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Vitamin D: A Key to Health

authored by Taylor Appel, MSCN, RH (AHG)

Vitamin D is well-known as an immune-booster. But did you know it also greatly influences a variety of metabolic processes that are critical to maintaining health? In fact, vitamin D influences over 3000 gene-regulated functions, and can even work prophylactically to prevent over 15 varieties of cancers and numerous other debilitating diseases.1 Maintaining healthy vitamin D levels has been shown to drastically impact not only our physical health, but mental health as well, helping to support both seasonal depression and anxiety disorders.2 Prioritizing vitamin D intake is essential, especially during the darker, winter months with shorter days and less sunshine available, as well as greater prevalence of colds and flu.

What is Vitamin D?

Vitamin D is a secosteroid structured molecule that chemically resembles cholesterol. Since it is a fat-soluble vitamin, you should always take vitamin D supplements with dietary fats to aid in absorption. Vitamin D can be found in multiple forms, such as D2 and D3. Vitamin D3, also known as cholecalciferol, is the more bioavailable form of vitamin D, and is therefore the preferred supplement form when food-based sources are unavailable or cannot be digested properly due to illness or other implications.3 

In addition to optimizing our immune system function, vitamin D brings a myriad of other positive benefits to the table that can have a considerable impact on health outcomes, especially if you have cancer or other chronic disease.

Therapeutic Benefits of Vitamin D

  • Cellular Growth - regulates cellular development, especially epithelial cells throughout the body
  • Calcium and Phosphorus Regulation - helps to regulate serum calcium level and improves bone density3
  • Bone Formation & Joint Health - directly impacts childhood growth and development, bone strength, and recovery from injury and inflammation; reduces chances of brittle bones, bone pains, risk for fractures, and risk of falling3,4
  • Enhances Radiation Efficacy - supports the eradication of radiation-resistant cancer cells when used as a combination therapy with proper supplementation3
  • Reduces Risk of Cancers and Chronic Diseases - improves immune function to help decrease inflammation and expedite illness recovery5

Vitamin D is often referred to as a hormone because of its pleiotropic nature and direct impact on so many disease outcomes.1 Research has clearly substantiated the importance of this vitamin in a variety of metabolic processes, from calcium and phosphorus absorption in bone-health regulation, to its ability to substantially lower the mortality rate of any disease by providing potent immune-supporting effects.6 Maintaining healthy vitamin D levels can directly impact our body’s response to disease, inflammation, and both physical and mental stress.1,5 

How Low Vitamin D Levels Impact the Body

Chronically low serum, or blood levels, of 25-hydroxyvitamin D, the appropriate biomarker used to analyze vitamin D levels, can greatly impact immune function and even lead to higher risks for autoimmune conditions. Chronic lower levels can also have a tremendous impact on emotional and mental health as well, commonly experienced by most as a seasonal depression in the less sun-filled months of winter. 

Chronically low vitamin D levels can lead to weakened tooth enamel (especially in children), muscle weakness and fatigue, dysregulated serum calcium levels, and the likelihood of becoming sick more often with longer recovery periods.3 Becoming chronically lower in vitamin D does not happen overnight. In fact, some populations are predisposed to a higher risk of deficiency simply due to physical characteristics such as having a darker skin complexion. Generally, the darker the pigment of the skin, the more trouble someone will have absorbing vitamin D from the sun, leading to a heightened risk of low serum levels.3-5 

Additionally, those with very fair skin, who constantly apply sunscreen and actively avoid the sun, are also at a higher risk of deficiency and should be regularly assessed for supplemental needs. Elderly are another at-risk population for vitamin D deficiency, as generally older individuals tend to eat a much less varied diet and are likely to spend less time outdoors due to physical impairments. Vegans and those with highly restrictive diets or absorption issues are also at a much higher risk to become vitamin D deficient and should consult with their healthcare provider to ensure they are adequately nourished.3-5 

Can You Take Too Much Vitamin D?

Toxicity from vitamin D can occur from over-supplementing and can cause many health complications, including kidney stones, calcium deposits in blood vessels, and adverse cardiovascular events. It is important to always discuss the type and dosing of your vitamin D supplement with your healthcare provider before beginning a new regimen to avoid unwanted and potentially harmful side effects. Spending time outdoors in the sun and gravitating toward foods rich in vitamin D is the easiest and safest option for improving vitamin D levels.5

Quality Food Sources of Vitamin D

Many foods are naturally rich in vitamin D. From dairy products, like milk and cheeses, to fish, eggs, cod liver oil, and mushrooms, vitamin D can be found in a variety of food sources. Many foods are even fortified with vitamins, including vitamin D2 (the less available form of vitamin D), non-food derived calcium, iron chelates, and more, to ensure we receive “enough” of each nutrient in our daily diets. Unfortunately, the bioavailability of these low-quality nutrients added to ultra-processed, fortified products is generally very poor, and therefore should not be used as your main source. Instead, whole-food sources of vitamin D offer a much better form to support overall health. A few of my personal favorite food sources of vitamin D include wild-caught salmon, fresh liver pate, and pasture-raised chicken.3,5

