What Is Malnutrition?

Malnutrition occurs when a person's intake or use of energy and nutrients does not adequately meet the body's needs.

Malnutrition does not simply mean "not eating enough."

It can result from:

• too little food
• too much energy intake
• too little of a particular nutrient
• an unbalanced diet
• poor absorption of nutrients
• illness that changes nutrient requirements or losses

Therefore, someone can consume plenty of food and still experience a form of malnutrition.

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The Main Forms of Malnutrition

Malnutrition can broadly involve:

Undernutrition

The body receives or absorbs insufficient energy or nutrients.

Micronutrient deficiencies

The body lacks sufficient amounts of particular vitamins or minerals.

Overnutrition

Energy or certain nutrients are consumed in excess relative to the body's needs over time.

These forms can sometimes occur together.

For example, a diet may provide excessive energy while still being deficient in particular vitamins or minerals.

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Undernutrition

Undernutrition occurs when the body does not receive or effectively use enough energy, protein, or other nutrients to meet its requirements.

Possible causes include:

• inadequate food intake
• limited access to nutritious food
• illness
• digestive disorders
• poor nutrient absorption
• increased nutritional requirements
• prolonged infection
• highly restrictive diets

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Effects of Undernutrition

The effects depend on:

• which nutrients are lacking
• severity
• duration
• age
• health
• individual nutritional requirements

Possible consequences include:

• weight loss
• reduced growth in children
• muscle loss
• fatigue
• reduced physical performance
• impaired immune function
• slower wound healing
• increased vulnerability to illness

Severe or prolonged undernutrition can be life-threatening.

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Overnutrition

Overnutrition occurs when the body consistently receives more energy or particular nutrients than it requires.

For energy:

energy intake > energy expenditure over time

can lead to increased energy storage.

Much of this excess energy can eventually be stored as:

body fat

Overnutrition is not simply about eating a large meal occasionally. Long-term dietary patterns are more important.

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Health Consequences of Long-Term Overnutrition

Long-term excess energy intake can contribute to excess body fat.

Excess body fat is associated with increased risk of several conditions, including:

• type 2 diabetes
• cardiovascular disease
• high blood pressure
• some cancers
• joint problems
• fatty liver disease

Risk is influenced by many factors, including:

• diet
• physical activity
• genetics
• age
• sleep
• smoking
• environment
• existing health conditions

Diet is important, but it is not the only factor affecting long-term health.

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Micronutrient Deficiency

A nutrient deficiency occurs when the body does not have enough of a particular nutrient to maintain normal function.

Micronutrient deficiencies commonly involve:

vitamins

or:

minerals

Examples include deficiencies of:

• iron
• vitamin A
• vitamin C
• vitamin D
• iodine

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Why Do Deficiencies Occur?

A deficiency can occur for several reasons.

Insufficient intake

The diet does not contain enough of the nutrient.

Poor absorption

The nutrient is present in food but is not absorbed adequately.

Increased requirements

Growth, pregnancy, illness, or other circumstances can increase nutrient requirements.

Increased loss

Certain illnesses or other conditions can cause nutrients to be lost from the body.

Therefore:

nutrient deficiency does not always mean that someone simply chose the wrong foods.

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Iron Deficiency

Iron is required for the production of:

haemoglobin

Haemoglobin is found in red blood cells and carries oxygen.

The relationship is:

iron → haemoglobin → oxygen transport

If insufficient iron is available, the body may be unable to produce enough normal haemoglobin.

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Iron-Deficiency Anaemia

One important consequence of iron deficiency is:

iron-deficiency anaemia

A person may experience symptoms such as:

• tiredness
• weakness
• shortness of breath
• reduced exercise tolerance
• difficulty concentrating

These symptoms occur because the blood's ability to transport oxygen can be reduced.

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Sources of Iron

Iron-containing foods include:

• meat
• fish
• beans
• lentils
• leafy green vegetables
• fortified cereals
• some seeds and nuts

Vitamin C can improve the absorption of non-haem iron, the form commonly found in plant foods.

