Zinc – what is it and why do we need it?
Zinc is a key micronutrient and mineral that is essential for several functions in the human body.
It affects how our cells respond to infections and can help keep inflammation under control. It also helps heal wounds, and supports normal growth. Zinc also helps stimulate the activity of at least 100 different enzymes and is involved in processing carbohydrate, fat and protein in food. A lack of zinc can make a person more susceptible to disease and illness.
Zinc & immune function
Severe deficiency of zinc is known to suppress immune function, and even mild to moderate deficiency can have a negative impact on the immune system’s ability to deal with infection. Zinc supports the function and proliferation of various immune cells, and without it, the capacity of the body to defend against harmful invaders is diminished.
There are a number of ways zinc boosts the immune system but primarily it activates enzymes that break down proteins in viruses and bacteria, so they are less able to spread. Zinc also increases the activation of cells responsible for fighting infection.
Zinc supports both innate (non-specific, short term, first line of defence) and adaptive (specific, longer term, second line of defence) immune responses. Interestingly, harmful pathogenic organisms also need zinc to invade and thrive, so the body has an important antimicrobial defence mechanism in place whereby it hides zinc away from potential pathogens so they cannot use it! Another important defence mechanism the body uses is to intoxicate intracellular microbes within macrophages (immune cells which engulf harmful organisms) with excess zinc.
Everyone needs optimal dietary zinc for their immune system to function properly, and particular consideration should be given to elderly adults who may be most at risk of having low zinc status. In fact, low levels of zinc are relatively common among the elderly and this is a likely factor contributing to age-related decline in immune function.
Ensuring optimal dietary zinc intake
Ensuring optimal levels of zinc, particularly in children and the elderly is essential to maintaining a healthy immune system. The body doesn’t have much ability to store zinc so it’s crucial that your diet supplies plenty. Whilst it’s vital to ensure you are regularly consuming plenty of zinc-rich foods, it’s also important to note that some compounds, for example phytates, (the major storage form of phosphorous in plant foods) can bind with zinc and inhibit its absorption. Phytates are found in whole-grain bread, cereals, and legumes. Zinc contained in grains and plants is not as well absorbed as zinc found in seafood and meat.
Phytates are antioxidant compounds found in whole grains, legumes, nuts and seeds. The chief concern about them is that they can bind to certain dietary minerals including iron, zinc, manganese and, to a lesser extent calcium, and slow their absorption in the intestines making them unavailable for the body to use. Phytates in your everyday meals should not be an issue as long as you’re eating a balanced diet. Most of us consume enough minerals in common foods to more than make up for the small amounts of these micronutrients that might be tied up by phytates.
Phytates themselves do have some health benefits, including anti-inflammatory effects. In laboratory research, phytates have helped normalize cell growth and stopped the proliferation of cancer cells. They also may help prevent cardiovascular disease and lower a food’s glycaemic load.(The glycemic load of food is a number that estimates how much the food will raise a person's blood glucose level after eating it.)
The best way to ensure optimal dietary zinc intake is to eat a balanced diet, and to include both animal and plant sources of the mineral. If you are completely reliant on plant sources of zinc, bear in mind that cooking reduces a food’s phytic acid content to some degree, as does soaking whole grains prior for use in baking. To help this breakdown, you can soak them in yoghurt, buttermilk, or water combined with lemon juice or vinegar. Foods such as garlic and onions may increase the absorption of zinc from plant foods.
Foods highest in zinc include:
- Nuts and seeds
- Dairy products
- Whole grains
- Some vegetables
How much zinc do I need?
The amount of zinc you need is about:
9.5mg a day for men (aged 19 to 64 years)
7mg a day for women
You should normally be able to get all the zinc you need from your daily diet.
You can take extra zinc in supplement form to keep your levels topped up and gently support your immune function. If you regularly take zinc in supplement form however (such as in a daily multi) it is important to balance this with copper, as excess zinc can cause copper deficiency and vice versa.
Zinc deficiency, cell-mediated immune dysfunction, susceptibility to infections, and increased oxidative stress have all been observed in elderly subjects. A 2007 randomised, double-blind, placebo-controlled trial of zinc supplementation was carried out on 50 elderly subjects and published in the American Journal of Clinical Nutrition. Following zinc supplementation, the researchers found that incidence of infections was significantly lower, plasma zinc was significantly higher, and generation of inflammatory and oxidative stress markers were significantly lower in the zinc-supplemented than in the placebo group.
Can I take too much zinc?
Zinc is a trace mineral which means we need a certain amount of it each day but taking high doses of zinc supplements can cause toxicity. Taking high doses of zinc reduces the amount of copper the body can absorb. This can lead to anaemia and weakening of the bones. Side effects include nausea, vomiting, a loss of appetite, a bad taste, and a loss of smell. Zinc supplements may also interact with medicines such as antibiotics, diuretics, and penicillin. Do not take more than 25mg of zinc supplements a day unless advised to by a doctor. You cannot over-consume zinc from zinc-containing foods.