Why is Vitamin D So Important? Sources, Benefits, and How to Make Sure You’re Getting the Right Amount


Approximately half the world’s population is deficient in vitamin D, an essential nutrient for many aspects of health and well-being. This means over a billion people globally are at higher risk of developing various chronic diseases.

But why is vitamin D so important, and how can you make sure you’re getting the right amount? Read on to learn what vitamin D is, what roles it plays in various systems of the body, and how to make sure you’re getting enough–without overdoing it.

What is vitamin D?

Vitamin D is a fat-soluble vitamin, naturally present in foods, that plays a crucial role in maintaining the health of our bones, teeth, immune system, and other important bodily functions. But, interestingly, it’s also a hormone that can be synthesized by our own bodies–namely, our skin when exposed to sunlight.

There aretwo main forms of vitamin D: vitamin D2 (ergocalciferol) and D3 (cholecalciferol). Vitamin D2 is found mainly in plant foods and fortified foods, while vitamin D3 is obtained from sunlight exposure, animal-based foods, and supplements.

Why is vitamin D so important?

Vitamin D plays a pivotal role in our health. It regulates the absorption of calcium and phosphorus, critical for the growth and development of bones and teeth. That’s why vitamin D deficiency can lead to rickets in children and osteomalacia in adults–both characterized by weak, fragile bones.

But vitamin D does much more than support healthy bones. It helps govern immune responses, such as regulating the activation of T cells, a key immune cell that helps us ward off infections.

Recent research even suggests a possible link between sufficient vitamin D levels and a reduced risk of developing autoimmune diseases like multiple sclerosis (MS) and type 1 diabetes. Studies also suggest that vitamin D levels have a significant impact on cardiovascular health, associating deficiency with increased coronary risk factors.

Given the many vital functions of vitamin D in the body, it’s essential to make sure you’re getting enough of this important nutrient.

Best sources of vitamin D

Sunlight is the primary source of vitamin D3 for many people. Our skin naturally produces vitamin D3 in reaction to ultraviolet B (UVB) rays from the sun.

To get your dose of vitamin D3 this way, some researchers recommend exposing about a third of your skin (by wearing a tank top and shorts) to the sun for 10 to 30 minutes without sunscreen three times a week.

Be careful to adjust that timing based on your skin sensitivity and color, applying sunscreen as needed to prevent burning. Wearing a hat and sunglasses to protect your face and eyes is fine, as skin on the head produces only a small amount of vitamin D.

Because getting out in the sun frequently may not be an option due to geographical location, season, or sun protection measures, prioritizing foods with high vitamin D content is also important. Although, it’s worth noting that getting enough vitamin D through diet alone can be difficult.

Here are some vitamin D-rich foods to enjoy:

  • Fatty fish like salmon, mackerel, and sardines
  • Cod liver oil
  • Vitamin D fortified foods such as milk, orange juice, and cereal
  • Yogurt
  • Beef liver
  • Some mushrooms (contain traces of vitamin D2)

Common health issues impacted by vitamin D

We’ve established the critical role of vitamin D in our overall health. Now let’s delve into how vitamin D impacts some specific, common health concerns.

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Osteoporosis and osteomalacia

Because of the role vitamin D plays in keeping our bones healthy, it’s particularly significant in the prevention of osteoporosis and osteomalacia. Both of these conditions cause bones to become weak and brittle, making them more prone to fractures.

Vitamin D helps prevent bone diseases in two ways. First, it promotes the absorption of calcium in the gut. Calcium is the primary building block of our bones and is vital for maintaining their strength and density. Without sufficient vitamin D, our bodies can’t absorb the calcium we consume in our diet, leading to calcium deficiencies and weaker bones over time.

Secondly, vitamin D plays a vital role in bone remodeling–our body’s continuous process of breaking down old bone and forming new bone. Adequate vitamin D levels support this process of maintaining strong, healthy bones.

Immune health

Vitamin D plays a key role in boosting immunity. It regulates the function of white blood cells that fight off pathogens, while also preventing an overactive immune response that can lead to harmful inflammation. This delicate balancing act is essential to maintain a healthy, robust immune system.

Specifically, vitamin D helps manage the behavior of B cells and T cells, integral components of the body’s innate defense against infections. This may explain why, according to some studies, upping your vitamin D intake can help shorten the duration of a cold and even reduce your risk of getting the flu.

Heart health

Recent research shows vitamin D can help regulate blood vessel function and reduce internal inflammation, both of which are essential for maintaining a healthy cardiovascular system.

Adequate vitamin D levels may also help prevent the development of heart-related conditions such as atherosclerosis (thickening or hardening of the arteries) and coronary artery disease (narrowing or blockage of the blood vessels that transport blood and oxygen to the heart).

It does this by reducing cholesterol build-up in your arteries, adjusting important proteins in your blood cells, and affecting how your blood clots.

High blood pressure

High blood pressure, or hypertension, has been linked to low levels of vitamin D in the body.

By modulating renin production (an enzyme produced in the kidneys that regulates blood pressure), vitamin D seems to play a role in keeping our blood pressure within a healthy range.

This likely explains why, according to a number of studies, people with higher levels of vitamin D have a lower risk of developing hypertension.

Type 2 diabetes

Vitamin D also plays a role in managing blood sugar levels, which has implications for type 2 diabetes.

Type 2 diabetes is a condition in which our bodies either don’t produce enough insulin (a hormone that regulates the movement of sugar into our cells) to maintain normal glucose levels or resist the effects of insulin.

Emerging research shows that vitamin D can improve the body’s sensitivity to insulin, making it more effective at regulating our blood sugar levels. With better insulin sensitivity, you’re at a notably lower risk of developing type 2 diabetes.