For example:

lentils + vitamin C-rich vegetables

can be a useful dietary combination.

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Preventing Iron Deficiency

Strategies can include:

• consuming appropriate iron-rich foods
• eating a varied diet
• including vitamin C-rich foods alongside plant sources of iron
• using appropriately fortified foods where available
• addressing medical causes of blood loss or poor absorption

Iron supplements may be recommended in some circumstances, but unnecessary high-dose supplementation can be harmful.

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Vitamin C Deficiency

Vitamin C is important for several functions, including:

• collagen formation
• wound healing
• antioxidant activity
• supporting iron absorption

Severe, prolonged vitamin C deficiency can cause:

scurvy

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Scurvy

Collagen is an important structural protein.

When vitamin C deficiency interferes with normal collagen production, tissues can become weakened.

Symptoms of scurvy can include:

• bleeding gums
• easy bruising
• poor wound healing
• fatigue
• weakness

Severe cases can cause serious complications.

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Preventing Vitamin C Deficiency

Vitamin C is found in many fruits and vegetables.

Sources include:

• oranges and other citrus fruits
• peppers
• strawberries
• broccoli
• tomatoes
• kiwi fruit

A varied diet containing fruits and vegetables generally helps provide adequate vitamin C.

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Vitamin D Deficiency

Vitamin D is important for maintaining appropriate calcium and phosphate levels.

It contributes to:

normal bone mineralization

The body can produce vitamin D in the skin when exposed to sufficient ultraviolet B radiation.

Vitamin D can also be obtained from:

• certain fish
• egg yolks
• fortified foods
• supplements when appropriate

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Rickets

Severe vitamin D deficiency in growing children can contribute to:

rickets

Rickets involves inadequate mineralization of growing bones.

Possible effects include:

• soft or weak bones
• skeletal deformities
• impaired growth
• bone pain
• muscle weakness

Vitamin D, calcium, and phosphate are closely connected to normal bone development.

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Vitamin D Deficiency in Adults

In adults, severe vitamin D deficiency can cause:

osteomalacia

This involves poor mineralization of bone.

It can contribute to:

• bone pain
• muscle weakness
• increased risk of fractures

This is different from osteoporosis, although both can affect bone health.

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Preventing Vitamin D Deficiency

Prevention may involve:

• appropriate dietary sources
• fortified foods
• suitable sunlight exposure
• supplementation when medically appropriate

The best approach varies according to:

• age
• skin pigmentation
• location
• season
• lifestyle
• health
• individual risk

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Vitamin A Deficiency

Vitamin A is important for:

• vision
• immune function
• growth
• maintenance of epithelial tissues

Severe vitamin A deficiency can affect vision.

One early problem can be:

night blindness

More severe deficiency can damage the eye and potentially lead to blindness.

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Sources of Vitamin A

Vitamin A or its precursors can be obtained from foods such as:

• liver
• eggs
• dairy products
• carrots
• sweet potatoes
• pumpkin
• dark green leafy vegetables

Orange and dark green vegetables often contain:

beta-carotene

which the body can convert into vitamin A.

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Iodine Deficiency

Iodine is required to make:

thyroid hormones

These hormones contribute to the regulation of:

• metabolism
• growth
• development

Insufficient iodine can interfere with thyroid function.

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Goitre

One possible consequence of iodine deficiency is enlargement of the thyroid gland.

This is called:

goitre

The thyroid is located in the neck.

However, goitre can have causes other than iodine deficiency, so the presence of an enlarged thyroid does not by itself identify the cause.

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Why Iodine Is Especially Important During Development

Thyroid hormones are particularly important during fetal and early childhood development.

Severe iodine deficiency during pregnancy can interfere with normal brain and nervous-system development.

This demonstrates an important idea:

the same nutrient deficiency can have different consequences at different stages of life.

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Preventing Iodine Deficiency

One important public-health strategy is:

iodized salt

Iodized salt contains added iodine.

