Zinc is very crucial! Notice some benefits:
"Zinc is a trace element that is necessary for a healthy immune system. A lack of zinc can make a person more susceptible to disease and illness...According to a study published in the American Journal of Clinical Nutrition, 'zinc-deficient persons experience increased susceptibility to a variety of pathogens'...Research conducted at the University of Toronto and published in the journal Neuron suggested that zinc has a crucial role in regulating how neurons communicate with one another, affecting how memories are formed and how we learn...A study from researchers at Oregon State University have found that improving zinc status through diet and supplementation may reduce the risk of inflammatory diseases. It has been known for decades that zinc has a significant role in immune function."
(Medical News Today, Dec. 2017)
Zinc is especially linked to male and female fertility, as well as to male testosterone. Excerpts from the following studies highlight the role of zinc in these areas:
"Dietary zinc restriction in normal young men was associated with a significant decrease in serum testosterone concentrations after 20 weeks of zinc restriction (baseline versus post-zinc restriction mean ± SD, 39.9 ± 7.1 versus 10.6 ± 3.6 nmol/L, respectively; p = 0.005). Zinc supplementation of marginally zinc-deficient normal elderly men for six months resulted in an increase in serum testosterone from 8.3 ± 6.3 to 16.0 ± 4.4 nmol/p (p = 0.02). We conclude that zinc may play an important role in modulating serum testosterone levels in normal men."
(Nutrition, Volume 12, Issue 5, May 1996)
"The effect of exhaustion exercise on thyroid hormones and testosterone levels of elite athletes receiving oral zinc...The study included 10 male wrestlers...Both resting and exhaustion total and free testosterone levels following 4-week zinc supplementation were found significantly higher than the levels (both resting and exhaustion) measured before zinc supplementation (p<0.05)...Findings of our study demonstrate that exhaustion exercise led to a significant inhibition of both thyroid hormones and testosterone concentrations, but that 4-week zinc supplementation prevented this inhibition in wrestlers. In conclusion, physiological doses of zinc administration may benefit performance."
(Neuro Endocrinol Lett. 2006 Feb-Apr;27)
"Effect of fatiguing bicycle exercise on thyroid hormone and testosterone levels in sedentary males supplemented
with oral zinc...The results indicate that exercise decreases thyroid hormones and testosterone in sedentary men; however, zinc supplementation prevents this decrease. Administration of a physiologic dose of zinc can be beneficial to performance."
(Neuro Endocrinol Lett. 2007 Oct;28)
"Effect of Zinc Supplement and Weight Lifting Exercise on Thyroid Hormone Levels...it can be said the zinc supplement applied four times a week during 6 weeks along with the weight lifting exercise lead to significant changes in the thyroid hormone levels of the athletes..."
(Indian J Physiol Pharmacol 2017)
"Scientists and fertility doctors have long tried to figure out what makes a good egg that will produce a healthy embryo. It's a critical to know which eggs isolated from a woman will produce the best embryos and ultimately babies. New research reveals eggs need a tremendous dose of zinc to reach maturity and be ready for fertilization..."
(Science News, August 9, 2010; Source: Northwestern University)
"Preconception zinc deficiency could spell bad news for fertility...A new study shows that zinc deficiency can negatively affect the early stages of egg development, reducing the ability of the egg cells to divide and be fertilized. This may affect fertility months in the future. Researchers will present their results at the American Physiological Society annual meeting at Experimental Biology 2018 in San Diego."
(Science News, April 24, 2018; Source: American Physiological Society)
"Zinc levels in seminal plasma and their correlation with male infertility: A systematic review and meta-analysis...Zinc is an essential trace mineral for the normal functioning of the male reproductive system...Twenty studies were identified, including 2,600 cases and 867 controls. Our meta-analysis results indicated that the seminal plasma zinc concentrations from infertile males were significantly lower than those from normal controls...The present study showed that the zinc level in the seminal plasma of infertile males was significantly lower than that of normal males. Zinc supplementation could significantly increase the sperm quality of infertile males."
(Sci Rep. 2016; 6)
"Zinc is an Essential Element for Male Fertility: A Review of Zn Roles in Men's Health, Germination, Sperm Quality, and Fertilization...Zinc (Zn) is the second most abundant trace element in human, which can't be stored in the body, thus regular dietary intake is required...Zn acts as a toxic repercussion against heavy metals and cigarette inflammatory agents. Zinc as a hormone balancer helps hormones such as testosterone, prostate and sexual health and functions as an antibacterial agent in men's urea system...Zn deficiency impedes spermatogenesis and is a reason for sperm abnormalities and has a negative effect on serum testosterone concentration."
