Zinc is an essential mineral, required for the formation and activity of over 100 enzymes that play a role in immune function, protein formation, wound healing, DNA synthesis, and cell division. Zinc supports normal growth and development during pregnancy, childhood, and adolescence. It is one of the minerals required to make the superoxide dismutase (SOD) enzyme, an important enzyme defence against dangerous free radical-producing carcinogens. Manifestations of zinc deficiency are rare in humans, but very low levels are linked with poor skin, nail and hair health, diarrhoea, an impaired sense of taste and smell, and poor wound healing. Many researchers have established a link between zinc deficiency and an increased cancer risk via a greater vulnerability to carcinogens, a weakened immune system and impaired DNA repair mechanisms.
Blood results from over 500 people who ordered the Cancer Risk Nutritional Profile (CRNP) have revealed that nearly 40% had zinc levels below the normal range, and only 2% had higher than normal levels. This does imply that, as a population as a whole, we need to concentrate on foods which contain a higher zinc content or even take a low-dose supplement 3 days a week (e.g. 20 mg of zinc gluconate). Be careful with higher dose supplements as they can be harmful. For example, in the Health Professionals Follow up Study (HPFS), which monitored the dietary and lifestyle patterns of 50,000 health care workers over many years, men who took supplemental zinc at levels of more than 100mg/day, or for long durations, were more than twice as likely to develop advanced prostate cancer. Taking a supplement of >40 mg per day may also prevent absorption of copper, another important essential mineral.
Recommended daily amount (RDA)
A daily intake of zinc is required to maintain a steady-state, as the body has no specialized zinc storage system. The for women is 8mg/day (women), while for men it is 11mg/day. Phytate (phytic acid), common in plant foods, can reduce zinc absorption by attaching to zinc in the digestive system. This could be a problem for vegetarians or people who get their zinc from high phytate sources such as whole grains, legumes, nuts and seeds. In these cases, zinc requirements may be up to 50% higher.
Sources of dietary Zinc
Oysters contain more zinc than any other food, but red meat and poultry provide the majority of zinc in a typical western diet. Other good food sources include seafood such as crab and lobster, whole grains, fortified breakfast cereals, beans, nuts and dairy products. The bioavailability of zinc from grains and plant foods is lower than that from animal foods. Some cold lozenges contain zinc, which can be absorbed. Supplements contain several forms, but Zinc citrate and zinc gluconate are thought to be the most reliable. Common sources of dietary zinc include:
|Food sources of Zn||Mg||Food sources of Zn||Mg|
|Oysters, 6 medium||76.7||Baked beans, canned, ½ cup||1.7|
|Beef, 90g||8.9||Chickpeas, ½ cup||1.3|
|Crab, 90g||6.5||Swiss Cheese, 30g||1.1|
|Pork, 90g||4.2||Almonds, 30g||1.0|
|Breakfast cereal (Zn fortified), ¾ cup||3.8||Chicken breast, ½ (skin removed)||1.0|
|Chicken leg /dark meat, 1 leg||2.7||Walnuts, ¼ cup||0.9|
|Lobster, 90g||2.5||Milk, 1 cup||0.9|
|Hummus, ½ cup||2.3||Kidney beans, cooked, ½ cup||0.9|
|Pumpkin seeds, ¼ cup||2.3||Peas, ½ cup||0.9|
|Tofu, ½ cup||2.0||Cheese, cheddar, 30g||0.8|
|Sunflower seeds, ¼ cup||1.7||White fish (e.g. Cod, sole)||0.6|
|Cashew nuts, ¼ cup||1.9||Mushrooms, ½ cup||0.6|