Vitamin D has been around for a long time, but I am hearing some confusing messages around this topic lately. The way for me to get clear on something is to research and write about it. Here we go!
1. Sunshine vitamin, Vitamin D, Hormone D? What is it anyways?
In the strict sense, a vitamin is defined as “an organic substance present in minute amounts in the natural diet that is essential to normal metabolism. Insufficient amounts of vitamins in the diet may cause deficiency diseases. A hormone is defined as a substance formed in one organ but transported in the blood to another organ and capable of altering the functional activity of that target organ”(1).
Since neither Vitamin D2 (ergocalciferol) nor Vitamin D3 (cholecalciferol) has the function of a hormone in the body, these two compounds cannot be classified as hormones. These are vitamins. However, once these vitamins are processed by the liver and kidneys, Calcitriol (activated vitamin D) is produced. This is a hormone.
2. Where does Vitamin D come from?
Vitamin D is a fat soluble vitamin. Our bodies naturally produces vitamin D by converting 7-dehydrocholesterol to vitamin D3 (cholecalciferol) through UV radiation (see graph). By the name of the precursor, you probably guessed that we need cholesterol and sunshine to produce vitamin D3.
Food is another source of vitamin D. Fish, eggs, beef liver, mushrooms, or fortified foods such as milk, cheese, yogurt are some main sources.
There are two forms of commercially available, non-prescription vitamin D supplements: D2 , obtained from plant sources; and D3 from animal sources. Studies have shown that D3 is more likely to convert to the active form of vitamin D, Calcitriol(4,5) .
For vitamin D2 and D3 to convert to the active form, first, the liver hydroxylates vitamin D2 and D3 through cytochrome P450 enzymes, turning vitamin D into 25(OH)D, or Calcidiol, the primary circulating form of vitamin D. Calcidiol is a prehormone. Although it is a glandular secretory product, it has minimal biologic potency.
The kidneys further hydroxylates calcidiol into the active form 1,25-dihydroxyvitamin D, 1,25(OH)2D, or calcitriol. For comparison, calcitriol is 1000 times more potent than calcidiol. Calcitriol maintains serum calcium through both direct effects on calcium absorption and excretion, and through a series of inter-relationships with serum phosphate and parathyroid hormone.
Calcitriol is also available commercially by prescription only. The medical indication for this drug is for patients with kidney disease who can’t make enough of the active form of Vitamin D. This medication is also used to prevent and treat certain types of calcium/phosphorus/parathyroid problems that can happen with long-term kidney dialysis or hypoparathyroidism.
3. What is Vitamin D good for?
Vitamin D was used to treat rickets (weakening and softening of bones) for children in poverty during Victorian era.
We now know, as numerous researches demonsted, the benefits of Vitamin D in preventing and treating bone fractures. Calcitriol is a calcium-regulating hormone, an adaptive hormone produced in response to calcium deficiency. Aside from calcium, vitamin D is also essential for phosphorous absorption, another mineral crucial to bone health.
Calcitriol functions the same way as other steroid hormones, namely by interacting with its corresponding vitamin D receptor (VDR). VDR is a ligand-activated transcription factor that functions to control gene expression, with Calcitriol serving as a transcriptional regulator of various genes(2,3,4). If you type in Vitamin D in Pub Med search now, you will find thousands of publications on vitamin D and association with:
• bone health
• Immune system, which helps you to fight infection
• Muscle function
• autoimmune conditions
• neurological disorders such as dementia
• Cardiovascular function
• Respiratory system –for healthy lungs and airways
Researchers and clinicians are still working to fully understanding how vitamin D effects our overall health. Hopefully more studies will provide some definitive answers here.
4. How do you know if you are Vitamin D Deficient?
Sun exposure, skin color, location, and even omega-3 fatty acid balance can influence your vitamin D levels.
Below are some reasons you may be deficient in Vitamin D:
• Not enough vitamin D in your diet
• Not absorbing enough vitamin D from food (a malabsorption problem)
• Not enough exposure to sunlight.
• Your liver or kidneys cannot convert vitamin D to its active form in the body (may be genetic or disease induced dysfunction).
• Your medication(s) may interfere with your body’s ability to convert or absorb vitamin D. These include: proton pump inhibitors (PPIs), glucocorticoids, anti-epilepsy drugs and statins, laxatives, and of course the use of sunscreen(6).
