Zinc

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Zinc is one of the 24 classical micronutrients needed for survival. It can be found in various meat, egg, and legume products and is especially high in oysters. Zinc is known as an aphrodisiac and Testosterone Booster, although the former is anecdotal and the latter only applies to the deficient (directly).

Zinc is highly involved in many enzyme systems in the body. Keeping normal zinc levels helps with the maintenance of these enzyme systems and acts as a hormonal and immune system aid. In very high doses, zinc can act as an aromatase inhibitor and lower estrogen levels but is a potent oxidant; especially in the male prostate. It is also implicated in repair of the intestinal mucosa at similarily high levels.

Zinc is also lost in sweat, as are many minerals, making mineral supplementation almost a necessity for athletes underconsuming the nutrient through food.

Zinc has it's intestinal uptake hindered by the other divalent minerals calcium, Magnesium, and iron when all four together exceed their transporter's uptake limit (around 800mg or so). Consuming these minerals alongside each other below this threshold is fine.

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15mg is the dose used for sedentary populations who may be deficient in zinc (vegetarians/vegans, caloric restriction) and 30mg the more common dose catered to athletes who lose zinc in sweat.

Doses up to 100-150mg are used as a cheap and potent aromatase inhibitor and doses around 300mg have shown efficacy in treatment of some gut dysfunction. Doses at this level, however, are probably not safe for chronic health given the Tolerable Upper Limit of Intake (TUL) is 40mg.

One of the more common micronutrient deficiencies in athletes, vegetarians/vegans, and those who sweat a ton. Not really a common deficiency otherwise.

Although theoretically it competes for absorption with Magnesium (which would be problematic given the ZMA formulation) if taken on an empty stomach there should be enough transporters for both minerals. Just don't take with calcium (as that micronutrient is much more abundant and, thus, can use up said transporters)

Kurtis Frank

• Does ZMA cause weird dreams?

Edit1. Sources in the diet

Zinc is one of the 24 essential vitamins and minerals, specifically a mineral. It is found in high levels in animal tissues and eggs, legumes, and fish; it is exceptionally high in shellfish such as oyster.^[4][5] It may also be fortified into cereal grains in developed countries.^[6]

Edit2. Roles in the body through adequate intake

Zinc's main role in the body is as a prosthetic group for several enzymes called metalloproteins, one of which is the Superoxide Dismustase enzyme; an endogenous anti-oxidant involving both zinc and copper.^[7][8][9] Zinc is also involved in regulating the immune system.^[10][11] A deficiency in zinc is related to delayed growth in youth and hypogonadism in adult males^[12] as well as general mental lethargy and skin abnormalities.^[13]

The RDA values for zinc are an Estimated Average Requirement (EAR) of 6.5mg for females, 8.5-10mg for pregnant or lactating females, and 12mg a day for men. The Recommended Daily Intake (RDI) values are 8mg for females, 10-12mg for pregnant or lactating females, and 14-15mg for males, and the Tolerable Upper intake Limit (TUL) is in the range of 35-40mg for adults of both genders (all numbers daily requirements).^[14][15]

Zinc is known as a mineral regulatory of testosterone levels, and body stores are positively correlated with testosterone levels.^[16]

Edit3. Maintaining Zinc Status

Supplementation is not generally needed if one has a good zinc intake through the diet. Thus practises to increase zinc absorption or to decrease zinc excretion could be potentially useful.

Zinc is lost during sweat and exercise^[17][18] and may be a contributing factor to why testosterone levels seem to be depressed after exhaustive exercise.^[19][20]

Edit4. Aging and Longevity

4.1. Absorption

At least one animal study has suggested that dysregulation occurs with intestinal zinc absorption during aging, and adequate dietary intake may in turn be metabolically insufficient due to poorer absorption.^[21]

Edit5. Immunology and Inflammation

5.1. Rhinovirus (Common Cold)

A meta-analysis (Cochrane)^[22] of 15 trials including 1360 persons overall noted that zinc, in the form of lozenges (gluconate) or syrup (sulfate), was associated with less duration and severity of the common cold when taken within 24 hours of onset that, after a week, had an odds ratio of 0.45 (less than half the risk) and noted that prolonged (5 month) usage was assocaited with less occurrence of the common cold with an incidence rate ratio of 0.64; this study could not make conclusions on persons with worse baseline health (immunosuppression, chronic illness) and did note wide variability in the study populations assessed.^[22] In this study, side effects were only noted with zinc lozenges rather than syrup and were limited to nausea and altered perception of taste, which is similar to results seen with past reviews on the subject matter.^[23] The dose range of the studies used was variable, ranging from 30-160mg daily.^[22]