Other dietary sources may include:

• seafood
• dairy products
• eggs
• some seaweeds

The iodine content of foods varies depending on environmental and agricultural conditions.

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Calcium Deficiency and Bone Health

Calcium is important for:

• bones
• teeth
• muscle contraction
• nerve signaling
• blood clotting

Long-term inadequate calcium intake can contribute to poor bone health.

However, bone health depends on more than calcium alone.

Important factors also include:

• vitamin D
• protein
• physical activity
• hormones
• age
• genetics

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Protein-Energy Undernutrition

Severe undernutrition can involve inadequate:

energy

and:

protein

Growing children are particularly vulnerable because they require nutrients for both:

maintenance + growth

Severe protein-energy undernutrition can interfere with:

• growth
• muscle development
• immune function
• organ function
• recovery from illness

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Marasmus

Marasmus is a severe form of undernutrition associated with major energy deficiency.

It can involve:

• severe wasting
• loss of muscle and body fat
• poor growth
• weakness

The body lacks sufficient energy to maintain normal growth and tissue stores.

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Kwashiorkor

Kwashiorkor is a severe form of malnutrition classically associated with severe dietary inadequacy and characterized by features that can include:

• oedema
• changes in skin and hair
• impaired growth
• enlarged fatty liver

Its biology is complex and cannot be explained simply as "protein deficiency alone."

This is an important example of why real nutritional diseases can be more complicated than simplified textbook descriptions.

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Deficiency Disease Summary

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A Deficiency Is Not Always Obvious

Someone can consume enough calories but still lack particular nutrients.

Consider a diet containing large amounts of:

• refined grains
• sugary drinks
• highly processed snack foods

but very little:

• fruit
• vegetables
• protein-rich foods
• varied nutrient sources

The person may consume sufficient or excessive energy while still having inadequate intake of some micronutrients.

This is sometimes described as the:

double burden of malnutrition

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The Double Burden of Malnutrition

A population, household, or even an individual can experience different forms of malnutrition simultaneously.

For example:

excess energy intake

may coexist with:

iron deficiency

or another micronutrient deficiency.

This demonstrates why body size alone does not tell us whether someone's nutritional intake is adequate.

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Malabsorption

Sometimes the problem is not the amount of nutrient in the diet.

The digestive system may not absorb the nutrient effectively.

This is called:

malabsorption

Conditions affecting the intestine can interfere with absorption of:

• iron
• vitamins
• fats
• carbohydrates
• other nutrients

Therefore:

adequate intake does not always guarantee adequate absorption.

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Nutrition and the Digestive System

The pathway from food to body cells involves several stages:

food

↓

digestion

↓

absorption

↓

transport

↓

cellular use

A problem at any stage can affect nutritional status.

For example:

nutrient present in food + poor absorption = possible deficiency

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Diet and Long-Term Health

Dietary patterns can influence health over many years.

Long-term patterns associated with better health generally include appropriate amounts and variety of:

• vegetables
• fruits
• whole grains
• legumes
• nuts and seeds
• protein-rich foods
• unsaturated fats

while limiting consistently excessive intake of:

• added sugars
• sodium
• saturated fats
• highly processed foods that displace nutrient-rich foods

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Diet and Cardiovascular Health

Cardiovascular disease affects the heart and blood vessels.

Long-term cardiovascular risk can be influenced by factors including:

• blood pressure
• blood cholesterol
• smoking
• diabetes
• physical activity
• body composition
• genetics
• diet

Dietary patterns containing plenty of fibre-rich plant foods and appropriate types of dietary fat can contribute to cardiovascular health.

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Diet and Type 2 Diabetes

Type 2 diabetes involves problems with the regulation of blood glucose.

Risk is influenced by multiple factors, including:

• genetics
• age
• body composition
• physical activity
• dietary patterns

Long-term excessive energy intake can contribute to excess body fat, which is an important risk factor for type 2 diabetes.

However:

diet is one risk factor among several

and should not be treated as the sole cause.