Furthermore, vitamin D may help reduce inflammation. Chronic inflammation is often associated with insulin resistance, a condition in which our cells don’t respond properly to insulin, leading to high blood sugar levels (a precursor to type 2 diabetes).

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More research is needed to fully understand vitamin D’s role in reducing the risk of diabetes. But maintaining healthy levels of the nutrient–along with regular exercise and a balanced diet–could be part of a fantastic preventative strategy.


Recent research suggests vitamin D has an influence on mental health–particularly depression.

Across a number of studies, scientists have found an association between low vitamin D levels and increased risk of major depressive disorder.

Although the exact mechanism isn’t fully understood, experts believe vitamin D plays a role in regulating the production of neurotransmitters, such as serotonin, which are essential for maintaining a balanced mood.

Multiple sclerosis

Research indicates that low levels of vitamin D may increase the risk of developing multiple sclerosis (MS), a complex autoimmune disease that affects the central nervous system. This may be because, according to some studies, vitamin D helps reduce the number of certain immune cells known to cause damage in MS.

Conversely, people with higher vitamin D levels have a reduced risk of developing multiple sclerosis. In fact, one study found that women who took more than 400 international units (IUs) of vitamin D each day had a 41% lower risk.

Although more research is needed to understand the exact relationship, it seems clear that maintaining adequate vitamin D levels may help protect against this potentially devastating condition.


Vitamin D’s potential impact on cancer risk is a topic of ongoing research. Early studies suggested people living in regions with high sunlight exposure (and, therefore, likely higher vitamin D levels) had a lower incidence of certain cancers, such as prostate, multiple myeloma, colorectal and breast cancer.

Animal studies also indicate vitamin D may slow the development and spread of cancer by promoting cell differentiation and inhibiting cell growth. However, results from human studies are mixed. Still, generally speaking, low vitamin D levels are associated with higher overall cancer mortality.

What are the symptoms of vitamin D deficiency?

Vitamin D deficiency can manifest in various ways. Some common symptoms include:

  • Fatigue
  • Weakened immune system, or frequent infections and illnesses
  • Bone, joint, and/or muscle pain
  • Muscle weakness
  • Depression and related symptoms, such as anxiety, difficulty sleeping, or trouble concentrating
  • Slowed wound healing
  • Hair loss
  • Weight gain

The more severe your vitamin D deficiency, the higher your risk of serious symptoms, diseases, and even mortality. So it’s crucial to be aware of these symptoms and make sure you’re getting enough of this vital nutrient.

Vitamin D as a supplement: how and when to take it

Ideally, we would get all our vitamin D from sunlight and food. But sometimes this isn’t possible, and supplementation can be beneficial.

When considering vitamin D supplementation, it’s important to start by identifying a deficiency. Your healthcare provider can perform a simple blood test to determine your levels and help you make informed decisions about how much and how long to supplement.

The general recommended daily allowance (RDA) of vitamin D is as follows, although you may need more if you have limited access to sunlight or other health concerns:

  • Birth to 12 months: 400 IU (10 micrograms mcg)
  • Children 1 to 13 years: 600 IU (15 mcg)
  • Teens 14 to 18 years: 600 IU (15 mcg)
  • Adults 19 to 70 years: 600 IU (15 mcg)
  • Adults 71 years and older: 800 IU (20 mcg)
  • Pregnant and breastfeeding women: 600 IU (15 mcg)
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Vitamin D2 vs D3: which should you take?

While vitamin D supplements are available in two forms (D2 and D3), some studies show that D3 is more effective at raising blood levels of the vitamin’s active form.

Supplements come in various strengths, and the appropriate dose for you will depend on your level of deficiency and specific needs.

When should you take vitamin D supplements?

Since vitamin D is fat-soluble, the best time to take it is with a meal that contains fats, as this helps increase absorption. Incorporating vitamin D-rich foods can also help you maintain optimal levels.

Be sure to consult with your healthcare provider before starting a vitamin D supplement to determine the right dose. Excess vitamin D intake can lead to toxicity, or overdose.

Overdosing on vitamin D: Can you take too much?

While essential for many bodily systems, it is possible to consume too much vitamin D.

Symptoms of vitamin D overdose

  • When you have too much vitamin D in your body, you may be at risk of a condition called hypervitaminosis D–although, it’s relatively rare, as most people are more likely to be deficient.
  • Still, it’s important to recognize the symptoms of hypervitaminosis D and understand the potential risks associated with taking too much vitamin D. Symptoms of overdose include:
  • Nausea and vomiting. High levels of vitamin D can cause gastrointestinal symptoms. These are often the first signs of toxicity.
  • Increased thirst and frequent urination. Excess vitamin D can lead to a higher concentration of calcium in the blood. This triggers increased thirst and more frequent urination as your body strives to regulate your calcium levels through excretion.
  • Weakness and fatigue. Too much vitamin D can cause muscle weakness and general tiredness, which can negatively impact your quality of life.
  • Joint and muscle pain. Vitamin D overdose can lead to increased calcium deposits in the joints and muscles, causing inflammation and pain.
  • Kidney stones and kidney damage. In extreme cases, excess vitamin D can cause calcium deposits to form in the kidneys, leading to the development of kidney stones and potential organ damage.

Striking the right balance of vitamin D–through sunlight, food, and/or supplements–is critical for the optimal functioning of many bodily systems. So keep tabs on your levels, and follow expert advice to make positive changes in your overall health and quality of life.





























































































Carrie Solomon

Carrie Solomon is a freelance health writer, copywriter, and passionate wellness enthusiast. She’s on a mission to help wellness-focused companies educate, engage, and inspire their audiences to make the world a healthier, happier place. Learn more about her at copybycarrie.com or on LinkedIn.

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