Introduction
The human growth curve has been characterised primarily by an attenuation of childhood, followed by a comparatively brief, intense adolescent spurt. The prolonged period of biological immaturity, has heightened sensitivity to the environment ensuing in a plasticity of growth as a consequence of environmental interactions. The growth, ‘”responses to the environment are part of the adaptive potentials of humanbeings.
In the’ past, demographic parameters were appropriate to the conditions of the environment and, when disease and malnutrition occurred though acute, they tended to be short-term. But in the current scenario, many populations exist under conditions of great social and economic disadvantages, with overcrowding, poverty, malnutrition and disease. Under these circumstances, environmental stress and deprivation, while ranging from moderate to acute, are chronic and intractable in the short term. This situation is exacerbated by the forces of acculturation, in which cultural values alter in response to changing norms, Thus, rather than providing an ecosystem within which individuals may reach their genetic potential, the environment becomes a systematic ‘force which constrains human development. The present unit provides a discussion on the influence of environmental factors on human growth and development.
(a) Nutrition
The growth of an individual to its innate potential exponentially depends on adequate supply of nutrition; It encompasses total energy intake and intake of energy yielding macronutrients (protein, fat, and carbohydrate), vitamins and minerals which are required for the growth, maintenance, repair and work during the course of human life. In population where food shortages are present growth delays occur, and children are shorter and lighter than in population with adequate or overabundant supplies of food. A child with nutritional growth retardation reaches a new energy equilibrium phase between their genetically determined growth potential and the present energy intake. Thereby, growth deceleration is the adaptive response to suboptimal energy intake but inadequate energy intake (and often protein) for a prolonged period of time evidently results into energy malnutrition (Rogol et al., 2000). . . .
Micronutrient malnutrition, characterised by the lack of essential vitamins and minerals affects children’s immune systems as’ well as their physical and cognitive development during formative years of growth. Iron deficiency anemia affects about one third of the world’s population whereas 2.2 billion are iodine deficient disposing them as most detrimental nutrients for growth. Greene (1973) studied Ecuadorian Indians inhabiting Andean region with chronic iodine deficiency. Individuals without clinical signs of iodine deficiency (e.g. goiter, cretinism, etc.) were on average taller (155:5 cm) than affected ones (146.2 cm). When compared, normal Ecuadorian individuals were lower in heights than Quechua Indians from Peru suggesting iodine to be the major environmental factor which determines the difference in the stature. In India, despite long standing efforts to combat Iodine Deficiency Disorders through a Universal Salt Iodization program, only 51% of households were using iodized salt in 2005. To justify the expansion of these active efforts, Bhat (2009) evaluated the causal link between the access to iodized salt and child health and proposed the positive impact of access to iodized salt on children’s height-for-age, especially for ·children living in rural settings. Increasing iodine concentration from 0 to 15 ppm seemed to drive the average height-for-age standard deviation from -1.91 (borderline stunted) to nearly +0.43 standard deviations above the NCHS standard. Bhatia and Seshadri (1993) evaluated the effect of iron supplementation on growth status of anemic and normal preschool children aged 3~5years. Iron supplementation resulted ·into weight gain and significantly higher weight for height, among anemic children than anemic children on placebo diet.
Although the deficiency of essential nutrient results in growth retardation, mild-tomoderate energy deficiency is foremost nutritional problem. Chronic undernutrition among children retards the growth in height and weight, and delay rate of maturation towards adulthood. The delayed maturation however may allow for some “catch-up growth”. For instance, the famines of World War I and II retarded the growth of children and adolescent exposed to them. Compared with pre-war levels, the mean stature of age-matched children decreased between 1939 and 1949. ‘Average heights returned to pre-war levels in 1953 for girls, but not until 1956 for boys. The growth of children who were between ages of birth and 12 years during war was affected more than the growth of older children. The post-war recovery in height and weight occurred more rapidly in large cities, followed by small cities, and then -rural mountain villages. Since improvements in diet also followed the same path, it is likely that the growth recovery was, in large part, due to better nutrition (Kimura, 1984). Delays in skeletal maturation do allow undernourished rural Thai children to grow for, average, at least a year longer than United States’ children (Bailey et al., 1984). The rural Indian boys with severe growth retardation in early life achieved a peak height velocity (6.9 cm/yr) similar to that of British boys (7.3 cm/ yr), though the event was postponed by 2 years from 14 years to 16 years. Despite their longer period of growth, the malnourished boys were significantly shorter than , the better nourished British boys at age 18 years (Satnarayan et al., 1980). Such studies indicated that the pattern of growth established before the age of five years may often continue unabated to adulthood which can be attributed to synergistic effects of undernutrition and disease on growth,’
An Indian study examined the pattern of growth faltering in preschool children, using World Health Organization (WHO) growth standards 2006 from the available datasets of first and third National Family Health Survey (NFHS 1 and 3). The National Family Health Survey (NFHS) provides three indices of children’s nutritional status: height-for-age, weight-for-height, and weight-for-age. Height-for-age measures linear growth retardation, primarily reflecting chronic (long-term) malnutrition. Weight-for-height measures body mass in relation to height, primarily reflecting acute (short-term) malnutrition. Weight-for-age reflects both chronic and acute malnutrition. These three indices are expressed in terms of standard deviations from the median for an international reference population specified by the World Health Organization (WHO, 2006). The study revealed that about half of the total faltering that had taken place. by the end of first three years of life was present at birth and much of the growth faltering in early life could be attributed to faltering in height-for-age i.e. stunting (Mamidi et al., 2011).
