Zinc for Muscle & Performance: Is Taking This Supplement Worth It?

Zinc for Muscle & Performance: Is Taking This Supplement Worth It?

Zinc is an essential nutrient that has many functions in the body. Potential benefits of taking zinc include everything from immunity, hormonal, heart health, and improved memory. Learn if taking zinc for muscle & performance is worth your time.

What Is Zinc and its Function

Zinc is a mineral not made by the body and must be obtained from the diet. It is required to facilitate the activity of over 300 enzymes. It also plays a role in immune function, taste, smell, metabolism, protein synthesis, wound healing, DNA production, and cell division [R, R, R].

Zinc is not stored by the body and needs to be consumed on a daily basis [R].

Who is at Risk for a Zinc Deficiency

Considering how zinc is essential to many body processes a deficiency can lead to a host of problems.

Signs of a deficiency include [R]:

  • Skin changes
  • Poor appetite
  • Mental lethargy
  • Delayed wound healing
  • Neurosensory disorders
  • Immune disorder
  • Poor sense of taste and smell
  • Hair loss
  • Changes in vision

Those at risk for zinc deficiency include the following [R]:

  • Pregnant and lactating women
  • Those with renal disease
  • Those with sickle cell anemia
  • Those with gastrointestinal problems
  • Conditions that cause severe diarrhea or malabsorption (IBS, Crohn's disease, ulcerative colitis, celiac disease)
  • Vegetarians and vegans with high grain and legume intake.
  • Those with low protein intake
  • Older adults
  • Those on medications

Zinc deficiency used to be something of a rarity but many could have subpar levels based on their stress levels. Chronic stress can lead to depleted levels of zinc [R].

Zinc Vitamin Benefits

Since zinc is needed for so many processes it is no wonder there are many potential benefits to this nutrient. It has been credited with everything from improved immunity and heart health to regulated hormone function, and enhanced memory.

Zinc and Immune Function

Zinc plays a role in immune function. A deficiency of this mineral impairs immune responses. Zinc is needed to make white blood cells and fight infection [R].

Zinc may be helpful in improving inflammatory conditions [R].

A group of 50 healthy older adults with low zinc levels had less oxidative stress and inflammatory markers after taking 45 mg of zinc gluconate daily for 12 months when compared with a placebo [R].

Zinc may be helpful to reduce the duration of a cold.

Daily supplementation of zinc gluconate or sulfate lozenges decreased the time someone was sick when taken within 24 hours of when symptoms began [R].

Zinc and Cardiovascular Health

Zinc deficiency is associated with atherosclerosis and hardening of the arteries [R]. Zinc supplementation was found to lower arterial inflammation [R].

Inflammatory markers indicating heart disease were reduced in healthy older adults at risk for a deficiency when supplementing 45 mg of elemental zinc gluconate daily for six months [R].

Zinc and Mood

Depression is associated with low zinc. Those with worsening depression often had lower levels of this mineral [R].

Depressive symptoms subsided in rats given two weeks of zinc supplement. Poor zinc intake also lowered the effectiveness of depression medications in these animals. [R].

Zinc alone or in conjunction with antidepressant medication reduced depression symptoms in humans after 12 weeks of supplementation [R, R].

Healthy young women given a multivitamin containing 7mg of elemental zinc had less depressive and aggression compared with those who took a placebo [R].

Zinc is also thought to stop the production of glycogen synthase kinase-3β. This compound is thought to cause mood disorders [R, R, R].

Zinc and Brain Health

Those with deficiencies of zinc may benefit from improved memory and learning [R].

Cognition improved in stroke patients with poor zinc intake when given 10 mg of elemental zinc than those who received a placebo [R].

On the flip side, too high an intake of supplemental zinc may cause memory impairment and could reduce zinc levels in the brain.

Rats given 60 ppm of zinc in their drinking water were found to have lower cranial levels of zinc [R].

Zinc and Hormone Function

The body needs zinc to facilitate the production of the sex hormone testosterone. High levels of testosterone were associated with optimal levels of zinc. When zinc is low testosterone production will also be low [R, R].

Testosterone is needed for bodybuilding and performance so lack of zinc could prevent muscle growth [R].

Deficient individuals given 250 mg of zinc sulfate over six weeks was found to increase testosterone levels by 84% in those on hemodialysis [R].

Wrestlers and cyclists with adequate zinc dietary intake (11.9 to 23.2 mg) saw no change in testosterone levels when supplementing elemental zinc or zinc sulfate [R, R, R].

The type of exercise may affect zinc levels. Strenuous exhaustive exercises can lower testosterone. Supplementation preserved zinc levels and restored depressed testosterone levels in exercising men not deficient in zinc [R, R, R].

