Popeye, the popular cartoon character, got it all wrong. He ate mounds of spinach, thinking it contained plenty of iron to make him strong.

Scientists in the 1890s made a mistake while calculating the nutritional value of various vegetables and put a decimal point in the wrong place when it came to Popeye's favourite food. For a long time, people thought spinach contained ten times more iron than it actually did.

It also isn't necessarily true that the more iron you eat, the stronger you become. Increasing your iron intake only makes you feel stronger if you are iron deficient. Iron is part of haemoglobin, the red pigment in the blood which carries oxygen to all the cells around the body.

Iron-deficiency anaemia results in a decrease in the amount of oxygen the blood is able to carry. Symptoms include unusual fatigue, lack of concentration, dizziness and palpitations. More advanced symptoms can be headaches, a sore or swollen tongue, pale skin, "restless" legs and a desire to eat unusual things, such as clay or cardboard.

A lack of iron may be due to dietary deficiencies or conditions which cause blood loss, such as heavy menstruation, piles, ulcers or gastro-intestinal bleeding.

Pregnant women, people with gluten intolerance, children or adolescents during a growth spurt, or those who don't produce enough gastric acid for proper digestion may be at risk of iron deficiency.

It is important to get a proper medical diagnosis and to be aware there could be many different reasons for fatigue, not just iron deficiency. The body also requires vitamin B12 and folic acid to produce red blood cells. If there is a lack of these, anaemia will develop.

The most absorbable form of iron is called "heme" iron and is found in red meat, eggs, the dark meat of chicken and turkey and oily fish such as sardines.

"Non-heme" iron is less well absorbed and is found in fortified cereals, beans, nuts, seeds, dried fruit and dark- green vegetables like spinach. Vegetarians who don't replace meat with iron-rich foods may be low in the mineral.

Only take supplements with iron if you have been diagnosed with iron deficiency because it can be harmful. Iron cannot be excreted by the body and must be either used up or stored. Excess iron storage promotes bacterial infections because bacteria requires iron for growth.

Iron supplements can also interfere with the absorption of other minerals, such as zinc, which is needed for a healthy immune system. Supplementing a zinc-deficient person with iron may weaken their immunity while stimulating bacterial growth.

Those who are at risk of iron deficiency should avoid wine, tea and coffee - these contain tannins which block the absorption of iron.

But Vitamin C increases the absorption of iron and some iron supplements include vitamin C to encourage its uptake.

Nutritionists can advise on suitable brands which are easier to absorb and lessen the risk of common side-effects of iron supplementation, such as constipation and stomach irritation.