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Environmental Factors Contributing to Health
(From Park's Textbook of Preventive and Social Medicine & supporting sources)
Overview
Health is determined by a combination of genetic (host) factors and the environmental factors to which a person is exposed. These two sets of factors interact continuously, and those interactions may be health-promoting or harmful. Hippocrates was the first to relate disease to environment (climate, water, air), a concept later revived by Pettenkofer.
Classification of Environment
| Type | Description |
|---|---|
| Internal environment | Every component part, tissue, organ, and organ-system and their harmonious functioning - the domain of internal medicine |
| External (macro) environment | All that is external to the individual human host, divided into physical, biological, and psychosocial components |
| Micro-environment | Personal environment - eating habits, smoking, drinking, use of drugs |
| Occupational environment | Workplace-related exposures |
| Socio-economic environment | Poverty, housing, education, income |
Key Environmental Factors Affecting Health
1. Physical Environment
- Air quality - Air pollution (PM2.5, SO₂, CO₂, smoke) is the leading environmental risk factor for NCDs. It causes ischemic heart disease, stroke, COPD, asthma, and lung cancer. About 7 million deaths per year are attributable to air pollution. (WHO)
- Climate and weather - Heat waves, extreme weather events, rising temperatures, and sea level rise. Climate change exacerbates cardiovascular, respiratory, and kidney diseases.
- Solar radiation - UV radiation affects skin (melanoma risk), eyes, and immune function.
- Noise pollution - Associated with hearing loss, hypertension, sleep disturbances, anxiety, and delayed cognitive development in children.
2. Water
Water is a vital environmental factor for all forms of life and plays a major role in socio-economic development. The WHO and the MDGs identified safe drinking water as a basic element of primary health care.
Safe and wholesome water must be:
- Free from pathogenic agents (bacteria, viruses, parasites)
- Free from harmful chemical substances
- Pleasant to taste, free from colour and odour
- Usable for domestic purposes
Water pollution is a major cause of ill-health in developing countries - it spreads cholera, typhoid, dysentery, and other waterborne diseases.
3. Sanitation and Housing
- Poor environmental sanitation (unsafe water, polluted soil, unhygienic disposal of excreta, poor housing, insects, rodents) is responsible for much of the ill-health in India
- High death rates, infant mortality, and disease burden are largely attributable to defective environmental sanitation
- Over 70% of India's population lives in rural areas, making rural sanitation a priority
4. Biological Environment
Includes all living organisms - bacteria, viruses, parasites, insects (vectors), and animals (zoonoses). These form the infectious disease pool from which humans are at risk.
5. Psychosocial and Socio-cultural Environment
- Social isolation, mental stress, discrimination, poverty, and racism
- These affect not only mental health but physical health outcomes through chronic stress pathways
- Access to safe parks, community centers, walking paths, and green spaces promotes mental well-being
6. Occupational Environment
- Exposure to chemicals, dust, radiation, and ergonomic hazards at the workplace
- Early life exposure to industrial chemicals and radiation increases NCD risk throughout the life course
7. Lifestyle and Behavioural Factors
Lifestyle refers to "the way people live" and includes cultural, behavioural, and personal habits:
| Harmful Lifestyle Factors | Health-Promoting Lifestyle Factors |
|---|---|
| Smoking | Adequate nutrition |
| Alcohol consumption | Sufficient physical activity |
| Drug addiction | Enough sleep |
| Poor diet | Personal hygiene |
Lifestyle diseases (coronary heart disease, obesity, lung cancer, diabetes) are strongly associated with lifestyle changes, particularly in developed countries.
Summary: Environmental Risk Factors and Health Impact
| Environmental Factor | Major Health Outcomes |
|---|---|
| Air pollution | IHD, stroke, COPD, asthma, lung cancer |
| Unsafe water | Diarrhea, cholera, typhoid, malnutrition |
| Poor sanitation | Infectious diseases, high infant mortality |
| Climate change | Cardiovascular, respiratory, kidney disease |
| Noise pollution | Hypertension, hearing loss, mental health |
| Chemical/radiation | Cancer, developmental disorders, NCDs |
| Psychosocial stress | Mental illness, CVD, immune dysfunction |
| Green spaces (positive) | Improved mental health, reduced mortality |
Environmental risk factors as a whole account for approximately 23% of all global deaths, with about two-thirds of those attributable to non-communicable diseases (NCDs). - WHO
Sources: Park's Textbook of Preventive and Social Medicine (26th ed.); WHO NCD Environmental Risk Factors; Healthy People 2030 Environmental Conditions
Balanced diet
A balanced diet provides all essential nutrients - carbohydrates, proteins, fats, vitamins, minerals, and water - in the right proportions to maintain health, support growth, and prevent disease.
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Balanced Diet
Definition
"A balanced diet is one which contains a variety of foods in such quantities and proportions that the need for energy, amino acids, vitamins, minerals, fats, carbohydrate and other nutrients is adequately met for maintaining health, vitality and general well-being, and also makes a small provision for extra nutrients to withstand short duration of leanness."
- Park's Textbook of Preventive and Social Medicine
Principles of Constructing a Balanced Diet
| Priority | Nutrient | Proportion of Daily Energy |
|---|---|---|
| 1st | Protein | 10-15% of daily energy intake |
| 2nd | Fat | 15-30% of daily energy intake |
| 3rd | Carbohydrates (rich in natural fibre) | Remaining energy (~55-75%) |
Micronutrient requirements (vitamins and minerals) must also be met alongside the above macronutrients.