Leptin is another hormone needed for maintaining muscle mass [R, R]. It is low in those with zinc deficiency [R].

Men given a marginal zinc deficiency for 30 days saw a 64% increase in leptin after taking 30 to 60 mg elemental zinc acetate daily for 6 to 12 weeks [R].

Leptin levels were not researched in those without zinc deficiency so the effects of normal levels are unknown.

Zinc for Muscle & Performance

With the improvements in memory and cognition, there can be speculation that zinc supplementation may help improve performance in athletes and endurance trainers.

Few studies have researched zinc solely as a performance vitamin and instead is in conjunction with other nutrients. Research is mostly aimed at the effects of improved immunity on exercise [R].

Zinc and Its Impact on VO2

There are inconsistencies among research on zinc and exercise performance.

Low doses of zinc gluconate (30 mg per day) improved aerobic and anaerobic power in female futsal players after six weeks of supplementation [R].

Zinc improvements in exercise performance could be due to its positive effects on protein synthesis, muscle development, and catalytic activities [R].

Zinc increases VO2 peak just as well as high-intensity interval training (HIIT). When taking zinc and doing HIIT there were even further improvements in the VO2 peak showing it to be an effective way to improve exercise performance.

Alternatively, taking 70 mg of zinc carnosine a day for two weeks had no effect on VO2 performance. Zinc did, however, reduce the incidences of leaky gut resulting from strenuous exercise by 71% [R].

A week-long intake of 20 mg of zinc did not improve the VO2 peak in healthy sedentary males when compared with a placebo [R].

Markers of improved oxygen delivery were found with zinc supplementation showing it may possibly enhance aerobic performance over time [R].

The inconsistent findings among VO2 may have to due to the delayed response of zinc supplementation.

Elite cyclists with zinc deficiency were given 22 mg of zinc for 30 days. A placebo was then used for another 30 days. Results indicated better zinc levels after placebo treatment. Copper levels decreased with an increase in the zinc-copper ratio. Insulin levels also increased. This indicated that too much zinc may impair glucose utilization during intense exercise [R].

Zinc and Its Impact on Insulin and Blood Sugar

Zinc improved insulin sensitivity in obesity [R] but some elite athletes had high insulin sensitivity [R].

There is also evidence showing that zinc was supposed to improve insulin sensitivity in exercise training [R, R, R], but this study contradicts that notion.

Zinc and Its Impact on Testosterone

Like aerobic performance, there is conflicting information on how zinc affects testosterone levels.

A six-week daily high dose (2.5 to 3 mg per kilogram body weight) of zinc combined with weight training four times a week increased testosterone levels in athletes and sedentary men when compared with no zinc [R].

Elite zinc-deficient male cyclists given 22 mg of zinc gluconate for 30 training days had no effect on thyroid hormone function [R].

There has also been evidence of zinc contributing to exercise-induced hormonal changes.

Free testosterone was increased in road cyclists following exhaustive exercise after taking 30 mg of zinc sulphate for 4 weeks when compared with a placebo in a double-blind controlled trial. Resting levels were not affected [R].

It may actually be resistance training that impacted hormonal changes and not the zinc.

Evidence on Zinc and Improved Athletic Performance is Limited

Though zinc is a popular supplement among athletes, there is little quality evidence showing improvements in performance.

VO2 peak was estimated and not actually measured so the true impact of zinc on aerobic capacity requires further investigation.

The effects of zinc on insulin resistance in zinc-deficient elite cyclists also need to be clarified.

Longer more comprehensive research needs to be done to find the true impact of zinc supplementation on athletic performance [R].

What to Look for in a Zinc Supplement

Zinc comes in pill, capsule, and liquid form. Like most supplements, it is not regulated by any federal standards. Be sure to get a reputable brand with third-party testing.

How to Take Zinc Supplements

There are different types of zinc that exist. The forms contain different amounts of elemental zinc. This tells the weight of the amount of zinc in the product [R].

Below are some of the forms of zinc available [R, R, R]:

  • Zinc acetate (~30% elemental zinc)
  • Zinc citrate (~34% zinc)
  • Zinc sulfate (~22% zinc)
  • Zinc gluconate (~13% zinc)
  • Zinc monomethionine (~21% zinc)
  • Zinc picolinate (~20% zinc)

The dose of zinc will vary depending on the elemental weight of zinc. It should also be listed on the product.

Research shows zinc gluconate, zinc citrate, and zinc picolinate are the best-absorbed form of zinc [R, R].

Absorption quality is also enhanced by a supplement with a chelator [R].

Zinc Dosage Recommendations

There is a low and high dosage of zinc. The low dose is 5 to 10 mg per day and the high dose is 25 to 45 mg per day.

