Vitamin D

If you follow nutrition news or run in health and fitness circles a lot, you’ve likely noticed an uptick in lavish health claims about vitamin D lately.  There are growing rumors that taking vitamin D supplements can protect you against… well, everything — the common cold, infections, autoimmune disorders, heart disease, depression, and cancer.  You’ve likely even heard it floating around that vitamin D can help you live longer.

If you’ve got a pretty good scam-radar, these seemingly out-of-the-blue magic-bullet claims about vitamin D almost certainly send up red flags.  It seems pretty unlikely that after knowing about vitamin D for a century, all at once it can suddenly cure all kinds of stuff.  It’s not like vitamin D just picked up one disease more than rickets — people are talking about half a dozen serious diseases basically overnight.  That’s odd.

Then, add into the equation that there is a serious vitamin D supplement industry looking to make big bucks if people think vitamin D is the holy grail of health and, boy, do you have an excellent reason to be skeptical.  

Skeptical, but not closed-minded.

Maybe all of it’s nonsense hyped up by the supplement industry.  Maybe only some of it is.  Or, maybe, it’s all true.

There is only one way to find out.  Research, here we come!

Disclosure – This post contains affiliate links.  Click here for details.

The Vitamin of the Day

Before you can decide how seriously to take these vitamin D health claims, the first thing you have to do is figure out: where are they coming from?

Well, a good portion of it looks like it’s coming from the mainstream media.  Recently, there has been a huge uptick in the number of stories about the health benefits of vitamin D supplements popping up on reputable media sites.  They’re on Forbes, the US News, Time, BBC, ABC, Reuters, the Independent, the Australian Associated Press and the Guardian.  Basically anywhere news site you go to, they’ve covered vitamin D in the last couple of years.

Hm. Well, those are much better sources than some random Facebook post or a vitamin D supplement blog!  If one of those had been the driving force behind these rumors, you could have dismissed them out-of-hand.  This large number of reputable news articles on the subject starting these rumors, though, that at least warrants some further investigation.

Alright, so what’s behind this sudden swell in media coverage?  Are these opinion pieces written by people who think the general public is suddenly really interested in vitamin D?

Nope.  The news is covering vitamin D more because there really is, all of the sudden, more there to cover.

Figure 1: Scientific Studies on Vitamin D Published on Pubmed (1972-Today)  

Check out the graph on this page.  It shows the number of scientific studies about vitamin D added to PubMed (one of the largest scientific databases in the world) each year.  See that jump between around 2000 and today?  That corresponds awfully closely to the spike in media coverage and public interest in the health benefits of vitamin D.  The news organizations are just reporting on the science as it’s being discovered.

Wait a second?  Does that mean all the health claims are true and we’re done here?  If only it were so simple.

While the news media has been reporting on breaking scientific research, the cutting edge of any scientific field is fraught with pitfalls, false hopes, missteps, backtracks and giant leaps forward.  Just because one or two new scientific studies show a phenomenon worth writing a news article on, doesn’t mean that phenomenon will necessarily hold up to scientific scrutiny going forward.

We’re going to have to go to the scientific literature and see how strong the evidence for each of these claims really is.

Vitamin D and Cancer

The idea that vitamin D might protect against cancer comes from studies like this that show that people who live in places where they get more sunlight (i.e. are able to make more vitamin D) are less likely to get cancer.  These findings are backed up studies looking at people’s blood — higher levels of vitamin D in the blood is linked to a decreased risk of cancer.

Wait. How is that even possible?

Doesn’t vitamin D help keep your bones healthy?  What could healthy bones have to do with a decreased cancer risk?

Well, it turns out vitamin D doesn’t only have effects on bone health.  See, vitamin D works to keep your bones healthy by helping your body keep proper levels of calcium, which it needs to make bone.  Vitamin D does this by changing how genes are expressed in your intestine and the pituitary gland in your brain.


Researchers now know that vitamin D has the ability to change how genes are expressed in many different cells in your body, not just the intestine and brain.  This allows it, at least theoretically, to influence diseases not related to bone health, such as cancer.