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Diet and Blood Pressure

Blood pressure is influenced by:

• genetics
• age
• physical activity
• body composition
• diet
• sodium intake
• potassium intake
• alcohol intake
• other health factors

Consistently high sodium intake can contribute to elevated blood pressure, particularly in salt-sensitive individuals.

This is one reason many dietary guidelines recommend limiting excessive sodium intake.

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Diet and Bone Health

Bone health depends on long-term nutrition and lifestyle.

Important factors include:

• calcium
• vitamin D
• protein
• physical activity
• hormones
• age
• genetics

Weight-bearing physical activity also helps stimulate bone maintenance.

Therefore:

healthy bones require both nutrition and appropriate physical activity.

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Poor Nutrition Can Affect Learning and Performance

Nutrition can influence more than physical growth.

Inadequate nutrition can affect:

• concentration
• energy levels
• physical performance
• recovery
• immune function

For students, adequate nutrition and hydration can therefore support participation in both:

learning

and:

physical activity

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Preventing Nutrient Deficiencies

A major strategy is eating a varied, balanced diet.

This can include:

• vegetables
• fruits
• whole grains
• legumes
• protein-rich foods
• appropriate fat sources
• adequate fluids

Different foods supply different nutrients.

Therefore:

dietary variety reduces the risk of missing particular nutrients.

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Food Fortification

Food fortification involves adding nutrients to foods.

Examples can include:

• iodine added to salt
• vitamin D added to some foods
• iron added to cereals or flour
• folic acid added to some grain products

Fortification can help increase nutrient intake across large populations.

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Supplementation

A dietary supplement provides concentrated amounts of particular nutrients.

Examples include:

• iron
• vitamin D
• vitamin B12
• folic acid

Supplements can be useful when:

• dietary intake is insufficient
• requirements are increased
• absorption is limited
• a deficiency has been diagnosed
• specific public-health guidance recommends them

However:

more is not always better.

Some nutrients can be harmful in excessive amounts.

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Prevention Through Public Health

Preventing malnutrition is not only an individual responsibility.

Public-health approaches can include:

• access to nutritious foods
• clean water
• sanitation
• nutrition education
• food fortification
• maternal and infant nutrition programs
• school meal programs
• disease prevention
• healthcare access

Malnutrition therefore involves both:

biology

and:

social and environmental conditions.

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Evaluating a Diet for Deficiency Risk

Consider this daily pattern:

Breakfast: sweetened drink

Lunch: white bread and chips

Snack: candy

Dinner: instant noodles

Possible concerns include low intake of:

• fibre
• protein
• iron
• calcium
• some vitamins
• vegetables and fruits

The diet may still provide considerable energy.

This illustrates:

high energy intake does not guarantee adequate nutrition.

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Improving the Diet

A more varied pattern could include:

Breakfast: oatmeal + fruit + yoghurt

Lunch: rice + vegetables + beans, tofu, fish, eggs, or chicken

Snack: fruit + nuts

Dinner: whole grains or potatoes + vegetables + protein source

Drinks: mainly water

The goal is to increase:

variety + nutrient density + appropriate balance

rather than simply increasing the amount of food.

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Case Study: Fatigue

A student frequently feels tired.

Their diet contains very little iron-rich food.

One possible nutritional explanation could be:

insufficient iron

↓

reduced haemoglobin production

↓

reduced oxygen-carrying capacity

↓

fatigue

However, fatigue has many possible causes.

A symptom alone cannot diagnose a nutrient deficiency.

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Case Study: Bone Development

A growing child has very low vitamin D availability.

Possible pathway:

low vitamin D

↓

impaired calcium/phosphate regulation

↓

poor bone mineralization

↓

increased risk of rickets

This demonstrates how a micronutrient can influence an entire organ system.

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Case Study: A High-Energy but Low-Quality Diet

A person regularly consumes enough energy but eats very little:

• fruit
• vegetables
• whole grains
• legumes
• varied protein sources

This person is not necessarily undernourished in terms of energy.

