Vitamin D

Last Updated: April 28, 2024

Vitamin D

Vitamin D, often hailed as the “Sunshine Vitamin,” is unique because our bodies can produce it when exposed to sunlight. It’s also found in certain foods and supplements. This nutrient undergoes a two-step process in the body to become active, supporting crucial functions like calcium absorption for strong bones and immune system regulation. Available in two dietary forms, D2 and D3, Vitamin D’s absorption is efficient and essential for maintaining optimal health. While measuring Vitamin D levels can be challenging due to testing variability, it’s a key indicator of bone health and overall well-being. Vitamin D is a vital nutrient that supports a range of bodily functions, from bone health to immune response, underscoring its importance in our daily lives.

What is Vitamin D?

Vitamin D is a fat-soluble nutrient essential for maintaining strong bones and teeth, supporting immune system health, and regulating muscle function. It’s unique because your body can produce it when exposed to sunlight. Besides sun exposure, you can obtain Vitamin D from certain foods like fatty fish, egg yolks, and fortified dairy products, as well as dietary supplements. This vitamin plays a crucial role in calcium absorption in the gut, which is vital for bone growth and remodeling. Its importance extends beyond bone health, as emerging research suggests links to reduced risks of chronic diseases, including certain cancers and heart disease.

What type of vitamin is vitamin D?

Vitamin D is classified as a fat-soluble vitamin, meaning it can dissolve in fats and oils. This property allows Vitamin D to be stored in the body’s fatty tissues and liver, making it available for use when needed, especially when sunlight exposure or dietary intake is limited. Fat-soluble vitamins differ from water-soluble ones, which need to be regularly consumed because they are not stored in the body to the same extent. Vitamin D’s role in calcium absorption, bone health, and immune function highlights its importance in maintaining overall health.

Structure of Vitamin D

Vitamin D includes compounds like vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol), which are crucial for calcium, magnesium, and phosphate absorption. Both have a similar steroid structure, with vitamin D3 formed in the skin from 7-dehydrocholesterol under UV light and vitamin D2 coming from plants and fungi. The main difference between D2 and D3 lies in their side chains.

Once ingested or synthesized, vitamin D is converted in the liver to 25-hydroxyvitamin D, the main circulating form. It’s further processed in the kidneys to the active form, 1,25-dihydroxyvitamin D, which interacts with receptors in the body to regulate various biological functions, including calcium metabolism and immune response.

Types of Vitamin D

There are two main types of Vitamin D: Vitamin D2 (Ergocalciferol) and Vitamin D3 (Cholecalciferol). Both types are crucial for maintaining optimum health, but they have different sources and functions in the body.

Vitamin D2 (Ergocalciferol)

  • Source: Vitamin D2 is primarily obtained from plant sources and fortified foods. It’s produced by fungi, yeast, and plants when they are exposed to UV light. Common sources include fortified foods like cereals, milk alternatives, and specific types of mushrooms that have been exposed to sunlight or UV light.
  • Function: Once ingested, Vitamin D2 is converted by the liver into 25-hydroxyvitamin D2, a form that the body can use. It helps in bone health by promoting calcium absorption in the gut. However, studies suggest that Vitamin D2 might be less effective than D3 in raising and maintaining overall Vitamin D levels in the body.

Vitamin D3 (Cholecalciferol)

  • Source: Vitamin D3 is primarily derived from animal sources and through skin exposure to sunlight. When skin is exposed to sunlight, specifically UVB radiation, it synthesizes Vitamin D3. Dietary sources include fatty fish (such as salmon, mackerel, and sardines), fish liver oils, and egg yolks. Vitamin D3 is also added to many fortified foods.
  • Function: Similar to D2, Vitamin D3 is metabolized by the liver into 25-hydroxyvitamin D3, the body’s preferred form of Vitamin D. It is more effective than Vitamin D2 in increasing and maintaining Vitamin D levels in the blood over time. D3 plays a critical role in bone health, immune function, and reducing inflammation.

Sources of Vitamin D


  • Sun Exposure: The skin produces Vitamin D when exposed to sunlight, specifically UVB rays. About 5-30 minutes of sun exposure between 10 AM and 3 PM, at least twice a week, can contribute significantly to Vitamin D levels. However, factors such as geographic location, skin pigmentation, and sunscreen use can influence this synthesis.