Edit6. Interactions with Hormones

6.1. Testosterone

Supra-physiological levels of zinc have been noted to influence steroid metabolism. Zinc has been used as an aromatase inhibitor in doses of 100-150mg. It has been noted to reduce aromatization of testosterone (via aromatase) in the rat liver^[24]. In addition to aromatase, Zinc has also been noted as an inhibitor of 5-alpha reductase^[25], which converts testosterone into dihydrotestosterone (DHT).

As stated earlier, zinc is a regulator of testosterone levels. Supplementation of zinc increases testosterone if one was deficient in zinc before yet does not necessarily increase testosterone above baseline levels.^[26] That being said, it can reduce the exercise-induced depression of testosterone and exert a protective effect during periods of intense exercise.^[27][28][29] This one study using Zinc supplementation in road cyclists with 2-3 hours of training daily for 5 days a week noted that 30mg Zinc Sulfate daily for 4 weeks on top of a Zinc sufficient (15mg) diet failed to be significantly better than placebo or Selenium at increasing total testosterone levels, although there was a small but significant increase in free testosterone levels relative to placebo but only when measured after exhaustive exercise; testosterone levels tended to increase after exhaustive exercise.^[30]

Edit7. Forms of Zinc Supplementation

7.1. Zinc Citrate

Zinc Citrate, at 50mg elemental Zinc (146mg) daily for 4 weeks is associated with a maintenance of Zinc status while placebo declines over time (told to maintain a low Zinc diet, estimated between 10-12mg).^[31]

7.2. Zinc Gluconate

Zinc Gluconate, at 50mg elemental Zinc (385mg), appears to be slightly more effective than Zinc Citrate (nonsignificant) and can increase serum and erythrocytic stores of Zinc in apparently healthy persons over a period of 4 weeks.^[31]

7.3. Zinc Picolinate

Zinc Picolinate (bound to picolinic acid, a metabolite of tryptophan), at 50mg elemental Zinc (144mg) in healthy persons appears to increase urinary and serum levels greater than placebo and the other two forms tested (Citrate, Gluconate).^[31]

Edit8. Gut permeability

Very high levels of zinc intake (330mg daily) has been implicated in alleviating leaky gut syndrome in those with Crohn's Disease.^[32] It can also prevent or alleviate damage to the intestinal mucosa and some to the liver done by alcohol^[33][34][35] and due to alcohol causing zinc depletion, can also provide therapeutic-like benefit in treating alcohol-induced damage to the gut and liver.^[36][37] Many of these effects were noted as dose dependent, but were seen at 3-5mg/kg bodyweight (an incredibly high dose).

