REGULAR ARTICLE

The effect of olfactory stimulation on energy expenditure in growingpreterm infantsRonella Marom1,2, Tamar Shedlisker-Kening1,3, Francis B. Mimouni2,4, Ronit Lubetzky2,3, Shaul Dollberg1,2, Irit Berger1,2,Dror Mandel (drorm@tasmc.health.gov.il)1,2

1.Department of Neonatology, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel2.Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel3.Department of Pediatrics, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel4.Pediatrics, Shaare Zedek Medical Center, Jerusalem, Israel

KeywordsEnergy expenditure, Metabolic rate, Odour, Preterminfants

CorrespondenceD Mandel, M.D., Department of Neonatology, TelAviv Sourasky Medical Center, 6 Weizman Street, TelAviv, 64239, Israel.Tel: +(972) 3692 5690 |Fax: +(972) 3692 5681 |Email: drorm@tasmc.health.gov.il

Received2 March 2011; revised 27 June 2011;accepted 1 July 2011.

DOI:10.1111/j.1651-2227.2011.02399.x

ABSTRACTAim: To test the hypothesis that olfactory stimulation in growing healthy preterm

infants leads to an increase in resting energy expenditure (REE).Design: A prospective, randomized clinical trial with crossover was conducted in 20

healthy, appropriate weights for gestational age, gavage-fed preterm infants. Infants were

studied while asleep and cared for in a skin servo-controlled convective incubator. Using a

pipette, 15 drops of saturated solution of vanillin (Aldrich, Fallavier, France) were dripped to

a cloth diaper that was placed on the opposite side of the incubator. REE was measured by

indirect calorimetry (DeltaTrac II, Helsinki, Finland) exactly 1 h after feeding. Each infant

was studied twice by randomization: after a period of 20 min of vanillin odour or after

20 min without vanillin odour.Results: We found no statistically significant difference in REE of preterm infants

when exposed to vanillin odour (74.5 ± 10.1 kcal ⁄ kg ⁄ day) in comparison with their REE

when not exposed to vanillin odour (79.0 ± 11.3 kcal ⁄ kg ⁄ day).Conclusions: Vanillin odour does not significantly influence REE in metabolically and

thermally stable preterm infants.

INTRODUCTIONUsing indirect calorimetry, we have recently demonstratedthat auditory stimulation (specifically, music by Mozart) sig-nificantly lowers resting energy expenditure (REE) inhealthy preterm infants, which may in part explain theimproved weight gain resulting from the so-called Mozarteffect (1).

Recent investigations on preterm infants have suggestedthat these infants have well-developed functions in regardto detection, discrimination and memorization of odoursadministered nasally (2). Within 5 sec, olfactory stimulationby vanillin in normal newborn infants leads to an increasein orbito-frontal blood flow detectable by near-infraredspectroscopy (3). Furthermore, preterm infants exposed tounpleasant olfactory stimulation exhibit a decrease in orbi-to-frontal blood flow (4). In one study, olfactory stimulationwith vanillin was found to be of therapeutic value in thetreatment of refractory apnoeas in preterm infants (5). Inadults, olfactory stimulation during sleep increases heartrate (6). Olfactory stimulation in preterm infants may gener-ate sucking or general arousal responses that are related togestational age (7). It appears that there even is an olfactorymemory in preterm newborn infants, that is capable of hav-ing soothing effects upon pain stimulation (8).

We, therefore, aimed to study whether, similar to theeffect of music, olfactory stimulation also has effects onREE. Thus, we used a similar design and methodologicalapproach and conducted the following pilot study to evalu-ate changes in REE that may occur subsequent to vanillinodour exposure in healthy preterm infants. We specificallytested the hypothesis that contrary to Mozart’s music, olfac-tory stimulation in such infants leads to an increase in REE,because of the stimulation of general arousal responses pre-viously reported (7).

Key notes• Olfactory stimulation in preterm infants is known to

stimulate general arousal responses.• In this study, olfactory stimulation through vanillin

odour did not significantly influence resting energyexpenditure (REE) in metabolically and thermally stablepreterm infants.

• These results are in sharp contrast with the previouslyreported significant modulator effect of music uponREE.