Foods Rich in Vitamin D

  • Fatty Fish: Salmon, mackerel, and sardines are excellent sources of Vitamin D. A single serving of cooked salmon can provide more than the daily recommended amount of Vitamin D.
  • Egg Yolks: Eggs, especially the yolks, contain Vitamin D. Opting for eggs from free-range chickens can offer higher levels of the vitamin.
  • Fortified Foods: Many foods are fortified with Vitamin D to enhance their nutritional value. These include milk, plant-based milk alternatives (like soy, almond, and oat milk), orange juice, and certain cereals.
  • Mushrooms: Certain varieties of mushrooms, especially those exposed to UV light, can provide Vitamin D. The content varies significantly among different types of mushrooms.


  • Vitamin D Supplements: Available in two main forms, D2 (ergocalciferol) and D3 (cholecalciferol), supplements can help maintain adequate Vitamin D levels, especially in individuals at risk of deficiency.
  • Cod Liver Oil: An age-old source of Vitamin D, cod liver oil, also provides Vitamin A and omega-3 fatty acids.

Uses of Vitamin D

  • Bone Health: Vitamin D is crucial for the absorption of calcium and phosphorus, essential minerals for maintaining bone density and strength. It helps prevent rickets in children and osteoporosis in adults.
  • Immune System Support: It bolsters the immune system, aiding in the prevention of infections and autoimmune diseases by modulating the immune response.
  • Muscle Function: Essential for muscle health, vitamin D improves muscle strength and function, reducing the risk of falls and muscle weakness, especially in the elderly.
  • Cardiovascular Health: It contributes to heart health by regulating blood pressure and reducing the risk of cardiovascular disease.
  • Mood Regulation: Vitamin D has been linked to mood regulation and the prevention of mood disorders such as depression, particularly when taken during darker, colder months.
  • Inflammation Reduction: It has anti-inflammatory properties, which are beneficial in reducing pain and inflammation associated with various health conditions.
  • Diabetes Management: Vitamin D plays a role in insulin regulation and glucose metabolism, which can help manage and prevent type 2 diabetes.
  • Cancer Prevention: Some studies suggest that vitamin D may play a role in reducing the risk of certain cancers, particularly breast, prostate, and colon cancers, by influencing cell growth and development.
  • Neurological Health: It is being researched for its potential protective effects against neurodegenerative diseases such as Alzheimer’s and multiple sclerosis.
  • Pregnancy: Adequate levels of vitamin D during pregnancy are important for maternal health and can influence the development and health of the newborn.

Vitamin D Deficiency

  • Limited Sunlight Exposure: The body synthesizes Vitamin D upon exposure to sunlight. People who live in areas with limited sunlight or who spend most of their time indoors are at a higher risk.
  • Dietary Restrictions: Vitamin D is found in foods like fatty fish, egg yolks, and fortified products. Individuals with dietary restrictions may have lower intake levels.
  • Skin Pigmentation: Melanin, the pigment that gives skin its color, reduces the skin’s ability to produce Vitamin D from sunlight.
  • Age and Health Conditions: Aging decreases the skin’s capacity to produce Vitamin D. Certain health conditions, like Crohn’s disease or celiac disease, can affect absorption.

Symptoms of Vitamin D Deficiency

  • Bone Pain and Weakness: Insufficient Vitamin D can lead to softened bones, manifesting as pain and weakness.
  • Fatigue and Tiredness: A common but often overlooked symptom is a general feeling of fatigue and tiredness.
  • Muscle Weakness or Cramps: Vitamin D is essential for muscle function, and deficiency can cause weakness or cramps.
  • Mood Changes: Low levels of Vitamin D have been linked to mood swings and depression.

Effective Solutions for Vitamin D Deficiency

  • Sunlight Exposure: Regularly spend time outdoors, especially during midday, when the sun’s rays are strongest.
  • Dietary Adjustments: Include Vitamin D-rich foods in your diet, such as fatty fish (salmon, mackerel), egg yolks, and fortified foods like milk and cereal.
  • Supplementation: In cases where dietary intake and sunlight exposure are insufficient, Vitamin D supplements can be an effective solution. It’s important to consult a healthcare provider for the appropriate dosage.
  • Regular Testing: Individuals at risk should undergo regular blood tests to monitor Vitamin D levels and adjust their supplementation accordingly.


What Does Vitamin D Do for a Person?

Vitamin D supports bone health, immune function, and calcium absorption, playing a key role in overall physical well-being.

What Are the Signs You Need Vitamin D?

Signs include fatigue, bone pain, muscle weakness, mood changes, and frequent infections, indicating potential deficiency.

How Can I Increase My Vitamin D Levels Quickly?

To boost Vitamin D levels, seek sunlight exposure, consume fortified foods and fatty fish, and consider supplements.

Should I Take Vitamin D or D3?

Opt for Vitamin D3 as it’s more effective at raising and maintaining adequate Vitamin D levels in the body.

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