Strengthening the immune system is important—but what is the right way to do it?

What to expect in this article

What stands out in the research is a pattern: evidence primarily shows that certain factors weaken immune defense—not that anything boosts it beyond normal levels.

Four everyday factors repeatedly appear in research:

What is the immune system, anyway?

The immune system is not an organ but a network of cells, messenger substances, and tissues: bone marrow, thymus, spleen, lymph nodes, mucous membranes, and white blood cells. A network without a central regulator also has no switch that can simply be turned up.

Innate immunity: the fast, nonspecific rapid-response team

It is present from birth and responds within minutes to hours: phagocytes such as macrophages and neutrophils, natural killer cells, and the complement system. It does not recognize individual pathogens but general patterns. Fever and fatigue are therefore not signs of weakness, but of an immune response at work.

Acquired immunity: your body’s memory

The adaptive immune response needs several days, but works with great specificity: B cells produce precisely matched antibodies, while T cells destroy infected body cells. After an infection, memory cells remain that respond more quickly upon the next encounter—this is exactly the principle used by vaccinations.

Skin, mucous membranes, and the gut microbiome as the first barrier

Most pathogens fail before that: at the skin with its acidic protective film, in mucus and the cilia of the airways, and in stomach acid and tears. A large proportion of immune cells is located in the intestinal lining.

The gut microbiome contributes to this fine-tuning; its diversity is promoted above all by a high-fiber diet. By contrast, evidence that a probiotic reduces susceptibility to infections in healthy adults is weaker than advertising suggests.

Can the immune system really be “strengthened”?

The honest answer: A healthy immune system cannot be boosted beyond its normal level of performance—but it can be kept functional. It is not an engine with an accelerator pedal, but a balance: strong enough to fight pathogens, precise enough to spare the body’s own tissue.

Why “immune boosting” is a marketing term

The term does not exist in technical language. It suggests a measurable quantity that does not exist: no laboratory value shows “how strong” an immune system is. In the EU, only scientifically substantiated health claims are permitted.

More is not always better: a look at autoimmune diseases

An overactive immune system is not a desirable state. In autoimmune diseases such as Hashimoto’s thyroiditis or rheumatoid arthritis, the immune defenses attack the body’s own tissue; in allergies, they target harmless substances. The goal is not the strongest possible immune system, but one that is well regulated. Anyone taking immunosuppressive medication should discuss immune-stimulating preparations with a doctor.

Which levers are actually proven?

The most effective measures are unremarkable and usually cost nothing—they eliminate known weakening factors.

Sleep: the best-studied individual factor

During deep-sleep phases, processes take place that are important for immunological memory. People who chronically sleep too little become ill more often after exposure to pathogens, and antibody production after vaccinations is weaker. For most adults, seven to nine hours at consistent times provide the foundation.

Exercise: moderate and regular rather than rare and extreme

During exertion, more immune cells are released into the bloodstream and then patrol tissues and lymphatic organs more intensively. During very intense, prolonged exertion, the effect temporarily reverses—after a marathon without recovery, respiratory infections become more common. Regular moderate exercise is more beneficial than rare extreme workouts; during a feverish infection, take a break from exercise.

Nutrition: ensure adequate intake instead of chasing superfoods

Antibodies are proteins, and immune cells divide very quickly during an infection—both require protein, energy, and several micronutrients. Malnutrition is the most common cause of weakened immune defenses worldwide; in Germany, the problem is more likely to result from an unbalanced diet. No single food “strengthens” anything—the overall pattern over several weeks matters.

Stress: unproblematic in the short term, burdensome over time

Acute stress even activates the immune system temporarily; the critical factor is sustained stress over weeks. If cortisol levels remain elevated, this also dampens desirable immune responses. Indirect effects add to this: poorer sleep, less exercise, and increased alcohol and cigarette use.

Quitting smoking and alcohol: the greatest preventable burdens

Smoking attacks the immune defenses at their most vulnerable point: Smoke paralyzes the cilia in the airways and permanently alters the local immune response. According to the World Health Organization (WHO), tobacco use is one of the most significant preventable risk factors for respiratory diseases worldwide. Alcohol also impairs phagocytes and lymphocytes.

Vaccinations and hygiene: targeted protection instead of general strengthening

Vaccinations do not make the immune defenses generally “stronger”; instead, they train them to target a specific pathogen, measurable through antibodies and memory cells. According to the World Health Organization (WHO), vaccination is one of the most effective public health measures. Hygiene works differently: handwashing, ventilation, and keeping your distance reduce the pathogen load.

Which micronutrients have a proven immune function?

