Minerals: Fluoride and Iodine

This lesson covers two trace minerals — fluoride and iodine — as required by AQA GCSE Food Preparation and Nutrition (8585), specification section 3.2.2. Both are needed in very small amounts but have important and distinctive functions. Fluoride is primarily associated with dental health, while iodine is essential for thyroid function. Both have interesting real-world applications that AQA examiners like to test.

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Fluoride

Fluoride is a trace mineral that plays a specific and important role in dental health. It is technically the ionic form of the element fluorine.

Functions of Fluoride

Function	Detail
Strengthens tooth enamel	Fluoride is incorporated into the structure of tooth enamel (the hard outer layer of teeth), forming a compound called fluorapatite. Fluorapatite is more resistant to acid attack than the natural enamel mineral (hydroxyapatite).
Prevents dental decay (caries)	By strengthening enamel, fluoride reduces the ability of acids (produced by bacteria in the mouth from sugars) to dissolve the tooth surface, thereby preventing cavities.
Promotes remineralisation	When enamel has been slightly damaged by acid, fluoride encourages the repair (remineralisation) of the tooth surface by attracting calcium and phosphate ions.
Inhibits bacterial activity	Fluoride can reduce the ability of oral bacteria to produce acid from sugars, further protecting teeth.

How Dental Decay Occurs

Understanding how fluoride prevents dental decay requires knowing the decay process:

flowchart LR
    A["Sugary food<br/>consumed"] --> B["Bacteria in<br/>mouth feed<br/>on sugar"]
    B --> C["Bacteria<br/>produce acid"]
    C --> D["Acid attacks<br/>tooth enamel"]
    D --> E["Enamel<br/>dissolves"]
    E --> F["Cavity forms"]
    G["Fluoride"] -->|"strengthens<br/>enamel"| D
    G -->|"promotes<br/>remineralisation"| E

    style C fill:#c0392b,color:#fff
    style F fill:#e74c3c,color:#fff
    style G fill:#27ae60,color:#fff

Sources of Fluoride

Source	Detail
Fluoridated water	Some areas of the UK add fluoride to the public water supply (currently about 10% of the UK population receives fluoridated water, mainly in parts of the West Midlands and North East England). This is a public health measure to reduce dental decay.
Tea	Tea plants naturally accumulate fluoride from the soil. Tea is one of the most significant dietary sources of fluoride in the UK.
Toothpaste	Most toothpastes contain fluoride (usually sodium fluoride or stannous fluoride). This provides a topical application directly to the teeth.
Fish	Particularly fish where the bones are consumed (sardines, whitebait).
Fluoride supplements	Available on prescription in areas without fluoridated water, particularly for children.

Deficiency of Fluoride

• Increased risk of dental decay (dental caries) — without fluoride, tooth enamel is more vulnerable to acid attack from bacteria, leading to more cavities.
• Populations in areas without fluoridated water tend to have higher rates of dental decay, particularly among children from disadvantaged backgrounds.

Excess of Fluoride: Fluorosis

Excess fluoride intake, particularly during childhood when teeth are developing, can cause fluorosis:

Type	Description
Dental fluorosis	White or brown spots and mottling (discolouration) on the surface of the teeth. In mild cases, this is mainly a cosmetic concern. In severe cases, the enamel can become pitted and weakened.
Skeletal fluorosis	In areas with naturally very high fluoride levels in water (not relevant to the UK), excessive fluoride can accumulate in bones, causing joint stiffness, pain, and skeletal abnormalities. This is extremely rare in the UK.

Exam Tip: The fluoride/dental health link is straightforward but must be precise. State that fluoride strengthens tooth enamel, making it more resistant to acid attack by bacteria, and prevents dental decay. If asked about excess, mention fluorosis (mottling of teeth).

The Fluoridation Debate

Water fluoridation is a debated public health topic. Key points:

For Fluoridation	Against Fluoridation
Reduces dental decay, especially in children	Some consider it mass medication without individual consent
Benefits those who cannot afford dental care	Risk of dental fluorosis if levels are too high
Safe at recommended levels (1 mg/L)	Individual choice over what is added to water supply
Cost-effective public health measure	Difficulty in controlling total fluoride intake from all sources

Exam Tip: AQA may ask you to evaluate the arguments for and against water fluoridation. Present both sides in a balanced way, using specific points rather than vague statements.

