Why you need Vitamin D

You’ve likely heard of vitamin D being important for your body and that many of us are at risk of being deficient. But why is it important and how does it work in our bodies? In this article, I dive into the science of vitamin D and why it’s so critical for your health.

First, let’s understand how vitamin D works within our body.


Metabolism of vitamin D

Vitamin D is an essential fat soluble vitamin that is involved in many vital roles within our body. These roles range from calcium and bone maintenance, immunity and overall well-being. Vitamin D exists as vitamin D3 (cholecalciferol) which is the optimal supplemental form, or as its plant derivative known as vitamin D2 (ergocalciferol. Vitamin D is a unique nutrient because it can be made from sunlight, food, or through supplementation!

For Vitamin D to be bioavailable, it must be synthesized into the active form of vitamin D known as calcitriol. This transition is completed after UV exposure or ingestion by the help of  transport proteins and specific enzymes. For anyone who might be interested in how vitamin D transforms into its active form, we’ll briefly go through the steps that occurs after sun exposure. Why sun exposure? Because this is how you’ll likely get most of your vitamin D, unless you eat fatty fish or supplement regularly!

After direct sun (UVB) exposure, 7-dehydrocholesterol in the skin transitions into vitamin D3, which then travels through the blood by the help of vitamin D binding protein. Once it reaches the liver it is hydroxylated (a process that adds an addition -OH group to the molecule) into 25-(OH)D3. It then travels to the kidney where it becomes calcitriol, the active form of vitamin D.


Important details to keep in mind about sun exposure and vitamin D

Vitamin D synthesized from sunlight is heavily dependent on your location, season, type of clothing worn, time of day, and use of sunscreen. Folks located in the northern hemisphere will not produce vitamin D from sun exposure during October-February/March. Further, although sun protection is important for the prevention of skin cancer and overall skin health, it generally blocks UVB exposure which is necessary for conversion into the active form of vitamin D. Thus, it might be beneficial to implement some unprotected sun exposure for ~15-30 minutes to promote adequate vitamin D levels.

It also won’t hurt to incorporate conscious sunlight exposure since there are other associated benefits of sunlight such as such as improved sleep/wake cycles, elevated mood, improved focus, and more. Lastly, it’s important to note, slower rates of vitamin D synthesis occurs in people with darker skin tones due to the higher concentration of melanin in the skin.

Next, let’s discuss why vitamin D is doing for our body.


Vitamin D’s critical roles

Vitamin D’s most well-known function, and likely what you’ve heard about most frequently, is its role in the regulation of calcium and phosphorous levels. This mechanism is vital for bone health as it helps regulate bone formation, remodeling, and maintenance. This is particularly important since bones are constantly remodeled through-out our lifetime (during some stages of life more than others). Thus, vitamin D’s calcemic roles, along with regular weight training and consumption of a well-rounded diet supports optimal bone health and overall bone mineral density.

Strong bone mineral density is especially important because after about age 50, bone resorption generally begins to exceed bone formation. This makes it vital to maintain or increase bone mineral density thought out your life as it will lead to decreased risks of bone related conditions which have the capacity to negatively affect quality of life.

Besides vitamin D’s calcemic roles, sufficient vitamin D is also important for: optimal immunity, glucose metabolism, is a part of cell differentiation, apoptosis, gene expression, and insulin secretion. Further, deficiency of vitamin D has been associated with multiple sclerosis, arthritis, other autoimmune diseases, cardiovascular conditions, muscle spasms, mental health diagnoses, amongst other conditions. Although more research needs to be conducted for more specific guidelines regarding vitamin D’s influence on many of these diverse conditions, I think it’s safe to say that sufficient vitamin D will support overall health, immunity, and longevity!


Can’t have D without K

It is important to not think about nutrients in isolation and that vitamins and minerals often work synergistically with each other. This is why it’s important to consume a well-rounded, diverse diet of lots of “whole” foods in hopes to promote enhanced nutrient interactions and outcomes within the body. This leads to the discussion of another nutrient that is not frequently talked about when discussing vitamin D, but should be, since it is thought to synergistically work with vitamin D, and also plays a vital role in calcium metabolism.

I’m here to invite another fat soluble vitamin, vitamin K to the chat. Vitamin K enhances the duties of vitamin D, as it is thought to increase vitamin K dependent proteins which are thought to positively influence bone mineralization, decrease fracture risk,  improve glucose metabolism, and promote improvements in cardiovascular health. It might be helpful to supplement vitamin D and vitamin K2 (animal form) together to promote this synergistic relationship. You will find most high quality Vitamin D supplements have K2, as well. As always, it’s important to always consult with your physician and a registered dietitian before implementing any new supplement regimen.


Alright, so how do I monitor my vitamin D levels?

 First, getting blood work to measure your serum vitamin D levels is the most accurate way to see if you are within range, or deficient. From there, you can adjust your sun exposure and diet accordingly to be within the optimal range.

Some sources of vitamin D include sun, cod liver oil, fatty fish, and fortified products, sun dried vegetables and irradiated mushrooms.

Some sources of vitamin K include spinach, kale, broccoli, swiss chard, other leafy green vegetables, fermented dairy/soy products.

Those who might be at risk for vitamin D deficiencies include those who have limited sun exposure, obese individuals, those with kidney or liver conditions, and individuals with any gastrointestinal issues/malabsorptive issues. For most of us, working inside most of the day severely limits our sun exposure so it’s best to test and address your vitamin D levels as needed through lifestyle and dietary changes!



1. van Ballegooijen AJ, Pilz S, Tomaschitz A, Grübler MR, Verheyen N. The Synergistic Interplay between Vitamins D and K for Bone and Cardiovascular Health: A Narrative Review. Int J Endocrinol. 2017;2017:7454376. doi:10.1155/2017/7454376

2.Ross, A. C. , et al. Modern nutrition in health and disease. Eleventh Edition: Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins; 2012


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