In the EU, ten micronutrients may officially be advertised as contributing to the normal function of the immune system: vitamin D, vitamin C, zinc, selenium, iron, vitamin B12, folate, copper, vitamin A, and vitamin B6. This list is based on assessments by the European Food Safety Authority (EFSA).

The fine print is crucial: This statement applies to the contribution to the normal function. A deficiency impairs immune defenses—additional intake provides no benefit when levels are already adequate.

Who is at increased risk of a true deficiency?

The risk is elevated, among other groups, in people following a purely plant-based diet (vitamin B12, and in some cases iron and zinc), those with heavy menstrual bleeding (iron), during pregnancy and breastfeeding, in older age (vitamins D and B12), with chronic inflammatory bowel disease or celiac disease, and after bariatric surgery. Long-term medications such as proton pump inhibitors can also impair the absorption of vitamin B12. If you belong to one of these groups, targeted testing makes more sense than taking a blanket combination supplement.

Why is vitamin D the biggest bottleneck in Germany?

Vitamin D is the nutrient with the largest supply gap—for geographical reasons: The body produces most of it itself in the skin, but only with sufficient UVB radiation. During the winter half of the year, the sun is too low in the sky at our latitudes, and diet can barely compensate for this: significant amounts are found almost exclusively in oily sea fish.

These figures are annual averages; levels are significantly lower at the end of winter.

To put the evidence honestly into perspective, the research on vitamin D and respiratory infections is inconsistent: supplementation apparently helps mainly in cases of pronounced deficiency—no effect is seen in those with adequate levels. Anyone who wants to know where they stand can have their 25-OH vitamin D3 level measured and adjust the dosage accordingly.

What does not work or is overrated?

A large part of the “immune products” market promises more than it can substantiate.

High-dose vitamin C for colds

Vitamin C does not prevent colds in healthy adults—that is the central finding of the best-known systematic review on the subject.

Eight percent sounds like more than it is: With a seven-day cold, that is about half a day—and only with consistent use, not by simply reaching for an effervescent tablet. One exception: Under extreme exertion—marathon runners, skiers, and soldiers in subarctic conditions were studied—the risk of catching a cold was halved in five studies involving 598 participants (risk ratio 0.48). Nothing can be inferred from this for everyday life.

“Immune booster” shots and miracle cures

Ginger shots, acerola concentrates, and combination products with twenty ingredients are not harmful, but their benefits are systematically overstated: They usually provide exactly the nutrients that are already sufficient with a normal diet. The label test helps: “contributes to the normal function of the immune system” is the authorized EFSA wording for a nutrient contained in the product—not proof that the product prevents infections. The evidence for echinacea is contradictory.

Supplements without a known deficiency

“A little extra can’t hurt” is roughly true for water-soluble vitamins—but not for fat-soluble vitamins and trace elements. High-dose zinc can impair copper absorption over time, thereby causing a second deficiency.

When does too much become dangerous?

For several nutrients relevant to immune function, EFSA has established tolerable upper intake levels—the daily amount considered safe for healthy adults to consume over the long term.

Zinc: more is counterproductive

Zinc is the classic example of overdosing because many cold remedies contain high amounts. In the short term, nausea, stomach pain, and a metallic taste are possible; over several weeks, copper supply suffers. There is some evidence that zinc lozenges for an acute cold slightly shorten the duration of symptoms—but zinc is not intended as a long-term solution.

Selenium: narrow range between enough and too much

Selenium has the narrowest safety margin: The daily requirement is around 60 to 70 micrograms, while the upper limit is 255. Chronic overdosing can cause hair loss, brittle nails, and garlic-like breath. Be careful with Brazil nuts: Their selenium content varies greatly.

Vitamin D: the problem with high-dose supplements

Vitamin D is fat-soluble and stored in the body. An overdose practically never results from sunlight or diet, but from taking high-dose supplements over a prolonged period. This leads to an elevated calcium level in the blood, accompanied by nausea, intense thirst, and confusion; in the long term, kidney damage may occur.

When should you have it medically evaluated?

Recurring infections are usually harmless—especially with close contact with young children. However, there are circumstances in which the cause should be investigated by a doctor.

The distinction between frequency and severity is crucial: Six mild colds for a parent of a daycare child are unremarkable, but two severe infections requiring hospitalization are not. If impaired immune function is suspected, targeted tests are available—differential blood count, immunoglobulins, and further immunological diagnostics. Seek immediate medical help if you have a high fever with a strong feeling of illness, shortness of breath, neck stiffness, or confusion.

How mybody® gives you clarity about your nutrients

If nutrient deficiencies are the only proven nutrition-related weakness, measuring them is the logical first step—not taking supplements as a precaution.

