Vitamin-D and Immune Function

By: Cat Ebeling, RN, MSN-PHN, co-author of the best-sellers:  The Fat Burning KitchenThe Top 101 Foods that Fight Aging & The Diabetes Fix

Vitamin D from the sun has existed for a long time as an immune booster. In the 1800’s when many people had tuberculosis, sunshine was known to have curative powers, and sick patients flocked to sanitariums in sunny places to soak up the healing sunshine. Cod liver oil, also a rich source of vitamin D, has also been around for decades as a preventative for infections, colds and flu.

Studies show that vitamin D regulates many functions in the body, including hormone balance, metabolism, blood pressure, bone density, fighting cancer, and immune function (ever notice that people tend to get colds and flu in the winter when the sun is low?).

Vitamin D is critical for our health. We know that vitamin D is essential for healing and protecting against many contagious diseases and chronic diseases. Low levels of vitamin D are associated with upper and lower respiratory infections, heart disease, asthma, cancers, diabetes, multiple sclerosis, HIV, hypertension, inflammatory bowel disease, Alzheimer’s disease and other autoimmune diseases. Vitamin D deficiency is a worldwide public health problem in both developed and developing countries.

Did you know that our bodies contain cell receptors for vitamin D in virtually every system of the body? That tells us that vitamin D is necessary for virtually all body functions. Vitamin D actually influences the expression of over 200 health-supporting genes in our bodies.

There’s a lot of buzz about vitamin D boosting immune function to fight off colds, seasonal influenza, and other viruses. Research suggests that vitamin-D deficiency may one of the primary reasons people get more colds and flu in the winter when sunshine is less available.

As many as 70 percent of Americans are considered deficient in vitamin D. The elderly, females more than males, those who live the far north or south of the equator, people with darker skin pigmentation, those who work and stay inside during the day, and people with poor dietary habits generally have the lowest levels of vitamin D.

How does vitamin D boost immune function?


The immune system is an incredibly complex protective mechanism, but to simplify, we can divide the immune system into two main categories: innate immunity, and adaptive immunity.

Innate immunity is our nonspecific defense mechanism that activates in the presence of an invading pathogen. So, even if you have never been exposed to a virus or pathogen, your body has a built-in ability to protect itself from an invader. This part of your immune system is your first line of defense against any type of new type of germs—whether it is bacteria, viruses, and fungi. And it’s super important to be sure this line of defense is strong.

The other type of immune response is your adaptive immune response. This immune response is active against pathogens that you have previously encountered. The body recognizes, adapts and attacks specific invaders much more efficiently.

In the case of brand new types of influenza strains, the body has not had a chance to develop specific antibodies against it yet. So, this is where we call in the powers of our innate immune system to protect us. Vitamin D works to strengthen this innate immune system response.

Many different studies have associated vitamin D with its power to fight infection. One report looked at almost 19,000 people and found that the individuals with the lower levels of vitamin D were more likely to report upper respiratory tract infections, than those with sufficient levels of vitamin D.

This study looked at 800 people in Finland, and found that those with the lowest levels of vitamin D lost more days at work due to respiratory infections. Other studies have focused on how vitamin D helps to prevent influenza, colds and even HIV. And this well-designed study using therapeutic doses of vitamin D showed that vitamin D administration resulted in a statistically significant (42%) decrease in the incidence of influenza infection.

Vitamin D works by boosting the strength of the immune system while lowering inflammatory reactions. This makes vitamin D a powerful immune modulator. It helps boost immune power, but prevents the immune system from overreacting, as in the case of autoimmune disease.

How does it work? Vitamin D strengthens particular cells within the immune system, such as the T cells. It also helps to decrease levels of inflammatory cytokines, a part of the immune system that can overreact with dangerous outcomes.

There are three ways to get vitamin D levels up in your system. One—you can take a vitamin D3 supplement. D3 or cholecalciferol is most easily utilized in the body, over vitamin D2. Secondly, you can get some vitamin D from foods and third, you can get vitamin D from the sun—IF you are in an area where the sun is strong enough. Depending on the latitude where you live and the time of year, you may or may not be able to get vitamin D from the sun. In my opinion, however getting vitamin D from sunshine is the best way if you can.

