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immune system

vitamin a immune system


Vitamins are essential constituents of our diet that have been known to influence the immune system. But which vitamins have proven effective to help our immune system? Is a healthy diet enough? All these questions are constantly raised and become especially burning during epidemics. In turn, many studies test hypotheses and publish the results, sometimes breaking quite common myths. This time, to further expand on the topic of immunity health, we will review how vitamin A affects the immune system. We will also answer the question of how to check a deficiency / excess of this vitamin.

This article was last reviewed by Svetlana Baloban, Healsens, on February 23, 2020. This article was last modified on 22 February 2020.

To begin with, we note that vitamins cannot be sufficiently synthesized by our body and must come to us with food. So Albert Szent-Gyorgyi, who won Nobel Prize in Physiology or Medicine, said that “Vitamins and their metabolites are essential for a large number of physiological processes”. And that’s true. Vitamins and their metabolites are essential for a large number of physiological processes. They play an important role in the immune system, extending to both innate and adaptive immune responses

Vitamin A Helps Immune System


Many people know that vitamin A is crucial for maintaining vision. And, of course, who has not heard that it is widely used in cosmetics?! Vitamin A turned out to be the first vitamin approved by the Food and Drug Administration as an anti-wrinkle agent.1. Thus, it confirmed its ability to change the appearance of the skin surface and has anti-aging effects.

However, its functions do not end there. So, it is crucial for promoting growth and development and protecting epithelium and mucus. Did you know that it’s also called an anti-inflammation vitamin? It has to do with its critical role in enhancing immune function. For this function, vitamin A should be referred to as the vitamin that helps our immune system.

In turn, vitamin A deficiency impairs innate immunity by impeding the regeneration of mucosal barriers damaged by infection. It’s not just that our innate immunity suffers, but vitamin A is also required for adaptive immunity2. In severe cases, the immune system is so weak that it cannot even cope with a common cold.

There are several reasons why vitamin A deficiency may develop. First of all, nutritional deficiencies can affect the lack of this vitamin. So, we obtain vitamin A through diet in two forms. Retinol and retinyl ester come from animal sources such as meat, dairy products, and fish. Provitamin A (beta-carotenoid) is derived from colorful fruits and vegetables. Insufficient intake of the vitamin with food may result in its deficiency.

Second, vitamin deficiency is associated with certain diseases, such as liver disorder. Moreover, infectious diseases transiently depress serum retinol concentrations. Zinc deficiency can also impair the absorption, transportation and metabolism of vitamin A.

Let’s see how often vitamin A deficiency occurs in people?

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Vitamin A Deficiency and Its Impact on the Immune System

Vitamin A deficiency (VAD) is the single most important cause of childhood blindness in developing countries. Dietary surveys indicate that many US adults are not meeting dietary requirements for vitamin A3. According to their results, 51% of adults fall short of the Estimated Average Requirement.

But what about the situation in other countries? ? In 2018, a paper was published about vitamin A intake in China among 12,246 adults aged 18 to 64 years old. Approximately 87% of adults didn’t consume enough vitamin A4. Remarkably, retinol intake was significantly higher in younger adults compared to older adults, and in males compared to females.

Therefore, understanding the symptoms of vitamin A deficiency can be very helpful. So, classic symptoms include problems such as dry eyes and night blindness. Although eye problems are the most well-known issues related to vitamin A deficiency, this symptom may not be observed. Therefore, we consider other symptoms.

Dry skin also is suggestive of its deficiency but can be due to other causes. Moreover, poor wound healing, as well as acne, may indicate a problem of vitamin A.

To diagnose vitamin A deficiency, a serum vitamin A/retinol analysis is used. This lab test will be useful if levels are under 28 μg/dL. In this case, it will indicate an acute shortage. However, this analysis is not suitable if deficiency is mild. This is due to the fact that serum retinol concentrations don’t begin to decline in healthy individuals until liver reserves of vitamin A are dangerously low.

How is vitamin A deficiency treated and prevented?

In order to prevent vitamin A deficiency, it will be enough to include foods rich in vitamin A into your diet. Concentrations of preformed vitamin A are highest in liver and fish oils. Other sources of preformed vitamin A include such foods as:

  • Spinach, kale, collards, brocolli and other leafy green vegetables
  • Beta-carotene-rich fruits such as apricots, mango, and peaches, and highly-coloured vegetables such as carrots, squash, sweet potato
  • Milk or cereals enriched in vitamin A
  • Liver
  • Egg yolks
  • Fish liver oils

The recommended daily allowance (RDA) is 900 mcg and 700 mcg per day for men and women. So, one medium-sized raw carrot, weighing 61 g, contains 509 mcg RAE of vitamin A.