Acta Pædiatrica ISSN 0803–5253

ª2011 The Author(s)/Acta Pædiatrica ª2011 Foundation Acta Pædiatrica 2012 101, pp. e11–e14 e11

METHODSPatientsThe study was carried out in the neonatal intensive care unitat the Lis Maternity Hospital, Tel Aviv Medical Center, TelAviv, Israel. We aimed to study healthy, growing, appropri-ate weight for gestational age infants at the postmenstrualage of 32–35 weeks. Postmenstrual age was calculated incompleted weeks, based upon last menstrual period, consis-tent ± 1 week with early, first-trimester ultrasound exami-nation. All infants were clinically and thermally stable,while cared for in a skin servo-controlled incubator. At thetime of the study, they were all tolerating full enteral feeding(150–160 cc ⁄ kg weight ⁄ day) without significant gastricresiduals (<5% of total feed), they were all growing steadilyand had no electrolyte imbalance. None had any significantcomplication of prematurity, such as intracranial haemor-rhage (of any grade), periventricular leukomalacia, necro-tizing enterocolitis, supplemental oxygen requirements by28 days of age or by 36 weeks of postmenstrual age and atleast 1 week prior to measurement, active infection, patentductus arteriosus or episodes of apnoea of prematurity.They were all free of congenital anomalies or dysmorphism.According to our feeding protocol, infants were uniformlyfed (by gravity drainage) every 3 h, bolus feeds of theirmother’s breast milk or a preterm infant formula. The studywas approved by the local Institutional Review Board, andwritten informed consent was obtained from both parentsof each infant.

DesignThis study was a prospective randomized trial with cross-over of the effect of vanillin odour exposure (compared tono-vanillin odour) upon REE. The sequence in which vanil-lin exposure was given (odour first followed by no odour orthe opposite) was selected by randomization, using randomnumbers. Each infant was studied over two consecutivedays. For the purpose of odour exposure, using a pipette, 15drops of saturated solution of vanillin (Aldrich, Fallavier,France) were dripped to a cloth diaper that was put on theopposite side of the incubator. As in many other studies onolfaction, vanillin was chosen as a positive stimulus becauseof its properties to activate mainly the primary olfactory sys-tem, with very little effect on the trigeminal system (3). Thisspecific protocol was chosen after a preliminary study thatshowed that adult caretakers felt that with such a vanillindose, the smell was very strong. In both measurements, theenvironment was controlled to minimize possible unwantednoises and maintain noise constancy. The monitor alarmswere kept silent (visual alarm only), and the ward’s doorswere closed to minimize outside noise.

Metabolic studies were conducted while the infants wereprone and asleep (quiet sleep state, without movements),and at the same time of the day (noon time) for all infants,starting 1 h after the completion of the last feed. Thesepoints are important as sleep and prandial state modulateautonomic responses to odours (9). The same type (humanmilk or formula) and amount of food was given to theinfants on both study days. Measurements were stopped

during body movements (<5% of the time of measurement).During the metabolic study, infants were cared for in theirown, convective incubator. Air temperature inside the incu-bator was skin servo-controlled to keep temperature overthe back at 37�C. Thus, the two energy expenditure mea-surements were made in nearly identical thermal environ-ments.

MeasurementsMetabolic measurements were performed by indirect calo-rimetry, using the Deltatrac II Metabolic monitor (Datex-Ohmeda, Helsinki, Finland). This instrument uses the prin-ciple of the open-circuit system through a hood placed uponthe infant’s head that allows continuous measurements ofoxygen consumption (VO2

) and carbon dioxide production(VCO2

) using a constant flow generator. As the hood abovethe baby’s head is a closed-circuit system, the incubator wasfirst ‘primed’ with the vanillin-impregnated cloth.