The sun’s rays are too weak in the winter generally (depending on the latitude that you live). Even if you can get outside in the winter, if you live north of say, Los Angeles to the west and Atlanta Georgia to the east, you won’t be able to get enough sun from November through February.


The only way for our bodies to make vitamin D from the sun is to allow the UVB rays of the sun to reach our skin. That means we need to expose enough skin for 20-40 minutes without sunscreen at the strongest times of the day, between the hours of 10am and 2pm.

UVB rays are the rays that cause sunburn, just don’t overdo it! Full-body exposure of pale skin to summer sunshine for 30 minutes without clothing or sunscreen can result in the synthesis of between 10,000 and 20,000 IU of vitamin D.

However—if you don’t supplement with vitamin D3 in the winter you’re can pretty much count on being deficient in vitamin D in the winter.

Supplementing with vitamin D has a wide range of ‘suggested’ dosages, and you can overdo it with this fat soluble vitamin and create adverse health effects. While some doctors advise people to take 5000 to 10,000 Iu per day of vitamin D, this can be too much and a safer range would be around 5,000IU vitamin D3 per day.

According to Dr. Chris Kresser, the fat-soluble vitamins A, D, and K work synergistically, so adding adequate vitamin A and K2 may protect against toxic effects of excess vitamin D. Sufficient levels of potassium and magnesium have also been suggested to protect against vitamin D toxicity.


Lastly, be sure to get plenty of healthy food with natural sources of vitamin D, such as egg yolks, wild caught salmon and mackerel, organ meats, and some mushrooms. And avoid those processed foods with added vitamin D—those do nothing for your health.

Some of the best absorbed vitamin D comes from taking some cod liver oil daily. Make sure to take only small doses of cod liver oil (enough for 50% to 100% DV of vitamin D), as large doses can give you an overdose of Vitamin A.

One more thing to point out as we near the end of winter, sunlight has far more beneficial benefits for our health than just increasing our vitamin D.

A recent 20-year study following 29,518 subjects found that those individuals avoiding sun exposure were twice as likely to die from all causes. Sunlight helps us make more endorphins, the natural chemical in our bodies that makes us feel relaxed and happy.

Sunlight promotes production of a peptide that helps to dilate the blood vessels, lowering blood pressure, and it helps create another substance called ‘Substance P’, that promotes better blood flow and regulates the immune system in response to acute stressors. And one more benefit of sunshine, it helps to reduce appetite, increase the libido and gives you a nice looking golden glow, while regulating your sleeping/waking cycle better.

If you want to stay healthy and strong, it’s not only wise, but essential to spend time outdoors in the sunshine. Soak it up!




About The Watchdog

Mike Geary has been a Certified Nutrition Specialist and Certified Personal Trainer for over 15 years now. He has been studying nutrition and exercise for almost 25 years, ever since being a young teenager. Mike is originally from Pennsylvania, but has fallen in love with mountain life and now resides in the picturesque mountains of Utah. Mike is an avid adventurist and when he’s not spending his time skiing, mountain biking, hiking, or paddleboarding on the lake, he has enjoyed skydiving, whitewater rafting, piloting an Italian fighter plane (seriously), scuba diving, heli-skiing, and traveling all around the world, enjoying learning about different cultures. At the age of 40, Mike now feels healthier, stronger, and more energetic than when he was 20... All because of a healthy lifestyle and great nutrition!

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  1. Thank You, I was just thinking about taking Vitamin D again, I heard that it is a good immune-booster to prevent against Coronavirus.

    • Vitamin D3 or D2is not vitamin D. It is a Synthetic copycat made by big pharma. Very harmful to your health. The best source of vitamin D comes from the sun and cod liver oil. When you get a chance check out the on vitamin D

      • Actually Vit D is inactive until it passes through two stages in the body, firstly the liver converts it to 25 dihydrogenase…then the kidneys to 1.25 dihydrogenase the ACTIVE form…this process if its from the sun relies on the cholesterol in the skin layer which is why older people on statins fail to make enough.Vit D3 is the best form without sunlight….and is very beneficial because the body can convert this to active form of D.
        By the way it takes three days either way for the body to make enough to boost the Vitamin d receptors in the cells so dont think you boost immunity straight after being in the sun.
        ICU doctors are now giving 25 hydrogenase version because it speeds up the activation time…which helps recovery by about two days.

