Vitamin D: Defense Against the Flu Bug

Vitamin D Natural Defense Against the Flu

School is back in session, Monday night football has started and signs of fall are popping up everywhere (I’m not talking about the Halloween display at Costco – that’s been up since July 5th). You know what this all means don’t you? It’s the start of the cold and flu season. I can’t even pull into our local conventional grocery store without being bombarded with 15 signs for the flu shot, not that their marketing techniques have ever worked on me. I’ll save the flu shot debate for another post, because today’s blog post is about how to support your immune system and prevent the sick bugs from biting you in the butt by simply optimizing your vitamin D levels.

Did You Know

Knowing your vitamin D status and supplementing appropriately is a low-risk nutritional choice you can make that can support your immune system. A strong and robust immune system is more likely to fight off an invader than succumb to it.

Vitamin D triggers the body to make its own antibiotics called antimicrobial peptides which have been shown to inactivate the flu virus.

Seasons and the Flu

R. Edgar Hope-Simpson, a British family practice doctor, was the first to propose the idea that the yearly flu outbreak was related to the seasons of the year. He showed that flu outbreaks peaked during the two months surrounding the winter solstice. During the summer months in both hemispheres, influenza is virtually nonexistent. Aside from the flu, the common cold, which is actually a variety of more than 200 different viruses, also has a peak during the winter months.

Though people may be less likely to spend leisure time outdoors during the colder months, it’s unlikely the higher rates of sickness are caused by being around others more. Instead, it’s more likely the lower exposure to sunlight causes a physiological change in the body. The temperatures become cooler as certain hemispheres get less direct sunlight. This causes people to spend more time indoors, and even when they’re outside they do not get UVB light necessary for vitamin D, like they do during summer months. This has led researchers to look at vitamin D levels as a likely contributor to immune function.

The Sun

Vitamin D is produced when our naked skin (yes, without sunscreen), is exposed to sunlight. Many people correlate sun exposure to vitamin D, however, what most don’t realize is that for the body to produce sufficient amounts, the sun exposure needs to be at specific times of the day with the majority of the skin fully exposed. Where you live relative to the equator, the color of your skin and the amount of skin exposed, all affect how much vitamin D your body will produce. Sitting in front of a window with the sun shine peering in will do little to improve your vitamin D status. Taking an outdoor walk over lunch, while may be exhilarating, also will do little for your vitamin D status, unless of course you walk nearly nude.

Deficiency | Vitamin D Natural Defense Against the Flu

Vitamin D deficiency is more common than previously thought. The Centers for Disease Control reports that the percentage of adults achieving vitamin D sufficiency as defined by 25(OH)D of at least 30 ng/mL is approximately 30% in whites and about 5-10% in African Americans. Even when using a conservative definition of vitamin D deficiency, many patients encountered in clinical settings are found to be deficient in vitamin D.

Measurements and Ranges

When it comes to blood levels of vitamin D, it is easily measured and is becoming more common place, even among conventionally trained doctors. There is quite a range, from clinical deficiency to the levels required for optimal health. Blood vitamin D levels above 10 ng/mL may help one avoid rickets, but it takes more than 20 ng/mL to suppress parathormone levels. Levels of more than 30 ng/mL are necessary to increase calcium absorption and levels greater than 50 ng/mL have been shown to improve physical performance.

The authority on vitamin D status, the Vitamin D Council, suggests an optimal range of 40-80 ng/mL.

As is common in Western versus holistic medicine, there is an inconsistency of opinion on what is ideal when it comes to blood levels of vitamin D. It is important to remember that when it comes to lab values sufficient and optimal are two different things.


The amount of vitamin D one can safely take is going to vary from person to person. There is no standard recommended amount and before supplementing it is important to get your levels measured first. The blood test you need is called a 25(OH)D blood test.

When it comes to supplementation, The Vitamin D Council recommends taking vitamin D3 rather than vitamin D2. Vitamin D3 is the type of vitamin D your body produces in response to sun exposure, while vitamin D2 is not. Many people assume that adequate vitamin D intake can be obtained via diet alone. This assumption is erroneous. The vitamin D content of most foods, including fortified dairy products, is relatively low to nonexistent.

