There is a self-healing force within all of us that is more powerful than any medication in existence today. It is called the immune system, and its strength largely determines your health and overall quality of life.

The immune system acts both as prevention and as a cure. It protects you all the time and helps you preserve your health despite invaders like bacteria, viruses, pollution, and other factors that can damage it.

For many viral infections, such as Covid-19, an adequate immune response is essential. Scientists know this. That is why you can often hear and read about the importance of various immune system boosters such as vitamins, minerals, regular exercise, and sleep.

Vitamins play a significant part in many stories regarding a healthy immune system. Vitamin C is probably the most famous of them all. However, there are some, often overlooked, vitamins that are indispensable for proper immune function.

Vitamin D is one of them. In this article, you'll find all you need to know about vitamin D and the immune system.

The importance of vitamin D for your immune system

Most people believe that taking more vitamins will build up their immune system, much like lifting weights builds up physical strength. The truth is a bit different, though.

Vitamins are known as "essential nutrients" your body needs to maintain a proper functionality. So, correcting a lack of vitamins should be one of your top health concerns.

The body and the immune system require optimal levels of vitamins at all times. Therefore, taking more vitamins than you need will rarely result in a benefit and can even be harmful.

All you need to do is make sure that your diet, lifestyle, and potential supplementation provide you with the necessary amount of essential nutrients. With vitamin D, things are a bit different. Your skin can produce it, but it needs help from the sun. This is great news because vitamin D may be less available in the food you eat, depending on your diet. However, if you live in an area where sunlight is scarce, this can also pose a problem.

Lack of this vitamin, caused by low exposure to sunlight or limited dietary intake, can lower your immune system and provoke other health problems, especially during growth and development. Later in this text, we will give you more details about the effects of vitamin D deficiency on general health. But first, we must talk about the elephant in the room, which is the fact that too much sun can also be damaging to your health.

As we all know, excessive exposure to sunlight can put our health at risk. It can cause premature skin aging and unwanted skin changes, including cancer. The question is then: How does one get enough vitamin D if unable to obtain the normal daily value through dietary means or sun exposure? Supplements may be your answer. Let’s dive into the specifics of vitamin D!

What is Vitamin D?

Vitamin D is a common name for a group of fat-soluble vitamins. The two main forms of vitamin d include:

Vitamin D has many valuable roles in the body. It increases the intestinal absorption of magnesium, phosphate, and calcium. Also, it is indispensable for the proper development of muscles, bones, and teeth. Cell proliferation, differentiation, and apoptosis are, in part, modulated by vitamin D. Lastly, vitamin D is a potent immune system booster that helps your body fight infections and other diseases.

Despite its many roles, this nutrient may be less prevalent in food, depending on your specific diet. You can only get a significant quantity of vitamin D from fish liver oils, fatty fish, egg yolks, and mushrooms. The best natural source of vitamin D is sunlight. That's why it is also known as "the sunshine vitamin."

When exposed to the sun's UVB radiation, the skin produces vitamin D3 (cholecalciferol). However, neither of the two natural sources (food or sunlight) provides us with a physiologically active form. The skin-created and food-ingested vitamin D is inert. To become active, it has to go through a two-step transformation process called hydroxylation. That process takes place in the liver and then the kidneys.

That's not the only difference between vitamin D and other vitamins. After the second hydroxylation, vitamin D takes the form of calcitriol. In this form, it can interact with almost all types of cells found in the human body. Since it dissolves in fat rather than water, vitamin D tends to accumulate and stay longer in the body. That's a good thing for those who do not get enough of this nutrient through diet or sun exposure. It is estimated that around 40% of people in the U.S. have vitamin D deficiency. However, accumulation can be a bad thing as well. If you take too much of this vitamin daily, it has the potential to lead to toxic levels and cause various health complications.

Health Effects of Vitamin D

In the past, the effects of vitamin D deficiency were far more prevalent. Rickets, a condition that causes impaired bone growth and development, was common among children.