The synergism of hunger and disease leaves its mark on individuals who survived through childhood, and usually results into growth retardation (either height, weight, or both), reduced intellectual capacity and work capacity (Adair and Guilkey, 1997). ‘Each of these deficits impairs the individual, reduces chances of at) individual towards leading a productive and satisfying life, and increases the chance of hunger and disease to be recycled into next generation. The cycle of hunger, disease and despair can be broken by supplementing infant and children with quantitative food. An experimental study known as INCAP “Four village study” evaluated the effects of nutritional supplementation on physical and mental development of infants and adolescents (Martorell et al., 1975). It involved the supplementation of pregnant women, infants and children with one of the two drinks: atole or fresco. Atole is the local term for a gruel, prepared from corn meal and contain carbohydrate, protein, vitamins and minerals. The fresco is cool refreshing drink contained only carbohydrates, water and artificial flavor. The study disapproved the preexisting hypothesis that poor, rural people of less. developed countries like Guetamala has ‘adapted’ to a limited food supply, and would not benefit from additional food. The infants and children supplemented with atole grew considerably taller and heavier than the children getting the fresco. The atole supplemented children also performed better on cognitive tests than the children supplemented with fresco.
(b) Altitude
“More than 140 million human beings live in high altitude regions of the world; that is at altitudes of 2500 meters above the sea level or higher (Beall, 2000). High altitude environment impose a number of stresses on people, including hypoxia, high solar radiation, cold, low humidity, high winds, and rough terrain with severe limitations of agricultural productivity of the land. Of these, cold temperature and hypoxia, the lack of sufficient oxygen delivery to the tissues of the body, has been considered to be the most important determinants of growth at altitude (Bogin, 2001).
Cold requires a higher basal metabolic rate and robs the body of energy that could be used for growth. Hypoxia may be the most severe stress, since it cannot be overcome by any cultural or behavioural adaptation available to native high altitude. At altitudes, the arterial hemoglobin is only about 90 percent saturated with oxygen as compared to 97 percent at sea level. This decreased oxygen saturation is sufficient to disrupt cellular metabolism and may delay cell growth (Luft, 1972). Low birth weight evidenced among infants of high altitude indicates intrauterine growth retardation during prenatal period raising infant mortality rate (Moore and Rogensteiner, 1983): High altitude reduces birth weights, averaging a 100-g fall per 1000m elevation gain. Hass et al. (1980) reported mean birth weight of 3415gm among infants born at low altitude (Bolivia, 400 meter) as compared to 3133 gm among high altitude infants (3600 meters). The differences remain significant even when the effectsof confounding factors such as maternal nutritional status and smoking, gestation length, ethnic background and length of residence at high altitude were controlled. However, adaptations in multigenerational high altitude populations (e.g., Andeans and Tibetans) have lead to high birth weight infants. The increased maternal ventilation and arterial oxygen saturation during pregnancy at high altitude protect against altitude-associated intrauterine growth retardation-IUGR (Moore, 2003).