The low dose is recommended for most individuals as a preventative measure. The high dose should only be taken if someone is deficient. It should be used only under the care of a health professional.

Side Effects of Zinc Supplements

The tolerable upper limit for zinc is 40 mg per day. This is to prevent toxicity.

Side effects have been seen at both high and lower dosages. They include stomach upset, nausea, and vomiting, and other digestive issues [R, R, R].

Fever, cough, headache, fatigue, and other flu-like symptoms have been seen in those taking over 40 mg per day [R].

Zinc lozenges can cause nausea and a metallic taste. These are to be used only in the short term and should not exceed 75 mg [R].

Taking zinc with a meal may help prevent stomach upset.

Contraindications of Zinc Supplements

It is recommended to not take zinc doses higher than 40 mg per day unless it is prescribed by a medical professional who is monitoring zinc treatments.

There are also both medication and nutrient interactions with zinc.

Drug Interactions with Zinc

Zinc can affect the effectiveness of antibiotics. It has been found to decrease the amount of antibiotic absorbed. It is recommended to take zinc at least 4 hours after the antibiotic medication. Antibiotics that interact with zinc include the following [R]:

  • Ciprofloxacin (Cipro)
  • Enoxacin (Penetrex)
  • Norfloxacin (Chibroxin, Noroxin)
  • Sparfloxacin (Zagam)
  • Trovafloxacin (Trovan)
  • Grepafloxacin (Raxar).
  • Demeclocycline (Declomycin)
  • Minocycline (Minocin)
  • Tetracycline (Achromycin)

Zinc also interacts with the cancer medication Cisplatin and penicillamine used to treat Wilson's disease and rheumatoid arthritis. It is best to avoid zinc when on these medications.

Diuretics can deplete zinc levels so it is best to monitor zinc levels if on these medications [R].

There is also a minor interaction between water pills and zinc. It increases the amount of zinc in the body. The combination of water pills and zinc supplements may lead to excess levels of zinc [R].

If you have a health condition or are on any medications it is best to speak with your healthcare professional for specific zinc recommendations.

Nutrient Interactions with Zinc

Zinc may interfere with the absorption of certain minerals including calcium, magnesium, and iron [R].

Zinc Interferes with Copper

Large doses of zinc about 50 mg or more per day over a period of weeks affect copper levels. A high intake of zinc will decrease copper absorption. Taking under 40 mg of zinc per day should not affect copper levels [R].

Zinc Interferes with Iron

Zinc intake will prevent absorption from iron supplements in doses of 38 to 65 mg per day. Dietary iron was not affected by zinc supplements [R].

Supplementation in children of 10 mg of zinc a day for three months found significantly decreased iron levels when compared with a placebo. Other randomized control studies showed poor iron levels with chronic zinc supplementation [R, R].

It is best to take iron supplements between meals to decrease the effects of interactions from zinc [R].

To avoid any interactions it is best to take zinc about an hour separate from other supplements.

Zinc interferes with Calcium

High intakes of foods rich in calcium interfere with zinc absorption in animals, but human research has mixed results [R].

Postmenopausal women taking 890 mg of milk or calcium phosphate with a total calcium intake of 1,360 mg/day had reduced zinc absorption and levels [R].

There was also no change in zinc absorption or balance among adolescent girls with a total intake of 1,667 mg/day from calcium citrate malate [R].

Calcium intakes of about 1,800 did not impair zinc absorption in healthy women aged 21 to 47 years old [R].

Most recommendations regarding calcium and zinc show absorption may be limited and recommend taking zinc an hour apart from calcium supplements or food sources.

Folic Acid Interferes with Zinc

Zinc is needed for folate utilization. Those with low zinc also may have low folate levels. Folic acid may also affect zinc abortion in those who have low levels of zinc. Though one study did show high doses of folic acid for 25 days did not impair zinc absorption of status in those with a low zinc diet [R, R].

Phytates Interferes with Zinc Absorption

Phytates found in whole grain foods such as bread, legumes, cereals, corn, and rice bind zinc and prevent it from being absorbed. So these foods should not be consumed with zinc [R].

Risks of Zinc Supplements

Some zinc supplements may contain additional ingredients or too high levels of zinc.

ZMA is a mineral supplement containing zinc, magnesium aspartate, and Vitamin B6. It claims it can boost health and athletic performance but there is little research validating these effects.

Individuals with normal levels of zinc had increased urinary levels showing possible toxicity [R].

Zinc supplementation may lead to insulin resistance as seen with some elite athletes [R]. This could result in high blood sugar levels.

A combination of supplementation, fortified foods, and high zinc food intake may lead to elevated zinc levels. So monitoring how much zinc you are getting from all these sources is recommended [R].

