A new study published in late August showed that laboratory mice fed a diet high in zinc had 50-60% lower markers of inflammation in lung tissue samples than mice fed a diet low in zinc. The study authors suggest that supplementing zinc in COPD patients, asthmatics and smokers may be helpful in reducing inflammation associated with airway diseases (inflammation is believed to be a leading cause of breathlessness in COPD patients).
According to the study authors, “Zinc is a dietary trace metal that has been clinically and physiologically linked to airway inflammatory diseases, such as asthma and COPD. Patients with COPD have lower serum, plasma and hair zinc levels than healthy subjects. In addition, there is a negative correlation between plasma zinc and wheezing. Zinc supplementation had favorable effects on oxidant–antioxidant balance in patients with COPD.” (Lang CJ, et al. Dietary zinc mediates inflammation and protects against wasting and metabolic derangement caused by sustained cigarette smoke exposure in mice. Biometals. Published online ahead of print, August 29, 2010. (doi:10.1007/s10534-010-9370-9))
In other words, zinc seems to act as an antioxidant in lung tissue, particularly in cells of the lining of the lungs known as epithelial cells. According to the research team, zinc is naturally abundant in epithelial cells, but the effects of a diet that is low in zinc content combined with prolonged exposure to cigarette smoke depresses levels of this important nutrient and thus contributes to airway inflammation. By supplementing dietary zinc in laboratory mice exposed to cigarette smoke, the researchers hypothesized that signs of inflammation would be reduced.
As regular readers of our e-letters and blog know well, there are a host of antioxidants that have been studied (and continue to be studied) in relation to airway inflammation. You see, it’s clear from blood plasma samples that smokers and COPD patients are significantly deficient in antioxidant counts compared to healthy non-smoking adults. Scientists theorize that the pro-oxidative nature of cigarette smoke overwhelms the body’s supply of antioxidants consumed through diet or produced in the body creating a condition referred to as “oxidative stress”. Oxidative stress in simple terms is an imbalance of pro-oxidative molecules (too much of a bad thing) and anti-oxidative molecules (too little of a good thing) in the body. As a result of the imbalance, more pro-oxidative molecules get through to lung tissues and damage them, creating inflammation, which in turn leads to persistent shortness of breath.
Therefore, researchers seeking for ways to alleviate inflammation have been testing a variety of antioxidants to boost blood plasma levels of these protective nutrients to judge whether doing so has a positive effect on airway inflammation. In this particular zinc study (and in a growing number of other studies on other antioxidants) the answer appears to be yes.
But a word of reason – from the scores of studies we’ve reviewed on antioxidants and airway inflammation, it is clear that there is no single magic antioxidant. The human body absorbs, processes and produces a wide range of antioxidants and so the best advice is to eat a diet rich in foods that contain high levels of antioxidants (most often colorful fruits and vegetables) and if you desire to add additional antioxidants through dietary supplements, favor products that give you a broad base of different antioxidants rather than massive doses of a single antioxidant.
In the Biometals zinc study itself, the research team divided the laboratory mice into three groups. One group was fed a diet of whey protein that is low in zinc content, one group was fed the same whey protein supplemented by additional zinc sulfate, and a third group received the same basic diet but with a much higher level of supplemented zinc.
Then the mice were exposed to smoke from 2 cigarettes for 15 minutes, 3 times a day, 5 days a week for 8 weeks. Then the mice were euthanized and their lung tissues sampled and examined for a variety of measures.
One of the measures the researchers looked at were the number of macrophages (white blood cells) present in alveolar (lung) tissue samples – one outcome of the inflammation process is the production of white blood cells (in fact the body over-produces white blood cells because the inflammation process makes the body think there is a massive infection occurring). Here the researchers found that cigarette exposed mice who were fed the diet supplemented with high zinc content had 50-60% fewer macrophages – thus demonstrating a significant reduction in the inflammatory response to cigarette smoke.
As the study authors noted, “The 50–60% reduction in alveolar macrophages in Zn-supplemented mice supports our evolving hypothesis that Zn is an important anti-inflammatory mediator of airway inflammation. Restoring airway Zn levels through dietary supplementation may lessen the severity of lung inflammation when Zn intake is low.”
Now, unfortunately, there is no specific guidance in the study on how much supplemental zinc is beneficial for smokers/COPD patients for reducing airway inflammation, and it is not a matter of simply translating the amount fed to the mice per unit of body weight and multiplying it by your own body weight.
That said the odds are high that you have a zinc deficiency if you smoke and/or have COPD, but before you go crazy adding massive amounts of zinc to your diet, we would recommend you ask your doctor to order a blood or hair sample test to determine whether you have a deficiency and how severe your deficiency is. From there, you and your doctor can determine a supplemental zinc dosage level appropriate for your particular circumstance.
In the meantime, for a good listing of foods high in zinc content published by the National Institutes of Health’s Office of Dietary Supplements that you can access by clicking here. This same web page provides additional information about the daily recommended intake of zinc from food/dietary supplements and provides guidance on how much is too much.
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