TOPIC OVERVIEW

People are much more prone to become ill in the winter. On the one hand, because they stay more often in heated, closed rooms with low humidity and other persons and catch an illness – for example, through a droplet infection. On the other hand, because our immune system is weaker in the winter – we eat less fresh products and salads, thereby reducing the natural vitamin supply through our diet. In addition, we spend less time in the open air during the winter. Towards the end of the winter, our vitamin D3 reservoir dwindles because it is hard for our skin to synthesize new vitamin D3 through sunlight. In addition, our immune system is naturally exposed to cold temperatures, snow and rain. This is the reason why flu and cold virus seasons are so rampant, especially in the cold time of the year.

The three biofactors zinc, vitamin C, and vitamin D are important building blocks of our immune system and perform different tasks that mutually support one another. A well-adjusted biofactors balance helps us to fight off colds and other infections and recover from them in a natural way – that we can rely on a strong immune system throughout the year.

Vitamin C, also called ascorbic acid, is one of the most important vitamins. It performs numerous functions in our body. One of them is of strengthening the immune system. It stimulates the formation of white blood cells responsible for eliminating germs, thereby accelerating the body's defense reactions. In addition, vitamin C is a strong antioxidant because it reduces oxidative stress. This means that it binds damaging free radicals in the blood, regenerates the body's own substances that have antioxidant effects, and reduces unwanted cell stress. Vitamin C is used up in all of these reactions inside our body – this is why our need for vitamin C increases when we are ill. Known as a home remedy for a long time, a medical study carried out during a period of 5 years at the University of Tokyo could prove that vitamin C makes a decisive contribution to reduce the risk of catching a cold. The subjects who took vitamin C on purpose became ill fewer than the comparison group. Further studies were able to confirm this result as well in older persons as in school children.

Contrary to other mammals, human beings cannot produce vitamin C themselves and need to get it through their diet. Citrus fruits contain a lot of vitamin C, but onions, bell peppers or broccoli also have quite a bit of it. Therefore, when you are filling your children's Christmas stockings, apart from the delicious chocolate, think of vitamin C-rich tangerines and oranges!

The recommended daily intake of vitamin C for healthy adult men is 110 mg and 95 mg for women. A 40% higher dose (155 mg and 135 mg per day, respectively) is recommended for smokers because of higher metabolic losses of vitamin C. Smoking liberates more free radicals into the blood, which must be neutralized before they can inflict damage to the vascular walls.

Zinc is one of the trace elements with the greatest number of functions in our body. After iron, it is also the most common one. Apart from the functions it has in hormone balance and the growth of hair and finger nails, it is significantly involved in strengthening the immune system. Due to its wound healing function, zinc is often an ingredient in beneficial ointments. If there is no zinc, normal cells as well as immune system cells such as the T helper cells and T killer cells are not activated and our body’s defense mechanisms cannot be effective. Zinc can also dock onto rhino viruses, which are responsible for colds (rhino is Latin for "nose"), thereby preventing them from reproducing and entering our body cells – a highly effective defense mechanism. Thus, sufficient zinc supply helps to strengthen the immune system by supporting its normal functioning so that many infections do not even have a chance or at least the risk is reduced. If one catches a cold after all, a well functioning immune system can fight off these viruses more effectively. The duration and severity of the colds can be reduced by taking sufficient zinc.

Contrary to other biofactors, our bodies cannot store zinc in one organ. Most of it is found in the cells of many different kinds of tissue and organs. Our body depends on a regular supply through our diet. The daily recommended intake of zinc for healthy adults is 7-10 mg. Animal origin foods such as beef, oysters or cheese, in particular, have a lot of zinc. Plant-based foods contain less zinc – nonetheless the leaders oats and Brazil nuts still contain approx.4 mg of zinc for each 100 g. However, Zinc from vegetarian foods cannot be utilized as well as zinc from animal sources – the bioavailability of zinc is influenced by various dietary ingredients. Phytates, which are found in grains and legumes, inhibit the absorption of zinc in our body. Citric acid (found in various fruit varieties and citrus fruits), in turn, improves the availability of zinc found in natural quantities in vegetarian foods, thus boosting its absorption from the diet. Especially vegans and those with a one-sided diet should therefore pay attention to their zinc balance, not only if they are sick.

Vitamin D is indispensable not only for healthy bones, but also for having a strong immune system. In various processes, it activates our immune system, and performs key functions in controlling it. Through its modulating effect, vitamin D protects the body from misguided attacks perpetrated by its own immune system, thereby contributing to lower the risk for autoimmune diseases and chronic inflammation. If you suffer from vitamin D deficiency, your T cells and other antibodies are not sufficiently activated the germs in our blood and tissues are not detected very well and cannot be eliminated. When our vitamin D reservoir is slowly depleted at the end of the year, this weakens our immune system and we become more prone to get sick and catch the flu.

Vitamin D is one of the rare biofactors that we can produce and store ourselves. For this reason, vitamin D is strictly speaking no vitamin, but a hormone. It is also known as the sun hormone – because its precursor is made from cholesterol in our skin through the action of sunlight (or UV-B radiation, to be more precise). After transformation in the liver, it can be stored in our fatty tissue for the darker winter months. When it is needed by the immune system, it is activated through the kidneys and is then involved in the normal functioning of the immune system. However, various protective barriers (e.g. clouds in the sky or clothes on our body) can prevent enough UV-B radiation from reaching our skin to trigger vitamin D synthesis. Sunscreen protects us very good that UV-B is blocked. Moreover, in the winter months solar radiation is very weak for a few months, that UV-B radiation in northern latitudes no longer reaches the Earth. Thus, our own vitamin D production virtually ceases between autumn and spring. Luckily, vitamin D3 can be absorbed through certain foods – albeit in small quantities – like fatty fish (e.g. herring or salmon), fish oil, cod liver oil, and eggs. 

Therefore, especially in the cool and cloudy winter months, think about a balanced diet and sufficient supply of the vital biofactors vitamin D3, zinc, and vitamin C – your immune system will reward you!

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