Protect Our Immune System During This Difficult Time – Part II
Author: Xuan Huang, Ph.D.
The author would like to acknowledge Cody Hanick (MS; PhD student in Nutrition Science) and Janelle Schirmer (RD) for providing feedback. The author also wants to thank Alex Zotov and Dr. Nuo Xu for proofreading the article.
Part II: Minerals
In our last blog, we learned vitamin C and E are important to our immune system because of their function as antioxidants. Why are antioxidants useful for our immune system? Because immune activities expose us to oxidation. Free radicals normally form during energy metabolism, but they can also form when our immune system generates inflammation to fight infections. These free radicals can cause cell damage. Antioxidants work by stabilizing free radicals or converting them into less damaging substances. Besides vitamins, many trace minerals are powerful antioxidants too, and that’s what we cover in this part: zinc, selenium, copper, manganese, and iron.
Zinc
The highest Zinc concentrations can be found in mollusks such as oysters, mussels, and scallops, and crustaceans such as crabs, lobsters, and shrimp. In general, red meat is a great source for zinc. If you are vegetarian or vegan, zinc can be of concern. But by choosing carefully, many legumes, vegetables, nuts and seeds can provide an adequate amount of zinc. The top Vegan choices would be tofu, beans of all sorts (kidney, black, navy, white, etc.), black-eyed peas, green split peas, lentils, as well as mushrooms, spinach, asparagus, and broccoli rabe. My mushroom-loving friends: do you know that mushrooms are not technically “plants”? They are fungi and they cannot produce their own food like plants do.
Figure 5a. Zinc density (mg/Cal) distribution and boxplot of each food group of USDA SR Legacy food items.
Figure 5b. Zinc density (mg/Cal) distribution and boxplot of each food group of USDA SR Legacy food items with outliers display disabled. The red line is derived density level from the zinc Recommended Dietary Allowance (RDA).
Selenium
Selenium is necessary for our bodies to synthesize selenoproteins, some of which participate in antioxidant enzyme systems that regulate our immune response and inflammation [8].
Selenium is high in the “Finfish and Shellfish Products” food group and reliably high in other animal products. The same “Finfish and Shellfish Products” foods that top zinc density also top selenium density: oysters, mussels, scallops, crabs, lobsters, and shrimp, together with tuna, cod, and halibut. Selenium is also available through plant sources, however, the amount of selenium in plants depends on the selenium content of the soil in which the plant is grown. Use the data provided by USDA with a grain of salt, because depending on where you live, the selenium level of the plant-based foods may not provide you an adequate amount of selenium. You may want to consider using Se supplement – but always ask your physician or a registered dietitian first. Brazil nuts, though, are exceptions. Just one Brazil nut a day can provide the selenium Recommended Dietary Allowance of 55 mcg for adults. But more is not better. Brazil nuts are very high in calories.
Figure 6a. Selenium density (mcg/Cal) distribution and boxplot of each food group of USDA SR Legacy food items.
Figure 6b. Selenium density (mcg/Cal) distribution and boxplot of each food group of USDA SR Legacy food items with outliers display disabled. The red line is derived density level from the selenium Recommended Dietary Allowance (RDA).
Copper, Manganese, and Iron
In addition to zinc, copper and manganese are also required by one important antioxidant enzyme called superoxide dismutase [7]. Iron is yet another micronutrient that was shown to be important to the immune system. However, research has found iron can be a double-edged sword because excess iron consumption also promotes growth of the pathogen – the virus, bacteria, parasites, and neoplastic cells [9]. Not to mention, excess iron consumption, especially from animal foods, can actually be a pro-oxidant [10].
All of these elements are naturally abundant in foods. Vegetables, legumes, nuts and seeds are rich in copper and manganese, while the first two food groups (vegetables and legumes) are also high in iron. A bowl of minestrone or chili will likely meet all your needs.
[7] Thompson, J., Manore, M., & Vaughan, L. (2019). Science of Nutrition, 5th edition. Pearson Higher Ed.
[8] Avery, J. C., & Hoffmann, P. R. (2018). Selenium, Selenoproteins, and Immunity. Nutrients, 10(9), 1203. https://doi.org/10.3390/nu10091203
[9] Cassat, J. E., & Skaar, E. P. (2013). Iron in infection and immunity. Cell host & microbe, 13(5), 509–519. https://doi.org/10.1016/j.chom.2013.04.010
[10] Sousa, L., Oliveira, M. M., Pessôa, M. T. C., & Barbosa, L. A. (2019). Iron overload: effects on cellular biochemistry. Clinica Chimica Acta. https://10.1016/j.cca.2019.11.