Intakes of 100 to 160 mg of zinc were found to lower “good” HDL cholesterol levels in healthy men and women [R, R].

Sources of Zinc

Zinc can be found in many foods. The best sources of zinc include the following [R]:

  • Oyster
  • Beef chuck
  • Ground beef,
  • Dungeness crab
  • Fortified, whole-grain toasted oat cereal
  • Dark meat turkey
  • Pork loin,
  • Soybeans
  • Dark meat chicken
  • Pine nuts
  • Cashews
  • Plain yogurt
  • Sunflower seed kernels
  • Pecans
  • Brazil nuts
  • Chickpeas
  • Milk
  • Cheddar cheese
  • Almonds
  • Baked beans

Final Thoughts on Zinc Supplements

Zinc is an essential nutrient the body needs for optimal health. It has shown to have many potential health benefits improving immunity, heart, hormonal, and brain health. When it comes to athletic performance zinc has shown to have some positive effects on aerobic and strength training activities but it is hard to say if zinc is truly the cause of these physical enhancements. Supplementation may be helpful to those at risk for a deficiency, have subpar zinc levels, or eat a diet high in phytates. It is recommended to start with a low dose and avoid any nutrients that may have interactions with this vitamin. Zinc supplementation can also affect copper levels so periodically getting levels tested helps avoid toxicity. If you are on any medications or have pre-existing health conditions you should talk with your doctor before starting this supplement.