Evidence for a Role of Vitamin D in Cancer Prevention

Is there any evidence that vitamin D could positively affect gene expression in cells that could have something to do with cancer?

Yes.  Vitamin D has been shown to be able to keep cancer cells from using genes it needs to keep growing, causing cancer cells to turn on genes that can cause them to undergo apoptosis (i.e. commit cellular suicide), and help your immune system turn on genes that it needs to prevent cancer growth.

This is really good evidence to suspect vitamin D could help protect against, or maybe even help treat, cancer.  You don’t really know, though, until it’s tested on real people.  To test this, scientists just have to give some people vitamin D supplements and some people fake vitamin D supplements.  Then, they have to see if the ones taking vitamin D develop less cancer, or survive better if they have cancer.

A few of these types of studies have been done, and, unfortunately, so far the results aren’t conclusive.  One of the latest review articles (which draws together all the research to date into one paper) concludes there is not yet enough evidence to say for sure if vitamin D really does protect against cancer or not.  There are a couple of huge studies underway with thousands of people, though, which may provide a definitive answer in the near future.

Vitamin D and Infections

Much as with cancer, the core evidence suggesting vitamin D can help protect against infections like the common cold, blood infections, hepatitis C, tuberculosis and other lung infections come from big population studies.  Researchers have found that those with lower blood levels of vitamin D are more likely to get infections and more likely to have more severe infections.

This observation makes sense, too.  After all, we just talked about how vitamin D helps boost the ability of your immune system to work properly.  It would be logical for this to lead to your body being better able to fight off infections.

Alright, what happened when researchers tested whether adding vitamin D supplements could help protect against infections in groups of people?  The same as with cancer: they couldn’t tell if it really helped or not.  Drat.

Vitamin D and Autoimmune Diseases

If vitamin D is so good at boosting immune function, maybe it can help with autoimmune diseases?  There is some good evidence to think it might.

As with cancer and infections, those with lower vitamin D levels in their blood have been found to have a higher risk of developing autoimmune diseases, such as rheumatoid arthritis (RA) and multiple sclerosis (MS).  What’s more, studies also show that the lower the level, the worse the person’s symptoms are, for both MS and RA.

Add to this the fact that researchers could also show that vitamin D can specifically help turn off the immune cells that drive most autoimmune diseases, Th17 cells, and you’ve got a pretty strong case.

What happened when vitamin D was put to the test with RA and MS?  For multiple sclerosis, the results are tentatively positive, but researchers aren’t willing to give it the full thumb’s up just yet.  For rheumatoid arthritis, it appears the studies haven’t been done, but they are surely in the pipes.

Related: Good Gut Health: The Secret to Preventing Autoimmune Disease?

Vitamin D and Depression

Population studies suggest there could be a link between low vitamin D levels and depression as well.  Large meta-analyses (studies where the data from multiple other studies are mathematically analyzed together), like this one and this one, have found a small, but significant, increase in the risk of depression when people have lower levels of vitamin D in their blood. 

Is there any reason to think that vitamin D is able to change brain function and help protect against depression?  Yes.  Researchers hypothesize vitamin D’s ability to help nerve cells in the brain produce calcium channels (by changing gene expression) keeps calcium from building up in the nerves.  Too much calcium in certain nerves in the brain is believed to cause depression.

Alright, so, once again, what happened when researchers tried to use vitamin D supplements to prevent or treat depression?  They saw no effect.

Vitamin D and Heart Disease

Low levels of vitamin D are linked to an increased risk of heart disease, heart attack and stroke, particularly among people of European descent.  This relationship has been found consistently, as have links between low vitamin D status and other blood markers known to be risk factors for heart disease, such as elevated homocysteine, uric acid and C-reactive protein levels.  

Is there a plausible reason that vitamin D might be able to protect your heart health?  Several, actually.  Normal levels of vitamin D can help keep calcium from building up in your artery walls, keep your immune system calm (which could otherwise damage your arteries) and can help your artery cells make enough of a chemical called nitric oxide, which is crucial for your artery walls to work properly.  

