As we all know, weather changes coming in the autumn and lasting through the winter are not very favorable, both for our mood and for health. It is not difficult to get flu and colds, and a deteriorated health condition does not make it easier to perform a busy schedule of activities and duties, not to mention more serious diseases, where we additionally bear the costs associated with medicines.
Prophylaxis is the best solution as always. Appropriate supplementation in this period will help us to protect ourselves against diseases, or help in suppressing any disease symptoms in the bud. We can distinguish many effective substances that increase immunity, and we will try to distinguish those that demonstrate extremely effective action.
One of the most popular supplements, as well as the first recommended for the treatment of routine diseases. And there are solid evidencies to include vitamin C for supplementation, both prophylactic and already during the disease. Doses of 1-2 g resulted in a shortening of the cold period by 8-14%, a reduction in its severity was also observed 1. The effect was even more pronounced in the case of exposure to extreme effort, where the risk of catching cold fell by half! 
A word about laevorotatory
The last boom in vitamin C popularity has caused a lot of confusion in what vitamin C is the best. The most pronounced statement here is laevorotatory vitamin C. And here are a few reservations.
The fact is that ascorbic acid is biologically active mainly in the form of L. However, immediately after this fact, there are many misunderstandings that should be explained.
First, there is a common belief that the abbreviation L placed before the acid name indicates that it is laevorotatory. This is not true. L is a prefix that indicates the type of ascorbic acid form (there are two forms - L and D, differing in chemical structure, but having the same composition - the phenomenon of isomerism).
Secondly, L-ascorbic acid (the form on which we care) is actually dextrorotatory (in simplicity, the twistability indicates in which direction a given compound twists the beam of light), and the form of the compound itself does not define the right or left of rotatory.
Third, and perhaps the most important - legal issues. If we buy vitamin C, it must be L-ascorbic acid or a derivative of it. This is legal regulation 
Herb application successfully in traditional Chinese medicine. It is distinguished by an exceptional, very beneficial content of isoflavonoids (compounds that increase the immune response of the body) . Astragalus itself also has confirmed immunostimulatory effect . Studies indicate that the compounds found in the herb tragacanth, increase the production of immune cells, while preventing the formation of inflammation , which could occur with a naturally occurring reaction of this type of organism.
One of the key micronutrients, requiring supplementation from external sources. Mainly determines the right number of cells responsible for the immune response of the body . In the most common colds, zinc significantly reduces their severity and duration of , and used prophylactically, in continuous supplementation for one year, showed even more than 50% effectiveness in reducing the risk of general infection  .
How many times have you heard about the miracle-making in matters of health prevention of onion juice or garlic? Have you ever wondered what magic is behind this phenomenon?
The effect of the above-mentioned properties is, among others, allicin, a substance created during cutting or crushing of onions or garlic, which, however, is degraded during culinary treatments.
The use of a relatively high dose of allicin during a cold has phenomenal effects. During the tests, as much as 64% lower frequency of common cold was observed in the research group, and 70% shortened time of common cold, in case of its occurrence 10. It can therefore be stated with certainty that it is worth including preparations containing allicin in anti-cold supplementation.
N-acetylcysteine has recently been a triumph in assisting liver regeneration. Is it also good for improving immunity? Research indicates that the most.
NAC is a precursor to glutathione, which is one of the most important antioxidants in the body,
crucial in maintaining the immune system in check. It also helps to remove mucus from the upper respiratory tract (it makes the mucus getting excess in the time of colds or flu becomes less sticky). Getting rid of mucus not only improves comfort (there is someone who likes to have a stuffed nose?), But also allows quicker getting rid of harmful microorganisms from the body, which reduces the intensity of infection 
More specifically, the Annona muricata, used in traditional medicine in regions of South America and Africa. Since relatively recent, attention has been paid to him in the context of supporting the body's immunity in constant supplementation.
The studies found the influence of graviols on the improved immune response of the body, mainly by intensively increasing the activation of specific immunity cells (macrophages), and the intensification of signaling in the context of stimulus response .
It also acts as an antioxidant, eliminating the unfavorable activity of free radicals in the body. It also has anti-inflammatory properties, reducing the pain that may occur during infection .
Black walnut (Juglans Nigra) is another ingredient often used in traditional medicine, mainly due to the high content of bioactive components such as flavonoids, polyphenols and quinones, which have multi-functional health effects for the body.
Research indicates its intense antifungal properties and it was in the context of treatment of such diseases that people started using it. This is especially important in the case of developing candidiasis.
Black walnut shows great support in diseases related to the digestive system, not only fungal, but also bacterial. In the case of any stomach poisoning, the use of black walnut will be a good choice. 
Very often a neglected product during supplementation to improve immunity, which is unfortunately a very big mistake. During the use of drugs, or even more antibiotics, the appropriate selection of probiotics, can greatly increase comfort (especially in the field of gastric revolutions) , and accelerate rehabilitation, associated with the renewal of beneficial intestinal microflora, which also partially disappears during antibiotic therapy.
Of course, apart from the antibiotic support itself, probiotics in themselves support immunity, mainly affecting the increase in activation of genes associated with antiviral defense, and stimulating the immune response of the body .
Of particular interest in the context of improving health will be the L-137 strain of the Lactobacillus plantarum type (found inter alia in Swanson Immuno-LP20 or Jarrow Immune PF). It is a strain particularly studied in this field, and according to research shows very promising immunostimulatory properties, especially in the case of people strongly exposed to stress. It has a profound effect on the activity of natural immune cells of the body and their increased amount, and in the context of diseases, this effect apparently was characterized by the treatment of upper respiratory tract infection (ie those with which we struggle the most) [17,18]
The best choice?
There is no best choice. Each of the above products has a positive effect on the immune system in a slightly different way and one particular favorite can not be identified here.
If we were to indicate specific guidelines after all:
Vitamin C - continuous supplementation. There is practically no situation in which vitamin C will not support the body's immunity.
Astragalus - it works best when supplementing for pain relief due to inflammation during the disease.
Zinc - continuous supplementation, and during the disease period increase the supplementation dose. It exhibits an outstanding preventive action.
Allicine - will always work on the first symptoms of infection. It will be the better choice for people trying to keep closer to natural substances.
NAC - will check again at the first symptoms of the disease, especially in the case of upper respiratory tract infection and excessive irritation.
Graviola - will be useful for people looking for new solutions in the matter of supporting immunity, both prophylactic and intervention, especially if we want to stick to the most natural solutions
Black Walnut - the best for infections associated with the digestive system; stomach flu or candidiasis.
Probiotics - continuous supplementation. Especially recommended for genetic problems with intestinal microflora, or for antibiotic therapy.
In summary, never too much health as they say! And the supplements described above will certainly help in its maintenance, especially in a very unfavorable period of weather fluctuations.