Noise and Children
Summary
The world of the child is becoming noisier and noisier. Compared to the mid-fifties environmental noise levels (sources such as road traffic, aircraft) increased substantially, causing higher noise levels during day- and night-time at home, at school and during out- and indoors leisure time activities. Also, children spend increasingly more time in situations with (many) other children, such as in day care institutions and kindergartens, with high noise levels due to a combination of loud voices, loud toys, and bad acoustics. In an unknown percentage of households, nowadays television or audio-equipment is turned on for the whole day, thus creating an everlasting noisy environment for the child. Children may be more annoyed or otherwise adversely affected by noise than adults, in part because they possess less well-developed coping responses, and are often less able to control their environments. It is unknown to which extent aggressive behaviour, helplessness, and hyper-activity are (in part) a consequence of the everlasting noise exposure of the young and older child.
In contrast to the extent of noise exposure of children is the extent of research into the effects of noise exposure on their health. It is largely unknown which adverse noise-induced effects occur in children and also at which levels these effects start to occur. Usually environmental noise regulations based on exposure effect relationships for adults are assumed to be applicable to the child as well.
This report gives an overview of the adverse effects of noise exposure on the health of children. The overview is based on data obtained from the literature. In this summary the possible effects of noise on children’s health are discussed, with children classified according to age. Health is assumed to include biological (physiological, somatic), psychological, social and emotional aspects.
Fetus
Three types of possible effects due to high noise levels during gestation of the mother have been considered:
The information available on noise-induced effects on the fetus shows hearing impairment associated with exposure to high occupational noise levels during gestation. On-going research indicates that also growth retardation of the child is associated with extensive occupational noise exposure of the pregnant mother. It cannot be excluded, but is seems unlikely, that environmental noise causes fetal abnormalities. Overall, the studies on the effect of environmental noise on the fetus have been hampered by serious methodological limitations, both in terms of assessment of noise exposure and effect, and failure to control for known determinants of the effects under investigation.
Pre-term and full-term babies
There are substantial differences between the pre-term and full-term baby. Pre-term babies must cope with their environment with immature organ systems. The auditory, visual and central nervous systems are the last systems to mature. These last stages occur, in part, during the time the pre-term child is in the incubator or neonatal intensive care unit (NICU). Also, the sleep-wake patterns differ markedly among pre-term and full-term infants.
It has been recognised for long that high noise levels exist in the NICU and incubators, the environment in which the premature baby usually lives for shorter or longer periods up to months. Measurements in the NICU have shown equivalent sound levels from 60 to 90 dB(A) with maximal levels of very loud events up to 120 dB(A). The equivalent sound levels in the incubator are 60 to 75 dB(A), and when ports of the incubator are closed maximal sound levels up to 100 dB(A) occur.
Four types of adverse noise-induced effects on the pre-term baby have been considered:
Hearing impairment
In premature babies the hearing organ is still developing after birth. Taking into account the extra vulnerability for hearing impairment during development of the hearing organ, higher levels of NICU and incubator noise is to our opinion able to produce noise-induced hearing impairment in pre-term babies. However, there is no research carried out which could support this statement.
Sleep disturbance
Noise events in the NICU and incubators are sufficiently loud to have an effect on sleep, either by awakening the infant or by changing the sleep state. Pre-term infants who have difficulty maintaining stable behavioural states experience the same or greater sleep disruption as do term infants to similar stimuli.
Somatic effects
Through the increased number of awakenings and associated crying the effect of noise in the incubator and the NICU is a potential cause of hypoxemia and source of neonatal morbidity. Fluctuations in arterial oxygen tension, blood pressure and intracranial pressure may contribute to hypoxic brain damage. The decrease in oxygen saturation of blood can affect all the vital organs. The infant residing in the NICU or incubator can experience acute effects many times in the period of rapid brain growth. Potential consequences include increased risk of weakened vessel walls in the cerebral vasculate. Unfortunately in-depth research on this subject is lacking.
Auditory perception and emotional development
Current knowledge strongly suggests that stimulation provided by the auditory environment plays a role in the emotional development and in the development of auditory perception of the baby. The sound quality in the NICU and incubator is reduced, since speech and other relevant sounds are masked. It is also difficult for infants in an incubator to localise the origin of air-borne sounds and these sounds contain less higher frequency components. This impaired sound quality implies that the pre-term infant may have difficulties in making fine discriminations with respect to (the intonation of) the voice of the mother and caretakers. The possible emotional implications for the pre-term baby at a later stage are unknown.