Earlier, the delayed growth during postnatal period at high altitude revolved around the dogma of hypoxic condition. In a classic study among Peruvian India children, , Frisancho and Baker (1970) characterized the high altitude children as having a slow rate of growth, a prolonged growth period lasting to age 22 years and a late and poorly defined growth spurt. Slow growth is associated with delayed skeletal maturation and delay in the age at which epiphyseal union takes place. The Andean studies carried out in Peru, Bolivia and Chile, also found greater chest dimensions relative to stature among high-altitude individuals as compared to lowlanders. The proportionally greater chest cages seems to be an adaptation to low partial pressure ‘of oxygen. Muller et a1. (1980) summarized these studies as an adaptive response to atmospheric hypoxia delays, linear growth and maturation as well as enhances functional capacity of the oxygen transport system with a constant increase in total lung volumes.
In contrast, Clegg et a1.(1972) found that high altitude, living Ethiopians were taller and heavier than ethnically similar people living at low altitude in Ethiopia. In this case, the growth of lowland population was compromised by the suffering from malaria and intestinal parasite. Frisancho et a1.(1975) also reported that chronically undernourished Peruvian children living in the slums of Lima (Peru, 500 meters) were shorter and lighter than better nourished Indian children at high altitude. Sherpa living at high altitude (3500-4500 meters) in Nepal were taller, heavier, and fatter than Sherpa migrants to lower altitude (1000-1500 meters) area of India (Gupta and Basu, 2005). Thus accumularing evidences indicate that the insults of undernutrition and disease in low altitude environment may have a greater negative effect than the hypoxia of altitude on growth and development. ‘
Perhaps the distinct evaluation of the effect of hypoxia on growth, comes from the work of Stinson (1982) that included 323 Spanish-Indian school children aged 8-14 years belonging to middle to upper socioeconomic status (SES), healthy and well nourished. Stinson found a negative correlation between stature and length of residence in La Paz. According to this study, shortest children had lived at high altitude the longest time. However, the altitude effect was small with about 2.5cm difference in height between children with the longest and shortest residence at’ high altitude. In a study of Bolivian children living at high and low altitudes, Post et a1.(1997) found that both, poor nutrition and high energy expenditure cause the short stature of low socio economic status groups. However, in another study on Bolivian children of European ancestry living in high altitude, Greska (2005) found that chronic exposure to hypobaric hypoxia results in a delay in liner growth and maturation in European children, as well as in an enhancement of their lung volumes.
(c) Climate
The climatic effect on human growth and development, often measured by variation in body size and proportion follow to the ecological rule of biological adaptation to thermal environment: Allen and Bergmann. The Bergmann rule states that “within the same species of warm-blooded animals, populations having less bulky individuals are more often found in warm climates near the equator, while those with greater bulk, or mass, are found further from the equator in colder regions”. Allen’s rule states that “among warm-blooded animals, individuals in populations of the same species living in warm climates near the equator tend to have longer limbs than do populations living further away from the equator in colder environments”.
Based on the world-wide sample, Roberts (1953) found a negative correlation between body weights and mean annual temperature that is, higher body weight in colder region (Bergmann’s rule). In subsequent analysis, he discerned that the ratio of sitting height to total height decreased as temperature increased that is people in warmer regions have relatively longer legs and arms (Allen’s rule). Compiling the findings, it can be stated that people in colder climates tend to be heavier with relatively larger trunks and shorter legs, while in hotter climates tend to be lighter and relatively longer legged. Schreider (1964) on the basis of height and weight data from populations residing at different latitudes found that body surface area increases from colder to hotter climates. A survey in sub-Saharan African population revealed positive correlation of stature with the mean temperature of the hottest month and negative with humidity of the driest month. That is Africans living in hot-dry areas tend to be taller than Africans living in hot-wet areas (Froment and Hiernaux, 1984).
Hiernaux (1974) considered the small stature and lean body build of the Ambuti pygmies and other pygmy people of Africa as an adaptive response to severe stress of high humidity and moderately high temperature of the rain forest. Such climatic condition limits the heat loss from the body by evaporation. Thereby small body mass maximizes the avenue for heat loss by radiation and convection.
Crognier (1981) surveyed 85·European, North African and Middle Eastern populations and compared with climate variables with 14 anthropometric measurements. He hypothesized that the mean annual low temperature would strongly influence the body size and proportion of the population study. The results were true for most cranial measurements, such as head length and head breadth, but the post cranial measurements have their strongest correlation with heat and dryness. The findings were explained in terms of effective cultural adaptation to cold, such as fire and clothing which have been in practice since humans occupied the temperate latitudes. He argues that the brachycephalic head suited better for the cold than dolicocephalic head, since a sphere affords maximum volume for heat retention and minimum surface area for heat loss. However, the ecological and other similar arguments for a biological functions for head shape, is not very compelling as Eskimos who are as dolicocephalic as African protect the head by cultural means (fire and clothing).