The disease develops due to a lack of vitamin D and calcium. It softens and weakens the bones causing deformities. Nowadays, rickets is rare in the developed world. That's mostly due to vitamin D-enriched staple foods, such as milk, cooking oil, cereals, margarine, etc.

We now know how valuable vitamin D is for our health and that it plays a vital role in the following:

  • Supporting the immune system
  • Promoting healthy teeth and bones
  • Boosting brain and nervous system health
  • Regulating insulin levels
  • Supporting cardiovascular health and lung function
  • Influencing the expression of genes

We've already explained rickets as an example of vitamin D's important to bone health. However, the lack of this vitamin can also cause problems in adults with already developed bones. It can trigger Osteomalacia, a condition that causes muscle weakness and inadequate bone density. Osteoporosis is also associated with vitamin D deficiency.

Vitamin D is so valuable for proper bone development because it helps facilitate calcium absorption from your diet, which strengthens the bones by increasing their density. It also reduces the risk of fractures.

Low vitamin D levels are also associated with depression, impaired cognitive ability, dementia, and Alzheimer's disease. Although there may be a correlation, it is still unclear if vitamin D deficiency could be the underlying cause of such conditions.

Maintaining the optimal levels of vitamin D during pregnancy could reduce the risk of pre-eclampsia and gestational diabetes.

For different reasons, vitamin D deficiency is still common today. However, in most people, it is not chronic or severe. It occurs seasonally (during winter months) and improves later in the year. Long-lasting vitamin D deficiency can result in:

  • Frequent infections
  • Brittle bones
  • Hair loss
  • Muscle pain
  • Fatigue
  • Mood swings
  • Decreased wound healing
  • Cardiovascular problems
  • Pregnancy complications

Vitamin D and Immune System

The health benefits of vitamin D reach beyond bone and teeth health. Its crucial role in the immune response to infections is apparent to scientists. The question we want to answer is: What does vitamin D do for the immune system?

The simple answer would be that vitamin D boosts the immune system in general. It boosts the immune system's antiviral, antibacterial, and anti-inflammatory potential. By doing this, vitamin D significantly lowers the risk of infections, including respiratory tract infections such as the Flu and Covid-19.

Vitamin D activates the innate and the adaptive immune system. That means it helps recruit the immune cells at infection sites and plays a part in antibody creation to fight off specific pathogens. It also helps with the formation of immunological memory. This enables the immune system to respond better and quicker to future infections by the same or similar pathogens. Optimal levels of vitamin D may also reduce the risk of and improve certain autoimmune diseases.

Which parts of the body benefit the most from vitamin D?

Vitamin D is invaluable for overall health. However, some parts of the body benefit more from this powerful nutrient. Here's what vitamin D does for specific parts of the body:

  • Bones: Increases calcium absorption, bone density, and bone strength.
  • Teeth: Reduces gums inflammation and regulates the absorption of calcium and phosphorus.
  • Muscles: Enables the proper growth and development of muscle fibers.
  • Heart: Helps blood pressure regulation, lowers the risk of stroke and myocardial infarction.
  • Blood vessels: Optimal levels of vitamin D reduce the risk of arterial stiffening and hyperlipidemia.
  • Lungs: Helps to maintain normal lung function.
  • Brain: Supports neurodevelopment and potentially reduces the risk of dementia.

Antiviral Properties of Vitamin D

Traditionally, the flu season is the time of the year when we get to read and listen about the importance of a sturdy immune system. So, we all know how valuable vitamins are in the fight against cold and flu, right? Well, most people believe that they understand this connection between vitamins and a healthy immune system. But, the truth is much less straightforward than they think. The immune system works in a very intricate way. It requires stimulation to initiate an adequate response to different threats.

That stimulation has to be optimal. Too much stimulation can trigger autoimmune diseases, while too little keeps the immune system inert and opens the door to frequent invaders.

Interestingly, low levels of vitamin D may be associated with both the worsening of autoimmune diseases and the slowing down of the immune system activity. That does not mean vitamin D deficiency is the underlying cause of these health issues. It shows that the lack of this essential nutrient has the potential to cause an immune system imbalance.