Pre-school and school children
The following effects have been considered:
Noise-induced somatic effects (such as on blood pressure and hormone levels) can best be considered as part of a stress response of children to their noisy environment. Psychological and cognitive processes also play a role in this stress response of children. Therefore, somatic (physiological) results should be considered together with psychological outcomes to give an overall insight in the problem.
It is an important question whether prolonged noise exposure results in increasingly adverse effects on children or whether those exposed for longer periods adapt to the situation with effects disappearing after a while. The relevance for health and development is clear if the effect or effects studied have a permanent nature and do not disappear. On the other hand, if a survey shows that adaptation of the measured effect variables occurs, it is unsure what the price of these temporary effects is on other variables that were not measured. For instance, if a real life study on the effect of noise exposure on psycho-physiological stress-related variables (blood pressure, cognitive performance) shows that the child adapts to the noise situation at school, it is uncertain what the price is on other functions such as aggressive behaviour, unless that variable was measured as well.
Hearing impairment
The investigations undertaken so far show that environmental noise exposure does not have an effect on hearing threshold levels of children, with the exception of exposure to noise from extremely low flying military aircraft. However, taken into account the very high noise levels present during 24 hours in mega-cities, research in this area might show hearing impairment in children associated with these very high noise exposures. Given the high noise emissions of specific toys and equipment, some noisy activities may impair the hearing of children. Potential sources of hearing impairment in children are: toddlers noisy toys, fire-crackers, tractors and other agriculture machines, snow mobiles, shooting equipment, power tools, musical instruments, walk- and disc-mans. Although hearing impairment has been reported in isolated cases, the results of large-scale hearing surveys with school children fail to show increases in hearing impairment attributable to noise exposure.
Effects on sleep
There are only a few observations with respect to the effects of noise during sleep on sleep parameters of children. The few test results do not contradict the hypothesis that – in analogy with physiological reactions in the waking state - physiological responses occur in children at a lower event level than in adults. On the other hand, even if the child is awake, as measured by sleep EEG, it usually does not produce a behavioural response, such as pressing a button. In particular during REM sleep, noise events of sufficient intensity are able to cause EEG awakenings in children. During the last third of the night, in which REM sleep is predominant, children under experimental conditions show 50% EEG awakenings due to noise signals with maximal levels of up to 95 dB(A) above threshold. Although children exposed at home may show less awakenings, this is an important finding, because of the necessity of REM sleep for memory consolidation. The few test results obtained so far give an indication that noise events in the first part of sleep (evening-time) do have less impact on sleep of children than noise events in the early morning. Since sleep is very important to health and development of children, much more research is needed to obtain a more detailed insight in possible adverse noise-induced effects.
Somatic effects
Only one, older, cross-sectional study showed unambiguously that environmental (aircraft) noise exposure is associated with an increase in (rested) systolic and diastolic blood pressure. In the more recent Munich aircraft noise study, noise-induced increase in stress hormone (epinephrine and nor-epinephrine) levels could be established. In all other studies, covering aircraft and road traffic noise, differences in physiological parameters of noise-exposed children and children not exposed to high levels of noise effects were either not statistically significant, absent or it could not be excluded that intervening variables could (partly) explain these differences.
With respect to physiological adaptation, the data presented on road traffic noise show an increase with age in the differences in blood pressure between noise-exposed and not exposed children (no adaptation), whereas all data on aircraft noise exposure show decreasing differences with duration of exposure (adaptation). If possible effect-modifying factors would not have played a role, this would imply that children physiologically adapt to a certain degree to aircraft noise, but not to road traffic noise. As pointed out earlier, this does not imply that the child also adapts to aircraft noise exposure in all other aspects or that long-term consequences are absent.
Psycho-social effects
Some of the adverse effects of environmental noise on children may be caused indirectly by noise effects on their caretakers. Studies show significant interruptions and lost teaching time in schools with high traffic noise levels. Also, teachers in these schools report noise annoyance and irritation due to the noise and dissatisfaction with their working situation. Parents in noisier homes, with most of the noises generated indoors, are less responsive to their children than those in quiet homes. Perhaps the speech patterns of the parents, teaching and demonstrating behaviour or engagement in cognitive related activities (reading aloud) is adversely impacted by noise. There are no studies available on behaviour of parents living in homes with high environmental noise levels.