(d) Seasonal Variations
Climatic variation during the year influences the growth rate. At temperate latitudes, healthy well nourished children grow more quickly in height during the spring and summer while fall or winter is the season of maximum weight gain. Several researchers proposed that minimum weight gains, or weight losses, occur simultaneously -with the gain in height (Bogin, 1979; Tobe et aI., 1994). Seasonal variation observed in tropical zone extends to temperate region also. The probable cause of such variation in growth rate may be attributed to seasonal periodicity in sunlight which acts on human endocrine system. The sunlight synchronizes the body’s fluctuations in growth regulating hormone activity so that all the necessary hormones are working simultaneously to speed-up or slow-down the rate of skeletal growth. Nylin (1929) experimentally tested the sunlight effect on a sample of Swedish boys in Stockholm. He exposed a group of 45 boys to ‘sunlamp’ treatment (a lamp that produces both visible and ultraviolet light) during winter months and compared their growth to another group of 292 boys not receiving treatment The experimental group averaged 1.5 cm more growth in height than the control group. During summer, controls grew at a faster rate than the experimental group, so that over the entire year there was no difference between groups in ‘total height gain. Vincent and Dierickx (1960) found that healthy children living near the equator in Zaire grew rapidly in height in the dry season than in the rainy season. Although day length was slightly longer during the rainy season, there was far more hours of insolation (bright sunlight), and more opportunity for children to be exposed to 23
sun, during the dry season. A relation between light and growth has been known since 1919, when it was shown that ultraviolet light could cure rickets, a disease of bone growth. A few years later it was demonstrated that vitamin D3 is synthesized by the skin when people are exposed to ultraviolet light. The physiological action of vitamin D3 is to increase the intestinal absorption of calcium and to control the rate of skeletal remodeling and the mineralization of new bone tissue.
Billewicz and McGregor (1982) analysed the growth of children and-adults living in two Gambian (West Africa) villages. The villagers grow food by traditional horticulture methods. The agricultural cycle is determined by climates: dry season and rainy season. The rainy Season lasts from late May to the end of October with August and September being the wettest months. Food supplies are lowest from August to November and, typically, adults lose 2.5 kg in body weight during the rainy season. Children grow significantly faster in height and weight during the dry season than during the rainy season. For boys and girls aged five to nine years old, the dry season increase in height averages 6.1 cm and the rainy season increase averages 4.2 cm. Food shortages during the rainy season occur simultaneously with an increase in the incidence of malaria, intestinal parasites, and childhood gastroenteritis. These diseases may decrease the food intake, or intestinal absorption, of affected individuals, increase protein and energy expenditures to combat disease, or decrease the nutrient value of foods consumed (due to parasite competition, diarrhea, etc.). The combination of these insults result in severe undernutrition during the rainy season directly reflected in the. poor growth of children and the weight losses of adults.
Billewicz and McGregor (1982) found that the growth deficits associated with rainy season under-nutrition could not be compensated during the dry season, and that over the year the people suffered from a net shortaje of calories. As a result, the Gambian children grew less at every age compared with a reference sample of British children. The adolescent growth spurt of Gambian boys is delayed compared with better nourished boys; peak height velocity takes place at 16.3 years for the boys compared with about 14years for British or high SES Guatemalan boys. The intensity of the spurt is reduced, peak height velocity is 6.9 crn/yr compared with 8.2 crn/yr for British children and 9.3 cm/yr for high SES G’ratemalan boys. The Gambian boys have a longer total growth period, which makes up some of the difference in height, but the net result of a Iife time of undernutrhion is a significant reduction in height and weight compared with better nourished populations.
The seasonal variation in the rate of growth in weigh’: could be explained by seasonal food shortages or disease experienced by Gambian population. Weight growth variation is clearly due to increases and decreases in energy balance during the year. But for other, well-nourished populations as Guatemala, this explanation is not sufficient. Thereby, suggesting existence of endogenous seasonal rhythm. There has been considerably more agreement regarding the significance of seasonal variation in the intake of fat and carbohydrates. Carbohydrates and fat have a peak intake during the winter and a minimum in the summer. In both China and India variability in micronutrients, such as beta carotene, was larger than macronutrients (Hebert et aI., 2000; Cai et aI., 2004). This may indicate a reasonable shift to more affordable and accessible sources of carbohydrate, fat, and protein to compensate in seasonal variations” in cost and availability in what are large sources of macronutrients in virtually all populations (Ma et aI., 2006).
