Before you rush to the store or add the supplementsto your online checkout cart to combat COVID-19, it's important to know if you are vitamin D deficient.

Although vitamin D is called a vitamin, it's actually more of ahormone. When ultraviolet rays from sunlight strike your skin, the rays trigger vitamin D synthesis. You canbuild up your vitamin D levels through certain foods and supplements.

Genetics and age can play a big role in how muchvitamin D you have:

If you are worried that you are at risk of vitamin D deficiency, ask your physician to check your blood work.

It'sbeen known for years that vitaminD is essential formaintaining healthy bones and teeth. Without it, bones can become thin, brittleor misshapen.

Vitamin D also plays an important role in helping immune systems function. Low levels can lead to autoimmunity when the immune system attackshealthy cells and increase the chance of infection.

The immune system is like an army that prevents invaders, such as viruses and bacteria, from taking over the homeland your body.It is composed of the innate and adaptive immune systems.

Let's say a virus is present in a patient's lungs, specifically in the air sacs (alveoli), which can lead toacute respiratory distress syndrome (ARDS).

The first line ofdefenseis the innate immune system:Itcomes into play immediately or within hours of antigen detection.Antigens areproteins on the surfaces ofbacteria, fungi and viruses that the body doesnt recognize as its own.

Natural killer cells and macrophages, along with other immune cells, recognize, engulf and destroy pathogens.The main purpose of these cells is to prevent the spread and movement of harmful substancesthroughout the body. They are akin to soldiers shooting indiscriminately all over the enemy's camp.

Although the exact role of vitamin D in the immune system is not fully understood, studies have shown it may influence both innate and adaptive immune systems.

When the innate immune system is activated, its cells turn certain genes on to become more efficient at killing pathogens. Vitamin D binds to these cells and enhances this transformation, helping the innate immune system kill viruses.

If the pathogen manages to dodge the innate immune system, adaptiveimmunity kicks in.

The second line of defense is the adaptive immune system: Itrelies on B cellsandT cellsto carry out its tasks. These cells produce billions of antibodies.Antibodiesrecognize antigens and bind to them. They are like high-ranking officers thatconduct specific missions targeting only certain enemies. Antibodies makefuture responses against a specific antigen more efficient.

The problem with infections such as COVID-19, is that most of us are believed to be naive to the infection. So we don't have memory B cells ready, which means that adaptive immunity, even though it might be super powerful, can't recognize the pathogen, says Vadim Backman, professor of biomedical engineering at Northwestern University.

Cells of the adaptive immune system produce cytokines. These small proteins attract more immune cells and trigger inflammation. Sometimes, cytokines become too abundant and create a cytokine storm when immune cells spread beyond infected body parts and attack healthy tissue.

The way our immune system responds to the virusmay be a big part of this puzzle, Backman says. What does seem to be critical is acute respiratory distress syndrome. ARDS is caused by an overreaction of the immune system called a cytokine storm, which seems to be induced by the adaptive immune system, Backman says.

Backman saysVitamin D binds to the cells of the adaptive immune system and turnssome genes on while switching others off. This causes cells to produce fewercytokines, reducing inflammation and the possibility of cytokine storm.

When activated immune cells surge into the lungs as a result of a cytokine storm, the lungs can become inflamed. Fluid from the smallest blood vessels leaks into the tiny air sacs, resulting in acute respiratory distress syndrome (ARDS). The fluid prevents the lungs from filling with enough oxygen, so less reaches the bloodstream, causing organs to fail.

Many COVID-19-infected patients develop ARDS. Researchers in China examined risk factors for 191 coronavirus patients who died while being treated in two hospitals in Wuhan. The study showed50 of the 54 patients who died had developed ARDS; only nine of the 137 survivors developed ARDS.

A study in 2015showed that patients with ARDS and those at risk of developing it had vitamin D deficiency. Researchers demonstrated that vitamin D canreduce damage to capillaries that connect the alveoli to larger blood vessels that may prevent ARDS. In another study, Vitamin D was shown to have a protective effect on the lungs.

Another mystery of COVID-19 is why fewer children are seriously affected.

