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The Importance of Vitamin D and Its Effects on Your Immune System

Updated on June 11, 2014

Covered in This Article

  • Importance of Vitamin D
  • What Happens Without Vitamin D
  • Vitamin D & Your Immune System
  • Foods & Sources of Vitamin D

When Polish scientist Casimir Funk first discovered what he called "vital amines" in 1912, he revolutionized the study of nutrition. Researchers are still discovering the roles vitamins play in the human body, and recent studies suggest one vitamin could play a larger part in overall good health.

Nutritionists already know Vitamin D has some unusual properties. For one thing, it's the only vitamin the human body can make on its own with the help of sunlight. For another, the nutrient also functions as a regulatory hormone once it's activated as calcitriol within the body. It's no surprise, then, to find that this already uncommon compound could affect the expression of genes controlling risks of cancer, heart disease and autoimmune disorders. It may also help stave off contagious illnesses, including the flu and the common cold.

The Importance of Vitamin D

Whether you get your vitamin D from a glass of milk, an afternoon in the sun or a supplement, the micronutrient plays a pivotal role in bone and heart health by regulating the calcium balance in your blood. It's also necessary for calcium absorption in the gut, which is one reason why calcium-rich foods are frequently fortified with it. Bone is a living tissue that regularly interacts with the rest of the body. Without sufficient calcium intake, the body mines its own bones for the calcium needed to keep your brain functioning, your heart beating and your cells communicating with one another.

Both dietary and synthesized forms of vitamin D are inert until they reach the liver where they're converted to calcidiol and then to the kidneys where they undergo another alteration to calcitriol. When you get enough calcium in the foods you eat, vitamin D helps you process that calcium. In the bloodstream, calcitriol boosts the level of calcium in the blood either through faster dietary uptake or, if not enough calcium is available via the gut, from bones.

Vitamin D is especially important for proper bone formation in children. As some families found, however, there can be too much of a good thing. Vitamin D, like vitamins A and K, is fat-soluble and can accumulate in the body's tissues. During the post-war years and into the 1950s, vitamin D fortification became so common that young children were consuming too much of it. The German ban on milk fortification is still in place today, but without it, the majority of the population isn't getting sufficient vitamin D. What might that deficiency mean for the future?

What Happens Without Vitamin D?

Even before vitamins were discovered, or given names, deficiency diseases were well known. Scurvy, the lack of vitamin C, may be the most notorious, but too little vitamin D results in its own constellation of symptoms. Children who suffer from a vitamin D deficiency develop rickets, a bone disorder that causes deformities to the legs, wrists and spine. Rickets can also cause bone pain, dental problems and susceptibility to fractures. Even children who get enough calcium can't metabolize it without enough vitamin D.

In adults, a similar disease called osteomalacia causes softening of the bones, muscle weakness and pain. The disorder initially resembles osteoporosis, but unlike osteoporosis, deficiency-related osteomalacia is partially or fully reversible with enough vitamin D. New research suggests too little vitamin D also damages your immune system, and although the mechanisms by which it works are still being studied, the evidence for its importance beyond bone health is mounting.


  • In 2010, the Institute of Medicine tripled the old requirement for vitamin D intake from 200 international units per day to 600 IU and doubled the maximum recommended allowance from 2,000 to 4,000 IU.
  • Getting sufficient vitamin D could have a protective effect against invading pathogens, including the various rhinoviruses and influenza strains that cause everything from a case of the sniffles to a full-blown flu.
  • Participants with low vitamin D levels were at higher risk of autoimmune disorders and more inflammation.

Vitamin D and Your Immune System

In 2010, the Institute of Medicine tripled the old requirement for vitamin D intake from 200 international units per day to 600 IU and doubled the maximum recommended allowance from 2,000 to 4,000 IU. The Harvard School of Public Health, among others, suggests that even these new recommendations may be too low given the new findings on how vitamin D affects the immune system. The Journal of Investigative Medicine article on the effects of vitamin D on the immune system has an equally enthusiastic tone about the growing importance of the micronutrient. Lead researcher and rheumatologist

Dr. Cynthia Aranow puts it plainly: "Deficiency in vitamin D is associated with increased autoimmunity as well as an increased susceptibility to infection."

In other words, getting sufficient vitamin D could have a protective effect against invading pathogens, including the various rhinoviruses and influenza strains that cause everything from a case of the sniffles to a full-blown flu. In the largest such immunological study so far, vitamin D was consistently linked with higher rates of respiratory infections in more than 19,000 participants. Moreover, people who had existing respiratory conditions such as COPD and asthma faced an even greater risk of respiratory infections when they also had mild vitamin D deficiencies.

The immune system sometimes does more than ward off invading microbes. Autoimmune disorders happen when the otherwise finely tuned defense system turns on and attacks the body's own tissues. Rheumatoid arthritis, multiple sclerosis and type 1 diabetes are just a few of the most common autoimmune diseases. Collectively, such disorders affect an estimated 50 million Americans.

