Why Vitamin D is REALLY a Hormone

October 8, 2018
Ann Louise Gittleman, PhD, CNS

Ann Louise Gittleman, PhD, CNS

Award-winning nutritionist and New York Times bestselling author.

When you supplement with Vitamin D, you are actually giving your hormones a boost.

Very few people realize that when they are supplementing with “vitamin” D, they are actually taking hormone replacement therapy. Hormone D, as it should more accurately be called, is required to absorb calcium from the gut into the bloodstream. The liver and kidneys convert vitamin D produced in your skin during sunlight exposure. It is then taken up in the diet into the active hormone form, which is called calcitriol. When calcium in the blood decreases, the parathyroid glands produce parathyroid hormone, which sends a chemical signal to increase active Vitamin D, which increases calcium in the blood.

Calcium regulation isn’t the only job of hormone D. It also promotes mineralization and strengthening of the collagen matrix in bone, increasing bone density and overall health of bone tissue. This process starts in the intestine, then the signal travels to the bones and the bone marrow, and once the bone marrow is involved, so is the immune system. Vitamin D deficiency is known to increase autoimmunity and make you more susceptible to infections, so optimal levels are essential for healthy immune function.

Hormone D is also involved in sex hormone balance. When you are deficient in vitamin D, if you are a woman, your estrogen level drops, and if you’re a man, your testosterone level drops. So, if you have Low E or Low T, have your health care professional check your vitamin D levels through blood testing.

Since we know vitamin D is essential to bone health, why does a recent study show supplementing doesn’t give us stronger bones and less risk of fractures and falls? The answer to this may be in why we’re deficient in vitamin D in the first place.

Why Are We Deficient in Vitamin D?

Since the active form of vitamin D is really a hormone, we need to change the way we think about deficiency and realize it takes more than a “magic pill” to fix our issues. There are multiple tissues, organs, and chemical signals needed to turn vitamin D into hormone D and make it active in the body. If we’ve lost the ability to convert it into its active form, we can take the vitamin all day long without it becoming metabolically active and doing its job.

It can’t just be lack of sunlight exposure. Inuit populations living in far Northern regions that go through seasons of darkness and total lack of sunlight exposure still maintain healthy vitamin D levels through what they eat. It’s what they eat that keeps their levels up. So why is it when we eat the same oily fish like sardines, salmon, and mackerel, we don’t see the same rise in our levels?

  • Impaired detox. Your liver and kidneys need to be able to do their parts in converting vitamin D into hormone D, but if they are overloaded trying to process all the toxins you come in contact with through your food, air, and water, they may not be able to perform other critical functions. If you have kidney disease, kidney stones, or even just swelling in your ankles, these are signs your kidneys may not be able to do their part in converting D to its active form. If you have fatty liver, congested bile, or gallbladder disease, these are all signs your liver may not be able to do its job in the conversion to hormone D. My new Radical Metabolism goes into great detail on how to rescue a toxic metabolism and detox your way to better health and your ideal weight.
  • VDR gene mutations. When the Vitamin D Receptor (VDR) gene is mutated, the environment surrounding this gene can activate the mutation. This makes it difficult for your body to use Vitamin D properly. Vitamin D Receptors are found in the bones, bone marrow, small intestine, colon, and breast, as well as other tissues. Their functioning is essential for immune health, bone health, prevention of certain cancers, heart health, and so much more. If you have had your MTHFR/methylation gene profile done, you can look for the VDR gene mutation on the report to see if you have it. Some gene researchers have found supplementing with herbs like rosemary and sage in your daily diet can help with absorption of vitamin D and conversion to hormone D, with or without supplementation of vitamin D itself.
  • Missing cofactors. Supplementing with vitamin D isn’t always enough, especially when we are missing the minerals it needs to do its job effectively. If you are deficient in calcium or phosphate, your body may break down bone in an effort to restore healthy levels of calcium in the blood. Your body keeps a balance between calcium and magnesium. So, if magnesium is deficient (over 80 percent of Americans are), then calcium will be excreted rather than used, even if supplemented. While hormone D increases the amount of calcium in the blood stream, vitamin K sends it where it needs to go, including to the bones. So, if you are supplementing vitamin D without vitamin K, you may be depositing that calcium in your arteries and making plaque instead of bone.

