Zinc: Health Benefits, Symptoms of Deficiency and Overdose
As the second most common trace mineral in the body, zinc is found in all body tissues and more than 200 human enzymes. Some of its key roles include promoting cell reproduction and thus the growth and repair of tissues as well as promoting fertility in men. Zinc is vital for normal growth and development during pregnancy, childhood and adolescence. Nonetheless, it is probably best known as an antioxidant and for its ability to boost the immune system.
Although there are only 2-3 grams of zinc in the adult body, zinc has become an essential part of many popular dietary supplements. The amount of zinc that the body absorbs from the diet or supplements varies between 15% and 40%, depending on how much zinc is already present. However, there are also other factors that can affect zinc absorption. For example, the body absorbs zinc more easily from animal products than plants. This is because fiber and phytates in the plant foods bind zinc, preventing its absorption.
The protein albumin is the main transporter of zinc in the blood but some zinc is also carried by another protein called transferrin. If the intake of iron is too high, there may not be enough transferrin sites available for zinc. This can result in poor absorption of zinc. Likewise, excessive levels of zinc can prevent proper iron absorption.
Partially as a result of widespread use of dietary supplements, average intakes of zinc in the developed world exceed the recommended daily amounts and zinc deficiency is rare. Recommended dietary allowances (RDAs) and tolerable upper intake levels of zinc expressed in milligrams are as follows:
|Gender and Age||RDA (mg)||
Upper Limit (mg)
|Males and Females:||Birth to 6 months||2||4|
|19 and older||11||40|
|Females (not pregnant or nursing):||14-18 years||9||34|
|19 and older||8||40|
|Females (pregnant):||14-18 years||12||34|
|19 years and older||11||40|
|Females (nursing):||14-18 years||13||34|
|19 years and older||12||40|
However, vegetarians may need up to 50% more zinc due to its poor absorption from plant foods. Since alcohol decreases the absorption of zinc and increases the loss of zinc in urine, alcoholics may also require more zinc. In addition, infants who are still breastfeeding from 7-12 months of age may require age-appropriate foods rich in zinc, because breast milk cannot provide enough zinc for children that age.
Health Effects of Zinc
Zinc plays a crucial role in cell division and growth, thereby promoting the growth and repair of tissues. Therefore, pregnant women need more zinc to ensure normal growth and development of their baby. In fact, zinc can help prevent congenital abnormalities and reduce the risk of premature delivery. During childhood and adolescence, zinc helps activate bone development and is important to normal changes in height and weight.
In addition, zinc is associated with more than 200 human enzymes, including those that metabolize food and help the body use proteins, carbohydrates and fats. For example, this essential mineral is involved in the synthesis, storage and release of the blood-sugar regulating hormone insulin in the pancreas. Zinc is also often hailed as a powerful antioxidant because it is required for the activity of some antioxidant enzymes.
While the concentration of zinc in women is highest in muscles and bones, in men zinc is present in the testes at higher levels than anywhere else in the body. This helps ensure a continuous supply of testosterone, the hormone that plays a key role in the production of sperm and is, therefore, vital to male fertility.
Zinc’s other important roles in the body include:
- Affects thyroid hormone function
- Boosts the immune system
- Contributes to healthy growth
- Facilitates the transmission of information between neurons and the brain and spinal cord
- Influences behavior and ability to learn
- Interacts with platelets during blood clotting
- Protects nerve and brain tissue
- Protects the prostate gland from infection
- Protects vision and helps prevent night blindness and cataracts
Zinc lozenges or syrups are commonly used to fight common colds. While there is some scientific evidence indicating that zinc can shorten the duration of a cold by a day or two, there is also a number of studies that found no difference in symptoms.
Zinc Deficiency and Overdose
Zinc deficiency is rare in today’s world, though certain populations are more vulnerable. These include pregnant women (whose babies are at risk for birth defects), some infants who are still breastfeeding from 7 to 12 months of age that do not get zinc from other foods (who may experience impaired growth), the elderly and the poor. Alcoholics are at higher risk because alcohol impairs zinc absorption. Also, some vegetarians may not be able to obtain enough zinc from plant foods. Finally, people who have digestive system disorders that result in malabsorption, such as gluten intolerance, Crohn’s disease or short bowel syndrome, are at increased risk of zinc deficiency.
Symptoms of zinc deficiency. A moderate deficiency of zinc can hinder the body’s digestion and absorption mechanisms, resulting in diarrhea and malnutrition. Chronic zinc deficiency, however, can lead to damage of the nervous system and the brain, causing poor motor development and cognitive ability. Other health problems associated with zinc deficiency are:
- Brittle splitting nails (rarely)
- Canker sores
- Hair loss
- Impaired wound healing, including damage that occurs in muscle tissue after exercise
- Increased vulnerability to infection
- Male fertility problems
- Mental lethargy
- Reduced appetite and lowered ability to taste food
- Reduced sense of smell
- Skin and eye lesions
- Vitamins A and E deficiency
- Weight loss
Symptoms of zinc overdose. Although rare, excessive levels of zinc can also cause health problems. Moderately high doses of zinc may lower the body’s ability to absorb copper and iron, reduce levels of “good” cholesterol and cause problems in the urinary system of older adults. Much higher doses of zinc can impair a person’s immune system (just like zinc deficiency), whereas extremely high doses cause symptoms of zinc poisoning. These include diarrhea, gastric upset, vomiting, exhaustion, headaches and irritation to the stomach lining.
Dietary Sources of Zinc
Zinc can be found in a variety of foods, but keep in mind that it can be more easily absorbed from animal foods than plants. Good sources of zinc include:
- Oysters and other seafood
- Lentils (e.g., beans, chickpeas, peas)
- Seeds (e.g., sesame, pumpkin)
- Nuts (e.g., cashews, almonds)
- Milk and cheese
Where to Find More Information: International Zinc Association