Vitamin D: The ultimate multitasker (and why it really matters to overall health)

Published January 17, 2024

The human body, a complex network of cells, tissues, organs, and systems, operates with remarkable precision. And among the many essential components needed for good health, vitamin D emerges as a critical player. 

Why is vitamin D important?

Vitamin D is essential for the body’s absorption and storage of calcium and phosphorus (pronounced fos-fuh-rus). Without enough vitamin D, the body's ability to absorb and store these minerals is compromised. This can lead to health conditions like osteoporosis (pronounced ah-stee-oh-puh-roh-sis), a disease that weakens bones and makes them more likely to break.¹ 

But there’s more to vitamin D than just bone health. Vitamin D is a key player in keeping your heart, blood vessels, immune system, brain, muscles, and nerves healthy. It also helps regulate blood sugar levels and maintain normal blood pressure—making it important for overall health and wellness.¹

What is vitamin D?

Vitamin D is a fat-soluble vitamin that helps with all sorts of important functions in your body. There are 2 main groups of vitamins: water-soluble and fat-soluble. They are different in how they are absorbed and if they are stored by your body.² 

Water-soluble vitamins (think B vitamins) dissolve in water and are absorbed into the bloodstream through the digestive tract. And since your body doesn’t store these vitamins for long, it gets rid of any extra. This is why your urine might look bright yellow if you take vitamin B12. But that doesn’t always mean it’s not being absorbed. When your body gets more water-soluble vitamins than it needs, any extra will be flushed out of your body in your urine.³

But fat-soluble vitamins—like vitamin D—are different. Fat-soluble vitamins dissolve in fat instead of water. They are also stored in your body. After vitamin D is absorbed, it gets stored in the body’s fat cells where it will remain inactive until your body needs it. When needed, the liver and kidneys take over, turning the inactive form of vitamin D into the active form your body needs.⁴ 

Are there types of vitamin D?

Vitamin D is also called calciferol (pronounced kal-sif-er-all). The 2 main forms of vitamin D are⁴:

1. Vitamin D2, ergocalciferol (pronounced er-goh-kal-sif-er-all) - This form mostly comes from plants and is often added to foods and supplements.
2. Vitamin D3, cholecalciferol (pronounced koh-luh-kal-sif-er-all) - This form is naturally made by our bodies when exposed to sunlight. It can also be found in some animal-based foods.  

While vitamin D2 and D3 play the same role in your body, their chemical makeup is a bit different. This is because D2 comes from plants and D3 comes from people and animals. Despite this difference, your body can change both types into the active form of vitamin D and help keep your overall vitamin D levels in check.⁴ ⁵

How do you get vitamin D from the sun?

Vitamin D is known as the "sunshine vitamin" because our bodies mainly produce it when the skin absorbs sunlight. This process begins with special cells in our body called vitamin D receptor cells. When these cells are exposed to ultraviolet B (UVB) light from the sun, a series of events happen. The process starts with the conversion of cholesterol in the skin and eventually leads to the body producing vitamin D on its own. But vitamin D also needs help to travel through the bloodstream. So, it attaches itself to a carrier protein made in the liver, and these proteins carry vitamin D to where it's needed in the body.⁴

Sunlight has long been a natural source of vitamin D. But getting enough through sun exposure alone can be challenging, especially for those who live in areas with limited winter sunlight or spend most of their time indoors.

What foods are high in vitamin D?

Natural sources of vitamin D include fatty fish like mackerel, salmon, trout, and tuna. It’s also found in smaller amounts in beef liver and egg yolks. Mushrooms contain vitamin D2, and some are also treated with UV light to boost their levels. Because few foods naturally contain vitamin D, many people get their vitamin D from supplements or fortified foods like milk and some plant-based milks, cereals, orange juice, and other food products.⁵

Is it common to have a vitamin D deficiency? 

A vitamin D deficiency means that your body doesn’t have enough vitamin D. Vitamin D deficiency affects about 1 billion people worldwide, including 35% of adults in the US.⁶

What causes vitamin D deficiencies?

Some causes of vitamin D deficiency include a lack of vitamin D in your diet or exposure to sunlight. Certain medications and health conditions can also have an impact on how much your body absorbs and uses.⁶

What are the symptoms of a vitamin D deficiency?

People with low vitamin D levels might not have any symptoms, and if they do, symptoms could look like other health conditions.

Symptoms of vitamin D deficiency (too little) can include:

• Bone pain
• Muscle weakness, twitches, aches, or cramps
• Tingling in the hands or feet
• Tiredness
• Lack of energy
• Depression
• Mood changes
• Confusion
• Hair loss

What are the side effects of too much vitamin D?

As a fat-soluble vitamin, vitamin D is stored in the body. This means that any extra is stored in fat cells instead of being eliminated in the urine like water-soluble vitamins. When too much vitamin D is stored in the body, it can lead to potential health issues.⁷

Having too much vitamin D (toxicity) is rare. Usually, this only happens by taking too much of a vitamin D supplement or prescription medication.⁸ 

Symptoms of vitamin D toxicity (too much) can include:

• Nausea
• Weakness
• Vomiting
• Constipation
• Loss of appetite
• Stomach pain
• Weight loss

If you're experiencing any of these symptoms, speak to your doctor.

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References

1. National Institutes of Health. Vitamin D fact sheet for consumers. Accessed January 8, 2024. https://ods.od.nih.gov/pdf/factsheets/VitaminD-Consumer.pdf.
2. PubMed. Lykstad J, Sharma S. Biochemistry, water soluble vitamins. Accessed January 8, 2024. https://www.ncbi.nlm.nih.gov/books/NBK538510.  
3. Medical News Today. Bright yellow urine: colors, changes, and causes. Accessed January 8, 2024. https://www.medicalnewstoday.com/articles/313779. 
4. Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D. Washington DC: The National Academies Press (US); 2011. https://doi.org/10.17226/13050 
5. National Institutes of Health. Vitamin D. Accessed January 8, 2024. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional. 
6. Cleveland Clinic. Vitamin D deficiency: causes, symptoms, and treatment. Accessed January 8, 2024. https://my.clevelandclinic.org/health/diseases/15050-vitamin-d-vitamin-d-deficiency. 
7. Mayo Clinic. Vitamin D toxicity: What if you get too much? Accessed January 8, 2024. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/vitamin-d-toxicity/faq-20058108.
8. Cleveland Clinic. Vitamin D toxicity. Accessed January 8, 2024. https://my.clevelandclinic.org/health/diseases/24750-vitamin-d-toxicity-hypervitaminosis-d.