White blood cells are a vital part of the immune system, and they all have vitamin D receptors. That alone illustrates the complex role this vitamin plays in the fight against infections and other diseases. Studies show that optimal vitamin D levels can reduce the frequency of colds, influenza, and other acute respiratory infections. All of this also suggests that vitamin D supplements could be a valuable part of prevention and treatment for Covid-19 patients.

Vitamin D and Covid-19

Your immune system is your best defense mechanism against the new coronavirus that causes Covid-19 disease. Physical distancing, personal hygiene, and masks can lower the risk of infection. But, the immune system is your personal defense warrior that can help fight it off.

The purpose of vaccines, for example, is to strengthen the immune system response by enabling it to recognize and attack the virus. The success of vaccines also depends on your immune system's ability to defend you from infections. That's where vitamin D comes in handy. Recent research on hospitalized patients with Covid-19 suggests that those with optimal vitamin D levels have a lower risk of unfavorable outcomes.

Vitamin D covers different aspects of protection against SARS-CoV-2 (the new coronavirus). With its immunoregulatory and anti-inflammatory properties, it helps boost the immune system and promotes a strong immune response. Also, vitamin D boosts the function of macrophages, T cells, and other immune cells. That strengthens the body's defenses as well.

Very importantly, optimal levels of vitamin D help maintain normal lung function. That is incredibly valuable when you have to combat respiratory infections, such as Covid-19.

Obese and elderly, especially those who are institutionalized, have a higher risk of vitamin D deficiency and poor Covid-19 infection outcomes. However, it is still unclear if the two conditions are connected. Some scientists believe that a lack of physical activity and confinement to indoor spaces are to blame for the correlation.

The Best Ways to Get Vitamin D

Your skin can produce vitamin D with the help of sunlight. But, you can also get it from certain foods, which are natural sources. Numerous supplements can help you to maintain optimal levels of this nutrient. Just remember to keep the balance. Too much vitamin D can cause unwanted health problems.

Natural Sources of Vitamin D

Synthesis of vitamin D3 takes place in the lower layers of the epidermis. It is a chemical process that requires exposure to sunlight. More precisely, to the sun's UVB radiation.

That makes sun exposure the most important natural source of vitamin D. However, certain types of food are also good sources of this nutrient. These include:

  • Fish liver oils
  • Salmon
  • Mackerel
  • Herring
  • Tuna
  • Sardines
  • Beef liver
  • Egg yolks
  • Portobello mushrooms
  • Crimini mushrooms

Additionally, some staple foods contain artificially added vitamin D. Good examples of these are:

  • Cow's milk
  • Soy milk
  • Margarine
  • Cereals
  • Oatmeals
  • Flour
  • Orange juice

Vitamin D is a fat-soluble vitamin, which means your body can store it for longer.

Therefore, you do not need to necessarily take vitamin D every day. Your body can get it from fat tissue deposits. However, if you accumulate too much vitamin D in your body, you might experience some side effects. The buildup of calcium in the body, for example, can result in kidney problems.

So, the question many people ask is: How much vitamin D should I take to boost my immune system?

The answer: There is no such thing as vitamin D immune system dosage. Balance is the key.

You have to balance your daily intake with your vitamin needs to avoid vitamin D deficiency and also toxicity, while trying to boost your immune response.

The following are the recommended daily dietary allowance and the tolerable upper intake values for different age groups:

The Final Word

Optimal levels of vitamin D positively affects your health in many ways. Vitamin D improves cardiovascular, mental, and bone health. It also helps with type 2 diabetes and autoimmune diseases. But, most importantly, it boosts your immune system and your body's ability to fight unwanted invaders, like viruses and bacteria.

Vitamin D for the immune system is an essential component that modulates both innate and adaptive immune responses. That means it has a crucial role in the prevention and the quick resolution of infections. Therefore, maintaining adequate levels of vitamin D is one of the most valuable preconditions for long-term health and well-being.