In the Endocrine Society's Journal of Clinical Endocrinology and Metabolism, a study conducted in Ireland found a link between vitamin D deficiencies and damaged immune systems. Participants with low vitamin D levels were at higher risk of autoimmune disorders and more inflammation. In turn, inflammation has long been linked with a higher incidence of cardiovascular disease and cancer.

While the correlations between vitamin D deficiencies, inflammation and autoimmune system dysfunction aren't absolute or proven to be causative, they are persuasive enough that some physicians are recommending more vitamin D to their patients. Dr. Aranow agrees: "As immune cells in autoimmune diseases are responsive to the ameliorative effects of vitamin D, the beneficial effects of supplementing vitamin D deficient individuals with autoimmune disease may extend beyond the effects on bone and calcium homeostasis."

Vitamin D Effects

Quick Suggestions

  • Fatty fish, like tuna, mackerel, and salmon.
  • Foods fortified with vitamin D, like some dairy products, orange juice, soy milk, and cereals.
  • Beef liver.
  • Cheese.
  • Egg yolks.

Foods High in Vitamin D

One reason most industrialized countries add vitamin D to milk is that the nutrient isn't plentiful in the typical American and European diet. Outside of Germany, milk and plant-based milk products such as soy, coconut and almond milk are an excellent source of vitamin D thanks to fortification. With fortification, a cup of milk contains about 30 percent of your recommended daily intake of vitamin D. Not everyone enjoys milk or is willing to drink three cups of it daily, but other products can fill in the gaps. Some orange juices are fortified with vitamin D and calcium, making them a good choice for breakfast. Vitamin D also finds its way into yogurt and some fortified butters and margarines.

Some fish are also naturally high in vitamin D. A single four-ounce serving of salmon contains about 450 IU which is well above the pre-2010 requirements and 75 percent of the new recommended amount of 600 IU per day. Swordfish is even higher in vitamin D with about 560 IU; however, swordfish is notably high in mercury and shouldn't be a mainstay. The Environmental Protection Agency recommends that pregnant women, nursing mothers and young children avoid eating swordfish. Eggs, liver and sardines each supply about 10 percent of the daily recommended intake of vitamin D.

While each of these foods may not pack much of a vitamin D punch by themselves, they add up to a healthy intake. A breakfast of two eggs plus a glass of fortified orange juice and a salmon salad for lunch or dinner is enough to meet current recommendations for vitamin D intake. Add the occasional glass of milk or cup of yogurt to the menu, and meeting your vitamin D needs through diet is achievable.

Other Sources of Vitamin D

Unlike most other nutrients, you can boost your vitamin D intake without adding anything new to your diet. Getting a few extra minutes of sunlight is enough to provide many people with the vitamin D they lack, especially if you have fair skin and live in the south. For people who live in more northerly latitudes or who have darker complexions, vitamin D synthesis alone is not enough. Even for light-skinned southerners, the sun presents its own set of problems. Skin cancer rates have fallen with the rise of the spray-on tan, and doctors don't recommend lengthy sunbathing sessions to anyone.

Dietary Supplements

Supplements are another way to get enough vitamin D without risking healthy skin or drinking milk with every meal. Supplemental vitamin D contains the same nutrient found in fortified foods, so if you prefer to take it in capsule form, you're getting the same vitamin. One old-fashioned tonic, cod liver oil, contains 1,300 IU of vitamin D per tablespoon, but most people don't find it palatable. Cod liver oil in gel capsule form may be easier to swallow. Reading vitamin and supplement reviews can help you choose the kind of vitamin D supplement that works best for you. However, the best option is to speak with your doctor first, before taking any supplementation.

In Conclusion

Further study of the connections between vitamin D and the immune system is still ongoing, and researchers aren't yet ready to tip the scale from correlation to causation. Still, the early evidence is persuasive enough to suggest that an extra cup of milk or the occasional spoonful of cod liver oil might be a health-conscious choice.

Are You Getting Enough Vitamin D?

Do You Make Sure to Get Enough Vitamin D Every Day?

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    • EGamboa profile image

      Eileen Gamboa 

      3 years ago from West Palm Beach

      I think I'll go have a glass of milk now. Great article!

    • Rock_nj profile image

      John Coviello 

      4 years ago from New Jersey

      Wow! That was a very well written and balanced piece on the benefits of Vitamin D. I really enjoyed reading this, as I am very interested in nutrition.

    • poetryman6969 profile image


      4 years ago

      I tend to think that our diet has enough D in these days. But it is good to remind oneself once in a while.

    • ChitrangadaSharan profile image

      Chitrangada Sharan 

      4 years ago from New Delhi, India

      Well done, useful and informative hub about the importance of Vitamin D. I know and have seen, how its deficiency can affect our health adversely.

      Voted up and pinned!

    • womentips profile image


      4 years ago

      Very informative.vitamin D is essential for every one.Thanks for sharing .

    • Alphadogg16 profile image

      Kevin W 

      4 years ago from Texas

      This was an informative and well written article on vitamin D healthyfitness. Many people are unaware of the issues vitamin deficiencies can create. Thumbs up on your hub.


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