Nutrition Research

Summary

Meeting the recommended levels of intake for all essential micronutrients is important for optimal immune function (see Immunity In-brief article). When it comes to the common cold specifically, there is evidence that routine supplementation with vitamin C can reduce the occurrence and duration of the common cold in certain individuals. Use of oral zinc lozenges may influence cold symptoms and duration, but there are important caveats associated with their use.

Condition Overview

The common cold is a viral infection of the upper respiratory tract (nose and throat).

Causes

Any one of hundreds of viruses can cause a common cold, but rhinoviruses are the most common culprits. It is possible to get a cold at any time of the year.

Viruses that cause colds spread through the air and upon contact. Thus, avoiding contact with infected individuals and washing hands often help to reduce the risk of common cold.

Symptoms

Symptoms usually appear one to three days following exposure to a cold-causing virus and then last 7 to 10 days. Common cold symptoms include sore throat, congestion, runny nose, coughing, and sneezing. These symptoms may be accompanied by low-grade fever, mild headache, and slight body aches.

Common cold versus influenza (the flu)

Both the common cold and influenza (the flu) are contagious respiratory illnesses with similar symptoms. However, cold and flu are caused by different viruses and, in general, flu symptoms are worse than common cold symptoms. Additionally, fever, body aches, extreme tiredness, and dry cough are more common and intense with the flu. Serious illness and complications can develop from the flu, such as pneumonia, bronchitis, sinus and ear infections, and even death.

If flu is suspected (e.g., fever, aches, chills) and symptoms persist (fever lasting longer than three days or cough continues for several weeks), it is recommended to seek a doctor’s advice.

The nutrition information presented here refers only to the common cold. See the Centers for Disease Control and Prevention website for information about influenza.

Nutrition Research

Vitamin C

What it does

General

  • Vitamin C (ascorbic acid) is a water-soluble vitamin that neutralizes a variety of reactive oxygen species, recycles important cellular antioxidants, augments the functional activity of immune cells, and helps make collagen, L-carnitine, and several neurotransmitters.

Immune-specific

  • Immune cells generate reactive oxygen species to kill invading organisms; vitamin C protects immune and nearby cells from damage by these substances.
  • Vitamin C may increase the production and function of certain immune cells that help engulf and kill foreign invaders.
  • Vitamin C may reduce plasma histamine levels by destroying the histamine molecule directly. 
What we know
  • Routine supplementation with vitamin C (0.25 to 2 grams/day) does not reduce the occurrence of the common cold in the general population, but it does reduce the occurrence of the common cold in individuals undergoing heavy physical stress, such as marathon runners, skiers, soldiers in subarctic conditions, and individuals with marginal vitamin C status.
  • Routine supplementation with vitamin C slightly reduces the duration of the common cold in both children (14% reduction) and adults (8% reduction).
  • No beneficial effects are seen when vitamin C supplements are taken after the onset of cold symptoms.
DEFINITIONS
Reactive oxygen species – highly unstable oxygen-containing compounds that react easily with nearby cellular structures, potentially causing damage
Antioxidants - compounds that prevent or repair the damage caused by reactive oxygen species

For references and more information, see the section on the common cold in the Vitamin C article.

Vitamin C (ascorbic acid) Flashcard. Main Functions: 1) Antioxidant defense, 2) Enhances immune function, 3) Needed to make collagen, carnitine, and the neurotransmitters serotonin and norepinephrine. Good Sources: Fruit, 1 medium-sized kiwifruit = 90 mg; strawberries, 1 cup whole, 85 mg; Vegetables (broccoli, kale, tomatoes), sweet red pepper (one-half cup, chopped) = 95 mg. Daily Recommendation is 400 mg for all adults. Special Notes: 1) Heat destroys vitamin C. Try to eat fresh foods and cook by steaming, microwaving, or stir-frying. 2) Vitamin C in food is identical to vitamin C in supplements. 3) The Daily Recommendation listed is specific to the LPI based on extensive review of the scientific evidence. The Institute of Medicine's Recommended Dietary Allowance (RDA) is 90 mg/day for men and 75 mg/day for women.

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Zinc

What it does

General

  • Zinc is an essential trace mineral that is required for normal cell growth and development, facilitates oxygen transport and storage, and assists several antioxidant enzymes.

Immune-specific

  • Zinc is required for the growth and development of cells that carry out the immune response.
  • Zinc is also a structural and functional component of proteins and enzymes critical for normal immune function. One such zinc-containing antioxidant enzyme, superoxide dismutase, protects immune cells from reactive oxygen species that are generated to kill invading pathogens during an immune response.
  • It is not yet known precisely how zinc might influence the common cold. Test tube experiments indicate that zinc might block the attachment of rhinoviruses to the lining of the nasal cavity or inhibit the activity and replication of respiratory viruses.
What we know
  • High-dose zinc acetate lozenges started within 24 hours of cold symptom onset may reduce the duration and symptoms of the common cold. However, there are several important details to keep in mind regarding this effect:
    • Formulation - zinc acetate lozenges readily dissolve and release zinc ions, making them available to act locally in the pharyngeal region (the part of the throat behind the mouth and nasal cavity).
    • Dose - the effective dose is more than 75 milligrams (mg) of zinc per day. This dose is substantially higher than the recommended dietary allowance (RDA) and higher than the tolerable upper intake level (UL) for zinc.
    • Side effects - common side effects include bad taste and nausea.
  • Zinc nasal gels and sprays do not appear to benefit the duration or symptoms of the common cold and may cause loss of the sense of smell, a potentially irreversible side effect.
DEFINITIONS
Reactive oxygen species – highly unstable oxygen-containing compounds that react easily with nearby cellular structures, potentially causing damage
Antioxidants - compounds that prevent or repair the damage caused by reactive oxygen species

For references and more information, see the section on the common cold in the Zinc article.

Zinc Flashcard. Main Functions: 1) Assists in the production of hemoglobin, the oxygen-carrying component of red blood cells; (2) Critical for normal immune function; and (3) Structural component of hundreds of essential molecules. Good Sources: seafood (oysters, crab), 6 medium-sized oysters (steamed) = 49.9 mg; meat (beef, dark meat, pork), rib eye steak (grilled) 3 ounces = 5.9 mg; beans (chickpeas, black beans), black beans (canned) one-half cup = 0.7 mg. Daily Recommendation; 11 mg for men and 8 mg for women. Special Notes: (1) Some dietary factors affect zinc absorption: (a) Phytates and fiber in whole grains and beans inhibit absorption, and (b) Animal-based protein enhances absorption. (2) National dietary surveys indicate that most Americans meet the dietary requirement for zinc.

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This content was underwritten, in part, by a grant from Bayer Consumer Care AG, Basel, Switzerland.