A Pre-Raphaelite's ideal woman was very different from Miss Joan Hunter Dunn, who died last week. She was John Betjeman's muse, a forceful young female with the figure of a school tennis champion. She was lithe and athletic - “the speed of a swallow: the grace of a boy” - whereas women who inspired Tennyson or the Pre-Raphaelite painters tended to be aesthetic, passive and wan.

At times over the past 200 years it has been fashionable to be pale, anaemic, wasted and apparently fragile. Doctors' practices, other than those of specialist haematologists where vigilance in searching for undiagnosed anaemia is likely to be rewarded, are usually those catering for children, young women, the elderly, food faddists, or they may have an interest in cardiology and chest medicine. A large number of patients with anaemia first notice a shortness of breath, palpitations and persistent tiredness and are referred to cardiologists or respiratory physicians.

Anaemia is much more common than suspected. Often anaemia leaves clues far more subtle than a pale face and/or breathlessness brought on by climbing the stairs. To make the diagnosis more difficult, excessive fatigue from iron deficiency can worry a patient before anaemia is detectable because of a low haemoglobin level, the standard blood test. To make certain that a patient is not iron-deficient, estimates of serum ferritin, or total iron-binding capacity and serum iron, are needed. The most common cause of anaemia is iron deficiency, whether caused by a vegetarian diet deficient in the mineral, or by an excessive, but sometimes hidden, loss of blood.

A speciality that is not often associated with anaemic patients is dermatology. A dermatologist recently lamented that he was seeing too many patients with iron-deficiency anaemia, which had caused poor-quality skin, thinning lacklustre hair, flaky nails and, in women, a prolonged interval between periods and a longer premenstrual syndrome.

People who have had an iron deficiency for any length of time may suffer from koilonychia, a flattened or spoon-shaped nail. In parts of Africa, where it is endemic, children with iron deficiency may also lack a growth hormone from birth. They suffer smooth, brittle and flattened, sometimes spoon-shaped, fingernails. If in early childhood they have an adequate iron intake, by 8 or 9 their nails have usually recovered.

Professor Andrew Prentice, of the London School of Hygiene and Tropical Medicine, stresses that persistent gut problems in children may lead to malabsorption of iron, and this as well as a diet short of the mineral may lead to iron-deficiency anaemia.

Iron is absorbed less well from a vegetarian diet than one containing meat. As a result many vegetarians are iron-deficient. Iron isn't easily absorbed and is more readily taken into the system in the form of haem iron in meat, especially red meat, than it is from iron-rich vegetation. Human beings have evolved as omnivores and have many characteristics of carnivores. They have canine teeth like a wolf to tear meat and stomachs and colons that have evolved to be more like those of a lion than a sheep, cow or horse. Their gastrointestinal tract is ideally suited for meat eating.

The lesser-known disadvantages of iron deficiency include a defective immune system, loss of fertility, difficulty in swallowing, and inertia, irri- tability, even confusion. The advantages of avoiding these troubles by eating adequate red meat has to be balanced against the significant, but fractional, increase in large-gut cancers. The effect of iron deficiency on the immune system includes a reduction in the T-lymphocytes, and hence the ability to fight infection. A balance must be maintained between the risk of sacrificing some efficiency in the immune system through too little iron, against the chance that additional iron will encourage too many microorganisms.

Centenarians sometimes claim that longevity is the result of a balanced diet and lifestyle. An adequate iron intake also needs enough, but not too much, vitamins A, C, E and folic acid - essential for the absorption of iron from the small intestine. Doctors are alert to the possibility of damage from excessive iron levels as well as from iron deficiency. Too much iron in middle-aged men is more common than too little, partly because alcohol encourages iron absorption.