An essential nutrient for immunity and healthy aging
Zinc is a trace mineral that is essential for growth, reproduction, and good health throughout life.,, It is required for the structure and function of literally thousands of different proteins, including enzymes, transporters, and transcription factors.,
One of the most important roles of zinc is as a gatekeeper of the immune system., Zinc supports innate and acquired immunity through direct, indirect, and antioxidant mechanisms, all of which help the body fight infections.,,,
Mouse models have shown, for example, that just 30 days of suboptimal zinc intake can lead to a 30-80% loss of immune capacity. Notably, an investigation of the nutritional status of patients admitted to a hospital’s infectious disease ward revealed that two thirds of the patients were deficient in zinc.
In this article we’ll take a closer look at the impact of zinc on human health, starting with immunity.
Zinc and immunity
Even mild zinc deficiencies can increase the risk and severity of viral infections.
Zinc deficiency not only compromises immunity, but also shifts the immune system toward an inflammatory state that can predispose the body for damage to the lungs and other organs.,, Low levels of zinc, for example, are associated with greater disease severity in patients with sepsis, a life-threatening complication of infection.,,
Even mild zinc deficiencies can increase the risk and severity of viral infections, including respiratory infections such as influenza and pneumonia.,,, Moreover, studies have shown that zinc can inhibit the replication (and thus the potential burden of infection that the body has to fight in other ways) of influenza, coronavirus, rhinovirus, and respiratory syncytial virus in vitro.,,,,,,
As we all know, the risk of respiratory infections increases with age, due to a decline in immune function known as “immunosenescence”.,,, The process of immunosenescence is controlled in part by thymulin, a zinc-containing hormone produced by the thymus gland that regulates the production and maturation of a type of white blood cell known as the T-lymphocyte, or simply, T cell.,,,
Deficiencies of zinc and other necessary immune system nutrients also become more prevalent as we age.,,, Prolonged zinc deficiency leads to thymic atrophy, a reduction in T-cell populations, and diminished immunity. Fortunately, animal models have shown that the thymic atrophy associated with aging can be reversed by supplementing with zinc, suggesting that immunosenescence may not be inevitable.,,, Human studies support the animal data, finding that zinc supplementation (30 mg per day for three months) boosted T cell populations in elderly individuals.
A fascinating study published many years ago showed that white blood cells (WBCs) collected from elderly individuals produced less interferon (IFN) – a cytokine involved in viral killing – than those from young adults. Again, the IFN-producing capacity was not permanently lost: when WBCs from the elderly were incubated with physiologic concentrations of zinc, they produced IFN in amounts comparable to those from the younger subjects.
Zinc supplementation reduced the risk of pneumonia by 64% in critical care patients on ventilators.
Several clinical trials have been done to determine if supplemental zinc could influence the risk of infections such as pneumonia in the elderly.,,, In one randomized, double-blind, placebo-controlled trial, study participants were given a daily multivitamin and mineral supplement, including zinc, for one year. Individuals who developed normal zinc levels had a lower incidence and duration of pneumonia and less need for antibiotics compared to subjects with low serum zinc concentrations. Similarly, another study showed that zinc supplementation reduced the risk of pneumonia by 64% in critical care patients on ventilators.
Notably, the impact of zinc for healthspan extends beyond immunity, because zinc deficiency is associated with an increase in the risk for Alzheimer’s disease, atherosclerosis (hardening of the arteries), diabetes, osteoporosis, and certain cancers, including pancreatic cancer. Conversely, the maintenance of adequate zinc levels throughout life may help protect against chronic diseases of aging., Growing evidence suggests that individuals with adequate serum zinc concentrations have a reduced risk of mortality from all causes – suggesting zinc impacts lifespan as well as healthspan.,,
Zinc and chronic diseases of aging
Higher intakes of zinc were correlated with a 36% lower risk of atherosclerosis.
Zinc deficiency is more common in individuals with obesity and/or diabetes than in control populations,,,, and it can increase the risk of atherosclerosis, a major factor contributing to heart attack and stroke.
