Zinc

Overview

Zinc is an essential trace mineral that functions as part of about 300 different enzymes. As such, zinc plays a role in numerous biochemical pathways and physiological processes. More than 90% of the body’s zinc is stored in the bones (30%) and muscles (60%), but zinc is also found widely distributed in small amounts in virtually all body tissues. The richest dietary sources of zinc are seafood (especially oysters), meat, fish, eggs, and poultry. Because of the varied roles of zinc in the body, claims for zinc-containing dietary supplements are numerous, including those for improved wound healing, general immune system support (including reduced severity and length of colds and upper respiratory tract infections), and support of various “male” aspects of health (supporting a healthy prostate gland, preventing benign prostatic hyperplasia, and increasing fertility via enhanced sperm production.

Comments

Zinc lozenges have become one of the most popular natural approaches to treating the common cold and the scientific evidence generally supports this use for short periods of time (1-2 weeks). Zinc lozenges appear to reduce cold symptoms such as sore throats, hoarseness and coughing – and may even be able to shorten the duration of colds by a full day or so. Like vitamin C, zinc is an essential nutrient for optimal functioning of the immune system – and they both possess significant antiviral activity when consumed at elevated levels for a short period of time. It also appears, however, that some forms of zinc lozenges may be more effective than other forms (due to the total amount of ionized zinc that the lozenge actually releases into the mouth and throat). At least one study has shown that lozenges containing zinc gluconate plus citric acid, sorbitol or mannitol may not deliver high enough levels of ionized zinc – whereas those lozenges which contained glycine (an amino acid) appeared to deliver a higher quantity of ionized zinc.

Scientific Support

Because zinc is an essential part of nearly 300 different biochemical pathways, “structure/function” claims can be made for the nutrient’s role in a wide variety of processes including digestion, wound healing, energy production, growth, cellular repair, collagen synthesis, bone strength, cognitive function, carbohydrate metabolism (glucose utilization and insulin production), and reproductive function. Even mild zinc deficiency has been associated with depressed immunity, decreased sperm count and impaired memory. Perhaps the most popular claim for zinc is for its role in immunity, where zinc delivered in lozenge form may interfere with the replication of the cold virus (rhinovirus).

Zinc deficiency is common in developing countries and in some elderly and athletic populations (Bogden et al. 1990, Bunker et al. 1994, Johnson and Porter 1997, Mahalanabis et al. 2002, Penny et al. 1999, Sazawal et al. 1998, Singh et al. 1994) and in these populations, zinc supplementation at dosages of 10-25mg/day – improves most markers of immune function and duration of illness (diarrhea and upper respiratory tract infections).

Evidence exists to support the use of zinc lozenges in reducing the duration and severity of colds. Although concentrated zinc lozenges can help kill cold viruses in the mouth and throat, it is important to begin using them as soon as possible following the onset of cold symptoms (ideally within the first 24-48 hours). Test tube studies have shown that zinc can block the cold virus from replicating – an effect that could help the body’s natural immune defenses “get a jump” on killing the viruses. Most studies of the effect of zinc lozenges (typically zinc gluconate or zinc acetate) on the common cold have shown that subjects in the supplement group tend to have fewer “symptomatic” days (on average 2-3 fewer sick days) compared to subjects receiving a placebo (measured in terms of coughing, sore throat, nasal congestion and headache).

Occasionally, high dose zinc supplements are recommended to diabetic patients. Such patients commonly suffer from increased loss of zinc and reduced body stores of zinc. High doses of zinc have been shown to mimic the effects of insulin in reducing blood sugar and promoting wound healing. These effects, however, should be considered preliminary and high dose zinc supplements are not recommended for diabetics except on the advice of their personal physician.

Exercise performance has also been associated with adequate zinc status – especially in athletes who avoid red meat, concentrate their diets too much on carbohydrates or follow an overly restricted dietary regime. Low zinc intake (below 3mg/day) has been linked to reduced activity of a zinc-containing enzyme in red blood cells called carbonic anhydrase (which helps red blood cells transport carbon dioxide from tissues to the lungs to be exhaled). Mild to moderate zinc deficiency can lead to significant reductions in the body’s ability to take up and use oxygen, remove carbon dioxide and generate energy during high intensity exercise.

Safety / Dosage

The short-term use of zinc at therapeutic doses for cold relief (see below) is assumed to be safe and chronic supplementation with zinc at levels 2-3 times the current RDA should not be expected to pose any significant adverse side effects. However, high doses of zinc are not recommended for periods of more than two weeks due to concerns of immune system suppression, interference with copper absorption and other long-term health effects such as increased risk for heart disease. High doses of zinc (gram levels) can cause nausea, diarrhea, and vomiting.

The Daily Value for zinc is 15mg per day – a level that should be adequate for support of bone metabolism and optimal physical performance. As therapy for colds, however, higher levels are required – with levels in the range of 13-23mg (in lozenge form) taken every 2-4 hours for no more than 2 weeks. These levels appear to be quite effective for reducing duration and severity of cold symptoms compared to not taking zinc lozenges. It is also important to note that other supplements, particularly high levels of calcium and iron can decrease zinc absorption, while complexation (chelation) with various amino acids (such as glycine, histidine and aspartate) or other organic compounds (such as gluconate or picolinate) may increase zinc bioavailability. Zinc supplementation can also reduce absorption of copper (Bonham et al. 2003) and iron (Donangelo et al. 2002), but may also potentiate the effect of supplemental vitamin A on night vision and immune parameters (Christian et al. 2001).