Components of a Balanced Diet
1. Carbohydrates (Primary Energy Source)
- Main fuel for the body, especially the brain
- Sources: Cereals (wheat, rice, maize), millets, root vegetables, fruits, legumes
- Should be rich in dietary fibre (aids digestion, prevents constipation, lowers cholesterol)
- Recommended: 45-55% of total energy
- Excess leads to obesity and diabetes; deficiency causes fatigue and hypoglycaemia
2. Proteins (Body Building)
- Required for growth, repair, enzyme/hormone synthesis, and immune function
- ICMR recommendation: 0.88 g/kg body weight/day for adults
- Sources: Milk, eggs, meat, fish, pulses (dal), legumes, soybean
- Must provide all essential amino acids (EAAs): Histidine, Isoleucine, Leucine, Lysine, Methionine, Cysteine, Phenylalanine, Threonine, Tryptophan, Valine
- Requirements increase during pregnancy (+1-22 g/day by trimester) and lactation (+13 g/day)
- Young children (0-6 years) need proportionately more per kg body weight
3. Fats and Oils (Energy + Fat-Soluble Vitamins)
- Concentrated energy source; carry fat-soluble vitamins (A, D, E, K)
- Sources: Vegetable oils, nuts, seeds, dairy, meat, fish
- Should be limited to 15-30% of daily energy
- Include essential fatty acids (omega-3, omega-6)
- Excess saturated fat raises cardiovascular risk
4. Vitamins (Regulatory Micronutrients)
| Vitamin | Key Function | Source | Deficiency Disease |
|---|---|---|---|
| A | Vision, immunity | Liver, dairy, carrots, leafy greens | Night blindness, Xerophthalmia |
| D | Calcium absorption, bone health | Sunlight, fish, fortified milk | Rickets (children), Osteomalacia (adults) |
| C | Antioxidant, collagen synthesis | Citrus fruits, amla, guava | Scurvy |
| B1 (Thiamine) | Carbohydrate metabolism | Whole grains, legumes | Beriberi |
| B2 (Riboflavin) | Energy metabolism | Milk, eggs, meat | Angular stomatitis |
| B3 (Niacin) | Energy production | Meat, fish, groundnuts | Pellagra |
| B9 (Folate) | Cell division, DNA synthesis | Green leafy vegetables, pulses | Megaloblastic anaemia, Neural tube defects |
| B12 | Nerve function, RBC production | Animal products only | Pernicious anaemia |
5. Minerals (Structural + Regulatory)
| Mineral | Function | Source | Deficiency |
|---|---|---|---|
| Calcium | Bones, teeth, muscle contraction | Milk, ragi, sesame | Osteoporosis, Rickets |
| Iron | Haemoglobin synthesis | Green leafy vegetables, meat, jaggery | Anaemia |
| Iodine | Thyroid hormone synthesis | Iodised salt, seafood | Goitre, Cretinism |
| Zinc | Immunity, wound healing | Meat, legumes, nuts | Growth retardation |
| Magnesium | Enzyme function, bone health | Nuts, whole grains, green vegetables | Muscle cramps |
6. Dietary Fibre
- Indigestible plant material; promotes gut motility, reduces cholesterol, controls blood sugar
- Sources: Whole grains, vegetables, fruits, legumes
- Recommended: ~32-41 g/day (RDA for Indians, 2020)
7. Water
- Essential for all metabolic processes, temperature regulation, and waste excretion
- Requirement: ~2-3 litres/day (varies with activity and climate)
RDA for Indians (ICMR 2020) - Key Values
| Nutrient | Adult Men (Moderate Work) | Adult Women (Moderate Work) |
|---|---|---|
| Protein | 54 g/day | ~46 g/day |
| Dietary Fibre | 41 g/day | 32 g/day |
| Calcium | 1000 mg/day | 1000 mg/day |
| Iron | 19 mg/day | higher (due to menstruation) |
| Vitamin C | 80 mg/day | 80 mg/day |
| Vitamin A | 1000 µg/day | 840 µg/day |
| Vitamin D | 600 IU/day | 600 IU/day |
| Iodine | 150 µg/day | 150 µg/day |
Food Groups for a Balanced Diet
| Food Group | Main Nutrients Provided |
|---|---|
| Cereals and millets | Carbohydrates, B vitamins, fibre |
| Pulses and legumes | Protein, iron, folate, fibre |
| Milk and dairy | Protein, calcium, vitamin B12 |
| Meat, fish, eggs | Complete protein, iron, zinc, B12 |
| Fruits and vegetables | Vitamins (A, C, K), minerals, fibre, antioxidants |
| Fats and oils | Energy, essential fatty acids, fat-soluble vitamins |
Consequences of an Imbalanced Diet
| Imbalance | Consequences |
|---|---|
| Undernutrition | Stunting, wasting, underweight, PEM (Kwashiorkor, Marasmus), anaemia |
| Overnutrition | Obesity, Type 2 diabetes, cardiovascular disease, hypertension |
| Micronutrient deficiency | Specific deficiency diseases (scurvy, rickets, anaemia, goitre) |
| Malnutrition cycle | Poor maternal health → low birth weight → childhood malnutrition → adult disease |
Key Takeaway
A balanced diet is not about eating one "perfect" food - it is about eating a variety of foods from all groups in the right proportions. The goal is to meet all energy and nutrient needs while also providing a small reserve for periods of stress or illness.
Source: Park's Textbook of Preventive and Social Medicine, 26th ed.; ICMR RDA 2020
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