A New Study Shows Supplementing With Vitamin D Does Not Increase Bone Density

Vitamin D may not prevent osteoporosis at any dose, according to a large study just released. But does this mean we should stop taking it?

For years now, we’ve been told to take our Vitamin D during the winter months to ward off brittle bones as we age. But a new study done of over 53,000 people came to the conclusion that Vitamin D does not improve bone mineral density or prevent fractures and falls in adults, and advises health care professionals to stop recommending the supplements to most patients. Touted as a cure all for diseases like osteoporosis, hypertension, and cancer, the debate over the pros and cons of this “vitamin” that is actually a hormone continues, and I’m concerned about the effect this new study will have on people who are actually deficient.

This recent study is a meta-analysis, which means they compiled the data from 81 studies that involved over 53,000 people. Many different factors were involved, and researchers analyzed the results together to find the common health trends. This type of study is widely considered to be quite reliable, but I am concerned with some of the variables that weren’t accounted for in the analysis. For instance, only 6 percent of the studies analyzed were done on people with vitamin D deficiency, and they are the ones who stand to benefit the most from supplementation. Can you see how people who aren’t deficient wouldn’t benefit from supplementing and could completely change the results of the study?

Also, many of the trials included had a small number of participants and only supplemented with vitamin D for a short period of time. There were also studies included that supplemented only small amounts of vitamin D and may not have been high enough levels to have a therapeutic effect.

My Advice: Don’t Stop Taking Vitamin D

When I was a student at Columbia University, I was taught “one study does not make science.” Based on this study, I would not stop supplementing with vitamin D if I had bone density issues. In addition, I recommend cleansing, detoxing, and supporting your liver and kidneys with my Radical Metabolism lifestyle, check to see if you have the VDR gene and supplement with rosemary and sage if you do, increase magnesium levels with leafy greens and my Mag-Key supplement from UNI KEY Health, and supplement with Osteo-Key, also from UNI KEY Health, which contains the most absorbable forms of calcium and the necessary co-factors and minerals that are needed to get this calcium into the bones.

Related Articles and Podcasts

Ann Louise Gittleman, PhD, CNS, is an award-winning New York Times bestselling author of more than thirty books including The Fat Flush Plan series and her latest book, Radical Metabolism. She’s been rewriting the rules of nutrition for more than 40 years and is internationally recognized as a pioneer in the field of diet, detox and women’s health issues. 

For a FREE daily dose of tips and strategies for maintaining healthy weight, conquering insomnia, and much more…check out my Radical Health Tips.

I’d like to meet and greet you on my Facebook groups, so won’t you check us out at the Radical Metabolism RevolutionFat Flush Nation, or my Inner Circle!


  1. Beth Conway

    Amazing! Thanks for the update on this extremely important topic. I can always count on you for cutting edge advice.

  2. Barbara Hulin

    Vitamin D a Hormone?! Who knew this…happy for the enlightenment! I will motivate me to dive into my book RM to get more of this info! Thanks, Ann!

  3. dee

    Confused, if vitamin d causes plaque why should we continue taking?? I was diagnosed with low D while having a blood test for my low thyroid. I am on “Synthroid” and was told to drink cranberry juice (not from concentrate). Does this make sense to you?

  4. Wendy DeBusk

    This really bothers me that plaque might be building in my arteries. I have been taking it ever since 2014 when a blocked artery caused me to go into cardiac arrest.
    I asked my doctor about taking the vitamin K2 but she didn’t like the idea because the K has to do with clotting of the blood and since I have PVD she didn’t want me to take it.
    I do have Osteopenia and some degeneration in my hips. So what can I do?

  5. Debra Swihart

    I bought the book and never got the promised $28.00 credit at Unikey. who do I contact to get my discount? Thank you. [email protected]

  6. Team ALG

    Debra — You need to go to Radicalmetabolism.com and fill out the form first.

  7. Team ALG

    Wendy: We would recommend you consider more magnesium to help with bone density — typically up to 800 mg per day. Thank you.

  8. Bonnie

    Wonderful article. I take the Osteo-Key and am wondering how much extra Mag-key is optimal? I take it at bedtime. Til I reach bowel tolerance? I also take the Female Multiple.

  9. Team ALG

    Bonnie, Ann Louise has mentioned that the guideline for the total amount of magnesium is 5 mg per pound of body weight.


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