Emotional Health, Fundamentals of Wellness, Wellness

Vitamin D is NOT a vitamin. But it’s critical to staying well.

I originally wrote this article in 2013, and I’ve updated it annually with more research and to stress it’s importance in immunity. The COVID pandemic made it crystal clear we all need to maintain healthy levels, as our ancestors were outside, without sunscreen routinely. Do you know you can make your own D? All you need is skin, sun and no sunscreen (read on…)

vitamin-dEveryone should take a Vitamin D supplement.  Yes I said EVERYONE. Why?  There are multiple reasons.  Optimizing your vitamin D levels should be at the top of the list for virtually everyone, regardless of your age, sex, color, or health status, as vitamin D deficiency has been linked to an astonishingly diverse array of common chronic diseases.  Let’s explore what happens in our bodies, and why I think it is CRUCIAL to check your levels with your physician and make sure your body has enough available Vitamin D3.

Vitamin D is actually a group of fat-soluble secosteroids responsible for intestinal absorption of calcium and phosphate.  Basically it is a neuroregulatory steroidal hormone that influences THOUSANDS of gene interactions in your body.  One example of an important gene that vitamin D up-regulates is your ability to fight infections, as well as chronic inflammation. It produces over 200 antimicrobial peptides, the most important of which is cathelicidin, a naturally occurring broad-spectrum antibiotic. This is one of the explanations for why it can be so effective against colds and influenza. And why patients with low Vitamin D levels did worse with COVID.

The principal source of vitamin D is your own skin. A chemical compound naturally present in the superficial layers of skin is converted, on exposure to UV-B radiation, to cholecalciferol (vitamin D3).  We manufacture this vitamin D only if we expose our skin to UV-B radiation.   If we spend all day indoors or are never outside mid-day, then we simply do not get sufficient ultraviolet radiation from the sun to make enough vitamin D.  In addition, sunscreen messes this up, so if you spend all day outside but ALWAYS have on sunscreen, you’re also blocking that absorption advantage. Read about a study that confirms this here.  A light-skinned person, wearing a bathing suit, will make about 15,000 IU of vitamin D in 15–20 minutes in July at midday. Darker-skinned individuals can do the same, but it will take about twice as long.  The brief exposure needed to produce adequate vitamin D is not enough to cause skin cancer.  However, if you are worried about that risk, apply sunscreen after the first 15 minutes of exposure.  But spend 15 minutes in full sun when you can as often as you can.

Doesn’t my diet give me enough Vitamin D?

NO.  Mushrooms, raw milk and some wild caught fish are the best sources, but you really need to supplement.  Very few people, especially in North America, get enough UV-B exposure to generate adequate D3. It’s estimated that at least a billion of us still don’t get enough vitamin D — especially during winter, and in those who are obese, older, darker-skinned, living farther north, have inflammation, or are pregnant or nursing.

What happens and why —

The body converts vitamin D, whether taken by mouth or made in the skin, to a compound called 25-hydroxyvitamin D [25(OH)D]. This compound circulates in the blood and is the measure physicians use to assess vitamin D status.  High levels of blood 25(OH)D show that you are getting enough vitamin D, while low levels indicate deficiency. The body also converts some 25(OH)D each day into calcitriol, which acts as a hormone and signals the intestine to absorb calcium more efficiently, thus helping us get by on typical calcium intakes.  This is important for women and osteoporosis prevention.  In addition, calcitriol also regulates inflammation and neuromuscular responses.

Why should I care about my level?