(e) Socio-economic Status (SES)
Human growth is a r flection of the bio-cultural environment into which individual is conceived and developed. General living condition associated with socio-economic status include educational background of parents, purchasing power for food and in turn nutritional status, access to and use of health care facilities and programs, and lifestyle. Mothers’ education plays an Important role in terms of benefits for the next generation, as the socioeconomic status, actions and choices of more educated mothers during pregnancy and child rearing can have a large bearing on children’s nutritional status, well-being and survival.
The human populations of southern Mexico and Guatemala include people of various ethnic groups: Zepotac-speaking Indians, rural Ladinos, and urban Ladinos from the state of Oaxaca, Mexico who are engaged in a continuum of occupations from subsistence agriculture (low SES) to professional and technical jobs (high SES), rural and urban residents, and citizens of two different nations. Children of higher SES, from urban areas, and of Ladino ethnicity are generally larger, in most dimensions, than children of lower SES, from rural areas, or Native American Ethnicity. The most significant difference between samples is for the triceps skinfold measure, an indicator of energy reserves (i.e., adipose tissue) and, hence, nutritional adequacy (Bogin, 2001).
Nutritional anthropometry of preschool children of poor socioeconomic status (agriculturalist) was carried out in a rural community of Uttar Pradesh, India. Weight and height for age of the boys and girls in the study were below the international , standard. Height for age indicates the past nutritional history, these underheight children had suffered growth failure either for a short period at an early age or for a longer period at a later age (Verma et aI., 1980). Chatterjee and Mandal (1991) found that girl, from rural West Bengal were lighter and shorter as compared to Indian norms for girls from higher socio-economic status groups. The mean height and weight of rural boys and girls of Karnataka were significantly below NCHS (50th percentile) and ICMR standards. The positive relation between family income and physical growth imply inaccessibility of the economically deprived parents to provide quality nutrition, medical care and opportunities necessary for proper physical growth of children (Hunshal etal., 2010). Improvement in mothers’ education and economic status simultaneously with nutrition knowledge enhances children’s nutritional status, well-being, and survival. As educated mothers have better knowledge about health care and nutrition, have healthier behaviour, thus they provide more sanitary and safer environments for their children. In addition to the nurturing effect, educated mothers are more likely to have better health, which leads to better health for their children. The larger family size tends to imply poor socio-economic status and is indirect estimate of birth ‘spacing or birth crowding. In larger families, less attention is paid for the fulfillment of nutritional requirement of the children. The percentage of undernourished children and severity of malnutrition increased significantly with the family size in Patna (Kumari, 2007).
Even within a seemingly homogeneous population, subtle differences in SES have a significant influence on growth. Johnston et al. (1,980) analyzed the longitudinal growth records of 276 rural Mexican children. All the children came from families practicing traditional subsistence agriculture, with minimal opportunities for wage labor. The sample of children was divided into two groups, one, with evidence of chronic under nutrition and growth failure, and another with satisfactory nutrition and growth status. Out of 38variables measured for their impact on growth and nutrition, three were significant: socioeconomic status, father’s linear size, and mother’s linear size. Malnourished and poorly growing children came from poorer families, with less-well-educated parents, and had parents with smaller linear dimensions , . (height, biacrominal breadth, etc.) than better nourished children. Since small body size is likely to be the result of poor living conditions, the effect of parental linear dimensions may itself be due to the low SES environment of the parents when they were children. Garn et al (1984) called this trans generational influence of low SES the effect of ‘recycling of poverty’.
SES effects on rate of maturation
A girl’s age at menarche is known to be a sensitive indicator of environmental conditions of growth, and girls from lower SES backgrounds usually have a later mean age at menarche than girls from higher SES backgrounds (Johnston, 1974). It is often argued that SES is, only a proxy for better health care, which reduces childhood mortality and morbidity, and also results in increased growth (Malina. 1979). However the SES effect is more subtle than this. Bielickiand Welon (1982) listed four primary factors relating SES and growth: (1) higher SES,allows for better nutrition, (2) better health care, (3) reduces physical labor for children, and (4), greater growth-promoting psychological stimulation from parents, schools, and peers.