Studies in a mice revealed that zinc deficiency promoted atherosclerosis, apparently by increasing blood vessel inflammation and arterial plaque formation. A randomized controlled trial (RCT) done in healthy men and women (aged 56-83 years) also showed that supplemental zinc (45 mg daily) significantly improved blood markers of inflammation and oxidative stress, suggesting that zinc may help reduce the risk of atherosclerosis. These findings confirmed earlier studies demonstrating that higher intakes of zinc were correlated with a 36% lower risk of atherosclerosis.
Obesity can predispose individuals to diabetes in addition to atherosclerosis, and these conditions are all linked to inflammation., Compared with placebo, zinc supplementation (30 mg per day for eight weeks) was shown to significantly reduce the levels of inflammatory markers in obese women, suggesting it may lower the risk of atherosclerosis in obese or overweight individuals.
In another study, supplemental zinc was shown to ameliorate insulin resistance (indicative of prediabetes) in obese individuals who were following a calorie-controlled diet. Zinc even facilitated weight loss: the zinc-supplemented group lost more weight on average than the placebo group after 15 weeks. The study authors suggest that zinc supplementation, combined with a restricted calorie diet, may play an effective role in the management of obesity.
Zinc supplementation can improve blood glucose control in both prediabetic and diabetic patients.
Zinc also plays a role in insulin signaling, helping to regulate blood glucose levels.,, An RCT in individuals with prediabetes showed that zinc supplementation lowered blood glucose and cholesterol levels, and reduced the number of individuals who progressed to full-blown diabetes. A meta-analysis of 32 studies, involving 1,700 participants, concluded that zinc supplementation can improve blood glucose control in both prediabetic and diabetic patients. The effective doses of zinc in the meta-analysis generally ranged from 20 to 50 mg per day.
Interestingly, obesity and/or diabetes are underlying conditions that can increase a person’s risk for respiratory infections.,, Zinc may be one of the common links: obesity and/or diabetes increase the risk for zinc deficiency, which in turn increases the risk for infections. However, zinc is not alone in this regard: inadequate vitamin D levels also are associated with obesity, diabetes, and infections.,
Who is at risk for zinc deficiency?
The body has no specialized storage system for zinc, so it is necessary to consume this mineral every day to maintain adequate levels.
The body has no specialized storage system for zinc, so it is necessary to consume this mineral every day to maintain adequate levels. Population studies suggest that the prevalence of marginal zinc intakes ranges from 12% of younger adults, to 30% or more of individuals over the age of 60.,,,
Zinc is found in many different foods but it is particularly concentrated in meat, poultry, and shellfish. Vegetarians, and especially vegans who consume no animal products, have an increased risk of zinc deficiency, particularly if they also avoid nuts and seeds which contain relatively high levels of zinc.,, The zinc present in plant-based foods is also less bioavailable due to the presence of phytates, which strongly bind zinc and prevent its absorption.,,
Individuals with celiac disease who are consuming gluten-free (GF) diets may also be at risk for a deficiency of zinc and several other nutrients. One study reported that 67% of newly diagnosed adult patients with celiac disease had suboptimal serum zinc levels, while another study observed that 40% of individuals consuming long-term GF diets still were deficient in zinc. Zinc supplementation (25 to 40 mg per day) was recommended for nutritional support.
While diet is one factor, studies also show that intestinal malabsorption (which often exists in celiac disease),, inflammatory bowel disease, autoimmune disease, kidney or liver disease,,, cancer or cancer treatments, and the use of medications (including antibiotics, statins, and blood pressure medications),, can all contribute to zinc deficiency.
How much zinc do we need?
Zinc is a micronutrient, meaning that small amounts are needed every day. The RDA for zinc is 8–12 mg daily depending on age and gender. One study suggested that supplementation with 10 mg of zinc daily may increase the quantity of IFN-producing cells and thereby strengthen the immune system against viral infections. More recent studies indicate that 30 mg per day may be a better target intake for immune support.,
As with other metal nutrients, such as selenium, there is a relatively narrow dosage window for good health. While moderate doses of zinc (<50 mg per day) have been shown to improve immune function, higher doses of zinc may actually impair cellular immunity. Also, zinc can interfere with copper absorption, so higher intakes of zinc should be accompanied by copper supplementation at a 10-15:1 Zn:Cu ratio., Current guidelines hold that zinc intakes greater than 40 mg daily should be avoided unless otherwise advised by a health professional.
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