The measurement ranges for both O2 consumption andCO2 production of 5–2000 mL ⁄ min allow measurements inpreterm infants with small tidal volumes. Prior to the mea-surement, the device performs a self-calibration based onindependently measured barometric pressure. Measure-ments were started after time was allowed for equilibrationof the system and calibration with the infant inside. Addi-tionally, periodic testing for accuracy was performed byalcohol burning according to the manufacturer instructions.This method is safe and allows prolonged measurementswhile allowing reasonable access to the infant for routinecare. Validation studies have shown the technique to giveresults equivalent to direct measurements (10,11). In ourhands, the instrument has an intra-assay coefficient of varia-tion of 3%. Importantly, whenever vanillin was used, theodour was perceptible to adults both at the beginning and atthe end of REE measurements. Each 20-min period of mea-surement, with and without (or without and with) vanillinodour, followed the previous period with an interval of 24 hbetween the two measurements.

Statistical analysisThis pilot study was designed to estimate the effect size ofvanillin odour upon REE. Thus, an empirical number of 20infants (that is 40 measurements) was chosen. Comparisonof energy expenditure values between groups was per-formed using paired t-test. For this purpose, REE results(recorded every minute by the instrument) were averagedover the first and the second 20-min periods of study time,whether it was a vanillin or no-vanillin exposure period.Results are expressed as mean ± SD; a p-value of £0.05 wasconsidered significant.

RESULTSTwenty preterm infants were recruited to the study. Perina-tal and demographic characteristics are depicted in Table 1and describe their gender, birthweight, gestational age, Ap-gar scores, weight and chronological age at the time of thestudy, as well as major medications given or procedures

The effect of olfactory stimulation on energy expenditure Marom et al.

e12 ª2011 The Author(s)/Acta Pædiatrica ª2011 Foundation Acta Pædiatrica 2012 101, pp. e11–e14

undertaken. Of note, 14 of 20 infants received caffeine for ahistory of previous apnoeas of prematurity, but did not haveany active apnoeas, and there were no changes in drug dos-age during both periods of the study.

Table 2 depicts the REE measurements during vanillinand no-vanillin according to the randomization schedule(vanillin first then no-vanillin or no-vanillin first then vanil-lin). There were no statistically significant difference in REEof preterm infants when exposed to vanillin odour(74.5 ± 10.1 kcal ⁄ kg ⁄ 24 h, range: 58 – 94 kcal ⁄ kg ⁄ 24 h) incomparison with their REE when not exposed to vanillinodour (79.0 ± 11.3 kcal ⁄ kg ⁄ 24 h, range: 66–108 kcal ⁄ kg ⁄24 h) (p = 0.16 by paired t-test and = 0.207 by Wilcoxontest). When multiple regression analysis was used, the effectof vanillin odour upon REE did not correlate significantlywith gestational age at birth or with postmenstrual age atthe time of the measurement.

Assuming that the minor and insignificant ‘drop’ in REEduring vanillin exposure is true, we would need 170 infantsto detect a significant difference in REE, at an a risk of 0.05and a power of 0.8.

DISCUSSIONIn this pilot randomized clinical trial with crossover of van-illin odour exposure versus no-vanillin odour exposure, wedemonstrated that healthy preterm infants studied at a

postmenstrual age of 32–35 weeks have no significantchange in REE. Moreover, contrary to our hypothesis, thesmall and insignificant change (approximately 6.6% frombaseline) in REE was a decrease, rather than increase, aftervanillin odour exposure. Would this effect be true, it wouldtake more than 170 infants for this difference to reach a sig-nificance level of <0.05. Such a number of infants would beimpractical to recruit, especially for a study requiring signifi-cant amount of time and technology for each patient. More-over, if the 6% difference is true, it is a small one and itsclinical significance in relation to human health, if any, isquestionable.

A limitation of our study is that it was a pilot one in nat-ure and was limited to a very short period of time (20 minonly). The measurement of REE for 20 min allows only apunctual assessment of one’s energy metabolism and maynot reflect his ⁄ her total energy expenditure. It is also theo-retically possible that the vanillin effect is delayed, and inessence, by studying the infants for only 20 min after expo-sure, we essentially ‘missed it’. This is unlikely to happenbecause (i) in Bartocci’s (3,4) studies, it took 5 sec to detecta discernable change in orbito-frontal blood flow after van-illin exposure, and (ii) in our study on the effects of musicon REE, within 10 min of exposure to music, there alreadywas a discernable drop in REE (1).