To talk about vitamin A deficiency, it treated with vitamin A palmitate oil. For such cases, a dosage of 60,000 IU is taken orally for 2 days. Then the dosage reduced to 4500 IU orally per day.

An alternative dosing is:

  • 50,000 IU for infants below 6 months of age
  • 100,000 IU for infants 6–12 months of age
  • 200,000 IU for 12 months through adulthood

Hypervitaminosis A or Vitamin A Toxicity

Vitamin A is fat-soluble. Therefore the body is able to accumulate it, mainly in the liver. Accordingly, its excessive consumption can lead to its excess, which is toxic (hypervitaminosis A). But do not worry that a regular diet can lead to such results. As already mentioned, a study of dietary preferences came to exactly opposite conclusion.

Nevertheless, excessive consumption of foods rich in vitamin A has been observed. For example, the authors of “Carrot man” tell a story of a 48-year-old male. The man complained to his primary care physician of abdominal discomfort and yellow/orange skin discoloration. It turned out that he ate 6-7 lb of carrots per week which lead to health problems. However, once he abandoned carrot diet, everything returned to norm within 1 month5. As for severe poisoning cases, it is known that researchers in the Arctic in the XIX died after they ate a polar bear liver rich in vitamin A.

To summarize, under normal conditions, an excess of vitamin A is not related to nutrition. As a rule, an excess is usually associated with the consumption of excessive amounts of vitamin A from supplements.

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недостаток цинка


Immune response is the main mechanism of host defense against infections and pathogenic microbes, it helps to eliminate toxic or allergenic substances that enter our body through mucosal surfaces. So, the importance of immune response can hardly be overestimated. However, a wide range of factors can disrupt it. And by reason of it, it is so important to understand what exactly causes the failure. In this article, we will talk about the role of zinc in the immune system and this will open a series of articles on the topic of maintaining immunity.

This article was last reviewed by Svetlana Baloban, MD on 18 March 2020. This article was last modified on 7 February 2020.

How to boost the immune system

When talking about ways to strengthen our immune system, we cannot help recalling some general recommendations. Usually, general recommendations look exactly the same as those for maintaining a healthy lifestyle, namely:

  • Don’t smoke
  • Eat a diet high in fruits and vegetables.
  • Exercise regularly.
  • Maintain a healthy weight.
  • If you drink alcohol, drink in moderation.
  • Get adequate sleep.
  • Take steps to avoid infection, such as washing your hands frequently and cooking meats thoroughly.
  • Try to minimize stress.

But the most effective means of preventing infection are still vaccines.


Even though this list of general recommendations is non-exhaustive, these recommendations are universal and will work for everyone. And since you probably heard about them, we will talk about other factors that can negatively affect immunity. So, there is evidence that various micronutrient and vitamin deficiencies result in a weak immune system. These, for example, include vitamin A and vitamin D deficiencies, lack of zink, selenium, and others. As we have already said, we will begin our review with the effect of zinc on immunity. We will loop over the role of zinc in the immune system, talk about diagnostics and analyze treatment methods.

About Zinc

Zin is a mineral that’s important to the body in many ways. It is the second most abundant trace metal in the human body after iron. In contrast to the latter, zinc cannot be stored and has to be taken up via food daily to guarantee sufficient supply. So, it plays a role in cell division and growth, wound healing, and the breakdown of carbohydrates. Zinc also provides normal brain functioning, improves memory, and mental performance. In addition, it contributes to maintaining healthy bones, skin, hair, nails.

Moreover, zinc is an antioxidant and has anti-inflammatory effect. This ability plays a role in the prevention of free-radical-induced injuries during inflammatory processes1.

Zinc and Immune System

But the functions of zinc in the body do not end there. Zinc deficiency, as well as zinc excess lead to a weak immune system, which can result in increased susceptibility to infections and the development of inflammatory diseases.

This is primarily due to the fact that zinc is crucial to normal development and functioning of cells which indirectly affect innate immunity, neutrophils and NK cells. Zinc deficiency also affects cells which absorb particles that are foreign or harmful to the body (macrophages). And in addition, zinc deficiency adversely affects the growth and function of major immune cells (T and B cells).

As far back as 1963, Dr. Prasad for the first time proved the existence of zinc deficiency. Since then, knowledge about zinc evolved rapidly. It has been proven that marginal-to-moderate zinc deficiency leads to a weak immune system, delays wound healing, and increases oxidative stress.

When zinc deficiency was first discovered, it was thought to be a rare disease. However, subsequent studies have found that zinc deficiency is very common, with an estimated two billion people worldwide being affected2. As for zinc excess, it needs to be said, that it is quite rare. As a rule, its symptoms are mostly due to copper deficiency.

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Zinc Deficiency Symptoms

As it was already mentioned above, the lack of zinc is a fairly frequent phenomenon. In addition, it especially affects industrial countries and the elderly. Therefore, let’s look at its indirect and direct signs that can be determined.

