Over the last year, so much focus has been placed on not getting sick and staying healthy.  We all know that eating well, getting enough sleep, and washing our hands are some of the keys to keeping ourselves healthy.  Part of the reason these elements work is because they affect our immune system.  There are so many factors that go into keeping our immune system functioning properly.  One factor that many may not know about, is maintaining adequate levels of vitamin D.  Vitamin D is most known for helping with bone health but like most nutrients, it has so many other roles.

First, let’s take a quick look at how the immune system works.  Our immune system is divided into two different parts.  The first part of the immune system is innate immunity, also called nonspecific immunity.  You are born with the innate immune system.  This system includes our natural barriers like our skin, mucus in our airways, the cough reflex, tears, and stomach acid. The innate immune system also includes certain types of white blood cells called neutrophils, macrophages, and natural killer cells, along with chemicals produced by our bodies called complement.  All these components are just waiting for pathogens, or germs, to try and enter the body to cause harm. Once these intruders enter, the innate immune system springs into action and tries to kill them.  The second part of the immune system is adaptive immunity, also called acquired immunity.  This system develops over time and responds to specific pathogens.  Adaptive immunity involves a type of white blood cell called lymphocytes.  It is these cells that produce antibodies to help fight infections.  Lymphocytes develop memory, so that if the body ever encounters the same germ it can quickly respond to prevent infection.  This is the idea behind vaccines!  Vaccines act like a “germ” to make your immune system develop a memory of what the germ looks like.1  

So, how does vitamin D fit into all of this?  Vitamin D is involved in both the innate and adaptive immune systems.  The functions of vitamin D in the immune system are:

Lack of vitamin D has been linked to autoimmune diseases like rheumatoid arthritis, psoriasis, multiple sclerosis, irritable bowel syndrome, and type-1 diabetes.  Our immune system walks a fine line between causing enough inflammation to protect us from infections and allowing inflammation to get out of control.  When the inflammation gets out of control, damage and autoimmune diseases can occur.  As stated above, vitamin D helps control the inflammation caused by our immune system.  Maintaining adequate levels of vitamin D can also help with controlling these autoimmune diseases and vitamin D supplements are often used as part of a treatment plan.  While data is limited, maintaining appropriate levels of vitamin D is a good idea for everyone since it plays a role in so many aspects of the body functioning properly.2,3

Studies have shown that maintaining adequate vitamin D levels can also help fight off respiratory infections.  One study showed that those who took vitamin D supplements were about 40% less likely to get the flu than those who did not take vitamin D.  There has also been some evidence that adequate vitamin D levels can help with COVID-19 infections, as well.  While taking vitamin D is not a fool proof method to prevent getting sick, it can certainly help keep your immune system in top shape to fight off infections.  Remember, your body is all about balance and it needs the correct building blocks to perform at its best.4

Now that we know how important vitamin D is to our body, how do we make sure we are getting enough?  One source of vitamin D is sunlight.  Vitamin D is formed in your skin when exposed to the sun.  Unfortunately, the amount of vitamin D absorbed from the skin is variable and excessive sun exposure can increase your risk of skin cancer. We can’t rely only on sunlight to get the amount of vitamin D we need.  Vitamin D is also naturally found in some foods.  These foods include salmon, swordfish, tuna, cod liver oil, sardines, and beef liver.  Many foods, like milk, cereals, and orange juice are fortified with extra vitamin D.  It is hard to get adequate amounts of vitamin D from food alone.  Thankfully, vitamin D supplements are very common and easy to find in any pharmacy or grocery store.  When looking at vitamin D supplements, you will notice that the amount is listed in “IU” or international units. The recommended amount of vitamin D you need daily depends on your age.  For adults aged 19 to 70 years old, it is recommended that you get 600 IU daily. If you are over 70 years old, then it is recommended you get 800 IU daily.  The maximum amount anyone should consume daily is 4,000 units.  One easy way to get enough vitamin D is to take a daily multivitamin.  By taking a multivitamin you are also ensuring that you are getting other needed vitamins and minerals as well!  You can also take supplements that contain only vitamin D or vitamin D and calcium.  Many people take these when they need extra support for bone health.  It is important to talk with your provider about any supplement you take, just to make sure nothing interacts with the medications you are taking.  Also, your doctor may want to check your vitamin D level and if your levels are really low, they may recommend a higher dose to get your levels back up to normal.5  

At the end of the day, the most important thing to remember is that your body is an amazing and complex system that needs the proper building blocks to perform at its best.  So, now go out and get yourself a good multivitamin and help your body do what it was made to do!


  1. Immune response: MedlinePlus Medical Encyclopedia [Internet]. 2021 Feb 26 [cited 2021 Mar 21]. Available from: https://medlineplus.gov/ency/article/000821.htm
  2. Aranow C. Vitamin D and the Immune System. J Investig Med. [Internet] 2001 Aug [cited 2021 Mar 21]; 59(6): 881–886.  Available from:  https://jim.bmj.com/content/59/6/881.long
  3. Charoenngam N, Holick M. Immunologic Effects of Vitamin D on Human Health and Disease. Nutrients. 2020 Jul 15;12(7):2097. 
  4. Siska, Gunda. Vitamin D Helps the Immune System During Cold and Flu Season: The Pharmacy Times [Internet]. 2019 Sep 20 [cited 2021 Mar 21]. Available from: https://www.pharmacytimes.com/view/vitamin-d-helps-the-immune-system-during-cold-and-flu-season
  5. Vitamin D: The Nutrition Source [Internet] 2021 [cited 2021 Mar 21].  Available from: https://www.hsph.harvard.edu/nutritionsource/vitamin-d/.
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