However, they could still have inadequate intake of particular:

vitamins, minerals, fibre, or other nutrients.

This is why malnutrition cannot be judged simply by how much someone eats.

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Diet Is About Patterns

Eating one highly nutritious meal does not guarantee long-term health.

Eating one less nutritious meal does not create a deficiency disease.

Nutritional health reflects patterns developing over:

days → weeks → months → years

This is especially important when evaluating the relationship between diet and chronic disease.

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Risk Is Not Certainty

Suppose a particular dietary pattern is associated with increased risk of a disease.

This does not mean:

diet → guaranteed disease

Instead:

diet + genetics + activity + environment + age + other factors → overall risk

Nutrition often changes the probability of health outcomes rather than determining them completely.

This distinction is essential when interpreting health information.

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Evaluating Nutrition Claims

Imagine an advertisement says:

"This drink contains 100% of your daily vitamin C, so it keeps you healthy."

A scientific evaluation should ask:

• What else does the drink contain?
• How much sugar does it contain?
• What is the serving size?
• What other nutrients does it provide?
• What does the person's overall diet look like?
• Does the evidence support the health claim?

One nutrient does not determine the nutritional quality of an entire diet.

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Common Misconception: Malnutrition Means Starvation

Starvation is an extreme form of inadequate energy intake.

Malnutrition is a much broader concept.

It can include:

undernutrition

micronutrient deficiency

and:

overnutrition

A person does not need to be starving to be malnourished.

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Common Misconception: Someone Who Eats a Lot Cannot Be Malnourished

A person can consume excessive energy while receiving insufficient amounts of particular nutrients.

For example:

high energy + low iron intake

could still contribute to iron deficiency.

Nutritional status depends on:

quality + quantity + absorption + individual needs

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Common Misconception: Deficiency Diseases Develop Immediately

Most deficiency diseases develop after inadequate nutrient availability persists.

The body may store some nutrients.

For example, certain vitamins and minerals can be stored to varying degrees.

Therefore, symptoms may appear only after stores become depleted or physiological functions are affected.

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Common Misconception: Supplements Prevent Every Deficiency

Supplements can be useful in appropriate circumstances.

However, they cannot automatically compensate for every problem associated with an unbalanced diet.

Foods provide combinations of:

• nutrients
• fibre
• energy
• protein
• fats
• carbohydrates
• other food components

A supplement usually provides only selected substances.

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Connecting Malnutrition to Homeostasis

The body attempts to maintain stable internal conditions.

Malnutrition can interfere with this.

For example:

iron deficiency → impaired oxygen transport

water deficiency → impaired fluid balance

iodine deficiency → altered thyroid function

vitamin D deficiency → impaired bone mineralization

energy deficiency → use of body energy stores

Nutrition is therefore closely connected to:

homeostasis

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Connecting Malnutrition to Growth

Growing organisms require both:

energy

and:

raw materials

for new tissues.

A child experiencing prolonged undernutrition may have insufficient resources for normal growth.

This can affect:

• height
• muscle development
• bone development
• immune function
• organ development

Good nutrition is therefore particularly important during periods of rapid growth.

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Did You Know?

Nutrient deficiencies can sometimes occur even when food appears plentiful.

This is sometimes called hidden hunger.

A person's diet may provide enough calories but insufficient amounts of important micronutrients such as:

• iron
• iodine
• vitamin A
• zinc

The problem may therefore be difficult to recognize simply by looking at how much food is available.

