We often hear about taking Vitamin C for colds or Calcium for bones, yet one nutrient shines above the others: Vitamin D. Often called the “Sunshine Vitamin,” Vitamin D is more a hormone of light than a “vitamin.” And your body can build this medicine directly from the sun’s rays.
It’s the ultimate “super-nutrient” that plugs you right into the Earth’s energy.
Right now, a massive “cloud” of deficiency covers the world. Despite its importance, research suggests that nearly half the world’s population, including roughly 75% of Americans, suffer from low Vitamin D levels. This isn’t just a minor nutritional gap; it is a significant public health concern linked to everything from the common cold to chronic diseases. (1)
When you lack Vitamin D, your “inner battery” runs low, and your health starts to fade.
So What Is Vitamin D?
Vitamin D, despite its name, is better explained as a pro-hormone. As a comparison, beta-carotene is a pro-vitamin A; your body uses this nutrient to manufacture Vitamin A. Your body uses sunlight to create Vitamin D, which then goes through further processes in the body to reach the important nutrient your body needs.
Vitamin D is a fat-soluble nutrient that helps your body absorb calcium and phosphorus, which are essential for strong bones and overall health. Unlike most vitamins, your body can produce vitamin D on its own when your skin is exposed to sunlight (specifically UVB light). It can also be obtained from certain foods and supplements.
Specifically, Vitamin D...
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refers to a group of fat-soluble compounds (mainly D₂ and D₃) that act like hormones in the body.
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helps the intestines absorb calcium and phosphate, which keeps your bones and teeth strong.
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through its influence on calcium balance, also affects muscle function, immune response, and more.
How the Body Creates Vitamin D
☀️ Your body makes Vitamin D through a step-by-step process:
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Sunlight Hits the Skin: When ultraviolet-B (UVB) rays from sunlight reach your skin, they trigger a chemical reaction with a molecule called 7-dehydrocholesterol in the skin. This forms vitamin D₃ (cholecalciferol).
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First Conversion in the Liver: Vitamin D₃ enters the bloodstream and travels to the liver, where it’s changed into 25-hydroxyvitamin D (calcidiol) — the main form measured to assess vitamin D status.
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Activation in the Kidneys: Calcidiol then moves to the kidneys, where it is converted into the active hormone form called 1,25-dihydroxyvitamin D (calcitriol). This active form helps regulate calcium and phosphate in the body.
Other Sources of Vitamin D
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Food sources: fatty fish and fish liver (think cod liver oil), fortified dairy and cereals, egg yolks.
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Supplements: vitamin D₂ (from plant sources) or D₃ (often from animal sources).
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Sunlight is the main source for most people, especially where dietary vitamin D is low.
Why This Matters
Without enough vitamin D:
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Calcium absorption drops.
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Bone mineralization suffers.
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Conditions like rickets (in children) or osteomalacia (in adults) can occur.
Balancing sun exposure, diet, and sometimes supplements helps maintain healthy vitamin D levels for bones, immunity, and overall well-being.
Here's what could happen if you don't get your daily dose of Vitamin D:
1. Cancer
The body generates around 10,000 cancer cells each day. Vitamin D deficiency allows these cancer cells to proliferate and invade new tissue. When vitamin D levels are optimal, the body works harder to inhibit cancer progression and decrease inflammation. Vitamin D is an important part of a powerful and healthy immune system that nips cancer cells at the bud. When the body is deficient in vitamin D, autoimmune complications increase, which allows cancer cells to grow and spread. A long-term vitamin D deficiency leaves you at risk for multiple types of cancer, including breast, prostate, cervical, ovarian and pancreatic. (2)
2. Type 2 Diabetes
Some studies have shown that young people who have higher vitamin D levels decreased their chances of developing type 2 diabetes later in life, compared to those with lower vitamin D levels. Researchers believe that vitamin D can help the body manage blood sugar levels by regulating calcium. Without adequate vitamin D, the body may have a harder time managing blood sugar, which can lead to type 2 diabetes. (3) 
3. Asthma
The exact cause of asthma is unknown, but one theory is that not getting enough sun exposure and vitamin D may cause the illness. Here's where the link is: Individuals are more likely to get asthma if they live in a city, are obese or are African American. These three groups of people are also more likely to be vitamin D deficient. When a person has asthma, their airways swell, clog with mucus and tighten due to inflammation. When the body has adequate vitamin D, inflammation is significantly reduced. (4)
4. Inflammatory Bowel Disease
Studies have shown that people with IBD are more likely to have low levels of vitamin D. Vitamin D receptors are found on the surface of a cell where they receive chemical signals. These chemical signals direct a certain cell to divide or die. Vitamin D receptors can be found on cells in the digestive direct and the immune system. When the body has an adequate amount of vitamin D, it can reduce levels of inflammatory proteins that get produced. In someone who is vitamin D deficient, these inflammatory proteins are able to multiply, causing IBD. (5) 
5. Bone Fractures / Poor Bone Development
We all need calcium to build strong bones, right? Well, did you also know that Vitamin D plays an important role in helping the body absorb calcium, which is essential for strong bones? Yep, and a vitamin D deficiency can cause a condition known as osteomalacia, which is a softening of the bones. It can also cause brittle bones and weak muscles. (6)
6. Hypertension
Studies over the years have varied about the relationship between Vitamin D and blood pressure. "According to Dr. Nissen, vitamin D does play an integral part in the regulation of blood pressure, but it’s a complicated process." (7)
So let's uncomplicate it!
You see, Vitamin D and calcium play important roles in the body, and calcium build up in soft tissues (that's your arteries, folks!) can lead to hypertension. At times, the body can produce too many cells in the muscle that lines your blood vessels. A build-up of these cells can cause plaque, making it harder for blood to travel through the body. Researchers have found that vitamin D can bind to these cells and help reduce the risk of plaque build-up. (8)
Despite a recent meta-analysis of randomized control studies concluding that vitamin D supplementation has little to no effect on hypertension, they admitted that participants did not have low vitamin D levels to begin with. So maybe, just maybe, their hypertension was caused by something other than Vitamin D deficiency. But that does not prove that actual Vitamin D deficiency does not lead to hypertension and therefore increasing serum D will improve blood pressure. (9)
