 2000. At 0400 and 1600 blood eosinophils were counted in aCoulter counter (Beckman Coulter, Fullerton, CA). FEV

1

values wereobtained every 4 h over a 24-h period by a pneumotachograph (Mas-terscreen I.O.S.; Jaeger, Wurtzburg, Germany). The FEV

1

was mea-sured until three reproducible recordings were obtained, with the bestof three being used for analysis. Reference values for the FEV

1

arethose of Zapletal and coworkers (15). FEV

1

values before the metha-choline challenge at 0400 and 1600 were used for the asthma group.The inhalation provocation tests were performed with a nebulizer(DeVilbiss, Somerset, PA) attached to a French–Rosenthal dosimeter.Solutions of methacholine (Chemie Brunschwig, Basel, Switzerland)and AMP (Sigma, St. Louis, MO) were administered at room tempera-ture as aerosols. After inhalation of 0.9% sodium chloride solution,doubling concentrations of methacholine bromide (0.15–39.3 mg/ml)or AMP (0.04–160 mg/ml) were inhaled. The challenge was stoppedwhen the FEV

1

had fallen by

�

20% of the prechallenge level or whenthe highest concentration had been administered. PD

20

values werecalculated by linear interpolation between the last two data points.

Statistical Analysis

Data were analyzed with the Statistical Package for Social Sciences(SPSS, Chicago, IL) for DOS version 5.0 and Windows version 9.0.Normal distribution was checked visually by probability plots of theresiduals and tested formally by the Kolmogorov–Smirnov test. Dif-ferences between groups were tested by parametric or nonparametrictest as appropriate. The Student

t

test was used to test differences inFEV

1

%pred (FEV

1

as a percentage of the predicted value) betweentwo groups. One-way analysis of variance (ANOVA) was used to testdifferences in mean FEV

1

%pred between three groups. Nonparamet-ric tests (Mann–Whitney U test or Kruskall–Wallis test) were used totest differences between groups in terms of levels of cortisol and PD

20

methacholine and PD

20

AMP at 0400 and 1600. The effect of meancortisol level over 24 h on FEV

1

at 2000, 0000, 0400, 0800, 1200, and1600 on eosinophil count at 0400 and 1600, and on methacholine andAMP responsiveness at 0400 and 1600 was estimated by means of

multiple linear regression. All regression analyses were performed forall dependent variables separately, with additional adjustment for ageand sex. The effect of the 24-h variation in cortisol [

�

cortisol

24h

�

(highest

lowest cortisol value)/mean cortisol value] on FEV

1

, eosin-ophil count, and methacholine and AMP responsiveness at the vari-ous time points was estimated in the same way. A p value

�

0.05 wasconsidered significant.

RESULTS

Subjects

Twenty-eight children with asthma (16 boys), mean age 13.1

�

1.8 yr, were included. Ten children (6 boys), mean age 13.1

�

1.4 yr, had nocturnal asthma defined as an FEV

1

variation

�

15% (NA

, mean FEV

1

variation 24.9 [15.9–45.4]%), and 18had an FEV

1

variation

�

15% (NA

, mean FEV

1

variation 8.9[(5.1–14.9]%). Eighteen children (7 boys) were included in thehealthy control group, mean age 13.1

�

1.9 yr. There was asignificant difference between the three groups in mean FEV

1

%pred (SD) over a 24-h period, the NA

group having thelowest values (86.7 [10.1]%pred), the NA

group having inter-mediate values (92.2 [11.2]%pred), and the control subjectshaving the highest values (101.6 [6.8]%pred) (p

�

0.001). Thesame pattern was seen at 0400 and 1600 (Table 1).

Cortisol Measurements

Mean serum cortisol levels were lower in the asthma groupthan in the control group, and this was significant at midnight(p

�

0.05) (Figure 1). The latter was true both for the groupswith and without nocturnal worsening of asthma comparedwith the control group. At 0800 and 1200, the NA

group hadlower cortisol levels than the control subjects as well (p

�

0.05). Although the NA

group had lower mean cortisol val-ues than the NA

group, differences did not reach significance(Figure 2). No significant differences between the groups werefound regarding the mean serum cortisol level over 24 h, or re-garding the mean 24-h variation in serum cortisol (

�

cortisol

24h

)and

�

cortisol

1600

0400

/mean cortisol value, respectively.