I personally take 5000 IU daily of supplemental vitamin D and get my levels checked twice a year. I feel my best with my levels in the mid-70 ng/mL range, have never opted for the flu shot and have not gotten bit by the flu bug for as long as I can remember.

If you are looking for a high-quality vitamin D supplement, there are two I recommend, this one (liquid) and this one (pill).

For more information on how to optimize your immune system (hint: gut health is really important too) before the flu season strikes read: Set Your Immune System Up For Success.

The fact of the matter is that if your immune system is operating optimally, your chances of contracting a cold or flu-like illness or influenza are very slim. Vitamin D is an important player in overall healthy immune function, but it’s also an effective antimicrobial agent in its own right, producing 200 to 300 different antimicrobial peptides in your body that kill bacteria, viruses and fungi. So optimizing your vitamin D levels will help combat viruses in more ways than one. ~Dr. Mercola Source: Things to Consider Before Getting the Flu Vaccine

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  1. says

    I don’t understand the correlation between immune system and vitamin D, unless there are more than one immune system in the body.

    My Vitamin D levels (checked earlier this year) were 96 nd/dL — above the range. My doctor told me not to supplement AS MUCH as I had been doing. so I toned it down a bit.

    Also, I had been taking Vitamin D3 for years without my numbers being out of the mid-30 range (low) for years. And they didn’t budge until I started taking Vitamin K2. So it is necessary to take vitamin K2 (using it as a catalyst to boost your body’s absorption of D3).

    But my main concern is that my immune system is very low — you could say I am immunosupressed. In the secretory IgA immune system test (I took it in March and again in September) my scores were so low. The range for a normal functioning immune system is 25-60. My first test result was a 6! Yes, a mere 6! And then 6 months later, after focusing on my gut, my immune system, etc. it checked out at a 7. HOLY COW.

    So… my doctor discussed a few options for me, but I just want to tell you that he did say that the Vitamin D in my body helped fight off bacteria and viral infections AFTER I got them. So while my high levels of D won’t prevent me from getting a cold, it will help me battle it so that it lasts only a day or two.

    So I cannot say now that it is a “Flu Preventer” as it doesn’t prevent illness… it only makes your body able to fight the illness quicker and easier.

    Thoughts on this? I would love to hear your perspective. I truly believe vitamin D is super important, but I don’t know how well it works to “boost your immune system to prevent illness”… I think it works well to fight the invaders after they have invaded.

  2. Carol says

    I used to have horrible Athsma my whole life, was on cortisteroids and other meds that weren’t working. The docs wanted me to get on even stronger meds when I found out that long term use of ventolin wreaks your heart. I found an article on vit d deficiency and asthma, got my levels checked and my doc said I was “a little low”.but no reason to supplement. I started taking 3 to 4ooo iu’s a day anyway and totally cured my asthma. It’s been almost a year and I have been off meds completely since the first week. So upsetting that not one doctor ever told me to get on supplements.

  3. says

    After learning more about flu shots I have chosen not to get them for me and my kids this year. This makes me very nervous as I have heard the flu is really bad this year and that lots of healthy people will be getting it.

    After reading your post and a few others I am planning to get our vitamin D levels checked this next week. My question is, where can I research the optimum D levels for children. I have a six and nine year old and wonder what their healthy range should be. Thanks for any resources you can provide!

  4. VitD says

    Another thing to anyone who is experiencing seasonal depression: get your vitamin D level checked! One person I know got an urgent call from the doctor, who found “dangerously low” levels of vitamin D.

    There are many studies under way regarding vitamin D deficiency in arctic communities. Many of these studies deal with infant vitamin D deficiency and bone/teeth development.

    Still waiting for that definitive piece of research regarding vitamin D and its role in multiple sclerosis.

    I’m sure insufficient vitamin D levels plays a role in the development of many conditions and diseases. We’re just beginning to learn the long-term consequences to health.


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