Zinc, a nutrient found throughout your body, helps your immune system and metabolism function. Zinc is also important to wound healing and your sense of taste and smell.

With a varied diet, your body usually gets enough zinc. Food sources of zinc include chicken, red meat and fortified breakfast cereals.

People use oral zinc to help treat colds, but it can decrease the effectiveness of certain drugs and cause side effects.

The recommended daily amount of zinc is 8 milligrams (mg) for women and 11 mg for adult men.

Research on oral zinc for specific conditions shows:

• Zinc deficiency. People who have low levels of zinc appear to benefit most from zinc supplements. This kind of deficiency isn't common in the United States.
• Colds. Evidence suggests that if zinc lozenges or syrup is taken within 24 hours after cold symptoms start, the supplement can help shorten the length of colds. However, use of intranasal zinc has been linked with the loss of the sense of smell, in some cases long term or permanently.
• Wound healing. People with skin ulcers and low levels of zinc might benefit from oral zinc supplements.
• Diarrhea. Oral zinc supplements can reduce the symptoms of diarrhea in children with low levels of zinc, such as from malnutrition. There isn't enough evidence to recommend use of oral zinc for children with diarrhea who have a healthy, varied diet.
• Age-related macular degeneration. Research suggests that oral zinc might slow the progression of this eye disease.

Zinc that's used topically is known as zinc oxide. Zinc oxide cream, ointment or paste is applied to the skin to prevent conditions such as diaper rash and sunburn.

Oral zinc can cause:

• Indigestion
• Diarrhea
• Headache
• Nausea
• Vomiting

When oral zinc is taken long term and in high doses it can cause copper deficiency. People with low copper levels might experience neurological issues, such as numbness and weakness in the arms and legs.

The National Institutes of Health considers 40 mg of zinc a day to be the upper limit dose for adults and 4 mg of zinc a day for infants under age 6 months.

Don't use intranasal zinc. This form of zinc has been linked with the loss of the sense of smell.

Possible interactions include:

• Antibiotics. Using oral zinc while you're taking quinolone or tetracycline antibiotics can interfere with their ability to fight bacteria. Taking the antibiotic two hours before or four to six hours after taking zinc can minimize this effect.
• Penicillamine. Using oral zinc with the rheumatoid arthritis drug penicillamine (Cuprimine, Depen) can reduce the drug's ability to ease arthritis symptoms. Taking zinc at least two hours before or after taking the drug might minimize this effect.
• Thiazide diuretics. These blood pressure drugs increase the amount of zinc lost in urine.