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Major Deficiency Relationships

Iron deficiency

↓

less normal haemoglobin production

↓

reduced oxygen transport

↓

iron-deficiency anaemia

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Vitamin C deficiency

↓

impaired collagen formation

↓

weakened connective tissues

↓

scurvy

---

Vitamin D deficiency

↓

impaired calcium and phosphate regulation

↓

poor bone mineralization

↓

rickets in children / osteomalacia in adults

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Vitamin A deficiency

↓

impaired visual and epithelial function

↓

night blindness and potentially eye damage

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Iodine deficiency

↓

reduced thyroid hormone production

↓

altered thyroid function

↓

goitre may develop

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Deficiency Disease Summary

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Key Terms

• Malnutrition: Inadequate, excessive, or imbalanced intake or utilization of energy and nutrients.
• Undernutrition: Insufficient energy or nutrients to meet the body's requirements.
• Overnutrition: Excess intake of energy or nutrients relative to requirements.
• Nutrient deficiency: Inadequate availability of a particular nutrient.
• Deficiency disease: Disease or disorder resulting from inadequate availability of a nutrient.
• Micronutrient: Vitamin or mineral required in relatively small amounts.
• Anaemia: Condition involving insufficient healthy red blood cells or haemoglobin; it has multiple possible causes.
• Iron-deficiency anaemia: Anaemia caused by insufficient available iron.
• Scurvy: Disease caused by severe vitamin C deficiency.
• Rickets: Disorder of bone mineralization in growing children, often associated with severe vitamin D deficiency.
• Osteomalacia: Poor mineralization of adult bone.
• Goitre: Enlargement of the thyroid gland.
• Malabsorption: Inadequate absorption of nutrients from the digestive system.
• Fortification: Addition of nutrients to foods.
• Supplementation: Use of concentrated nutrient preparations to increase intake.
• Nutrient density: Amount of useful nutrients provided relative to energy content.
• Hidden hunger: Micronutrient deficiency despite apparently adequate energy intake.
• Energy balance: Relationship between energy intake and energy expenditure.
• Chronic disease: Health condition that develops or persists over a long period.
• Homeostasis: Maintenance of relatively stable internal conditions.

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Key Takeaways

• Malnutrition occurs when energy or nutrient intake or utilization does not adequately match the body's needs.
• Malnutrition does not simply mean starvation.
• Malnutrition includes undernutrition, micronutrient deficiencies, and overnutrition.
• A person can consume enough or excessive energy while still lacking important micronutrients.
• Undernutrition can result from inadequate food intake, disease, poor absorption, or increased requirements.
• Prolonged undernutrition can impair growth, immunity, physical performance, and tissue repair.
• Overnutrition can occur when energy intake consistently exceeds energy expenditure.
• Long-term excessive energy intake can contribute to excess body fat.
• Excess body fat is associated with increased risk of several chronic diseases.
• Iron is required for haemoglobin and oxygen transport.
• Iron deficiency can cause iron-deficiency anaemia.
• Vitamin C is important for collagen formation.
• Severe vitamin C deficiency causes scurvy.
• Vitamin D contributes to calcium regulation and normal bone mineralization.
• Severe vitamin D deficiency can contribute to rickets in children and osteomalacia in adults.
• Vitamin A is important for vision and tissue health.
• Severe vitamin A deficiency can cause night blindness and more serious eye damage.
• Iodine is required for thyroid hormone production.
• Iodine deficiency can interfere with thyroid function and may cause goitre.
• Severe energy and nutrient deficiency can lead to serious forms of undernutrition.
• Nutrient deficiencies may result from inadequate intake, poor absorption, increased requirements, or increased losses.
• A varied and balanced diet helps prevent many nutritional deficiencies.
• Food fortification can help prevent deficiencies across populations.
• Supplements can be useful in specific situations but should not automatically replace a balanced diet.
• Nutritional needs differ with age, growth, activity, pregnancy, illness, and other factors.
• Diet can influence long-term health, but it is one factor among genetics, physical activity, environment, and other influences.
• Associations between diet and disease represent changes in risk, not guarantees that a particular person will develop a disease.
• Nutritional status cannot be determined simply from body size or the amount of food someone eats.
• "Hidden hunger" describes micronutrient deficiencies that can occur even when energy intake appears adequate.
• Long-term health depends on dietary patterns developing over months and years rather than a single meal.
• A useful way to think about nutritional health is: enough energy + enough essential nutrients + appropriate balance + effective absorption = better support for normal growth, function, and long-term health.