You should apply three criteria to every provider: analysis in a certified laboratory, transparent reference ranges, and GDPR-compliant handling of your health data. According to its own statements, mybody® (MYBODY Lab GmbH) meets them: an ISO-certified laboratory in Germany, SSL-encrypted transmission, and pseudonymized processing.

Nutrient | VitalCheck Complete

15 blood values from a capillary blood sample collected at home—including seven of the ten nutrients with recognized immune functions: 25-OH vitamin D3, zinc, selenium, copper, ferritin, vitamin B12 and folate. In addition: transcobalamin, calcium, magnesium, sodium, manganese, as well as HDL, LDL and triglycerides.

Price: €169.00 (instead of €199.00)  ·  Sample type: Capillary blood (at home)  ·  Processing time: approx. 10–15 working days  ·  Laboratory: ISO-certified, GDPR-compliant

View the nutrient check

For an honest assessment, two limitations should be mentioned. First: Vitamin C is not included in this test, nor are vitamin A or vitamin B6. This is reasonable because vitamin C deficiency is rare in Germany—but you should still be aware of it.

Secondly, and this is the more important point: The test measures your nutrient status, not your immune function. It shows whether a building block is missing—not how well your immune defenses are working. In cases of genuine susceptibility to infections, it therefore does not replace medical evaluation, but it can help prepare for it.

Information on price, sample type, processing time and markers comes from the mybody® product page (as of July 2026) and may change.

Putting it into context: What a test can—and cannot—do

A nutrient blood test gives you a snapshot of your status: It shows whether your values are within the reference range and makes changes over time visible.

What it cannot do: assess the performance of your immune system—no single value can reflect that. Nor does it identify causes: A low ferritin level does not indicate whether the underlying issue is insufficient intake, heavy menstrual bleeding or a source of bleeding. Determining this is a doctor’s job.

The greatest benefit comes from using the results as a basis for discussion—with specific figures, your medication list and your symptoms.

Conclusion

You cannot “boost” the immune system, but you can protect it. The effective measures are unspectacular: get enough sleep, exercise moderately, eat a varied diet, reduce chronic stress, do not smoke, limit alcohol, check your vaccination status and take hygiene seriously.

When it comes to micronutrients, one rule applies: A deficiency weakens you; an excess does not help. The most relevant bottleneck is vitamin D during the winter months—high-dose zinc, selenium or vitamin D supplements without a known deficiency offer no benefit, but do pose a risk.

And the most important caveat: A well-nourished immune system is not a promise of protection. Even those who do everything right will catch colds. If infections occur unusually often, are severe or prolonged, this should be medically evaluated—not addressed with a supplement.

Frequently asked questions (FAQ)

Sources

1. European Food Safety Authority (EFSA): Health Claims – scientific assessment of health-related claims under Regulation (EC) No. 1924/2006. efsa.europa.eu
2. EFSA: Dietary Reference Values and Tolerable Upper Intake Levels (including zinc 25 mg/day and vitamin D 100 µg/day); selenium upper limit of 255 µg/day according to the 2023 EFSA opinion. efsa.europa.eu · Selenium opinion
3. Robert Koch Institute (RKI), Journal of Health Monitoring 2/2016: Fact Sheet “Vitamin D status in Germany” – 30.2% of adults below 30 nmol/L, 38.4% at or above 50 nmol/L. rki.de
4. German Nutrition Society (DGE): Reference values for vitamin D intake – estimated value of 20 µg/day in the absence of endogenous synthesis. dge.de
5. Hemilä H, Chalker E (2013): “Vitamin C for preventing and treating the common cold”, Cochrane Database of Systematic Reviews. cochranelibrary.com
6. World Health Organization (WHO): Fact Sheet “Immunization coverage”. who.int
7. IQWiG / gesundheitsinformation.de: “Common cold” – frequency, progression, and treatment options. gesundheitsinformation.de

Source attribution: Health Claims [1], Upper limits [2], Vitamin D status [3], Estimated intake value [4], Vitamin C [5], Vaccinations [6], Frequency of colds [7]. Product information comes from the mybody® product page; subject to change.

mybody® Editorial & Expert Team

Immunology fundamentals Micronutrients Laboratory diagnostics Nutritional science

This article was created by the mybody® editorial and expert team, which brings together expertise in laboratory diagnostics, nutritional science, and nutrigenetics. Learn more about our team on our editorial and authors page.

Published on July 27, 2026 · Last updated on July 27, 2026

Medical note: This article is intended for general information and does not replace medical advice, diagnosis, or treatment. A well-supported immune system is not protection against infections. If you experience frequent, severe, or prolonged infections, have a known immunosuppression, or are considering taking high-dose supplements, please consult a doctor.