      • Gert Bo Thorgersen

        You forget to mention that you need cholesterol and K2 for in the skin transforming the sunshine into the vitamin D. But still the bought vitamin D is quit as good as sunshine, which especialle research finished in 1937 showed. Where among other one of the researchers during 2 weeks daily took 3 million IU of the vitamin D

  2. Jagdish Vasantlal Jariwala

    Eat a less but healthy balanced diet. Include green vegetables, dry fruits in your daily food habits. Exercise daily for 40 to 50 min. of your choice and walking for 30 min. 10 min of sunlight morning to get Vitamin Keep your words, deeds, and mind under Divine wisdom. Be Good Do Good. Be Kind and spread kindness.


      I had malignant melanoma therefore stay out of the sun especially during the afternoon. When I’m out I do need sunscreen. I take Vit D daily 1,000 MG and have my Vit D level checked every 6 mo. Do you have any other suggestions for me?

      • Yeah, go way higher and take K1/K2 with it. But I am not a doctor. Covid is extra dangerous to Type A blood types. I am A neg. I take 30,000 IUs of D3 and a three Life Extension Super Ks.

      • You’ll probably find that you will never sunburn if you include a teaspoon of blackstrap molasses in your daily diet; but you should still get your vitamin D – unlike what happens with sunblock use. Molasses is a 50-fold concentrate of the mix of inorganic and organic constituents circulating in plant tissues for enduring daylong sun exposure.

  3. I’d like to know if any studies have been done on lack of Vitamin D absorption since our real sun has either dimmed and/or is being blocked by the NASA sun simulator (the huge white blinding set of bulbs that has replaced our real sun for many years now). I live in Florida, where it used to be sunny every day until the chemtrail and aerosol programs continued to get worse as the years have passed, since the late 90’s. Many people I know have gotten their Vitamin D levels checked and they are low, and these are people who eat healthy and are outside a lot.

    • Here in Ireland, our skies are destroyed as well. I thought, with the lockdown, and less flights over us, that clear skies would return. But they are very bad, even though most people think the weather is nice, because it is dry.

      So much has been dumped over the years on dangerous climate modification by chemtrails, that it will take our skies a long time to recover,. In turn, the natural source of Vitamin D is not guaranteed yet????

    • don’t know about the sun simulator…. and if it could be done…. what is wrong with the US energy policy…. which is acting like this technology does not exist.
      Do you use sunscreen in Florida… because sunscreen will block the benefit. All in all, oral dosing is OK and will bring up your serum Vit D level.

    • So,,if 70% Americans have low of vitamin D in their blood,but America have been devastated so much ,even being the most tremendous cases in the world in the pandemic.Can anyone explain me about this relationship ……

    • I am told, that for vitamin D, D3, or many other vitamins to get fully absorbed, you need to have adequate levels of magnesium. In many places in the country where our foods are grown, and produced, the soil lacks adequate magnesium.

  4. How can I print these articles without all the extra graphics/pictures etc. I only want the information.


  5. Thank you

  6. i was Suspicious that, perhaps, the Reason African Americans were dying at greater rates of Covid 19
    was Vitamin D deficiency and the underlying inflammation that comes with it. This only
    Strengthens that belief.

    Everyone, but especially persons of darker skin, should insure they get enough
    Vitamin D as a minimum precaution for General Health and this Pandemic.
    Google Vitamin D Foods and get a Quality Supplement asap imho.
    To Stay Safe be proactive.


    • Vitamin D created in the body by the skin’s exposure to sunlight, requires that the sun, penetrate to the layers in the skin where the synthesis occurs. For people with lighter skin color, the sun’s rays penetrates more readily. For people with darker skin, which acts to protect them from skin damage due to over exposure to sunlight, it takes a lot longer for the sunlight to penetrate the skin and reach the layers where vitamin D3 is created. In other words, people of color need to spend more time in the sun in order for them to gain the same benefits from sunlight, as people with lighter color skin. If people lack adequate magnesium in their bodies, vitamin D3 will not synthesize as well and damage from sunlight becomes easier, leading to skin damage and cancer.