References

1.Abbasi AA, Prasad AS, Rabbani P, DuMouchelle E. Experimental zinc deficiency in man. Effect on testicular function. J Lab Clin Med. 1980 Sep;96(3):544-50.

2.Bogden JD, Oleske JM, Lavenhar MA, Munves EM, Kemp FW, Bruening KS, Holding KJ, Denny TN, Guarino MA, Holland BK. Effects of one year of supplementation with zinc and other micronutrients on cellular immunity in the elderly. J Am Coll Nutr. 1990 Jun;9(3):214-25.

3.Bogden JD, Oleske JM, Lavenhar MA, Munves EM, Kemp FW, Bruening KS, Holding KJ, Denny TN, Guarino MA, Krieger LM, et al. Zinc and immunocompetence in elderly people: effects of zinc supplementation for 3 months. Am J Clin Nutr. 1988 Sep;48(3):655-63.

4.Bonham M, O'Connor JM, Alexander HD, Coulter J, Walsh PM, McAnena LB, Downes CS, Hannigan BM, Strain JJ. Zinc supplementation has no effect on circulating levels of peripheral blood leucocytes and lymphocyte subsets in healthy adult men. Br J Nutr. 2003 May;89(5):695-703.

5.Brun JF, Dieu-Cambrezy C, Charpiat A, Fons C, Fedou C, Micallef JP, Fussellier M, Bardet L, Orsetti A. Serum zinc in highly trained adolescent gymnasts. Biol Trace Elem Res. 1995 Jan-Mar;47(1-3):273-8.

6.Bunker VW, Stansfield MF, Deacon-Smith R, Marzil RA, Hounslow A, Clayton BE. Dietary supplementation and immunocompetence in housebound elderly subjects. Br J Biomed Sci. 1994 Jun;51(2):128-35.

7.Christian P, Khatry SK, Yamini S, Stallings R, LeClerq SC, Shrestha SR, Pradhan EK, West KP Jr. Zinc supplementation might potentiate the effect of vitamin A in restoring night vision in pregnant Nepalese women. Am J Clin Nutr. 2001 Jun;73(6):1045-51.

8.Couzy F, Lafargue P, Guezennec CY. Zinc metabolism in the athlete: influence of training, nutrition and other factors. Int J Sports Med. 1990 Aug;11(4):263-6.

9.Donangelo CM, Woodhouse LR, King SM, Viteri FE, King JC. Supplemental zinc lowers measures of iron status in young women with low iron reserves. J Nutr. 2002 Jul;132(7):1860-4.

10.Hunt CD, Johnson PE, Herbel J, Mullen LK. Effects of dietary zinc depletion on seminal volume and zinc loss, serum testosterone concentrations, and sperm morphology in young men. Am J Clin Nutr. 1992 Jul;56(1):148-57.

11.Johnson MA, Porter KH. Micronutrient supplementation and infection in institutionalized elders. Nutr Rev. 1997 Nov;55(11 Pt 1):400-4.

12.Lukaski HC. Magnesium, zinc, and chromium nutriture and physical activity. Am J Clin Nutr. 2000 Aug;72(2 Suppl):585S-93S.

13.Mahalanabis D, Chowdhury A, Jana S, Bhattacharya MK, Chakrabarti MK, Wahed MA, Khaled MA. Zinc supplementation as adjunct therapy in children with measles accompanied by pneumonia: a double-blind, randomized controlled trial. Am J Clin Nutr. 2002 Sep;76(3):604-7.

14.Nishi Y. Anemia and zinc deficiency in the athlete. J Am Coll Nutr. 1996 Aug;15(4):323-4.

15.Penny ME, Peerson JM, Marin RM, Duran A, Lanata CF, Lonnerdal B, Black RE, Brown KH. Randomized, community-based trial of the effect of zinc supplementation, with and without other micronutrients, on the duration of persistent childhood diarrhea in Lima, Peru. J Pediatr. 1999 Aug;135(2 Pt 1):208-17.

16.Peretz A, Neve J, Jeghers O, Pelen F. Zinc distribution in blood components, inflammatory status, and clinical indexes of disease activity during zinc supplementation in inflammatory rheumatic diseases. Am J Clin Nutr. 1993 May;57(5):690-4.

17.Sazawal S, Black RE, Bhan MK, Jalla S, Sinha A, Bhandari N. Efficacy of zinc supplementation in reducing the incidence and prevalence of acute diarrhea--a community-based, double-blind, controlled trial. Am J Clin Nutr. 1997 Aug;66(2):413-8.

18.Sazawal S, Black RE, Jalla S, Mazumdar S, Sinha A, Bhan MK. Zinc supplementation reduces the incidence of acute lower respiratory infections in infants and preschool children: a double-blind, controlled trial. Pediatrics. 1998 Jul;102(1 Pt 1):1-5.

19.Sazawal S, Jalla S, Mazumder S, Sinha A, Black RE, Bhan MK. Effect of zinc supplementation on cell-mediated immunity and lymphocyte subsets in preschool children. Indian Pediatr. 1997 Jul;34(7):589-97.

20.Singh A, Failla ML, Deuster PA. Exercise-induced changes in immune function: effects of zinc supplementation. J Appl Physiol. 1994 Jun;76(6):2298-303.

21.Smith JC, Makdani D, Hegar A, Rao D, Douglass LW. Vitamin A and zinc supplementation of preschool children. J Am Coll Nutr. 1999 Jun;18(3):213-22.

EDITOR'S NOTE: This monograph can be found in The Health Professional's Guide to Dietary Supplements (Lippincott, Williams & Wilkins) by Shawn M. Talbott, PhD and Kerry Hughes, MS.