"Mortality and complications keep going up and up and up as age increases,"Backman says. Young children don't have mature adaptive immunity. They primarily rely on the antibodies that they have from their mother.

"There are always exceptions, but most children don't tend to overactivate their adaptive immune system. They don't develop cytokine storms because they just don't have the mechanisms, Backman says.

The research is in the early stages. According to a preprint studyBackman co-wrote, countries with low average vitamin D blood levels in the population had higher numbers of COVID-19 cases and deaths. A study from the U.K. looked at the nearly 450 patients diagnosed with COVID-19 and did not finda link between vitamin D concentrations and risk of COVID-19 infection.

In apaperpublished in theBritish Medical Journal,21 experts from the U.K., Ireland and the USA concludes that although vitamin D is essential for good health and may bolster the immune system, itcanbe dangerous in high doses.

Worldwide, about 1 billion people have inadequate levels of vitamin D in their blood, andinsufficiency affectsalmost 50% of the population. Most commonly, low levels of vitamin D are caused by insufficient exposure to sunlight.

In Louisiana, African Americans account for more than 50% of COVID-19 deaths despite representing only 32% of the population.

African Americans are at greater risk for vitamin D deficiency because they havehigher presence of melanin.Melanin reduces the bodys ability to produce vitamin D.PeoplefromSouth Asian backgroundsalso may not get enough vitamin D from sunlight in the summer.

Studies also have shown that African American adults have higher rates of hypertension, which isassociated with more severe cases of COVID-19.

"Vitamin D may simply correlate with some factor x, which for all we know has not been identified yet," Backman says."And that's factor x which causes or prevents complications."

Vitamin D deficiency can be caused by obesity.A body mass index greater than 30 is associated with lower vitamin D levels.The skin's ability to make vitamin D decreaseswith age.People who are homebound or rarely outside may have low levels of vitamin D as a result ofnot being able to getsun exposure.

If your levels are within normal ranges,here are some foods that will help with maintaining daily recommended value.

How much vitamin D you need depends on many factors, including age, race, latitude, season, sun exposure, clothing and more. The U.K.'s National Health Service recommends consuming 400 international units (10 micrograms) of vitamin D daily for adults.

"Let's say I knew that I'm vitamin D deficient," Backman says."It's something that is important for health. There are no benefits of vitamin D deficiency.So it's really guilt-free, risk-free to expose yourself to the sun for 20 minutes, get supplementation, get your levels within the normal level."

According to the NHS, people shouldn't take more than 4000 IUs (100 mcg)of vitamin Da day as it could be harmful.Children under 10 shouldn't have more than 2000 IUs(50 mcg) a day.

Taking too many vitamin D supplements over a long period of time can causetoo much calcium to build up in the body potentially weakening bones and damaging kidneys and heart.

Nutritionists say sticking to a healthy diet that includes a variety of nutrient-rich foods can boost the immune system.

"Ahealthy diet means eating food that is as close to its natural form is possible," says TamaraWard,a specialist in oncology nutrition at the University of Cincinnati Cancer Center."I don't say just eat real food. Because to a lot of folks, a box of Kraft macaroni and cheese is real because you can touch it, but it is highly processed. That little packet of flavoring isn't real food."

Other nutrients along with vitamin D aidtheimmune system. Consuming foods high in vitamin C, such as grapefruits and oranges, may increase white blood cell productionkey to fighting infection.

Adding carrots, spinach or kale to yourdiet mightbe a good idea. They containbeta-carotene that converts into vitamin A an anti-inflammation vitamin that enhances immune function.

Vitamin B-6 is essential in the formation of healthy red blood cells and is present in chicken, turkey and bananas. Garlic contains compounds that stimulatecertain immune cellsand helpregulate the immune system. Vitamin E and zinc are beneficial for fighting off diseases.

Ward recommends foods containing probiotics, such as yogurt:

"Once your gut is functioning really well, then that helps your gut to absorb all of the other nutrients that are in these foods, like zinc, vitamin B-6, vitamin D, the beta carotene," she says.

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Can vitamin D help with symptoms of COVID-19? Possibly, it's key to helping your immune system function - USA TODAY

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