Another limitation of our study is that our findings areonly applicable to vanillin. For instance, Bartocci et al. (3,4)have shown that orbito-frontal blood flow may increase ordecrease depending upon the type of olfactive stimulus,such as a ‘pleasant’ one (vanillin) or ‘unpleasant’ one (deter-gent or disinfectant). Human infants are extremely sensitiveto the ‘pleasant smell’ of human milk or colostrum (12), andit is theoretically possible that would we have used one ofthe previously mentioned olfactive stimuli and we mighthave observed strikingly different results. Also, although weused a saturated solution of vanillin similar to that reportedby Marlier (5), we dripped the vanillin on the opposite siteof the incubator on a cloth diaper, while in Marlier’s study,15 drops of solution were applied on the periphery ofinfants cotton pillow. Consequently, the smell was consid-ered as very strong by adult observers, whereas in Marlier’sstudy, a slight vanillin odour was perceptible by adults nose.Whether or not such differences exist (the odour intensitywas not measurable) and ⁄ or may have affected the results isunknown, as we did not study, in this pilot trial, any kind ofdose–response effect. Also, as the hood above the baby’shead was a closed-circuit system, it is also possible that van-illin odour may have decreased in strength over time duringthe measurement.

When the results of this study are compared to that pre-sented by us in another study (1), the present results of REEare higher (74.5 or 79.0 kcal ⁄ kg ⁄ d as compared to averageresults between 53 and 62 kcal ⁄ kg ⁄ day in the previousone). We have to point out that these infants are not thesame as in the previous study, and different REE areexpected, in particular when there was a difference ofapproximately 1 week of gestational age between the twostudies. Nevertheless, the crossover design was chosen in

Table 1 Demographic and clinical characteristics of the study participantsPrenatal steroids (Betamethasone) (n, %) 14 (70)

Gender of infants (male:female) 12:8

Gestational age at birth (weeks) 30 ± 1.8 (27–34)

Birthweight (g) 1267 ± 259 (750–1673)

Apgar 1 7 (4–9)

Apgar 5 9 (5–10)

HFOV duration (days) 2.6 ± 1.8

CPAP duration (days) 2.7 ± 2.6

Erythropoietin treatment (n, %) 8 (40)

Caffeine treatment (n, %) 14 (70)

Postmenstrual age at measurement (weeks) 33.5 ± 1.3 (32–35)

Weight at measurement (g) 1400 ± 193.4 (1090–1800)

HFOV, high frequency oscillatory ventilation; CPAP, continuous positive airway

pressure.

All data are expressed as mean ± 1 standard deviation or N (%), except Ap-

gar scores, which are expressed as median (range).

Table 2 REE measurements according to randomization schedule

Randomization group

REE duringvanillin exposure(kcal ⁄ kg ⁄ 24 h)

REE duringno-vanillinexposure(kcal ⁄ kg ⁄ 24 h)

Vanillin first (n = 8) 70 ± 10 80 ± 13

Vanillin second (n = 12) 80 ± 8 78 ± 10

REE, resting energy expenditure.

Data are expressed as mean ± 1 standard deviation.

Marom et al. The effect of olfactory stimulation on energy expenditure

ª2011 The Author(s)/Acta Pædiatrica ª2011 Foundation Acta Pædiatrica 2012 101, pp. e11–e14 e13

view of the fact that there may be striking differences inREE among different preterm infants.

Our findings are only applicable to preterm infants thatreached a postmenstrual age of 32–35 weeks as in ourstudy. It has been shown by Sarnat that the olfactiveresponses of newborn infants are influenced by gestationalage. Thus, it is possible that the lack of or little response inREE observed in this study may have been caused in part bythe immature olfactive ‘skills’ of our infant population,although the work of Sarnat has shown that newborns canrespond to olfactory stimulations as soon as 28 weeks (7).

