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Health Studies
R Song

Lecture 5: Factors Influencing Child Growth: February 6, 2012 Environmental Factors Determinants of Human Growth and Development Environment 1. Genetic Factors (see diagram) 2. Endocrine System 3. Cultural Factors 4. Environmental Factors  Genes, Hormones, Environment (physical, cultural) Climate and Body Proportion  Bergmann’s Rule o Populations in colder climates are generally larger, with wider torsos/stockier stature, since reduced surface area relative to body weight limits heat loss  Those in warmer climates are more slender, increasing surface area relative to weight to maximize heat loss  Allen’s Rule o Populations in colder climates will have shorter arms and legs relative to height (to limit heat loss), while those in warmer climates will have longer arms/ legs  However, improved nutrition, particularly in tropical regions, is now reflected in weaker climate-body size relationship than in the past Temperature Altitude Seasonality Migration Activity Cold  Requires higher rate of basal metabolic rate and robs body of energy that could be used for growth Altitude  More than 25 million people live in high altitude regions (>3000 m above sea level): o Andes, Ethiopia, Himalayas, Tibet, NW U.S.  Stresses: hypoxia, high solar radiation, cold, low humidity, high winds, rough terrain – limiting life and agricultural productivity  Cold and Hypoxia: most important determinants of growth at high altitude Hypoxia  Most severe climatic stress, limiting sufficient oxygen delivery to body tissues  Cannot be overcome by any cultural or behavioural adaptation available to native high altitude peoples  At Sea Level: oxygen-saturated hemoglobin of RBC is about 97% saturated as it leaves lung o But at 3000 m: arterial hemoglobin is approx. 90% saturated with O2 o Enough to disrupt cellular metabolism and delay cell growth  Consequences: o statistically significant lower birth weight (i.e., Bolivia: 3.133 kg vs. 3.415kg), reduced length at birth  After birth, combined with poor nutrition: o several studies have found shorter and lighter kids, reduced rate of growth, prolonged growth period, late growth spurt in high altitude vs. low altitude regions o BUT: other studies suggest the opposite: better growth rates in high altitude vs. low altitude kids in same region (Peru, Nepal, Ethiopia) o Due to poorer health and nutrition in low altitude regions plagued with malaria and intestinal parasites (sanitation issues) – which are less common in highlands  While hypoxia can play a role, it is the synergistic relationship with poor nutrition (poverty) that results in compromised growth and development Seasonality  At temperate latitudes: Climate variation can influence growth  Healthy, well-nourished kids grow more quickly (height/weight) during spring/summer compared to fall/winter  Not completely understood, but probable that sunlight acts on human endocrine system to influence growth  Sunlight may synchronize body’s natural 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 (Bogin 1999: 290)  HEIGHT: Vitamin D3: increases intestinal absorption of Ca and controls the rate of skeletal remodelling and mineralization of new bone  WEIGHT: can be product of food availability (seasonal food shortages) Hormones and Human Growth  Hypothalamus (hormones that stimulate or inhibit release of pituitary hormones) (Brain)  Pituitary gland (stimulating hormones released into general circulation moving to specific target tissues) (Brain)  Thyroid hormones (thyroxin, triiodothyronine) (Thyroid)  Gonadal hormones (LH and FSH) (Gonads)  Adrenal hormones (glucorticoids [e.g., cortisol] and androgens) (Kidneys)  Growth hormone (general growth-promoting effect) ALSO: Insulin-like growth factors (IGF-1, IGF-2) (Liver) Pollutants and Child Growth Air Pollution  Natural and anthropogenic  Anthropogenic: human-made 1. Smoke o Fire/cooking/coal-burning/cigarettes: respiratory diseases, lung cancer 2. Smog o burning of fossil fuels, mixed with fog; photochemical smog – action of sunlight on chemicals found in air pollution (car exhaust) o Chemicals in Air Pollution (with industrialization / manufacturing / automobiles): carbon monoxide, nitrogen oxides, sulfur oxides, hydrocarbons, ash, metals, asbestos; RESULT in poisoning, strain on respiratory, cardiovascular systems; asthma, emphysema, cancer Water Pollution  Due to poor sanitation, chemical contamination (and natural disasters)  Toxic Chemicals: 1. Industrial sources – landfills, hazardous waste disposal sites, gasoline storage tanks: leakage into freshwater/marine environments, ground water (wells) 2. Agricultural sources – chemical fertilizers, herbicides, pesticides on crops, runoff into streams, lakes, rivers, seepage down to water table  Health effects: heavy-metal poisoning: neurological and other disabilities, fatalities (Minamata disease); toxic organic pollutants: childhood leukemia, kidney/liver disease; cancer Solid Waste Pollution  Human dumping of refuse; transport by animals  Can lead to: 1. Air pollution –when garbage burned, blown as dust 2. Water pollution –rain/water leads to seepage into surface and ground water  Health effects: poisoning (note: lead paint), respiratory problems Mercury and Minamata Bay  Methylmercury contamination of Minamata Bay, Japan  Central nervous system impairment due to severe mercury poisoning  Symptoms: numbness in extremities, muscle weakness, lack of coordination, vision and hearing damage, impaired speech, paralysis, coma and death in some cases  Congenital form affected fetuses, showing impairments similar to cerebral infantile paralysis  Effects on fetus more destructive than adults Lead and Child Development  One of the most common preventable poisonings of childhood  Children affected at any age; especially vulnerable due to rapidly developing nervous system that is very sensitive to effects of lead  Common sources of contamination: lead paint, gasoline, plumbing, batteries, lead in water and soil  Consequences (chronic exposure): behaviour: inattentive, hyperactive, irritable; cognitive impairment: learning and reading difficulties; hearing loss; kidney damage; delayed growth and development  High levels: permanent brain damage, muscle weakness, seizures, death  Fetal development: maternal exposure can pass lead to fetuses in amounts capable of cognitive impairment Quiz: The Minimata Bay disaster exhibits:  the effects of toxicants in the human diet Pollutants: Smoking  During pregnancy: can lead to altered fetal growth, low birth wt  With smoke exposure (2nd hand smoke): higher rates of respiratory conditions (asthma, pneumonia, bronchitis), SIDS, middle ear infections, cognitive impairment, behavioural problems (hyperactivity, depression, ADHD)  Later adult health problems (respiratory diseases, cancer) “Modern” life, Chemicals, and Human Growth and Development  Environmental contaminants and endocrine system  Endocrine “disrupters”  “Modern” threats: phthalates, persistent organic pollutants (POPs), microwave radiation (cell phone use, laptops), high voltage power lines, bisphenol A, changing diets and production methods: genetically modified food, antibiotics, hormones, etc. Case Study: Akwesasne Mohawk  A North American indigenous group that has experienced exposure from local industrial sources of pollutants that have contaminated local waterways and influenced their behaviour, and to some extent their culture (Schell et al. 2009)  Persistent organic pollutants (POPs): group of toxicants with some similar properties; includes: o DDT (dichloro-diphenyltrichloroethane) o Dioxin (the most toxic compound synthesized yet), and its closely toxic relative, dibenzofuran  Another group, the polychlorinated biphenyls (PCBs), share a basic common structure with dioxin but are highly variable PCB  Refers to any one, or any combination of 209 specific  Altered estrogen
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