Numbers of Eosinophils

Median numbers of eosinophils were significantly differentbetween the three groups both at 0400 (0.79 vs. 0.61 vs. 0.29

�

10

9

/L in asthmatic children with and without nocturnal asthmaand control subjects, respectively; p

�

0.05) and at 1600 (0.68 vs.0.39 vs. 0.21

�

10

9

/L, respectively; p

�

0.05) (Table 1).

TABLE 1. GROUP CHARACTERISTICS

Subjects with Asthma Control Subjects NA

NA

n 28 18 10 18Boys, no. 16 7 6 10Age, yr (mean

�

SD) 13.1

�

1.8 13.1

�

1.9 13.1

�

1.4 13.1

�

1.7Mean FEV

1

%pred, mean

�

SD 90.2

�

11.0 101.6

�

6.8* 86.7

�

10.1 92.2

�

11.2*FEV

1

%pred0400 h, mean

�

SD 87.4

�

13.6 102.6

�

9.8* 80.8

�

14.7 91.1

�

11.8*1600 h, mean

�

SD 92.3

�

11.0 102.7

�

10.3* 90.1

�

10.6 93.5

�

11.3*Eosinophils (

�

10

9

/L)0400 h, median (IQ range) 0.62 (0.43–0.90) 0.29 (0.09–0.76)* 0.79 (0.45–1.07) 0.61 (0.40–0.77)1600 h, median (IQ range) 0.46 (0.25–0.70) 0.21 (0.06–0.93)* 0.68 (0.29–0.78) 0.39 (0.25–0.61)

PD

20

methacholine, mg/ml0400 h, median (range) 2.1 (0.0–35.3) 1.0 (0.0–8.8) 3.2 (0.2–35.3)*1600 h, median (range) 2.1 (0.0–34.8) 1.5 (0.0–8.3) 3.9 (0.3–34.8)

PD

20

AMP, mg/ml0400 h, median (range) 17.2 (0.0–139.5) 13.5 (0.0–126.0) 65.3 (0.3–139.5)*1600 h, median (range) 72.0 (0.0–144.0) 36.0 (0.0–144.0) 89.8 (0.1–144.0)

Definition of abbreviations

: IQ ranges

�

interquartile ranges; NA

�

nocturnal asthma, defined as FEV

1

variation

�

15%; NA

�

nonnoc-turnal asthma, defined as FEV

1

variation

�

15%.* p

�

0.05 (parametric or nonparametric tests as appropriate;

see

M

ETHODS

).

710

AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE VOL 165 2002

Hyperresponsiveness

Median PD

20

methacholine was lower in the NA

than in theNA

group, which was significant at 0400 (1.0 and 3.2 mg/ml,respectively; p � 0.05; Table 1), but not at 1600 (1.5 and 3.9mg/ml, p � 0.07).

Median PD20 AMP was significantly lower in the NA

group than in the NA group at 0400 (13.5 and 65.3 mg/ml, re-spectively; p � 0.05; Table 1), but not at 1600 (36.0 and 89.8mg/ml). Individual PD20 methacholine and PD20 AMP valuesat 1600 and 0400 for both groups are shown in Figures 3 and 4,respectively.

Mean 24-H Serum Cortisol Level

A higher mean serum cortisol level over 24 h was significantlyassociated with a higher mean FEV1 %pred value at 0400,0800, and 2000 (p � 0.05) in the asthma group as a whole (Ta-ble 2). The mean 24-h level of cortisol also tended to be associ-ated with the FEV1 %pred at 1200 and 16.00 (p � 0.10).

Neither hyperresponsiveness to AMP and methacholine,nor the number of eosinophils, was significantly associatedwith mean 24-h serum cortisol levels. We found no significantassociations between the mean 24-h level of cortisol and theFEV1 %pred in the control group.

