Deficiência, excesso e suplementação de zinco

As well as many chemical reactions in our bodies, zinc is needed for:

• Our immune systems to work well to fight off infection.

• Healing of wounds.

• Growing.

• Building the proteins and molecules which are the basis of all our cells.

• Taste, smell and good vision.

What are the causes of zinc deficiency?

Uma dieta pobre

Zinc deficiency is more common in malnourished children and adults and in people who are unable to eat a normal diet due to circumstances or illness. Lots of zinc intake is from meat and seafood, so vegetarians may be more prone to deficiency. The greater demand caused by pregnancy and breastfeeding may also cause zinc deficiency.

Where do we get zinc from?

Zinc is readily available in many foods including:

• Red meat.

• Chicken and other poultry.

• Seafood, particularly oysters (which are loaded with zinc), crab and lobster.

• Nozes e sementes.

• Grains, beans, lentils and split peas.

• Spinach.

• Dairy products - milk, yoghurt, cheese.

• Fortified breakfast cereal.

Gut conditions

Problems with the guts can lead to problems absorbing zinc. This includes gut conditions such as colite ulcerativa, Doença de Crohn, e doença celíaca, and conditions where there is persisting diarrhoea.

Excesso de álcool

People who drink álcool em excesso can also not absorb zinc normally. Long-term illnesses, such as chronic liver or doença renal can also result in low absorption of zinc. High-dose iron supplements can also affect the way zinc is absorbed, leading to deficiency.

Acrodermatitis enteropathica

A rare inherited condition called acrodermatitis enteropathica is an occasional cause of zinc deficiency. In this condition, there is an absence of a transport protein which normally allows zinc absorption, resulting in severe deficiency. Where this is the case, symptoms begin soon after a baby is weaned off breast milk. A typical rash is often the first symptom.

Zinc supplements

The most common cause of zinc excess is taking too many zinc supplements. It is important not to take more than the advised dose.

Other causes are less common. If your kidneys are not working well (for example, if you have acute kidney injury) they do not get rid of excess zinc for you. In this case it can accumulate. Lesão renal aguda does not mean you have had a physical trauma to your kidney; it is a sudden loss of kidney function, usually due to an illness such as a severe infection.

Hemocromatose

If you have an uncommon condition called haemochromatosis, you are more likely to get zinc overload. This is because you have high levels of iron, which can affect the way that zinc is absorbed and used.

Zinc poisoning

Certain industrial compounds have high levels of zinc, and it is occasionally possible to get zinc poisoning through exposure to these substances. These include some pesticides and some components used in paints, dyes and rubber.

Symptoms of zinc deficiency depend on how deficient you are. Symptoms may be mild if the zinc level is just a little low, but can be very severe if there is severe deficiency. Symptoms can include:

• Not wanting to eat.

• Losing weight.

• Loose stools (diarrhoea).

• Having no energy.

• Being more prone to infections, such as the resfriado comum, coughs and chest infections.

• Losing your hair.

• Erupções cutâneas.

• Problems with eyesight, taste or smell.

• Impotence.

In children and adolescents there also can be:

• Halting of growth.

• Puberdade atrasada.

• Development of learning difficulty.

A number of different symptoms can occur if you have too much zinc in your system. For example:

• Dores de barriga (abdominais).

• Diarreia.

• Enjoo (náusea).

• Vomitar (vômito).

• Dores de cabeça.

• Cansaço.

• Tontura.

Too much zinc can also affect the levels in your body of other elements, such as iron, copper, magnesium or calcium. There can then be a knock-on effect of lack of these elements - for example, anaemia from a lack of iron.

Excess zinc can also affect the function of your heart and may possibly put you at risk of angina e ataques cardíacos.

A condition called metal fume fever can occur if zinc-containing fumes have been breathed in - for example, during welding or galvanising processes. This causes symptoms such as:

• Dor de garganta.

• Tosse.

• Dificuldade para respirar.

• Dores no peito.

• Alta temperatura (febre).

• Shakes.

• Dores musculares e articulares.

• Diarrhoea and vomiting.

There are various forms of zinc supplements, containing different forms and doses of zinc. These vary but some zinc supplements can have side-effects for some people. Many people have no side-effects. Read the information leaflet which comes with the packet. Possible side-effects can include:

• An unpleasant taste.

• Dores de cabeça.

• Dor de barriga.

• Sentindo-se mal (náusea), or being sick (vomiting).

• Diarreia.

• Indigestão.

• Cansaço.

Never take more than the recommended amount of zinc, due to the risks of excess, as described above.

How are zinc problems diagnosed?

The first test is a blood test to check levels of zinc. However, the levels in blood do not necessarily tally with the levels of zinc within the cells of the body. So it is possible to have a normal blood zinc level but actually be deficient in zinc. If the symptoms match and there is a likely cause of zinc deficiency then in some cases this may be assumed, regardless of the blood result. If giving zinc tablets causes the symptoms to resolve, then this confirms the diagnosis.

If you have an excess of zinc, however, this should be clear from the blood test result.

It may be possible to analyse zinc levels in cells by checking levels of zinc in hair in future. However, this is not yet widely available.

Are any other tests necessary?

You may also have blood tests for related elements such as:

• Ferro.

• Copper.

• Cálcio.

• Vitamina D.

• Vitamina B12.

• Magnesium.

This is because a deficiency or excess of zinc can affect absorption of some of these other elements, and vice versa. Also where there is a problem absorbing vital nutrients, others may also be deficient. So multiple deficiencies may need checking out.

Sometimes other tests are needed to exclude other causes for the symptoms, such as blood tests for thyroid function.

If you are severely unwell from either zinc deficiency or excess, other tests may be needed. For example, blood tests to check your kidney function, or tests to make sure you are not lacking in fluid (dehydrated).

Where babies have developed zinc deficiency early in life, or where there is a family history, genetic testing for the rare condition acrodermatitis enteropathica may be relevant.

This partly depends on the cause. Ideally, the underlying cause should be addressed and then the deficiency will correct itself. Zinc supplements may be needed and this would depend on the level of deficiency and on the cause.

There may be a need for dietary advice and for supplementation of other essential elements.

The treatment for zinc excess, poisoning or toxicity mostly involves removing the source of zinc excess and then treating the symptoms until the zinc level settles back down.

Oxygen treatment is usually needed for people who have inhaled zinc fumes (metal fume fever). Medicines such as paracetamol are used for pains and fevers.

Who should not take zinc supplements?

Most people who are healthy and eating normally do not need zinc supplements. People who have risk factors mentioned in the causes section may need to take zinc supplements. Those who might be advised by their healthcare professional to take zinc supplements include:

• Those with gut problems which cause problems absorbing zinc.

• Those in whom tests have confirmed zinc deficiency.

• People with Doença de Wilson, a rare condition affecting copper levels in the body.

• Children with diarrhoea, in developing countries only, on the advice of the World Health Organization (WHO).

Potential benefits of zinc supplements

Much research is underway looking at whether zinc supplements might reduce our chance of catching coughs and colds. Also, whether high-dose zinc supplements might make a cold better more quickly once you have one. There is some evidence that zinc might be helpful in these circumstances but there are not enough results yet for specific advice to be given. There is also some evidence that zinc supplements may slow the rate of degeneração macular relacionada à idade once it has developed. Your eye specialist may be able to advise.