Other Options for Supporting Vitamin D Levels

Although foods rich in vitamin D can be beneficial for supporting overall serum levels, nothing truly compares to good, old-fashioned, safe sun exposure. Spend 10-30 minutes each day in the sun, without sunglasses or coverings, and with as much skin exposure as possible to allow your skin to absorb vitamin D more efficiently. If you live somewhere with darker winter months, other tools can be used to adequately support blood-levels of vitamin D and reduce the risk of deficiency. Some of my favorite vitamin D-boosting tools include:

  • Bright light therapy (BLT): Research has shown this therapy is effective at supporting seasonal mood disorders by mimicking sunlight, improving systemic circulation, and lowering overall inflammation levels. It is recommended to use a light box device that emits full spectrum light for thirty minutes to two hours per a day to help combat seasonal affective disorder.7
  • Food-derived vitamin D supplementation: Choose a supplement that uses the D3 form of vitamin D, preferably from food-based sources such as shellfish and herbs. Natura Health Products has a top-quality supplement product called Vitamin D-A-K. This formula delivers highly bioavailable forms of vitamins D, A and K. Vitamin D, vitamin K and the carotenoid complex are known for their vast array of health benefits, especially in relation to healthy immune system response, cell-cycle functions, and skeletal health. The bioavailable form of vitamin D in this product supports deficiencies and optimizes immune system health, including for those with cancer and other chronic diseases.

Supplementing with Vitamin D

Here's additional information from Mederi Center founder and creator of Natura Health Products that you many find helpful:

  • It’s best to supplement with a food grown form that also includes a small amount of vitamin K (either K-1 or K-2, or both), and vitamin A.
  • Simply taking extra vitamin D is not the correct approach. Instead, the appropriate amount must be provided to maintain serum levels in a healthy range 25 OH (>45 <80).
  • Always check both forms of vitamin D; that means 25-OH and 1,25 dihydroxyvitamin (di OH). While 1,25 vitamin D is the most potent vitamin D metabolite, 25-OH vitamin D levels more accurately reflect vitamin D status because parathyroid hormone and other hormones do not influence it. If you only check 25-OH after supplementing with vitamin D, and the levels don’t increase, proceed by checking the 1,25 di OH level and the parathyroid hormone level. If these are either high normal, or elevated out-of-range, then you need to seek a professional skilled at normalizing vitamin D levels.

Optimizing vitamin D levels can profoundly impact your health, especially in the colder, less sun-filled days of winter. Regardless of the season, make sure to have your serum, or blood, levels assessed, so you can supplement appropriately. Always consult your healthcare provider before adding new supplements to your routine, as you can cause potential adverse side effects with improper dosing of vitamin D. By actively improving vitamin D levels through healthy dietary choices and regular sunshine exposure, you can feel confident that you are not only improving your immune system, but also lowering your risk for all diseases, especially cancers.6 Vitamin D is much more than a nutrient, it’s a key to vitality! 



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  1. Yance, D. (n.d.). Vitamin D Reseach Monograph.v.9.0.
  2. Akpınar Ş, Karadağ MG. Is Vitamin D Important in Anxiety or Depression? What Is the Truth?. Curr Nutr Rep. 2022;11(4):675-681. doi:10.1007/s13668-022-00441-0
  3. Marciano M, Vizniak N, 2nd ed. Vitamin D. Botanical Medicine. Professional Health Systems; 2019:90-91.
  4. U.S. Department of Health and Human Services. (n.d.). Office of dietary supplements - vitamin D. NIH Office of Dietary Supplements. 
  5. Sundaram S, Sea A, Feldman S, Strawbridge R, Hoopes PJ, Demidenko E, Binderup L, Gewirtz DA. The combination of a potent vitamin D3 analog, EB 1089, with ionizing radiation reduces tumor growth and induces apoptosis of MCF-7 breast tumor xenografts in nude mice. Clin Cancer Res. 2003 Jun;9(6):2350-6. 
  6. Saliba W, Barnett O, Rennert HS, Rennert G. The risk of all-cause mortality is inversely related to serum 25(OH)D levels. J Clin Endocrinol Metab. 2012;97(8):2792-2798. doi:10.1210/jc.2012-1747
  7. Campbell PD, Miller AM, Woesner ME. Bright Light Therapy: Seasonal Affective Disorder and Beyond. Einstein J Biol Med. 2017;32:E13-E25.
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