Variation in Cortisol over 24 H

There was no significant association between the 24-h cortisolvariation and FEV1 %pred values in the whole asthma group(Table 3). In the asthmatic children without nocturnal worsen-ing of asthma a higher 24-h cortisol variation was associatedwith a lower FEV1 %pred, and this was also the case inhealthy control subjects (Table 3). These associations weresignificant at all time points except for 0800 (p � 0.15) and1200 (p � 0.08) in the NA group (Table 3).

In the asthma group, a higher 24-h variation in serum corti-sol tended to be associated with higher numbers of eosinophilsat 0400 and 1600 (p � 0.1). In the NA group a higher 24-hvariation in serum cortisol was significantly associated withhigher numbers of eosinophils at both 0400 and 1600.

DISCUSSION

This study of 28 children with asthma and 18 healthy controlsubjects was designed to identify whether the mean 24-h levelof endogenous serum cortisol is lower and/or the 24-h varia-

tion is larger in children with asthma compared with normalcontrol subjects. We found that the children with asthma hadlower serum cortisol levels at all time points measured com-pared with the control group, and this difference was statisti-cally significant at midnight. Specifically, children with noctur-nal asthma had lower cortisol levels than the healthy controlgroup, and not only at midnight, but also at 0800 and 1200. Alower mean 24-h cortisol level in the asthma group was associ-ated with a significantly lower FEV1 %pred at 0400, 0800, and2000, whereas this association did not exist in healthy controlsubjects. A higher 24-h cortisol variation was associated with alower FEV1 %pred at all time points in both the healthy chil-dren and the asthmatic children without nocturnal airway ob-struction.

Our results suggest a relationship between serum cortisollevel on the one hand, and the overall level of FEV1 and noc-turnal fall in FEV1 on the other hand; that is, the higher the se-rum cortisol the better the lung function. A relationship be-tween serum cortisol levels and lung function has previouslybeen found in adults. Kraft and coworkers (12) compared se-rum cortisol values in three similar adult groups. They foundthat the cortisol levels in the nocturnal asthma group were sig-nificantly higher than in the other groups. This difference wascompletely explained by a significantly higher value at 2000 inthe nocturnal asthma group. In contrast to adults, we found asignificant negative association between the mean 24-h levelof cortisol and the level of FEV1 %pred at almost all timepoints. This is compatible with one other epidemiological studyshowing that adults with asthma have lower serum cortisollevels than healthy adults. Moreover, in accordance with ourobservation, they found an association between low cortisollevels and nocturnal asthma (13). Together these data supportthe notion that higher endogenous cortisol levels are associ-ated with better lung function values, and that they are of im-portance especially with respect to better nocturnal FEV1.

A few published studies have addressed the circadian vari-ation in serum cortisol. Szefler and coworkers (16) measuredplasma cortisol in 7 nocturnal and 10 non-nocturnal adultswith asthma and in 10 healthy volunteers at 4 A.M. and 4 P.M.They found no significant differences between the groups. Haenand coworkers (17) studied plasma cortisol at 4-h intervals for24 h in 10, untreated male patients with asthma and 8 healthymen. Contrary to our results, they did find a significantlyhigher 24-h mean serum cortisol level and a lower drop at

Figure 1. Mean (SEM) levelof cortisol (nM) at six dif-ferent time points in theasthma and control groups.*Asthma versus control sub-jects, p � 0.05. Controlsubjects; asthmatics.

Figure 2. Mean (SEM) levelof cortisol (nM) at six dif-ferent time points in thenocturnal asthma and non-nocturnal asthma groups.

NA ; NA.

Figure 3. Bronchial hyper-responsiveness to methacho-line. Shown are individualPD20 methacholine valuesat 1600 and 0400 of thenocturnal asthma and non-nocturnal asthma groups.

Figure 4. Bronchial hyper-responsiveness to AMP.Shown are individual PD20AMP values at 1600 and0400 of the nocturnal asthmaand nonnocturnal asthmagroups.

Landstra, Postma, Boezen, et al.: Serum Cortisol Levels in Children 711

night in their patients with asthma. The discrepancies in re-sults may stem from the fact that we have studied children,whereas Haen and coworkers have investigated adults. A clearrelationship between age and cortisol levels in adults has beenreported (18) and aging was associated with higher evening cor-tisol levels, which became apparent after midlife. The morningmaximum values remained stable across all age ranges (18).