The clinical implications of our findings belong to thefield of speculation. It is long known that preterm birth is amajor disruption in the normal developmental progressionof brain structures and may affect sensory-systems develop-ment (13). It has been suggested that targeted modificationsof the environment could minimize the iatrogenic effects(13). Individual strategies have also been combined to formprograms, such as the ‘Newborn Individualized Develop-mental Care and Assessment Program’ (NIDCAP) (13–15).Suggested interventions may include elements such as con-trol of external stimuli (vestibular, auditory, visual, tactile orolfactive), clustering of nursery care activities and position-ing or swaddling of the preterm infant (13). While it is theo-retically possible that exposure to the music by Mozartmight decrease REE (1) and enhance postnatal weight gainof premature infants and maybe as well other outcomes(16), we speculate from the current study that manipulationof growth through olfactory stimulation has a much lowerlikely potential to influence REE and growth, althoughthere is a strong potential for an effect of olfactory stimula-tion on oral ⁄ sucking behaviours or newborn feeding perfor-mances.

References

1. Lubetzky R, Mimouni FB, Dollberg S, Reifen R, Ashbel G,Mandel D. Effect of music by Mozart on energy expenditure ingrowing preterm infants. Pediatrics 2010; 125: e24–8.

2. Schaal B, Hummel T, Soussignan R. Olfaction in the fetal andpremature infant: functional status and clinical implications.Clin Perinatol 2004; 31: 261–85.

3. Bartocci M, Winberg J, Ruggiero C, Bergqvist LL, Serra G,Lagercrantz H. Activation of olfactory cortex in newborninfants after odor stimulation: a functional near-infrared spec-troscopy study. Pediatr Res 2000; 48: 18–23.

4. Bartocci M, Winberg J, Papendieck G, Mustica T, Serra G,Lagercrantz H. Cerebral hemodynamic response to unpleasantodors in the preterm newborn measured by near-infrared spec-troscopy. Pediatr Res 2001; 50: 324–30.

5. Marlier L, Gaugler C, Messer J. Olfactory stimulation preventsapnea in premature newborns. Pediatrics 2005; 115: 83–8.

6. Heuberger E, Hongratanaworakit T, Buchbauer G. East IndianSandalwood and alpha-santalol odor increase physiological andself-rated arousal in humans. Planta Med 2006; 72: 792–800.

7. Sarnat HB. Olfactory reflexes in the newborn infant. J Pediatr1978; 92: 624–6.

8. Goubet N, Rattaz C, Pierrat V, Bullinger A, Lequien P. Olfac-tory experience mediates response to pain in preterm new-borns. Dev Psychobiol 2003; 42: 171–80.

9. Soussignan R, Schaal B, Marlier L. Olfactory alliesthesia inhuman neonates: prandial state and stimulus familiarity modu-late facial and autonomic responses to milk odors. DevPsychobiol 1999; 35: 3–14.

10. Jequier E, Felber J. Indirect calorimetry. Ballieres Clin Endocri-nol 1987; 1: 911–9.

11. Bauer K, Pasel K, Uhrig C, Sperling P, Versdmold H. Compari-son of face mask, head hood, and canopy for breath sampling offlow through indirect calorimetry to measure oxygen consump-tion and carbon monoxide production of preterm infants lessthan 1500 grams. Pediatr Res 1997; 41: 139–44.

12. Marlier L, Schaal B. Human newborns prefer human milk:conspecific milk odor is attractive without postnatal exposure.Child Dev 2005; 76: 155–68.

13. Vandenberg KA. Individualized developmental care for highrisk newborns in the NICU: a practice guideline. Early HumDev 2007; 83: 433–42.

14. Symington A, Pinelli J. Developmental care for promotingdevelopment and preventing morbidity in preterm infants.Cochrane Database Syst Rev 2006; 19: CD001814.

15. Als H, Lawhon G, Brown E, Gibes R, Duffy FH, McAnulty G,et al. Individualized behavioral and environmental care for thevery low birth weight preterm infant at high risk for broncho-pulmonary dysplasia: neonatal intensive care unit and develop-mental outcome. Pediatrics 1986; 78: 1123–32.

16. Kemper KJ, Hamilton C. Live harp music reduces activity andincreases weight gain in stable premature infants. J AlternComplement Med 2008; 14: 1185–6.

The effect of olfactory stimulation on energy expenditure Marom et al.

e14 ª2011 The Author(s)/Acta Pædiatrica ª2011 Foundation Acta Pædiatrica 2012 101, pp. e11–e14