(J Reprod Infertil. 2018 Apr-Jun)
WHAT HINDERS ZINC ABSORPTION?
Those who regularly eat plenty of meat and dairy should get plenty of zinc. However, zinc can be greatly hindered or enhanced in the diet! Alcohol, soy-protein, phytates, cadmium, etc., inhibit zinc absorption:
"Marginal zinc deficiency and suboptimal zinc status have been recognized in many groups of the population in both less developed and industrialized countries. Although the cause in some cases may be inadequate dietary intake of zinc, inhibitors of zinc absorption are most likely the most common causative factor. Phytate, which is present in staple foods like cereals, corn and rice, has a strong negative effect on zinc absorption from composite meals...Cadmium, which is increasing in the environment, also inhibits zinc absorption. The amount of protein in a meal has a positive effect on zinc absorption...supplementation or fortification with zinc has been associated with increased linear growth (Brown et al. 1998), reduction in diarrheal disease (Black 1998), enhanced immune function (Shankar and Prasad 1998) and improved pregnancy outcome (Goldenberg et al. 1995)...even if net zinc intake appears adequate by most recommendations, compromised zinc status is common (Gibson et al. 1998). It is therefore important to identify and evaluate dietary factors that affect zinc absorption...It was shown early in animal studies that phytate has an inhibitory effect on zinc absorption (O'Dell 1969, Vohra and Kratzer 1964)...Because staple foods in most part of the world contain phytate (e.g., corn, cereals, rice, legumes), it is obvious that both zinc and iron status may be compromised in significant portions of the population...It is known that toxic levels of cadmium can inhibit zinc absorption..."
(The Journal of Nutrition, Volume 130, Issue 5, 1 May 2000)
"...a recent meta-analysis found zinc intakes and zinc status to be lower among males and females following a
vegetarian diet compared to those who consume meat...Up to 30 g of soy protein has been demonstrated to be an inhibitor of both iron and zinc absorption in single-meal studies..."
(Nutrients 2013, 5)
WHAT ENHANCES ZINC ABSORPTION?:
Protein, sourdough, and garlic and onions (as always!), enhance zinc absorption!:
"Amino acids, such as histidine and methionine, and other low-molecular-weight ions, such as EDTA and organic acids (e.g., citrate), are known to have a positive effect on zinc absorption and have been used for zinc supplements...It should also be emphasized that protein is a major source of dietary zinc that results in an increased zinc intake with increased protein content of the meal. Thus, in general, increased dietary protein leads to increased zinc intake and a higher bioavailability of the zinc provided...Animal protein (e.g., beef, eggs, cheese) has been shown to counteract the inhibitory effect of phytate on zinc absorption from single meals (Sandström and Cederblad 1980)...Leavening of bread was shown early to decrease its phytate concentration (Nävert et al. 1985), and fermentation in general also achieves the same effect, resulting in enhanced zinc absorption (Gibson et al. 1998, Svanberg and Sandberg 1988)..."
(The Journal of Nutrition, Volume 130, Issue 5, 1 May 2000)
"Higher bioaccessibility of iron and zinc from food grains in the presence of garlic and onion...In this context, we examined the influence of exogenously added garlic and onion on the bioaccessibility of iron and zinc from food grains. Two representative cereals and pulses each were studied in both raw and cooked condition employing two levels of garlic (0.25 and 0.5 g/10 g of grain) and onion (1.5 and 3 g/10 g of grain). The enhancing effect of these two spices on iron bioaccessibility was generally evidenced in the case of both the cereals (9.4 - 65.9% increase) and pulses (9.9 - 73.3% increase) in both raw and cooked conditions. The two spices similarly enhanced the bioaccessibility of zinc from the food grains, the extent of increase in cereals ranging from 10.4% to 159.4% and in pulses from 9.8% to 49.8%..."
(J Agric Food Chem. 2010 Jul 28;58)
In conclusion, let's eat plenty of meat and dairy. And when eating grains and other high sources of phytates, let us make sure we ferment them (sourdough, etc.). And along with them, eat protein, with lots of garlic and onions (as well as healthy sources of vitamin C). This will help insure healthy absorption levels of zinc and iron.