  7. Here in Ireland, our skies are destroyed as well. I thought, with the lockdown, and less flights over us, that clear skies would return. But they are very bad, even though most people think the weather is nice, because it is dry.

    So much has been dumped over the years on dangerous climate modification by chemtrails, that it will take our skies a long time to recover,. In turn, the natural source of Vitamin D is not guaranteed yet????

  8. I would like to add that the use and strength of sunblocks are one of the main reasons we are becoming more deficient in Vit D even in summer. Decades ago SPF’s were 10-15 at most now they are 50-100 and more. So in summer we are getting much less Vit D from the sun. A little sun without sunblock is good but we have to still be concerned about skin cancer. The second reason is the use of statins in my opinion overuse unless you have had a cardiac event in the past. Statins reduce cholesterol but cholesterol is needed to synthesize Vit D so we get less if on statins. Third is the lack of probiotics and the overuse of antibiotics which causes dysbiosis or altered bowel flora. Proper gut flora is also needed for Vitamin D to work better and for mood plus enhancing the immune system.

  9. I’ve been taking vitamin D for several yrs now, n on March 20 a wk after my bday I had the covid19 virus
    That was a terrible sickness, I’ve never had the flu n very seldom have a cold I guess my partying hardy that we for my bday n everyone else’s bday party that wk i had to catch something huh. Well the virus only lasted a few days by me qurantining myself medicating my self. By the following wknd I felt so good I felt like I can conquer the whole world. I’m feeling so great. Thx the Lord n me. I tell all my family n friends to take vitamin D.

  10. Hello, you mentioned Purathrive as a source for D3 and K2. I am reading that these two should be taken separately so there’s no competition between them getting in your body to work as you need them. I have since changed my brand to the ones made by Calton Nutrition. I always wondered why my D levels stayed low or borderline, perhaps taking that combo product is why.

  11. I take vitamin-D3 2000 IU daily. I originally come from Hawaii, miss the sun especially during winter here in the continental USA. I have Hemochromatosis and sometimes some of the foods suggested for health does not work for me. I do my own yard work and staining for my fence, sun deck and front porch which gives me lots of time
    in the sun….the vitamin D capsule comes in handy when I am not outdoors…..I’m 84 yrs young and enjoying my days in the sun. Just thought I’d brag a bit :).

  12. I wonder how many people who died during Covid would have adequate levels of Vitamin D Looking back at a time where a relative was diagnosed with cancer, who was regularly attending the doctor, never checked for D levels but finished up a level of 6, if D could help ward off the virus of flu why are they not recommending this instead of a flue injection.
    I have resisted the offer of flu jabs & instead take 4,000 iu per day for the winter /Spring months, I have never got a flue in 10 plus years and that is from a so called cocooner over 77.

    • The last time I got a flu shot I got the flu and said NEVER again! We don’t know what big pharma is putting in these vaccines and I don’t trust them! There is evidence that the MMR vaccine can cause autism and they’ve tried to discredit those studies. And now they’re all scrambling to introduce a Covid vaccine? No thank you!!!

    • The new covid-19 shots are a mRNA and change your natural DNA into a synthetic DNA factory, don’t take the shot ! There is NO turning back once you get it.

  13. can I get this in Australia

  14. We need more than 10 minutes of sun a day here in Minnesota. 10 minutes is nowhere near enough and not early morning, more mid-afternoon

  15. Mme sante Robin Zamor

    I have been taking Vit D for while due to dream that God had given me 4 yrs ago. I said thank you God even do I’m in Florida.

  16. My question is this:why am I not able to share and post this vital information to face book?
    Thank you in advnace.

  17. I filled the required fields marked * with my correct information and the comment was not published

  18. FOR SYLVIA.MEADOWS question of “why Facebook will not post this vital information”

    Because they censor any information that can really cure and prevent the current covid 19 virus like Vitamin D and C…
    Visit orthomolecular(dot)org to investigate Vit C and also D, and do a search for “Vitamin D Dr. Mercola” to see scientific articles on the topic… Curing is bad business for the Mainstream Pharma and Medical conglomerate.

