Does Vitamin D help with Immunity? 

By  Dr. Mike Hansen

Does Vitamin D help with Immunity – I’m going to address some frequently asked questions that have to do with the common cold, flu, and COVID.

Specifically, I will talk about how these viruses are affected by cold vs. warm weather and humidity levels. I’m also going to talk about vitamin C and vitamin D as possibilities for preventing these viral respiratory illnesses. So let’s go ahead and get started.

Does colder temperature make you more prone to getting a cold? Or Flu? Or COVID?

Most health experts agree that when it’s cold, people spend more time indoors and close contact with other people, which likely increases the spread of germs.

Also, experts believe that our immune system may be more active when our body is warmer, as in during the summer months.

And there are studies out there that have looked at how certain viruses are more likely to spread in people based on temperature and humidity level.

Back in 2007, there was this study…

In this particular study looking at the spread of the influenza virus, they put guinea pigs together in a chamber and carried out different environmental experiments on them. They found that low relative humidities of 20%–35% were most favorable for infection, while the transmission was completely blocked at high humidity of 80%.

They also found that when guinea pigs were kept at 5 °C, transmission occurred with greater frequency than at 20 °C, while at 30 °C, no transmission was detected.

The authors concluded that low relative humidities produced by indoor heating and cold temperatures favored the spread of the influenza virus.

I also want to add that cold weather, by itself, can cause a runny nose without necessarily having a cold, and this allows for the virus to be carried in those secretions, which probably facilitates transmission.

Rhinoviruses cause forty percent of common colds. The covid’s second most common cause of cold is the normal one, not this novel covid, aka SARS-CoV-2.

Its been shown that the rhinovirus reproduces more quickly at cooler temperatures means you might catch a cold more quickly if you’re chilly.

And this probably applies to the covid as well.

Does Vitamin D help with Immunity

It’s likely that with the combination of all of these 5 factors, meaning cooler temp, lower humidity, people staying indoors more often in winter months, cold weather causing runny noses, and our immune system being more active when it’s warmer, these combinations of factors likely explain why colds, flu, and COVID are more likely to cause infections in the winter months.

But there is likely a 6thfactor as well. And that is vitamin D.

Our bodies don’t normally make vitamin D unless we get sunlight. In the winter months, for most of us in this world, we don’t get enough sunlight to make enough vitamin D. Unless you live in a warm climate, then maybe you are the exception. So if you aren’t getting enough sunlight in the winter months, that means you have to get enough vitamin D in your diet. And if you don’t do that, you will have low vitamin D levels.

Vitamin D helps regulate or Calcium levels and is essential for bone and muscle health. It also plays a role in regulating our immune system, but its exact role is not known.

Why is this important when it comes to the common cold, flu, and perhaps with this novel coronavirus that’s causing COVID?

Well, vitamin D doesn’t affect these viruses themselves. Instead, it affects our immune systems.

Back in 2017, there was a large study in BMJ….

And it was a meta-analysis, meaning…it looks at a bunch of other studies, combines all the data from each of those studies, and analyzes and interprets these numbers in one HUGE study.

This meta-analysis specifically looked at over 25 randomized control trials, with a total of over 11,000 people who took vitamin D.

This meta-analysis showed a significant association between low vitamin D levels and more prone to developing respiratory infections.

It also showed that daily or weekly supplementation with Vitamin D had the most significant benefit for those with vitamin D deficiency. The ones who benefited the most were those with more severe vitamin D deficiency (specifically blood levels below 10 mg/ml), which decreased their risk of respiratory infection by 50%.

It also showed that all participants experienced some beneficial effects from regular vitamin D supplementation.

It also showed that taking occasional high doses of vitamin D did not produce significant benefits.

And these results were statistically significant, with a large n of over 11,000.

So what is my recommendation for taking Vitamin D?

The best thing to do is check with your doctor to see if you might have low vitamin D, and if it is down, you’ll def need to get more vitamin D, especially during the winter months.

Maybe this is done by getting more in your diet(show mild b-roll/footage)

Perhaps this is done by taking a vitamin d supplement.

Exactly how much you take should be a discussion between you and your doctor. Generally speaking, every day would be adequate to take 800 IU, roughly equivalent to 20 mcg.

Another option is to take 1000 IU every day or every other day. 1000 IU is equivalent to 25 mcg.

But again, that’s a generalization; you may need more, you may need less or none at all.