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Iodine

Iodine is a trace mineral essential for the production of thyroid hormones, which regulate the body's metabolic rate. Although needed in very small amounts, iodine deficiency has significant health consequences.

Functions of Iodine

Function	Detail
Thyroid hormone production	Iodine is a component of the thyroid hormones thyroxine (T4) and triiodothyronine (T3), which are produced by the thyroid gland in the neck.
Metabolic rate regulation	Thyroid hormones control the basal metabolic rate (BMR) — the rate at which the body uses energy at rest. They affect virtually every cell in the body.
Growth and development	Thyroid hormones are essential for normal growth and brain development, particularly during pregnancy and early childhood.
Body temperature regulation	Thyroid hormones help regulate body temperature by influencing metabolic heat production.

The Thyroid Gland

flowchart TD
    A["Iodine from Diet"] --> B["Absorbed in<br/>Small Intestine"]
    B --> C["Transported to<br/>Thyroid Gland"]
    C --> D["Used to make<br/>Thyroid Hormones<br/>(T3 and T4)"]
    D --> E["Released into<br/>Bloodstream"]
    E --> F["Regulate<br/>Metabolic Rate"]
    E --> G["Support Growth<br/>and Development"]

    style C fill:#8e44ad,color:#fff
    style D fill:#9b59b6,color:#fff
    style F fill:#27ae60,color:#fff
    style G fill:#27ae60,color:#fff

Sources of Iodine

Source Type	Examples
Seafood	White fish (cod, haddock), prawns, seaweed (very rich but variable)
Dairy products	Milk, cheese, yoghurt — the most significant source in the UK diet. Iodine content of milk is higher in winter because cattle are fed iodine-supplemented feed when housed indoors.
Eggs
Iodised salt	Salt fortified with iodine (common in many countries but not routinely used in the UK)
Some plant foods	Iodine content depends on soil iodine levels; generally unreliable as a source

Exam Tip: In the UK, milk and dairy products are the most important source of iodine. This is a key fact, especially when evaluating vegan diets — vegans who do not consume dairy must find alternative iodine sources (seaweed, iodine supplements, or fortified plant milks). Unlike many other countries, the UK does not routinely use iodised salt.

Deficiency of Iodine

Condition	Who It Affects	Description
Goitre	All ages	The thyroid gland enlarges (swells) in an attempt to trap more iodine from the blood. This creates a visible swelling in the neck. Goitre was historically common in areas far from the sea where iodine-poor soils led to low iodine in food.
Hypothyroidism	All ages	Insufficient thyroid hormone production leads to a slow metabolic rate, causing symptoms such as weight gain, fatigue, feeling cold, dry skin, and depression.
Cretinism	Newborns/children	Severe iodine deficiency during pregnancy can cause cretinism in the baby — characterised by severe intellectual disability and stunted physical growth. This is now rare in the UK but remains a concern in some developing countries.
Poor cognitive development	Children	Even mild iodine deficiency during pregnancy and early childhood can impair brain development and cognitive function.

Groups at Risk of Iodine Deficiency

Group	Reason
Vegans	No dairy or fish in the diet — two of the main UK sources. Must rely on seaweed, supplements, or fortified plant milks.
Pregnant and breastfeeding women	Increased iodine requirements for the developing baby's brain and thyroid.
Teenage girls	Some studies suggest UK teenage girls have inadequate iodine intake due to low dairy consumption.
People avoiding dairy	Those with lactose intolerance or dairy allergies may have reduced iodine intake.

Excess of Iodine

Excessive iodine intake is uncommon but can cause:

• Thyroid dysfunction — paradoxically, very high iodine intake can also cause thyroid problems, including either overactive or underactive thyroid.
• Seaweed (particularly kelp) can contain very high and variable amounts of iodine, so excessive consumption should be avoided.

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Comparing Fluoride and Iodine