Resources

  1. Micheletti, A., R. Rossi, and S. Rufini. 2001. “Zinc Status in Athletes: Relation to Diet and Exercise.” Sports Medicine 31 (8): 577–82. https://pubmed.ncbi.nlm.nih.gov/11475319.
  2. “Zinc in Diet.” n.d. https://medlineplus.gov/ency/article/002416.htm.
  3. “Zinc.” n.d. https://ods.od.nih.gov/factsheets/%20Zinc-HealthProfessional/.
  4. Prasad, A. S. 1995. “Zinc: An Overview.” Nutrition 11 (1 Suppl): 93–99. https://pubmed.ncbi.nlm.nih.gov/7749260/.
  5. “Zinc.” 2014. April 23, 2014. https://lpi.oregonstate.edu/mic/minerals/zinc.
  6. Córdova, A., and F. J. Navas. 1998. “Effect of Training on Zinc Metabolism: Changes in Serum and Sweat Zinc Concentrations in Sportsmen.” Annals of Nutrition & Metabolism 42 (5): 274–82. https://pubmed.ncbi.nlm.nih.gov/9812018/.
  7. Prasad, Ananda S., Bin Bao, Frances W. J. Beck, Omer Kucuk, and Fazlul H. Sarkar. 2004. “Antioxidant Effect of Zinc in Humans.” Free Radical Biology & Medicine 37 (8): 1182–90. https://pubmed.ncbi.nlm.nih.gov/15451058/.
  8. Prasad, Ananda S., Frances W. J. Beck, Bin Bao, James T. Fitzgerald, Diane C. Snell, Joel D. Steinberg, and Lavoisier J. Cardozo. 2007. “Zinc Supplementation Decreases Incidence of Infections in the Elderly: Effect of Zinc on Generation of Cytokines and Oxidative Stress.” The American Journal of Clinical Nutrition 85 (3): 837–44. https://pubmed.ncbi.nlm.nih.gov/17344507/.
  9. Singh, Meenu, and Rashmi R. Das. 2011. “Zinc for the Common Cold.” Cochrane Database of Systematic Reviews , no. 2 (February): CD001364. https://pubmed.ncbi.nlm.nih.gov/21328251/.
  10. Hennig, B., M. Toborek, and C. J. Mcclain. 1996. “Antiatherogenic Properties of Zinc: Implications in Endothelial Cell Metabolism.” Nutrition 12 (10): 711–17. https://pubmed.ncbi.nlm.nih.gov/8936496/.
  11. Beattie, John H., and In-Sook Kwun. 2004. “Is Zinc Deficiency a Risk Factor for Atherosclerosis?” The British Journal of Nutrition 91 (2): 177–81.https://pubmed.ncbi.nlm.nih.gov/14756902/.
  12. Bao, Bin, Ananda S. Prasad, Frances W. J. Beck, James T. Fitzgerald, Diane Snell, Ginny W. Bao, Tapinder Singh, and Lavoisier J. Cardozo. 2010. “Zinc Decreases C-Reactive Protein, Lipid Peroxidation, and Inflammatory Cytokines in Elderly Subjects: A Potential Implication of Zinc as an Atheroprotective Agent.” The American Journal of Clinical Nutrition 91 (6): 1634–41. https://pubmed.ncbi.nlm.nih.gov/20427734/.
  13. Siwek, Marcin, Dominika Dudek, Małgorzata Schlegel-Zawadzka, Agnieszka Morawska, Wojciech Piekoszewski, Włodzimierz Opoka, Andrzej Zieba, Andrzej Pilc, Piotr Popik, and Gabriel Nowak. 2010. “Serum Zinc Level in Depressed Patients during Zinc Supplementation of Imipramine Treatment.” Journal of Affective Disorders 126 (3): 447–52. https://pubmed.ncbi.nlm.nih.gov/20493532/.
  14. Tamano, Haruna, Fumika Kan, Mika Kawamura, Naoto Oku, and Atsushi Takeda. 2009. “Behavior in the Forced Swim Test and Neurochemical Changes in the Hippocampus in Young Rats after 2-Week Zinc Deprivation.” Neurochemistry International 55 (7): 536–41. https://www.ncbi.nlm.nih.gov/pubmed/19463882.
  15. Solati, Zahra, Shima Jazayeri, Mehdi Tehrani-Doost, Salma Mahmoodianfard, and Mahmood Reza Gohari. 2015. “Zinc Monotherapy Increases Serum Brain-Derived Neurotrophic Factor (BDNF) Levels and Decreases Depressive Symptoms in Overweight or Obese Subjects: A Double-Blind, Randomized, Placebo-Controlled Trial.” Nutritional Neuroscience 18 (4): 162–68. https://pubmed.ncbi.nlm.nih.gov/24621065/.
  16. Sawada, T., and K. Yokoi. 2010. “Effect of Zinc Supplementation on Mood States in Young Women: A Pilot Study.” European Journal of Clinical Nutrition 64 (3): 331–33. https://pubmed.ncbi.nlm.nih.gov/20087376/.
  17. Ilouz, Ronit, Oksana Kaidanovich, David Gurwitz, and Hagit Eldar-Finkelman. 2002. “Inhibition of Glycogen Synthase Kinase-3beta by Bivalent Zinc Ions: Insight into the Insulin-Mimetic Action of Zinc.” Biochemical and Biophysical Research Communications 295 (1): 102–6. https://pubmed.ncbi.nlm.nih.gov/12083774/.
  18. Gould, Todd D., Alyssa M. Picchini, Haim Einat, and Husseini K. Manji. 2006. “Targeting Glycogen Synthase Kinase-3 in the CNS: Implications for the Development of New Treatments for Mood Disorders.” Current Drug Targets 7 (11): 1399–1409. https://pubmed.ncbi.nlm.nih.gov/17100580/.