  19. FOR SYLVIA.MEADOWS question of “why Facebook will not post this vital information”

    Because they censor any information that can really cure and prevent the current covid 19 virus like Vitamin D and C…
    Visit orthomolecular(dot)org to investigate Vit C and also D, and do a search for “Vitamin D Dr. Mercola” to see scientific articles on the topic… Curing is bad business for the Mainstream Pharma and Medical conglomerate.

  20. A few years ago I saw a doctor on Dr Oz say to always take Vitamin D while eating something with fat in it. A blood test showed my levels were very low. I had wasted my time and money previously taking it first thing in the morning. From then on I made sure I always took them with food + fat. Never had any trouble since.

  21. 30000iu per week

  22. Jeremy Harrison-Roberts

    Thank you for another informative article.

    I have been taking vitamin D3 for many years & have my blood serum checked every 6 months.

    Despite taking 15,000 IU’s daily I struggle to achieve greater than 140 nmols. Any thoughts?

    • The limits for vitamin D in New Zealand is 50 to 150 nmols/L so by simple mathematics that would be 90% of the range.

    • My ex took 400 IU V of storebought Vitamin D of by itself to try and reverse statin damage. It had no effect on her. The body needs magnesium to process Vitamin D. I supplement 500 mg of time released Mg daily. To activate magnesium, the body requires zinc and vitamin B6. To achieve that, I supplement a trace minerals complex and the methylated folate, B12 and B6. It seems like a lot, but nutrition is cross dependant. The D I take is Bulletproof which also brings A and K2. You try that and I’ll bet that 15k IU will have you amped up. Me personally, I take 1 Bulletproof 3 times a week with a fatty meal. If I take 5K IU every day, I’m so amped I have trouble with anxiety and insomnia. That’s why I do it every other day. Hope this helps!

  23. Gregory Martin Wodark

    Very good article! I have one small criticism, though ( and a comment). According to an article I just read at: ( Life Extension Foundation), thé ration of vitamin D to vitamin A in cod liver oil, has drastically changed! It used to provide a predominance if vitamin D, and a small amount of vitamin A. Now, the proportion is reversed! They also said vitamin A competes for function with vitamin D. Therefore, a large amount if vitamin A will render inactive vitamin D. So, I would not take cod liver oil! Second, astaxanthin, ECGC, and a product Life Extension offers called “ Sun Shade Factor”,( which has 3 different supplements that all limit sun damage). I can attest that astaxanthin keeps me from getting sunburned for more than an hour. Two hours with higher doses and possible synergy with other polyphenols.

  24. It seemes to me Vitamin D is so important in our body in such a way to be aware try to consume every day at 4000 IU at least. Thanks so much for your information it is going to be so useful for my family

  25. I take vitamin 1000 mg of D daily should i be taking more i get some also from my diet i eat healthy?

  26. Gert Bo Thorgersen

    I now own around 800 health and doctor books as a result of the doctors here in Chiang Mai knows too litle, as they only have learned what the drug producers wants them to know. Concerning the vitamin D, to me it was excellent to read the book by Robert R. Barefoot: “Barefoot on Vitamin D, “The Cancer Inhibitor””. In which, among other, it was intersting to read newspapers titles starting way back nearly 80 years ago. One of these, from 1937, told about a 5 year research, in which dogs died by getting up to equal, if counted in personal weights, equal as if a 160 pound man daily got 14 million IU of vitamin. But one of the researchers during 2 week daily took 3 million IU, and no problem. And the nearly 800 research persons who got much much of D, not as much as 3 millions IU, they turned in increasing their health. A a result of this the FDA and the drug producers, wrote about dogs died by the viamin D, and warned against viamin D, telling it to be toxic if more than 400 IU/day, but at the same time started to produce and selling health drugs containing 50.000 IU of the D, and this became a success as people got healthy. Through out history it has been known how important sunshine/vitamin D is.


  27. I have just read all about your Vitamin D3 Tablet and would love to try it

    Is the USA the only country that can apply for this Vitamin D 3 Tablet

    I live in New Zealand

  28. D3 is cholecalciferol which is one of the main ingredients in Merck’s rodenticide. Not sure why anyone would think rat poison is healthy. Use the sun to get true vitamin D. Use DMiner to monitor it on your phone.

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