The first symptom of zinc deficiency is a weak immune system. So, if you often catch a cold or are susceptible to chronic allergies, it may be a sign of zinc deficiency.

Diarrhea and irritable bowel syndrome may also indicate a lack of zinc. And besides, deterioration of the skin, nails, and hair can mean a deficiency of this trace element. Lack of zinc can cause significant hair loss. Worsening night vision, decreased mood, sleep disturbances, and decreased appetite are also noted.

Vegetarians are more likely to have trouble getting enough zinc than others. This is due to the fact that they exclude meat from the diet, while meat is a good source of zinc. For such people, it would be useful to consider foods high in zinc. For example, you can vary your diet with pumpkin seeds, which can be added to any dishes, or almonds (see the full list of high products in zinc below).

Also, alcoholic beverages decrease the amount of zinc that the body absorbs and increase the amount lost in the urine.

In addition, studies reveal that nutritional deficiency of zinc is caused by high consumption of cereals, legumes, and oilseeds. They are all rich in phytate, which makes zinc unavailable for absorption.


To date, no specific and reliable biomarker of zinc status is known. Nonetheless, serum/plasma zinc concentrations can be seen as potentially useful. Unfortunately, this test is far from ideal, as some elderly people were subject to an increase in pro-inflammatory cytokines (zinc depletion factor) at normal plasma levels of zinc. That is why doctors can offer additional tests to show the content of zinc in the hair or its content in the urine. He may also suggest researching your diet to see how much zinc comes with food. But be as it may, a laboratory blood test for zinc is readily available, inexpensive, and good for primary diagnosing.

Lab Test for Zinc Deficiency

Reference Range (mcg/mL) for the age of 11 years old: 0.66 – 1.10 mcg/mL

Foods High in Zinc

A wide variety of foods contain zinc. Oysters contain more zinc per serving than any other food, but red meat and poultry provide the majority of zinc. Other good food sources include beans, nuts, certain types of seafood (such as crab and lobster), whole grains, fortified breakfast cereals, and dairy products.

It’s worth remembering that the bioavailability of zinc from grains is low because of phytates—which we already discussed earlier. Thus, animal foods will provide better sources of zinc.

The current recommended dietary requirements for zinc are as follows:

  • 11 mg for men
  • 8 mg for women, and 11 mg for pregnant women. It is recommended to receive as much as 12 mg of zinc during lactation.

An intake below these ranges can only be seen as an indicator of potential zinc deficiency because many other factors also play a role in decreased zinc intake3. Here’s a comparative table of foods with the highest zinc content.

FoodMilligrams (mg)
per serving
Oysters, cooked, breaded and fried, 3 ounces74.0672
Beef chuck roast, braised, 3 ounces7.067
Crab, Alaska king, cooked, 3 ounces6.559
Pine nut, 3 ounces6.4558
Sunflower seeds, 3 ounces545
Eggs, 3 ounces3.128
Almond, 3 ounces2.724
Chicken, dark meat, cooked, 3 ounces2.421
Yogurt, fruit, low fat, 8 ounces1.715
Cheese, Swiss, 1 ounce1.210
Almonds, dry roasted, 1 ounce0.97
Chicken breast, roasted, skin removed, ½ breast0.97
Peas, green, frozen, cooked, ½ cup0.54.5
Flounder or sole, cooked, 3 ounces0.32.7

*11 mg of zinc per day was taken as the calculation of the norm

Zinc Supplements

In dietary supplements, zinc is present in the forms of zinc picolinate, zinc gluconate, zinc sulfate, and zinc acetate. It is noteworthy that several studies indicate that zinc picolinate has the highest bioavailability as opposed to the other form.

And finally, if the supplementation seems to be the most acceptable option, keep in mind that prolonged zink intake in high concentrations may cause copper deficiency.

Be healthy!

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vitamin D


Modern books on wellness management often mention Vitamin D. It is commonly called overall health hormone1. And it makes sense! Vitamin d function is to help prevent chronic diseases and affect people’s longevity in general. Meanwhile, vitamin D insufficiency affects almost 50% of the population worldwide. An estimated 1 billion people worldwide, across all ethnicities and age groups, have its deficiency. That is and why sustaining its optimum level is critically important for your health.  

What is unique about vitamin D is that we don’t only get with food but can also produce it in our body by being exposed to sunlight. It plays a major role in keeping bones healthy, therefore it insufficiency can lead to child rickets, and adult malacosteon (bone softening) and osteoporosis (bone loss). But this vitamin’s role is not limited to this function.

Role of Vitamin D

Some recent studies have shown that it sufficiency is also associated with lower risks of getting diabetes milletus, multilocular sclerosis, cardiovascular diseases2, and tuberculosis3.


