Vitamin D: Do You Really Need To Supplement? Part 1

Supplements are a popular intervention that people use to, at the very minimum, meet their recommended dietary allowance (RDA) of nutrients like vitamins and minerals. Under the care of a health provider, supplements can be used to correct deficiencies or support body systems in certain health conditions. Vitamin D is an increasingly recommended supplement, by health providers, as many people show insufficiency or deficiency in their lab work. But is supplementation really necessary? For some people yes, but for others there may be avenues to try before jumping on the D train, especially without testing for deficiency first. In this two-part blog series we will look at the importance of vitamin D and how to determine if supplementation is truly necessary.

What Are The Functions Of Vitamin D In The Body?

Vitamin D is a nutrient that our body produces from ultraviolet B ray exposure and we get in lesser amounts from our diet. It must be activated by way of the skin, liver, and kidneys to be used in the body. Vitamin D is well known for its role in bone health, and deficiency can cause softening of the bone called Osteomalacia (also known as Rickets in children). 

But this vitamin has many other important roles in the body that impact our health. In addition to bone health, vitamin D is important to immune function, inflammation, cell differentiation and proliferation, neuromuscular function, glucose metabolism, and regulation of blood pressure. The active form of vitamin D is called calcitriol, also known as “hormone D”. 

Calcitriol is a seco-steroid, a subclass of steroid hormones, and therefore acts as a hormone in the body. Hormones are chemical messengers that relay information by binding to specific cell receptors, in this case vitamin D receptors (VDRs). And similar to hormones, vitamin D requires cholesterol to be synthesized. Therefore, if your cholesterol levels are low you may be at risk for low vitamin D levels.

Role in Bone Health

Vitamin D plays an integral role in the regulation of calcium homeostasis. Its role in calcium homeostasis is what makes it such an important nutrient for bone health. This regulation involves the collaboration of:

• 3 organ systems

  • Bone

  • Kidneys

  • Intestine

• 3 hormones

  • Parathyroid Hormone (PTH)

  • Calcitriol (active form of vitamin D)

  • Calcitonin (via thyroid)

Blood calcium levels are tightly regulated and when blood calcium levels are low, parathyroid hormone (PTH) stimulates bone cells to break down bone tissue for calcium and the kidneys to activate calcitriol, hormone D. 

Hormone D acts to:

1. Control the rate of bone calcification 

2. Enhances the absorption of calcium in the small intestine.

3. Stimulates the kidneys to reabsorb calcium, decreasing its excretion

Once calcium levels have risen, calcitonin is released to counter PTH and Calcitriol. This homeostatic relationship between calcium and vitamin D is why they are often recommended to be taken together to slow or prevent osteoporosis.

Because blood calcium levels are tightly regulated, this makes serum calcium levels an unreliable determinant for calcium status as they will naturally fluctuate. Additionally, high intakes of calcium with vitamin D can lead to hypercalcemia and a variety of issues, such as kidney stones, calcification of soft tissues (atherosclerosis, heart valves), arrhythmias, and even death.1 

Role in Cell Differentiation/Proliferation

Stem cells are the body’s cellular raw material, they are what all future cells differentiate from. Active vitamin D (calcitriol) induces differentiation of stem cells into a variety of cell types in the body: osteoclasts (cells that breakdown bone), osteoblasts (cells that build bone), macrophages, and monocytes (both are types of immune cells), and epidermal cells. This is why vitamin D plays an important role in bone health, immune function, and other bodily functions.

Vitamin D’s role in the differentiation and the decrease in proliferation of epidermal cells points to its use as an adjunct treatment for psoriasis. A meta-analysis was able to establish a significant relationship between low vitamin D levels and psoriasis.2 This diminishing effect on the proliferation of abnormal tissue cells also influences its role in cancer prevention, development, and treatment. Studies have found dose related correlations between vitamin D and cancer prevention and outcomes for prostate cancer,2 colorectal cancer, 3,4, and breast cancer, especially in premenopausal women.5,6

Immune Function and Associated Conditions: MS, Type 1 Diabetes, Cold/Flu

The exact role vitamin D plays in Type 1 Diabetes is unclear, but low serum calcitriol levels are associated with insulin secretion by beta cells in the pancreas and islet autoimmunity.7

Whereas, adequate serum calcitriol levels were associated with insulin sensitivity. Calcitriol calms adaptive immune responses and decreases the production of inflammatory cytokines by immune cells.7 

Again, the exact role that vitamin D plays in the prevention and development of Multiple Sclerosis is also unclear. What is clear is that vitamin D insufficiency and deficiency is common among individuals with MS.8 Furthermore, vitamin D seemed to show protective effects on the myelin sheath in individuals with Progressive MS.8