  19. Cope, Elise C., and Cathy W. Levenson. 2010. “Role of Zinc in the Development and Treatment of Mood Disorders.” Current Opinion in Clinical Nutrition and Metabolic Care 13 (6): 685–89. https://pubmed.ncbi.nlm.nih.gov/20689416/.
  20. Tahmasebi Boroujeni, S., N. Naghdi, M. Shahbazi, A. Farrokhi, F. Bagherzadeh, A. Kazemnejad, and M. Javadian. 2009. “The Effect of Severe Zinc Deficiency and Zinc Supplement on Spatial Learning and Memory.” Biological Trace Element Research 130 (1): 48–61. https://pubmed.ncbi.nlm.nih.gov/19183867/.
  21. Aquilani, Roberto, Paola Baiardi, Marco Scocchi, Paolo Iadarola, Manuela Verri, Paolo Sessarego, Federica Boschi, Evasio Pasini, Ornella Pastoris, and Simona Viglio. 2009. “Normalization of Zinc Intake Enhances Neurological Retrieval of Patients Suffering from Ischemic Strokes.” Nutritional Neuroscience 12 (5): 219–25. https://pubmed.ncbi.nlm.nih.gov/19761652/
  22. Flinn, J. M., D. Hunter, D. H. Linkous, A. Lanzirotti, L. N. Smith, J. Brightwell, and B. F. Jones. 2005. “Enhanced Zinc Consumption Causes Memory Deficits and Increased Brain Levels of Zinc.” Physiology & Behavior 83 (5): 793–803. https://pubmed.ncbi.nlm.nih.gov/15639165/.
  23. Zeng, Qiang, Bin Zhou, Wei Feng, Yi-Xin Wang, Ai-Lin Liu, Jing Yue, Yu-Feng Li, and Wen-Qing Lu. 2013. “Associations of Urinary Metal Concentrations and Circulating Testosterone in Chinese Men.” Reproductive Toxicology 41 (November): 109–14. https://pubmed.ncbi.nlm.nih.gov/23791927/.
  24. Lei, K. Y., A. Abbasi, and A. S. Prasad. 1976. “Function of Pituitary-Gonadal Axis in Zinc-Deficient Rats.” The American Journal of Physiology 230 (6): 1730–32. https://pubmed.ncbi.nlm.nih.gov/779495/.
  25. Griggs RC, Kingston W, Jozefowicz RF, Herr BE, Forbes G, Halliday D. Effect of testosterone on muscle mass and muscle protein synthesis. J Appl Physiol (1985). 1989 Jan;66(1):498-503. https://pubmed.ncbi.nlm.nih.gov/2917954/.
  26. Jalali, Ghanbarali Raeis, Jamshid Roozbeh, Azam Mohammadzadeh, Maryam Sharifian, Mohammad Mahdi Sagheb, Alireza Hamidian Jahromi, Sanaz Shabani, Fariborz Ghaffarpasand, and Raha Afshariani. 2010. “Impact of Oral Zinc Therapy on the Level of Sex Hormones in Male Patients on Hemodialysis.” Renal Failure 32 (4): 417–19. https://pubmed.ncbi.nlm.nih.gov/20446777/.
  27. Koehler, K., M. K. Parr, H. Geyer, J. Mester, and W. Schänzer. 2009. “Serum Testosterone and Urinary Excretion of Steroid Hormone Metabolites after Administration of a High-Dose Zinc Supplement.” European Journal of Clinical Nutrition 63 (1): 65–70. https://pubmed.ncbi.nlm.nih.gov/17882141/.
  28. Shafiei Neek, Leila, Abas Ali Gaeini, and Siroos Choobineh. 2011. “Effect of Zinc and Selenium Supplementation on Serum Testosterone and Plasma Lactate in Cyclist after an Exhaustive Exercise Bout.” Biological Trace Element Research 144 (1-3): 454–62. https://pubmed.ncbi.nlm.nih.gov/21744023/.
  29. Kilic, Mehmet, Abdulkerim Kasim Baltaci, Mehmet Gunay, Hakki Gökbel, Nilsel Okudan, and Ibrahim Cicioglu. 2006. “The Effect of Exhaustion Exercise on Thyroid Hormones and Testosterone Levels of Elite Athletes Receiving Oral Zinc.” Neuro Endocrinology Letters 27 (1-2): 247–52. https://pubmed.ncbi.nlm.nih.gov/16648789/.
  30. Kilic, Mehmet. 2007. “Effect of Fatiguing Bicycle Exercise on Thyroid Hormone and Testosterone Levels in Sedentary Males Supplemented with Oral Zinc.” Neuro Endocrinology Letters 28 (5): 681–85. https://pubmed.ncbi.nlm.nih.gov/17984944/.
  31. Sáinz, Neira, Amaia Rodríguez, Victoria Catalán, Sara Becerril, Beatriz Ramírez, Javier Gómez-Ambrosi, and Gema Frühbeck. 2009. “Leptin Administration Favors Muscle Mass Accretion by Decreasing FoxO3a and Increasing PGC-1alpha in Ob/ob Mice.” PloS One 4 (9): e6808. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2733298/.
  32. Hamrick, Mark W. 2017. “Role of the Cytokine-like Hormone Leptin in Muscle-Bone Crosstalk with Aging.” Journal of Bone Metabolism 24 (1): 1–8. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5357607/.
  33. Ott, E. S., and N. F. Shay. 2001. “Zinc Deficiency Reduces Leptin Gene Expression and Leptin Secretion in Rat Adipocytes.” Experimental Biology and Medicine 226 (9): 841–46. https://pubmed.ncbi.nlm.nih.gov/11568307/.