An important observation in our study is that the signifi-cantly lower cortisol levels over 24 h were found particularlyin our asthmatic children with a nocturnal fall in their FEV1. Itis not clear from this study whether this is a causal relation. Totest this hypothesis it would be necessary to perform a studywith cortisol replacement. However, studies investigating theeffects of inhaled and oral corticosteroids on nocturnal asthmahave clearly shown a beneficial effect, which points in thesame direction and lends support to the hypothesis that alower cortisol level may induce a higher susceptibility to noc-turnal asthma. This effect of a lower mean 24-h cortisol levelon the presence of nocturnal asthma may well occur via an ef-fect on airway wall inflammation. Herrscher and coworkers(19) investigated the effect of endogenous cortisol on the IgE-dependent cutaneous response. They found that a lower corti-sol level was associated with increased allergic inflammationby affecting the expression of cellular events at the late-phasesites. Earlier findings of our group have shown that airway wallinflammation is more extensive in those subjects with asthmawho experience symptoms at night than in those who do nothave nocturnal airway obstruction, and yet the difference inthe extent of inflammation between 0400 and 1600 is compa-rable in both groups (3, 20). We interpret the above-describedresults as suggesting that lower cortisol levels at both day andnight amplify the circadian rhythm of yet another factor thatinhibits airway obstruction at night. One such factor may wellbe the physiologic nadir of �-adrenergic receptor function atnight, hence the excellent response of nocturnal symptomsand airway obstruction to long-acting �-agonists (21).

We hypothesized that lower endogenous cortisol levels, orgreater 24-h swings in endogenous cortisol, are associated with

a lower degree of protection against stimuli inducing airway wallinflammation. Indirect evidence of increased inflammation innocturnal asthma is provided by the observation that bron-chial responsiveness is more severe in asthmatic subjects withnocturnal airway obstruction than in those without (14, 22, 23).In this study we measured responsiveness to methacholineand AMP at 0400 and 1600. We used both stimuli to find outwhether direct and/or indirect bronchial responsiveness playeda role in the nocturnal worsening of FEV1 values in childrenwith asthma, and whether the level of endogenous cortisol in-fluenced these two types of airway hyperresponsiveness. Wefound indeed that hyperresponsiveness to both methacholineand AMP was worse in the NA group, significantly so at0400. Furthermore, in six of eight children with nocturnalworsening of their asthma the PD20 AMP decreased duringthe night, but the PD20 methacholine did not decrease. How-ever, we found no association between endogenous mean 24-hcortisol levels or the 24-h variation in cortisol levels and thedegree of bronchial responsiveness. Thus, we could not sug-gest a relationship between endogenous cortisol and eithermuscarinic receptor function on airway smooth muscle cells,or with inflammatory cell processes such as mast cell activa-tion, which is under the influence of AMP.

We realize that interpretation of our results could be ham-pered by the fact that cortisol is a stress hormone that can beinfluenced by several factors. The literature provides severalstudies showing effects of the use of inhaled corticosteroids,exercise, sleep, and psychological factors on levels of cortisol(24–26). These factors accounted only to a small extent for thevariance in serum cortisol measures. One of the most impor-tant findings in the study by Dahl and coworkers (24) was thatsleep continuity resulted in lower nocturnal cortisol levels. Thisunderscores the finding that the observed low cortisol levels atnight in our study are not the result of sleep discontinuity.