Most studies on the psychological effects of noise exposure on children are focussed on aspects of cognition. Nearly all of these studies selected children in specific noisy and quiet schools as study and reference populations. School children, with a long-term exposure to high levels of traffic noise from either aircraft, road or railway traffic, do show impairments in performing cognitive tasks under quiet conditions. The best-documented noise effect is that on reading acquisition. Several studies have found indications of a negative relationship between long-term noise exposure and reading acquisition (measured under quiet conditions). There are fewer studies of noise effects on other aspects of cognitive processing, such as long term memory, attention, and motivation of children. The studies which have examined possible links between noise exposure and attention deficits among children show varying results. Several investigators found an effect of long-term noise exposure on the performance of a task (a visual search task or an auditory sustained attention task), while other researchers did not. Of interest is the finding that a visual coding task was performed better under acute noise conditions by children attending noisy schools than by children attending quiet schools, whereas they did worse on the task when performing it under quiet conditions. These and other findings suggest that attention deficits related to long term noise exposure in children occur because children learn how to ignore auditory stimuli (gate out distraction) as a way to cope with long-term noise exposure. Unfortunately, this tuning out process may over-generalise so that children learn to tune out not only noise, but also relevant other auditory signals, such as speech.
Some studies showed that children highly exposed to environmental noise for prolonged periods of time are less motivated when placed in situations where task performance is dependent on persistence. These motivational deficits in children related to long term noise exposure have been considered in the light of the learned helplessness theory. Prolonged exposure to uncontrollable stimuli has been shown across a wide variety of conditions, including noise, to induce feelings and behaviours indicative of helplessness. As the child continues to struggle unsuccessfully with an uncontrollable stimulus, it eventually learns that it is helpless to do anything about the situation, as manifested by feelings of hopelessness and reduced persistence. Like in adults, this effect is strongly mediated by personal characteristics.
Teenagers
There is a nearly complete lack of research into the somatic, psycho-physiological and behavioural effects of noise on teenagers, nor are there studies on noise-induced sleep disturbance of subjects of this age group. The only noise effect in teenagers to which a lot of studies have been devoted is noise-induced hearing impairment.
Hearing impairment
The potential sources of hearing impairment mentioned for schoolchildren (noisy toys, fire-crackers, tractors and other agriculture machines, snow mobiles, hunting equipment, power tools, musical instruments, walk- and disc-mans) may also impair the hearing of teenagers. In addition, it is not unlikely that noise levels in boom-cars and (under helmets) of motor cycles cause noise-induced hearing impairment in teenagers.
A part of the older teenagers is already employed. The relationships presented in ISO 1999 (1990) about noise-induced hearing impairment and noise exposure show that during the first 10 years of exposure hearing impairment at the most affected frequency (4000 Hz) is only somewhat less than after a life time exposure. Therefore, to preserve good hearing in case technical noise abatement measures are not taken, it is important that teenagers are instructed to use personal hearing protection from the beginning they start being exposed to high noise levels, not only at work but already at technical schools and polytechnics. The extent of hearing impairment in teenagers caused by occupational noise exposure and exposure at technical schools and polytechnics is unknown.
Most of the studies on hearing impairment in teenagers concern the effect on hearing threshold levels of exposure to pop music in discotheques, at pop concerts and house parties and when listening through headphones. Many of these studies have been limited to the assessment of the degree of hearing impairment in teenagers, without trying to specify exposure effect relationships. In a study about the relationship of hearing threshold levels and exposure to pop-music through headphones, it was made plausible that the model given in ISO 1999 for occupational exposure of adults also holds, albeit with a slight adaptation, for this type of exposure and for teenagers. Whether the model also applies to the much more irregular exposures of teenagers to pop-music at pop-concerts, discos and dance halls, is unknown.
Although noise-induced hearing impairment among teenagers has been reported in isolated cases, a comparison of the present
distributions of hearing threshold levels of young populations with those distributions 30 years ago fails to show increases in this distribution.