Besides, it is vital for a healthy immune system4. Without sufficient its amount our immune cells cannot properly react to threats, making our body more vulnerable to infections. In addition, vitamin D affects both inborn and acquired immunity.

It’s worth mentioning that vitamin D has anti-cancer effect for various types of cancer5. Emerging research supports the possible role of it against cancer, fractures and falls, autoimmune diseases6, influenza, type-2 diabetes, and depression. That’s why many health care providers have increased their recommendations for vitamin D supplementation to at least 1000 IU7. So, a meta-analysis published in 2007 showed that this supplementation was associated with significantly reduced mortality.

By now we have received the evidence of an increased risk of prostate and endometrium cancer, esophageal, stomach and pancreatic cancer, bladder and renal cancer, Hodgkin’s disease and non-Hodgkins lymphoma caused by vitamin D deficit.

It is remarkable that randomized double-blind examination shows significant 60% decrease in general oncological risk among postmenopausal women who were treated with vitamin D and calcium, as opposed to those who received placebo treatment during 4 years of observation8. The studies show the optimum 25 (OH)D in blood serum for cancer prevention to be 40-60 ng/mL (100-150 nmoles/L).

In addition, lower levels of vitamin D adjusted for BMI are also associated with an increased risk of hypertension9. Therefore, given the relatively safe and inexpensive route of vitamin D supplementation, some studies recommend prescribing vitamin D to hypertensive patients who fall below the target.

Chronic fatigue, low spirits may also be caused by vitamin D insufficiency. Besides, muscle weakness is considered a clear indicator of its clinical deficiency. Clinical symptoms of myopathy deficiency include proximal muscle weakness, diffusive muscle pains, and balance disorder. It also reduces age-related and general inflammations, which is critically important for cognitive function retention.

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How to Measure Vitamin D Levels

Your vitamin D can be tested in a blood test which measures its content (25-OH vitamin D). 25(OH)D is the main metabolite of it in the blood. Two main forms of 25(OH)D are cholecalciferol (D3) and ergocalciferol (D2). D3 is mainly formed in our skin under ultra-violet rays, while the source of D2 is food. Significantly, 25(OH)D concentration is made up of these two components, both forms are measured equimolarly. 25(OH)D is considered the best indicator of vitamin D in the body.  

Sun Exposure and Vitamin D

As mentioned above, you can get enough vitamin D in daily sun exposure. It happens because sunlight enables our body to synthesize it from cholesterol. To achieve this effect, some scientists recommend exposing about a third of your skin to the sun. This means that for most fair-skinned people, wearing a T-shirt and shorts for 10-30 minutes three times a week during the summer will be sufficient10. People with darker skin may need a bit longer than this.

However, a Korean study did not confirm the effectiveness of this recommendation. The experiment was Korean adults aged 20–49 years with serum 25-hydroxyvitamin D (25[OH]D) levels of < 20 ng/mL11.

The results showed that the sunlight exposure group showed a slight increase in serum 25(OH)D level. The sunlight exposure group had sunlight exposure on 20% to 30% of their body surface areas for 30–60 minutes per day, 3 times a week during the summer season.

Let’s see how much of vitamin D can be obtained through sunbathing? A Norway study found that 30 minutes of midday summer sun exposure of the whole skin is equivalent to taking 10,000-20,000 IU vitamin D orally12. At the same time, the winter levels of vitamin D are 10 to 100% lower than the summer levels. That means people in Norway cannot get vitamin D from sunlight between October and March.

There are a lot of factors that can affect your ability to make vitamin D from sunlight. Firstly, it depends on how sensitive your skin is to sunlight. Other factors include the time of day, your skin color, and how far you live from the equator. Secondly, it should be taken into account how much skin you expose to sunlight and whether you’re wearing sunscreen.

Does sunscreen reduce vitamin D production?

Since we mentioned sunscreen, let’s see how it affects vitamin D. Some studies estimate that sunscreen of SPF 30 or more reduces vitamin D production in the body by about 95–98%13. However, several studies have shown that wearing sunscreen has a small impact on your blood levels during the summer141516. Perhaps the differing results are related to different factors and the duration of the experiments. Another possible explanation is that even though you are wearing sunscreen, staying in the sun for a longer period may cause enough vitamin D to be made. Anyway, the effect of sunscreens on circulating vitamin D levels remains debated.

In conclusion, in order to resolve the dilemma of sunscreens, you may try going without sunscreen for just the first 10–30 minutes. This period should depend on how sensitive your skin is to sunlight. And then you need to apply sunscreen before you start burning.

This article was last reviewed on 12 March 2020. This article was last modified on 10 February 2020.

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Source: ©️2019 Healsens B.V. All right reserve


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