If you are getting your vitamin D levels measured, you want to aim for a level of between 20 to 30 ng/ml and do not exceed 39 ng/ml.

We also know that too much vitamin D can be a bad thing. Vitamin D is one of four fat-soluble vitamins, and that means that the body stores the vitamin more readily in the body than non-fat soluble vitamins. And this is significant because keeping it in the body means more potential for it to have toxic effects. So too much is not good. 

With Vitamin D, as well as other supplements, some brands are more trustworthy than others.

My go-to source to find trustworthy vitamins, supplements, and such is, an independent lab that tests various products. I have no association with them, no financial relationship with them.

Nature made. This is one of the recommended ones by consumer lab, and if you want to purchase it on amazon, I will provide a link below.

A close up of a bottle

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Vitamin C

Vitamin C is a water-soluble vitamin vital to the function of white blood cells that helps fight infections and overall immune system health. Vitamin C is also essential for iron absorption, and being deficient in iron can make you more vulnerable to infections in general.

The normal, recommended daily intake of vitamin C for adults from the diet and supplements is 75 to 120 mg. You can get about 80 to 90 mg from a cup of orange juice or sliced orange, or even more from kiwi fruit or a cup of sweet peppers.

It’s common folklore that taking vitamin C helps treat cold symptoms. But for the most part, that folklore doesn’t hold up to scientific study. In 2005, researchers analyzed 55 published studies that looked at vitamin C’s ability to fight symptoms of the common cold, and the findings were pretty underwhelming. Most of the studies found no benefit to taking vitamin C to treat a cold, though one prominent study found that people taking a massive dose (8,000 mg) at the start of a cold got better faster. Subsequent analyses were not able to confirm this, though. As of now, there’s not enough research to recommend that people take vitamin C—either before or after they get a cold.

So once again, the evidence taking vitamin C supplements, even at high doses, can protect people from infection from covid. This strategy is being promoted on various websites and in videos on social media. High doses of vitamin C, given intravenously, are currently being tested in COVID patients in China who have developed pneumonia. So those results are pending.

Taking in more vitamin C than you need can lead to side effects.

This includes stomach irritability and diarrhea. High doses of vitamin C over the long term increase the risk of kidney stones and possibly cataracts.

So until there are further studies that definitively show that vitamin C supplementation is beneficial in preventing and treating respiratory illnesses, such as the common cold, flu, and now COVID, I do not recommend taking extra vitamin C unless you are vitamin C deficient. Its highly unlikely that you are vitamin C deficient if you eat food daily.


Zinc has become one of the most popular suggestions for reducing symptoms of covid.

There have been conflicting results about the effect of zinc on the severity and duration of cold symptoms.

Some studies showed that zinc reduces the duration of a cold by half, while others showed no effect. Another study found that the type of zinc taken determined the result—zinc gluconate lozenges that provided 13.3 milligrams (mg) of zinc lessened the duration of colds, but zinc acetate lozenges that provided 5 mg or 11.5 mg of zinc did not.

Zinc has also been shown in a laboratory study to inhibit the replication of covid in cells:

A screenshot of a social media post

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There is no evidence suggesting that zinc lozenges can prevent or treat COVID, and additional research is needed to determine whether zinc affects colds.

Also, keep in mind that excessive zinc ingestion can lead to copper deficiency and impair antibiotics absorption. The use of zinc nasal gels or swabs has been linked to temporary or permanent loss of smell.


Traditionally, echinacea has been used to treat cold symptoms.

Multiple studies have suggested that taking it when cold symptoms first begin reduces the length and severity of symptoms. However, these studies were of low quality. Higher-quality studies have found no benefit to taking echinacea as a treatment for the common cold.

A final word regarding Herbs and supplements

It isn’t easy to talk about most herbs and supplements with scientific authority because most have not been well studied for effectiveness, side effects, and appropriate doses. Also, the FDA does not strictly regulate how herbs and supplements are manufactured. Therefore, there is a bigger unknown in strength, purity, and safety compared to OTC and prescribed medications.

It’s best to talk to your doctor before you start taking any supplements. May interact with medications and each other, and some are not recommended for people with certain health conditions. Most supplements should be avoided by women who are pregnant or breastfeeding. Most also haven’t been tested for safety in children and therefore should not be given to them.

Doctor Mike Hansen, MD
Internal Medicine | Pulmonary Disease | Critical Care Medicine

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