  34. Mantzoros, C. S., A. S. Prasad, F. W. Beck, S. Grabowski, J. Kaplan, C. Adair, and G. J. Brewer. 1998. “Zinc May Regulate Serum Leptin Concentrations in Humans.” Journal of the American College of Nutrition 17 (3): 270–75. https://pubmed.ncbi.nlm.nih.gov/9627914/.
  35. Saeedy, Malihe, Nahid Bijeh, and Mahtab Moazzami. 2018. “The Effect of Six Weeks of High-Intensity Interval Training With Zinc Supplementation on Some Humoral Immunity Markers in Female Futsal Players.” Annals of Applied Sport Science 6 (1): 11–19. https://pubmed.ncbi.nlm.nih.gov/20386120/.
  36. Heffernan, Shane Michael, Katy Horner, Giuseppe De Vito, and Gillian Eileen Conway. 2019. “The Role of Mineral and Trace Element Supplementation in Exercise and Athletic Performance: A Systematic Review.” Nutrients 11 (3). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6471179/.
  37. Davison, Glen, Tania Marchbank, Daniel S. March, Rhys Thatcher, and Raymond J. Playford. 2016. “Zinc Carnosine Works with Bovine Colostrum in Truncating Heavy Exercise-Induced Increase in Gut Permeability in Healthy Volunteers.” The American Journal of Clinical Nutrition 104 (2): 526–36. https://pubmed.ncbi.nlm.nih.gov/27357095/.
  38. Khaled, S., J. F. Brun, G. Cassanas, L. Bardet, and A. Orsetti. 1999. “Effects of Zinc Supplementation on Blood Rheology during Exercise.” Clinical Hemorheology and Microcirculation 20 (1): 1–10. https://pubmed.ncbi.nlm.nih.gov/11185677/.
  39. Smith, Michael M., Alexander R. Lucas, Robert L. Hamlin, and Steven T. Devor. 2015. “Associations among Hemorheological Factors and Maximal Oxygen Consumption. Is There a Role for Blood Viscosity in Explaining Athletic Performance?” Clinical Hemorheology and Microcirculation 60 (4): 347–62. https://www.ncbi.nlm.nih.gov/pubmed/23514971/.
  40. Marques, Lucianna Fernandes J. C., Carmen Marino Donangelo, Juliana Gastao Franco, Luciane Pires, Aderval Severino Luna, Gustavo Casimiro-Lopes, Patricia Cristina Lisboa, and Josely Correa Koury. 2011. “Plasma Zinc, Copper, and Serum Thyroid Hormones and Insulin Levels after Zinc Supplementation Followed by Placebo in Competitive Athletes.” Biological Trace Element Research 142 (3): 415–23. https://pubmed.ncbi.nlm.nih.gov/20809272/.
  41. Perseghin, G., A. Burska, G. Lattuada, G. Alberti, F. Costantino, F. Ragogna, S. Oggionni, A. Scollo, I. Terruzzi, and L. Luzi. 2006. “Increased Serum Resistin in Elite Endurance Athletes with High Insulin Sensitivity.” Diabetologia 49 (8): 1893–1900. https://pubmed.ncbi.nlm.nih.gov/16685503/.
  42. Bajpeyi, Sudip, Charles J. Tanner, Cris A. Slentz, Brian D. Duscha, Jennifer S. McCartney, Robert C. Hickner, William E. Kraus, and Joseph A. Houmard. 2009. “Effect of Exercise Intensity and Volume on Persistence of Insulin Sensitivity during Training Cessation.” Journal of Applied Physiology 106 (4): 1079–85. https://www.ncbi.nlm.nih.gov/pubmed/19196913/.
  43. Fisher, Gordon, Andrew W. Brown, Michelle M. Bohan Brown, Amy Alcorn, Corey Noles, Leah Winwood, Holly Resuehr, Brandon George, Madeline M. Jeansonne, and David B. Allison. 2015. “High Intensity Interval- vs Moderate Intensity- Training for Improving Cardiometabolic Health in Overweight or Obese Males: A Randomized Controlled Trial.” PloS One 10 (10): e0138853. https://www.ncbi.nlm.nih.gov/pubmed/26489022/.
  44. McGarrah, Robert W., Cris A. Slentz, and William E. Kraus. 2016. “The Effect of Vigorous- Versus Moderate-Intensity Aerobic Exercise on Insulin Action.” Current Cardiology Reports 18 (12): 117. https://www.ncbi.nlm.nih.gov/pubmed/27796854/.
  45. Cinar, Vedat, Laurentiu Gabriel Talaghir, Taner Akbulut, Mine Turgut, and Mucahit Sarikaya. 2018. “The Effects of the Zinc Supplementation and Weight Trainings on the Testosterone Levels.” Human Sport Medicine 17 (4): 58–63. https://www.researchgate.net/publication/322364874_The_effects_of_the_zinc_supplementation_and_weight_trainings_on_the_testosterone_levels.
  46. Frank, Kurtis, Kamal Patel, Gregory Lopez, and Bill Willis. 2020. “Zinc Research Analysis,” May. https://examine.com/supplements/zinc.