All of this is excellent evidence that vitamin D may play a key role in protecting you against heart attacks, heart failure and stroke.

What happened when researchers put this one to the test?  Again, the results didn’t pan out.

Vitamin D Defeat?

How disappointing.  So much population-based evidence that vitamin D is helpful.  Plus, evidence that vitamin D can actually make your cells and organs do what they need to in order to stay healthy, but tests on people don’t pan out.

So, that’s that, huh?

Well… maybe not quite so fast.  There are a couple of plausible explanations for why the tests might not have panned out even if vitamin D is actually protective.

Genetic Differences

Studies now show there are pretty large differences in how different versions of the gene for the vitamin D receptor — the protein that allows vitamin D to do its job in your cells — works.  That means, for the same amount of vitamin D in the blood, different people can have different effects.  What might be enough for one person to be protected might not be enough for another.  Then, when you compare those two people, you’d think vitamin D has no effect.  But that might not be true at all!  It might just be that the second person simply didn’t experience the effect because they didn’t have enough vitamin D for them.

Deficiency Debate

As if the genetic variation wasn’t tricky enough to work around, there is also the enormous problem in vitamin D research that no one agrees on how much vitamin D you need to have in your blood to not be deficient to begin with.

According to the 3 leading public health authorities that make recommendations about vitamin D, there are 3 totally different cut off points!


Vitamin D Deficiency Cut-Off Point


< 20 ng/mL of blood*

Endocrine Society

< 30 ng/mL of blood

Vitamin D Council

< 50 ng/mL of blood

Table 1: Vitamin D Blood Levels Considered the Cut-Offs for Deficiencies by Public Health Agencies *ng/mL stands for nanograms per milliliter. So if a milliliter of your blood contains less than 20, 30 or 50 nanograms (0.00000002, 0.00000003 or 0.00000005 grams) of vitamin D, you would be classified as having a vitamin D deficiency by these different public health institutions.

Naturally, to get blood levels up to these different levels, you have to get different amounts of sunlight or take differently dosed vitamin D supplements.  Check out the different daily doses of vitamin D recommended by each of these institutions to have healthy blood levels.


Daily Recommended Intake


600-800 IU**

Endocrine Society

2000 IU*

Vitamin D Council

5000 IU

Table 2: Daily Recommended Intake of Vitamin D from Leading Health Institutions  *While blood levels of vitamin D are in ng/mL, intakes are typically given in international units (IU) to make package labels easier to read and compare across brands and countries.  One IU is equivalent to 25 ng.
**Note that this number is strongly suspected to be a mathematical error, even for the low cut of for deficiency. Though this error was pointed out years ago, the NIH has not corrected the value.

I imagine you can see how this is a huge problem for putting together studies, interpreting results and giving participants the right doses to actually see an effect!  If you need 5,000 IU a day and you’re only given enough to get up to 800 IU, of course there you won’t be protected — you’re still deficient.  

So, it may very well be that vitamin D does protect against these diseases.  The studies haven’t shown it, though, because the subjects weren’t given the right doses!

Healthiest Vitamin D Levels

So, are you just out to sea without a paddle until authorities can agree on how much vitamin D you really need before you can even begin to decide about adding a vitamin D supplement to your daily routine?

Maybe not.  There is actually pretty good evidence, from several lines of argument, pointing to which of the suggested cut-offs is healthiest: <30 ng/mL.  

Arguments for 30 ng/mL as Deficiency Cut Off

The first line of evidence supporting a 30 ng/mL cut off for vitamin D deficiency comes from this study, a meta-analysis which looked at blood levels of vitamin D and the risk of dying from any disease.  What they found is that more vitamin D is protective, with the risk of death dropping off rapidly until 30 ng/mL, and with a tiny bit more gain between 40 and 49 ng/mL.  After that, you don’t see any more benefit for higher levels.

The second argument is based on this study, a population study done on native populations in Africa who still live today the way our ancestors did millions of years ago.  Guess what their average vitamin D levels were?  46 ng/mL.