References

1. Zinc-Induced Copper Deficiency A Report of Three Cases Initially Recognized on Bone Marrow Examination
2. CNS demyelination associated with copper deficiency and hyperzincemia.
3. Fatal copper deficiency from excessive use of zinc-based denture adhesive.
4. Guéguen M, et al. Shellfish and residual chemical contaminants: hazards, monitoring, and health risk assessment along French coasts. Rev Environ Contam Toxicol. (2011)
5. Maret W, Sandstead HH. Zinc requirements and the risks and benefits of zinc supplementation. J Trace Elem Med Biol. (2006)
6. Brown KH, Hambidge KM, Ranum P; Zinc Fortification Working Group. Zinc fortification of cereal flours: current recommendations and research needs. Food Nutr Bull. (2010)
7. Anzellotti AI, Farrell NP. Zinc metalloproteins as medicinal targets. Chem Soc Rev. (2008)
8. Vallee BL, Auld DS. Zinc metallochemistry in biochemistry. EXS. (1995)
9. Abreu IA, Cabelli DE. Superoxide dismutases-a review of the metal-associated mechanistic variations. Biochim Biophys Acta. (2010)
10. Prasad AS. Zinc in human health: effect of zinc on immune cells. Mol Med. (2008)
11. Prasad AS. Clinical, immunological, anti-inflammatory and antioxidant roles of zinc. Exp Gerontol. (2008)
12. Prasad AS. Clinical manifestations of zinc deficiency. Annu Rev Nutr. (1985)
13. Prasad AS. Zinc deficiency in human subjects. Prog Clin Biol Res. (1983)
14. Nutrient Reference Values for Australia and New Zealand: Zinc
15. Recommended Dietary Allowances: 10th Edition
16. Chang CS, et al. Correlation between serum testosterone level and concentrations of copper and zinc in hair tissue. Biol Trace Elem Res. (2011)
17. Lukaski HC. Magnesium, zinc, and chromium nutriture and physical activity. Am J Clin Nutr. (2000)
18. Campbell WW, Anderson RA. Effects of aerobic exercise and training on the trace minerals chromium, zinc and copper. Sports Med. (1987)
19. Galbo H, et al. Thyroid and testicular hormone responses to graded and prolonged exercise in man. Eur J Appl Physiol Occup Physiol. (1977)
20. Hackney AC, et al. Comparison of the hormonal responses to exhaustive incremental exercise in adolescent and young adult males. Arq Bras Endocrinol Metabol. (2011)
21. Wong CP, Magnusson KR, Ho E. Increased inflammatory response in aged mice is associated with age-related zinc deficiency and zinc transporter dysregulation. J Nutr Biochem. (2012)
22. Singh M, Das RR. Zinc for the common cold. Cochrane Database Syst Rev. (2011)
23. Marshall S. Zinc gluconate and the common cold. Review of randomized controlled trials. Can Fam Physician. (1998)
24. Om AS, Chung KW. Dietary zinc deficiency alters 5 alpha-reduction and aromatization of testosterone and androgen and estrogen receptors in rat liver. J Nutr. (1996)
25. Stamatiadis D, Bulteau-Portois MC, Mowszowicz I. Inhibition of 5 alpha-reductase activity in human skin by zinc and azelaic acid. Br J Dermatol. (1988)
26. Koehler K, et al. Serum testosterone and urinary excretion of steroid hormone metabolites after administration of a high-dose zinc supplement. Eur J Clin Nutr. (2009)
27. Kilic M, et al. The effect of exhaustion exercise on thyroid hormones and testosterone levels of elite athletes receiving oral zinc. Neuro Endocrinol Lett. (2006)
28. Kaya O, et al. Zinc supplementation in rats subjected to acute swimming exercise: Its effect on testosterone levels and relation with lactate. Neuro Endocrinol Lett. (2006)
29. Kilic M. Effect of fatiguing bicycle exercise on thyroid hormone and testosterone levels in sedentary males supplemented with oral zinc. Neuro Endocrinol Lett. (2007)
30. Shafiei Neek L, Gaeini AA, Choobineh S. Effect of zinc and selenium supplementation on serum testosterone and plasma lactate in cyclist after an exhaustive exercise bout. Biol Trace Elem Res. (2011)
31. Barrie SA, et al. Comparative absorption of zinc picolinate, zinc citrate and zinc gluconate in humans. Agents Actions. (1987)
32. Sturniolo GC, et al. Zinc supplementation tightens "leaky gut" in Crohn's disease. Inflamm Bowel Dis. (2001)
33. Zinc Supplementation Inhibits Hepatic Apoptosis in Mice Subjected to a Long-Term Ethanol Exposure
34. Preservation of Intestinal Structural Integrity by Zinc Is Independent of Metallothionein in Alcohol-Intoxicated Mice
35. Zhou Z, et al. Zinc supplementation prevents alcoholic liver injury in mice through attenuation of oxidative stress. Am J Pathol. (2005)
36. Zinc Deficiency Mediates Alcohol-Induced Alveolar Epithelial and Macrophage Dysfunction in Rats
37. Kang YJ, Zhou Z. Zinc prevention and treatment of alcoholic liver disease. Mol Aspects Med. (2005)
38. Ebben M, Lequerica A, Spielman A. Effects of pyridoxine on dreaming: a preliminary study. Percept Mot Skills. (2002)
39. De Souza MC, et al. A synergistic effect of a daily supplement for 1 month of 200 mg magnesium plus 50 mg vitamin B6 for the relief of anxiety-related premenstrual symptoms: a randomized, double-blind, crossover study. J Womens Health Gend Based Med. (2000)

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