  47. Saper, Robert B., and Rebecca Rash. 2009. “Zinc: An Essential Micronutrient.” American Family Physician 79 (9): 768–72. https://pubmed.ncbi.nlm.nih.gov/20141096/.
  48. Barrie, S. A., J. V. Wright, J. E. Pizzorno, E. Kutter, and P. C. Barron. 1987. “Comparative Absorption of Zinc Picolinate, Zinc Citrate, and Zinc Gluconate in Humans.” Agents and Actions 21 (1-2): 223–28. https://pubmed.ncbi.nlm.nih.gov/3630857/.
  49. Wegmüller, Rita, Fabian Tay, Christophe Zeder, Marica Brnic, and Richard F. Hurrell. 2014. “Zinc Absorption by Young Adults from Supplemental Zinc Citrate Is Comparable with That from Zinc Gluconate and Higher than from Zinc Oxide.” The Journal of Nutrition 144 (2): 132–36. https://pubmed.ncbi.nlm.nih.gov/24259556/.
  50. Science, Michelle, Jennie Johnstone, Daniel E. Roth, Gordon Guyatt, and Mark Loeb. 2012. “Zinc for the Treatment of the Common Cold: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.” CMAJ: Canadian Medical Association Journal = Journal de l’Association Medicale Canadienne 184 (10): E551–61. https://pubmed.ncbi.nlm.nih.gov/22566526/.
  51. Lönnerdal, B. 2000. “Dietary Factors Influencing Zinc Absorption.” The Journal of Nutrition 130 (5S Suppl): 1378S – 83S. https://pubmed.ncbi.nlm.nih.gov/10801947/.
  52. Barceloux, D. G. 1999. “Zinc.” Journal of Toxicology. Clinical Toxicology 37 (2): 279–92. https://www.tandfonline.com/doi/abs/10.1081/CLT-100102426.
  53. Chan, S., B. Gerson, and S. Subramaniam. 1998. “The Role of Copper, Molybdenum, Selenium, and Zinc in Nutrition and Health.” Clinics in Laboratory Medicine 18 (4): 673–85. https://pubmed.ncbi.nlm.nih.gov/9891606/.
  54. “Zinc: Uses, Side Effects, Interactions, Dosage, and Warning.” n.d. Accessed October 16, 2020. https://www.webmd.com/vitamins/ai/ingredientmono-982/zinc.
  55. Carter, R. C., R. Kupka, K. Manji, C. M. McDonald, S. Aboud, J. G. Erhardt, K. Gosselin, et al. 2018. “Zinc and Multivitamin Supplementation Have Contrasting Effects on Infant Iron Status: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial.” European Journal of Clinical Nutrition 72 (1): 130–35. https://www.ncbi.nlm.nih.gov/pubmed/28876332/.
  56. de Oliveira, K., Donangelo, C. M., de Oliveira, A. V., Jr, da Silveira, C. L., & Koury, J. C. (2009). Effect of zinc supplementation on the antioxidant, copper, and iron status of physically active adolescents. Cell biochemistry and function, 27(3), 162–166. https://www.ncbi.nlm.nih.gov/pubmed/19277992.
  57. Whittaker, P. 1998. “Iron and Zinc Interactions in Humans.” The American Journal of Clinical Nutrition 68 (2 Suppl): 442S – 446S. https://pubmed.ncbi.nlm.nih.gov/9701159/.
  58. Wood, R. J., and J. J. Zheng. 1997. “High Dietary Calcium Intakes Reduce Zinc Absorption and Balance in Humans.” The American Journal of Clinical Nutrition 65 (6): 1803–9. https://www.ncbi.nlm.nih.gov/pubmed/9174476/.
  59. McKenna, A. A., J. Z. Ilich, M. B. Andon, C. Wang, and V. Matkovic. 1997. “Zinc Balance in Adolescent Females Consuming a Low- or High-Calcium Diet.” The American Journal of Clinical Nutrition 65 (5): 1460–64. https://www.ncbi.nlm.nih.gov/pubmed/9129477.
  60. Hunt, Janet R., and Jeannemarie M. Beiseigel. 2009. “Dietary Calcium Does Not Exacerbate Phytate Inhibition of Zinc Absorption by Women from Conventional Diets.” The American Journal of Clinical Nutrition 89 (3): 839–43. https://pubmed.ncbi.nlm.nih.gov/19176739/.
  61. Kauwell, G. P., L. B. Bailey, J. F. Gregory 3rd, D. W. Bowling, and R. J. Cousins. 1995. “Zinc Status Is Not Adversely Affected by Folic Acid Supplementation and Zinc Intake Does Not Impair Folate Utilization in Human Subjects.” The Journal of Nutrition 125 (1): 66–72. https://pubmed.ncbi.nlm.nih.gov/7815178/.
  62. Hooper, P. L., L. Visconti, P. J. Garry, and G. E. Johnson. 1980. “Zinc Lowers High-Density Lipoprotein-Cholesterol Levels.” JAMA: The Journal of the American Medical Association 244 (17): 1960–61. https://pubmed.ncbi.nlm.nih.gov/7420708/.
  63. Freeland-Graves, J. H., B. J. Friedman, W. H. Han, R. L. Shorey, and R. Young. 1982. “Effect of Zinc Supplementation on Plasma High-Density Lipoprotein Cholesterol and Zinc.” The American Journal of Clinical Nutrition 35 (5): 988–92. https://pubmed.ncbi.nlm.nih.gov/7081096/.