The third line of evidence comes from looking at breastfeeding mothers.  Breastfed babies should be able to get all the nutrients they need to survive (and thrive) from breast milk.  This includes between 400-500 IU of vitamin D per day to prevent rickets and promote healthy bone growth.  At what maternal blood level does breast milk have the greatest ability to prevent rickets?  Between 45-50 ng/mL.

It seems prudent to think, with the evidence we have now, that a vitamin D level in the 40-49 ng/mL range is the healthiest for humans, with 30 ng/mL being the bare minimum, an opinion shared by many renowned vitamin D researchers for a solid decade now!

How much vitamin D do you have to take to get your blood levels between 30-50 ng/mL?  Around 2,000 IU per day.  

How Do You Get Vitamin D?

Is that hard to get?  Well, in the winter, when you have to rely solely on food for vitamin D everywhere north of San Francisco and Richmond, it could be.

To get 2,000 IU from food alone, you would have to consume:

  • 20 cups of fortified orange juice
  • 43 eggs
  • 12.5 oz of salmon
  • 50 oz of tuna
  • 67 tsp of fortified margarine

Basically, if you don’t want to eat a large portion of salmon every day (which, honestly, sounds expensive and tedious), it’s going to be tricky!

Luckily, there are lots of vitamin D supplements that allow you to get this exact dose every day.  Check out the table below for some well-rated options that offer a full 2,000 IUs of vitamin D3 (which is the easiest form for your body to absorb) per day!

Disclosure – This post contains affiliate links.  Click here for details.


Serving Size

Percent 5-Star Amazon Rating

Fertile Moon

1 mL Liquid Vitamin D


MaryRuth Organics

2 Gummies



1 Tablet



1 Tablet


Nordic Naturals

0.5 mL Liquid Vitamin D


Table 3: Commercially Available Vitamin D Supplements that Provide 2,000 IUs per Serving.  All supplements listed are vegetarian/ vegan-friendly. Please double check for other allergens.

Recommended Vitamin D Supplements

Fertile Moon Liquid Vitamin D3 VeganMaryRuth VEGAN Vitamin D3 + B12 GummiesMegaFood – Vitamin D3 2000 IUVegLife Supreme Vegan D Vegan TabletsNordic Naturals – Vitamin D3 Vegan

Vitamin D Supplements: Yay or Nay?

That was a bunch of back-and-forths!  Where do I come out in the end?  Vitamin D supplements: yay or nay?


There are 4 facts that, when combined, cinch the argument for taking vitamin D supplements for me:

  • The population studies definitively and consistently show a benefit of higher vitamin D level for human health.
  • The scientifically proven cellular mechanisms that explain how vitamin D can protect you against chronic diseases.  This helps prove that population studies are not picking up helpful effects of vitamin D by accident (for example, it can’t be that those that get more exercise get more sun and have higher vitamin D levels, but it’s just the exercise that’s making them healthier).
  • The reasonable explanations for why controlled tests have not yet panned out.
  • The fact that taking moderately dosed vitamin D supplements has been proven extremely safe.  Doses up to 4,000 IU are believed to be entirely safe, though that number could be as high as 10,000 IU.

Ever growing evidence that taking a 2,000 IU vitamin D supplement can protect against chronic disease with basically no added risks?  I’m sold!  In fact, I’ve personally upped my daily vitamin D supplement dose from 1,000 IU to 2,000 IU because of my research for this post!

Take Home Message

The rumors floating around about vitamin D seem outlandish, but there is quite a bit of scientific evidence to back them up!  Though the links between vitamin D and chronic conditions, such as cancer or depression, have not been proven, there are clear mechanisms that underpin the relationship and good explanations for why randomized trials have, to date, not shown strong results.  Based on the current evidence, getting 2,000 IU of vitamin D each day is probably good for your health.

Read Next: Vitamins Guide: What are the Main Vitamins Your Body Needs?


  1. Make sure you get enough of it. You can die not getting enough water or vitamin C. JAMA says that 76% of Americans do not get enough vitamin D. You need it but is is not a vitamin. It is a hormone. If you do not get it in supplement form, you need to get it from the sun. Food is a bad source.

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