Biology of Disease

Nearly half of dietary fluoride is taken up by bone and can influence its

mechanical properties. The incorporation of fluoride in tooth enamel as

fluorapatite makes teeth more resistant to dental caries as it resists breakdown

by acids. Fluoride deficiency leads to impaired bone formation and dental

defects (Box 10.5).

Iodine deficiency causes an enlargement of the thyroid gland called goiter

(Figure 10.34), while a prolonged deficiency in children can lead to cretinism

(Chapter 7). Iodine deficiency is commonest in upland areas with thin

limestone soil because minerals, such as iodine are easily leached from these

types of soils and plants in the area are iodine deficient. The situation is

exacerbated if commercial iodized salt is not available. In some areas of Africa,

Brazil and the Himalayas, more than 90% of the population may develop goiter

due to iodine deficiency. Excessive intake of dietary iodide can also lead to

goiter. This is most commonly seen in Japanese communities who have a high

dietary intake of seaweed.

A lack of iron leads to anemia, which is described in Chapter 13. Increased

intake of dietary, medicinal or transfused iron can cause hemosiderosis,

X]VeiZg&%/ DIET AND DISEASE

'+) W^dad\nd[Y^hZVhZ

Figure 10.33 Computer-generated molecular

models of (A) vitamin K 1 and (B) warfarin. Note

the structural similarities in the ‘left-hand’ sides

of the models. Oxygen atoms are shown in red,

carbon in black and hydrogen in gray.

The bulk of the tooth is composed of a hard tissue called

dentine. The exposed part of the tooth or crown is covered with

enamel. Dental caries or tooth decay is caused by bacteria in

the plaque and is the commonest cause of toothache (Chapter

3 ). It is particularly common in children. Bacteria in the plaque

catabolize sugars producing organic acids that can demineralize

the enamel and the underlying dentine. The development of

dental caries depends upon a balance between the plaque

and bacteria and the ability of enamel to resist attack. The

commonest cause of dental caries is poor dental hygiene and

a frequent intake of dietary sugars. Regular brushing of the

teeth can remove plaque and reduce acid production since it

takes about 24 hours for the bacteria to reestablish themselves.

Treatment of caries involves removing the decayed part of the

teeth by drilling and replacing the decayed material with a

filling.

Epidemiological studies have demonstrated the benefits of

adding fluoride to drinking water (fluoridation) because as little

as one part per million (ppm) can prevent dental caries. Studies

in the UK showed that children living in areas with water fluoride

concentrations of about 1 ppm had 50% fewer cases of dental

BOX 10.5 Dental caries and fluoride

Figure 10.34 A well developed goiter. Courtesy of

S.J. Nixon, Royal Infirmary of Edinburgh, Scotland.

Warfarin is often used therapeutically

as an anticoagulant (Chapter 13).

However, because of the similarities

in structures, it is a vitamin K

antagonist (Figure 10.33 (A)and(B)).

Patients on warfarin therapy require

increased amounts of the vitamin.

Margin Note 10.5 Warfarin and

vitamin K i