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The Sunshine Vitamin that Acts as a Hormone


woman kissing the sun

Last week we talked about sunscreens, so this week I wanted to talk about the sunshine hormone.


Indeed: Vitamin D!


Vitamin D is a fat-soluble vitamin and it’s not only a vitamin, but also acts as a steroid hormone and doesn’t only play an important role in your immune health, but is also vital for gut health and hormone balance and bone health. Vitamin D deficiency can even play a role in migraines and headaches: go back to my blog post here to read more.


  • Vitamin D reduces the production of nitric oxide (NO). Nitric oxide is a signaling molecule in the body that causes blood vessels to widen and stimulates the release of certain hormones, such as insulin and human growth hormone. NO affects neurotransmission and vasodilation and is considered a key mediator in migraine. Therefore, it is possible that vitamin D can diminish the frequency of migraine attacks by inhibiting NO synthase production.

  • Vitamin D also influences the release of dopamine and serotonin, which are known to be connected with migraine. In addition, Vitamin D deficiency may also cause depression, which often coexists with all types of headache.


Almost every cell in your body expresses the vitamin D receptor, giving vitamin D control of over 200 genes (and the proteins they regulate)! The vitamin D receptor gene provides instructions for making a protein called vitamin D receptor (VDR), which allows your body to respond to vitamin D. To put it more simply: almost every cell in your body is equipped to respond to vitamin D and transform it.


Now you can imagine that vitamin D is heavily involved in many biological processes, including immune function, cell differentiation, gut barrier function, nutrient absorption (particularly of calcium, magnesium, and phosphorus), bone formation, cardiometabolic health, and neurological health.



It’s probably easier to ask what vitamin D DOESN’T do!


How does vitamin D specifically impact your hormone balance?

Vitamin D receptors are present in various endocrine glands, like your hypothalamus, pituitary gland, and adrenal glands. These receptors enable vitamin D to modulate your hormone production.


Vitamin D is known to influence sex hormone production and activity: It has been found to affect estrogen and testosterone levels and SHBG (Sex Hormone Binding Globulin - It's a protein made mostly in your liver. It binds to sex hormones in your blood and therefore helps control the amount of sex hormones that are actively working or available to use in your body.) especially. The lower the level of vitamin D, the lower the level of testosterone, estrogen and SHBG Source


Vitamin D and insulin: Studies have shown that vitamin D deficiency may impair insulin production and increase insulin resistance, therefore contributing to imbalanced blood sugar levels. Source


Vitamin D and thyroid hormones: Research suggests that vitamin D deficiency may impair thyroid hormone synthesis and contribute to hypothyroidism. Adequate vitamin D levels are essential for proper thyroid hormone production and a healthy functioning thyroid.


Vitamin D has been found to modulate cortisol levels, helping to regulate the stress response. Adequate vitamin D levels can help support a healthy stress response.



Did you know that vitamin D is one of the hardest nutrients to get from your diet?


Yep and this is also what I see in my practice: there’s hardly a client who’s not deficient in vitamin D! Studies show that 100% of people don’t get enough vitamin D from their diets.


Ok, there is some vitamin D in fatty fish, but in fact, sun exposure is the major way to get your vitamin D.

If you're deficient or insufficient, it can be very (very, very) tough to bring levels up to the optimal range from sun exposure and foods alone.


Your body is actually producing vitamin D by the interaction between UV radiation and a special sterol in your skin. Your skin contains a sterol that reacts with ultraviolet B (UVB) light from the sun to produce vitamin D3 (cholecalciferol). Cholecalciferol then travels to the liver via the vitamin D-binding protein, where it’s further modified (into 25-hydroxyvitamin D), and then to the kidneys, where it’s activated into 1,25(OH)2D). And the same happens with dietary vitamin D3 and D2 when you consume it. You can see that vitamin D deficiency can also be linked to your liver and/or kidney health.


Now, last week we talked about protecting your skin from the sun and using sunscreen… yes, unfortunately that UV filter that protects your skin, also inhibits the production of vitamin D, even if you are exposed to the sun!


So besides not getting enough vitamin D from food and not getting enough sun exposure, what else can impact deficiency?

  • Blood sugar dysregulation and insulin resistance are linked to vitamin D deficiency. One study even found a direct correlation between low Vitamin D and diabetes.⁠

  • Systemic inflammation is associated with lower vitamin D.⁠

  • Deficiencies in vitamin K2, magnesium & boron are also associated with chronically low vitamin D.⁠

  • Overuse of sunscreens and lotions with SPF, and lack of time outdoors.

  • If your fat digestion is not working optimally, it will impact your absorption of vitamin D (as stated above, vitamin D is a fat soluble vitamin, meaning it needs to be linked to fatty acids so that your body can absorb it)

  • Genetic predisposition to vitamin D deficiency: variants in the VDR gene impact absorption, metabolism and utilization of vitamin D.

  • Skin pigmentation (people with dark skin produce less vitamin D from sun exposure or rather need to spend more time in the sun in order to produce vitamin D)

  • Due to the importance of the liver and kidney in converting inactive vitamin D into its active form, people with liver or kidney disease are also more likely to experience low vitamin D levels.⁠


Consider supplementing with vitamin D: you want to aim for a minimum of 2,000 to 5,000 IU daily depending on what your base levels are. Recheck your levels every 6 months to make sure both that you are getting enough vitamin D and that you don’t get too much of it. Vitamin D in excess of 150 ng/mL can be toxic!


Why you should always take vitamin D with K2

In the absence of vitamin K2, calcium circulating in the body that has been absorbed from food by vitamin D is also deposited in the soft tissues of the body and in the arteries, leading to arterosclerosis. Vitamin D3 should therefore always be taken in combination with vitamin K2.



⁠So if you have been consistently supplementing with vitamin D and it’s still low or symptoms continue to persist, it’s time to start looking for other causes.


I hope you found this article helpful? Give me a like if you did 🙂




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