The immunomodulatory, and therefore anti-inflammatory, actions of vitamin D also enhance the body’s resistance to infections, such as the cold or flu. Vitamin D has a powerful regulatory effect on T cell (T1 and T2) proliferation, IFN-y and Interleukin-17 (IL-17) production, all of which limited immune mediated and pathogenic disease progression.9

High doses of vitamin D also decreased the expression of IL-8 found abundantly in the airways of those with Cystic Fibrosis.10

How We Make Vitamin D

Humans can synthesize vitamin D from cholesterol in sun exposed skin, and given the right conditions our body is capable of synthesizing what it needs. The RDA for vitamin D can be achieved with as little as 30 minutes of sun exposure, specifically the ultraviolet B rays from the sun, to at least 30% of the skin. People with darker complexions will need to increase their exposure time in relation to the melanin content in their skin. Additionally, UVB light cannot pass through glass, so sitting near a window will be ineffective and the exposure must be directly from the sun. 

Other things to consider when seeking UVB rays as a source of vitamin D:

• It is harder to achieve adequate UVB rays in the northern hemisphere, especially between the months of Oct - April, and supplementation is often needed for this demographic. This is especially true if your serum vitamin D levels are lower than 40 in September and again in late March. 

• Sunscreen blocks UVA and UVB rays to protect us from radiation damage that can lead to skin cancer. The caveat is that it blocks the UVB rays that we need to produce vitamin D via the skin. A good rule of thumb is to soak up the sun based on the depth of your complexion, and certainly before you start to turn pink, then apply sunscreen for the remainder of the time you are outside. This way you will get the UVB rays you need for vitamin D production and protect yourself from sun damage. 

Now that the importance of vitamin D to various functions in the body has been highlighted, we will look at how to determine if supplementation is right for you, how to increase your vitamin D status, and how to do that safely.

Coming up next: Assessing Vitamin D Status: Symptoms of deficiency/toxicity, who is at risk, food sources and supplementation.

References

1. National Institutes of Health: Office of Dietary Supplements; Vitamin D Health Professional Fact Sheet. Last updated: March 26, 2021. Retrieved from: https://ods.od.nih.gov/factsheets/vitamind-healthprofessional/ 

2. Pitukweerakul S, Thavaraputta S, Prachuapthunyachart S, Karnchanasorn R. Hypovitaminosis D is Associated with Psoriasis: A Systematic Review and Meta-Analysis. Kans J Med. 2019;12(4):103-108. Published 2019 Nov 25.

3. Trump DL, Aragon-Ching JB. Vitamin D in prostate cancer. Asian J Androl. 2018;20(3):244-252. doi:10.4103/aja.aja_14_18

4. Dou R, Ng K, Giovannucci EL, Manson JE, Qian ZR, Ogino S. Vitamin D and colorectal cancer: molecular, epidemiological and clinical evidence. Br J Nutr. 2016;115(9):1643-1660. doi:10.1017/S0007114516000696

5. Zhang L, Zou H, Zhao Y, et al. Association between blood circulating vitamin D and colorectal cancer risk in Asian countries: a systematic review and dose-response meta-analysis. BMJ Open. 2019;9(12):e030513. Published 2019 Dec 23. doi:10.1136/bmjopen-2019-030513

6. Song D, Deng Y, Liu K, et al. Vitamin D intake, blood vitamin D levels, and the risk of breast cancer: a dose-response meta-analysis of observational studies. Aging (Albany NY). 2019;11(24):12708-12732. doi:10.18632/aging.102597

7. Estébanez N, Gómez-Acebo I, Palazuelos C, Llorca J, Dierssen-Sotos T. Vitamin D exposure and Risk of Breast Cancer: a meta-analysis. Sci Rep. 2018;8(1):9039. Published 2018 Jun 13. doi:10.1038/s41598-018-27297-1

8. Infante M, Ricordi C, Sanchez J, et al. Influence of Vitamin D on Islet Autoimmunity and Beta-Cell Function in Type 1 Diabetes. Nutrients. 2019;11(9):2185. Published 2019 Sep 11. doi:10.3390/nu11092185

9. Abbatemarco JR, Fox RJ, Li H, Ontaneda D. Vitamin D and MRI measures in progressive multiple sclerosis. Mult Scler Relat Disord. 2019;35:276-282. doi:10.1016/j.msard.2019.08.014

10. Cantorna MT, Snyder L, Lin YD, Yang L. Vitamin D and 1,25(OH)2D regulation of T cells. Nutrients. 2015;7(4):3011-3021. Published 2015 Apr 22. doi:10.3390/nu7043011

11. Dauletbaev N, Herscovitch K, Das M, et al. Down-regulation of IL-8 by high-dose vitamin D is specific to hyperinflammatory macrophages and involves mechanisms beyond up-regulation of DUSP1. Br J Pharmacol. 2015;172(19):4757-4771. doi:10.1111/bph.13249