When reviewing the relationship between nocturnal adre-nal function and the use of inhaled corticosteroids, Kallenbachand coworkers (27) concluded that the majority of the studiesperformed in children do not show hypothalamic–pituitary–

TABLE 2. ESTIMATED EFFECT OF MEAN 24-H LEVEL OF CORTISOL ON FEV1 %pred AT SIX TIME POINTS IN CHILDREN WITH ASTHMA AND IN CONTROL SUBJECTS*

FEV1 at 0400 FEV1 at 0800 FEV1 at 1200 FEV1 at 1600 FEV1 at 2000 FEV1 at 0000

B (SE) p Value B (SE) p Value B (SE) p Value B (SE) p Value B (SE) p Value B (SE) p Value

Subjects with asthma 0.01 (0.15) 0.92 0.07 (0.03) 0.04† 0.07 (0.04) 0.06 0.06 (0.04) 0.09 0.08 (0.04) 0.04† 0.06 (0.04) 0.15Control subjects 0.03 (0.03) 0.23 0.03 (0.02) 0.17 0.04 (0.03) 0.15 0.05 (0.03) 0.11 0.04 (0.02) 0.06 0.03 (0.02) 0.13

Definition of abbreviation: B � unstandardized coefficient with standard error.* Linear regression analyses were performed for groups and all time points separately and adjusted for age and sex.† p � 0.05.

TABLE 3. ESTIMATED EFFECT OF THE 24-H CORTISOL VARIATION ON FEV1 %pred AT SIX TIME POINTS IN CHILDREN WITH ASTHMA AND IN CONTROL SUBJECTS AND IN THE NOCTURNAL AND NONNOCTURNAL ASTHMA GROUPS*

FEV1 at 0400 FEV1 at 0800 FEV1 at 1200 FEV1 at 1600 FEV1 at 2000 FEV1 at 0000

B (SE) p Value B (SE) p Value B (SE) p Value B (SE) p Value B (SE) p Value B (SE) p Value

Subjectswith asthma 0.01 (0.15) 0.92 0.05 (0.12) 0.70 0.10 (0.15) 0.53 0.05 (0.12) 0.69 0.01 (0.14) 0.97 0.00 (0.14) 0.98

Controlsubjects

0.21 (0.05) 0.002† 0.16 (0.06) 0.01† 0.20 (0.06) 0.003† 0.21 (0.07) 0.01† 0.22 (0.4) 0.001† 0.18 (0.06) 0.01†

NA 1.09 (0.25) 0.01† 0.48 (0.29) 0.15 0.38 (0.18) 0.08 0.69 (0.24) 0.03† 0.98 (0.29) 0.01† 1.16 (0.20) 0.001†

NA 0.18 (0.08) 0.04† 0.15 (0.07) 0.03† 0.22 (0.07) 0.002† 0.15 (0.07) 0.03† 0.16 (0.08) 0.08 0.12 (0.09) 0.18

Definition of abbreviations: B � unstandardized coefficient with standard error; NA � nocturnal asthma, defined as FEV1 variation � 15%; NA � nonnocturnal asthma, defined asFEV1 variation � 15%.

* Linear regression analyses were perfomed for groups and all time points separately and adjusted for age and sex.† p � 0.01.

712 AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE VOL 165 2002

adrenal cortical axis suppression, when dosages of inhaled cor-ticosteroids ranging from 300 to 800 g/d are being used. Oth-ers confirmed this (27) and indicate that dosages of inhaledcorticosteroids up to and including 800 g/d do not suppressthe hypothalamic–pituitary–adrenal cortical axis. Because thechildren in our study used inhaled corticosteroids rangingfrom 100 to 500 g/d before they stopped their medication (2 wkbefore they entered the study), it seems unlikely that the se-rum cortisol values in our study were influenced.

In conclusion, we found that children with asthma hadlower serum cortisol levels compared with healthy controlsubjects at all six time points of the day that we measured cor-tisol. A lower mean 24-h cortisol level was associated withlower FEV1 values in the asthmatic population, and signifi-cantly so at 0400, 0800, and 2000. A higher circadian variationin cortisol was associated with lower FEV1 levels in healthyvolunteers and asthmatic subjects without nocturnal asthma.Furthermore, we found more severe hyperresponsiveness tomethacholine and AMP and higher numbers of peripheralblood eosinophils in the asthmatic children with nocturnal air-way obstruction. We found no relationship between those pa-rameters and the level and/or variation of serum cortisol. Ourdata suggest that cortisol concentrations indeed contribute toboth overall lower FEV1 values in asthma, especially at night,contributing to the presence of nocturnal airway obstructionin asthma.

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