  1. Our population is outside less, so our ability to convert Vitamin D (requires sunlight exposure) is compromised.
  2. The research on this is recent, and not commonly known among all physicians.  This is a situation where you have to be your own advocate.
  3. We are eating more processed food, and although milk and other things are “fortified” with D, it isn’t enough to maintain adequate levels.
  4. The use of sunscreen prevents the conversion to [25(OH)D], which lowers the circulating D3, and decreases your calcium absorption.
  5. Recent studies indicate higher levels of Vitamin D help with depression.  SAD or Seasonal Affective Disorder is helped greatly by increasing D, due to low light exposure and low Vitamin D levels.
  6. Patients diagnosed with certain cancers often have very low Vitamin D levels.  There appears to be an anti-tumor effect when Vitamin D levels are high normal.  Low Vitamin D levels are a predictor of a worse prognosis with some cancers, including colon, ovarian and breast.
  7. Very recent studies show that uterine fibroid growth can be shrunk if Vitamin D is increased.

How much to take?

From the National Institutes of Health, Office of Dietary Supplements:  The safe upper limit for vitamin D3 is:

  • 1,000 to 1,500 IU/day for infants
  • 2,500 to 3,000 IU/day for children 1-8 years
  • 4,000 IU/day for children 9 years and older, adults, and pregnant and lactating teens and women (and I think you can easily DOUBLE this if you’re levels are low, see data at end of post, I think they are under-shooting this based on research).
  • New Research: that taking vitamin D3 in combination with K2 helps drive calcium into the bones where we want it — thus preventing hardening of the arteries, and preventing osteoporosis. They work in tandem and they should always be taken together. There are many manufacturers now that use the combination. Just look for a combo D3/K2.

NEVER take Vitamin D2, Only take Vitamin D3, here’s why:

  • D3 is approximately 87 percent more potent in raising and maintaining vitamin D concentrations and produces 2- to 3-fold greater storage of vitamin D than does D2.
  • Regardless of which form you use, your body must convert it into a more active form, and vitamin D3 is converted 500 percent faster than vitamin D2.
  • Vitamin D2 also has a shorter shelf life, and its metabolites bind poorly with proteins, further hampering its effectiveness.
  • The research on Vitamin D2 is old.  That is why some physicians still prescribe it.  It did prevent Ricketts in children, but we now know a lot more about D2 vs. D3 and D3 is far superior.  Why make it hard for your body to utilize it?  And D supplements are NOT expensive.

Final thoughts:

If you have low levels,  especially if they are below 50, I would suggest taking ~5,000 to  10,000 units of Vitamin D3/day and re-checking them with your physician in a month or two.  (I take 5-10,000 u/day and I’ve never had a vitamin D level higher than 60).   Or take 4,000 units/day but make a point of getting 15 minutes of sun at least 5/week.  Toxicity from supplements can occur but is extremely rare.   Excessive sun exposure doesn’t cause vitamin D poisoning because the body limits the amount of this vitamin it produces.

Check your Vitamin D levels from your home! Here’s a review of the most reliable companies, updated 2022.


2017 update from NIH found a mistake in tabulating “normal” levels were accidentally too low!! I stand by the above table. 

2023 Article by Dr. Perlmutter on Cognitive Decline and D3 research

See 2017 update HERE

2015 Articles from JAMA on cognitive decline and low D levels

Vitamin D Levels and the risk of Dementia

January 2015 Update: A study in the American Journal of Pediatric & Adolescent Gynecology found teens with low Vitamin D levels were twice as likely to have major PMS symptoms and pain and by supplementing, reduced their symptoms markedly.

Read article here.

July 2013 update:  A small new study, which is now expanding, notes women with Type 2 Diabetes had a much lower incidence of depression when they were supplemented with Vitamin D. Read the paper here.


Article on Uterine Fibroids and Vitamin D levels: 

Vitamin D Levels and Cancer:  a trial  http://ajcn.nutrition.org/content/85/6/1586.full




  1. Thanks so much for the info, Eileen. My level is 39 and I had no idea that was low. I’m in the sun all the time and don’t wear sunscreen because I really don’t burn. I thought that would be enough. Off to the pharmacie tomorrow.

  2. kayak63 says

    Great article, I was tested and had extremely low level. Now that I am in the normal range my pain has dropped dramatically . I so appreciate the doctor who realized it could be helpful. Thank you

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