(f) Pollutants
A pollutant may be defined as a material or energy that is unwanted to some degree, is thought to interfere with health or well-being, and is produced by human activity either in part or entirely. However, it should be noted that some pollutants, such as sulphur dioxide and methane, are created by natural processes (Ulijaszek et aI., 1998). Human physical growth may be adversely affected by pollutants, even at low to moderate doses. Evidence is strongest for effects of lead, mercury, noise, air pollution, ‘and’ a group of dioxin-like compounds including the polychlorinated biphenyls and dibenzofurans. Effects of pollutants on growth would be consistent with one of the traditionally accepted indicators of toxicity:
- Weight loss in mature mammals and
- Lack of weight-gain in immature ones.
Lead is retained in the body (90% in the adult skeleton) after exposure, and measurement in teeth and skeleton, hair and blood can provide estimates of longterm exposure, exposure over the past few months, and contemporary exposure, respectively. Lead enters the body primarily by ingestion and to a far lesser extent by respiration (Ulijaszek et al., 1998). Lead poisoning, once commonly defined as a level of lead above 60 micro grams per deciliter and in frequently observed today, is known to reduce post-natal physical growth. However, more recently the low levels of lead which is now common in industrialized countries (for example, below 25 micrograms per decilitre), have also been shown to affect post-natal physical growth and development. Among a national probability sample of United States children aged 6 months to 7 years (National Health and Nutrition Examination Survey II) significant negative relationships were observed between lead level and height, weight and chest , circumference. At the mean blood-lead level each of these dimensions was reduced by 1.5percent compared to a blood-lead level of zero (Ulijaszek et aI., 1998). Among 5-13 years old children in the American Hispanic Health and Nutrition Examination Survey, those with lead levels between 11-40 micro grams per decilitre had a one centimetre deficit in stature compared to children with lower lead levels. ‘
Prenatal exposure may influence prenatal growth and size at birth as well. Several ‘ longitudinal studies begun in the 1970s and 1980s, when lead levels in the . environment were decreasing, have examined this relationship and discovered that levels of lead below 15 micrograms per decilitre may reduce birth-weight with each log unit of lead associated with a 150-200 gram decrement in birth-weight. Head circumference and body-length are not affected,or are affected very little, while skinfolds may be affected most. Early effects on growth may extend into the postnatal period (Ulijaszek et al., 1998). The Cincinnati cohort study carefully examined the contributions of prenatal and postnatal lead level to postnatal growth, and found that high exposures in both periods were related to depressed post-natal growth inthe second and third year of life, but catch-up growth was evident among children whose postnatal lead levels declined to the sample median or below it (Ulijaszek et aI., 1998). The Centers for Disease Control have set 10 micrograms per decilitre as the level above which a health intervention should occur to protect human health and child development.
Polychlorinated biphenyls (PCB), one of the persistent organic pollutants reduce size at birth, advance sexual maturation and alter hormone levels related to thyroid regulation (Schell et aI., 2006). Evidence for dramatic effect of PCB poisoning comes from Japan and Taiwan, when rice-oil contaminated with PCBs and closely related compounds (dibenzodioxins and dibenzofurans) was consumed (Masuda, 1985). The resulting skin disease was termed as Yusho and Yu-cheng means “oil disease” in Japan and Taiwan respectively. In utero exposures lead to babies small for gestational age while postnatal exposures delayed growth of children. The subsequent growth curves were lower than normal children (Yamaguchi et al., 1971). As variety of halogenated hydrocarbon compounds were present in the contaminated oil, the contribution of Pf.Bs alone is not certain. However, there is evidence that low levels of PCB exposure may interfere with neurobehavioral development (Aoki, 2001). High doses of pollutants are associated with reduced physical growth, both prenatal and postnatal, as well as with slowed skeleton development. Since air pollution is a very heterogeneous entity, it is difficult to know which component of it contributes to growth impairment.
Impaired growth and development due to hazardous waste sites have been demonstrated by the Love Canal, New York, a leaking hazardous waste site discovered in 1978. The studies indicated that children born and raised near this canal were significantly shorter than children from a community similar in social characteristics but located far from the dump-site (Ulijaszek et aI., 1998).
Energy, such as noise and electromagnetic fields, may also be considered as pollutants. Studies of exposure during pregnancy to airport noise on size at birth have been conducted in Netherlands (Knipschild et al., 1981), United States (Schell, 1981) and Japan (Wu et aI., 1996). All have reported a negative relationship between size at birth and noise exposure. Noise may affect growth through hormonal pathways since it activates the typical stress response, including reactions from the adrenal cortex and the autonomic nervous system. The fetus may be affected by the mother’s reaction to noise stress, and the child could be affected directly.