If you are not sure if you need Vitamin D or not, ask your healthcare practitioner for a blood test first to determine your need before starting on a supplement. When you get your vitamin D level tested at a lab, they are testing your 25-hydroxy Vitamin D (Calcidiol) level. This is the first metabolite of vitamin D (see above). By testing this pre-hormone, we are assuming that our kidney is functioning optimally and that these pre-hormones will convert into active 1,25(OH)2D. 1,25(OH)2D is usually measured only for patients with hypercalcemia, or chronic kidney disease.
You may see from your own lab report, level between 20 ng/mL to 50 ng/mL is considered adequate for healthy people. Experts from The Endocrine Society conservatively recommends blood levels of 30 ng/ml; another study by Cannell et.al. indicated that treatment should be sufficient to maintain levels found in humans living naturally in a sun-rich environment, that is, greater than 40 ng/ml(7); The Vitamin D Council places the ideal level at 50 ng/mL. Bottom line is, scientists don’t have definitive evidence yet about how much vitamin D one should take for good health. Personally, I am sticking with the higher level until I am proven wrong. And you will be the first to know.
5. If you need more vitamin D, what should you take?
Try getting your vitamin D from real foods and sunshine before grabbing the first bottle of supplement you see. Here is a good list put together by Dieticians of Canada.
Given the pathyway of vitamin D conversions, there are individual variations on absorption and metabolism of vitamin D. If you require a supplement, don’t assume that just because you are taking a daily dose of 1000IU vitamin D supplement that you would be fine. Check with your healthcare professional for a lab test again in a few months to determine if what you are doing is helping you.
If you need to take a supplement, you have many options. I usually recommend buying a reputable brand with dosing from 400IU to 1000IU or more, depending on your lab results. Personally, I take 1000IU daily. I live in Vancouver, and I don’t get a lot of sunshine.
If supplement is not your thing and sitting in sunlight is a rare opportunity (especially if you live in rainy Vancouver!), here is a new way of gettting vitamin D. Solius developed a light booth specifically to induce vitamin D production. The light generated will enable your body to produce its own vitamin D, much like sunlight. However, the harmful ray (UVA) has been removed so you will not experience tanning or photoaging. Exposure to this light for 2 minutes every week is all you need to sufficiently to boost your vitamin D level. The first light booth is available at Wellness Garage in White Rock, BC.
6. Overdose is possible. Excessive intake can lead to severe toxicity
Did you know that some rat baits contain large quantities of Vitamin D as a rodenticide?
25(OH)D levels above 150 ng/ml are considered potentially toxic and potentially harmful to your health. The consequence of vitamin D toxicity is a buildup of calcium in your blood (hypercalcemia), causing nausea, vomiting, weakness, tiredness, and frequent urination. Symptoms might progress to bone pain and formation of calcium stones in the kidneys. If you suspect you have an overdose situation, please contact your physician immediately.
As always, please ask your health care professional to confirm your needs. If you are currently taking prescription medications, ask your pharmacist if your meds are depleting your nutrients.
Questions about vitamin D? Feel free to ask using the form below.
1. Vieth, R. (2004 May). Why “Vitamin D” is not a hormone, and not a synonym for 1,25-dihydroxy-vitamin D, its alanogs or. J Steroid Biochem Mol Biol., 80-90(1-5):571-3.
2. Sassi F, T. C. (2018 Nov 3). Vitamin D: Nutrient, Hormone, and Immunomodulator. Nutrients, 10(11). pii: E1656. doi: 10.3390/nu10111656.
3. Pike JW, Meyer MB. The vitamin D receptor: new paradigms for the regulation of gene expression by 1,25-dihydroxyvitamin D(3). Endocrinol Metab Clin North Am 2010; 39(2):255-69.
4. Tripkovic L, L. H.-N. (2012 Jun). Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. Am J Clin Nutr. , 95(6):1357-64.
5. Lehmann U, H. F. (2013 Nov). Bioavailability of vitamin D(2) and D(3) in healthy volunteers, a randomized placebo-controlled trial. J Clin Endocrinol Metab. 2013 Nov;98(11):4339-45. doi: 10.1210/jc.2012-4287. Epub 2013 Sep 3., 98(11):4339-45. doi: 10.1210/jc.2012-4287.
6. Stargrove, M., Treasure, J. and McKee, D. (2008). Herb, nutrient, and drug interactions. 1st ed. St. Louis, Mo.: Mosby/Elsevier.
7. Cannell JJ, H. B. (2008). Diagnosis and treatment of vitamin D deficiency. Expert Opin Pharmacother, 9(1):107-18.