Vitamin D

What is vitamin D?

Vitamin D (calciferol) is a nutrient that is crucial for human health and wellbeing. It is a fat-soluble vitamin, meaning it requires fat to be absorbed in the body. There are two major forms of vitamin D: vitamin D₂ (also called ergocalciferol) and vitamin D₃ (also called cholecalciferol). Vitamin D₂ is often added to foods, and vitamin D₃ is produced in the body after exposure to sunlight, and naturally found in certain animal-based foods.¹ While they are obtained from different sources, these two forms of vitamin D are processed by the body in the same way. Both forms are converted into active vitamin D (also called calciferol), which occurs primarily in the kidneys.¹

Why we need it

Vitamin D is essential for many bodily processes. One of its major functions is supporting bone health. Vitamin D helps regulate levels of calcium and phosphorus, which are two minerals that make up bone. For example, vitamin D increases the absorption of calcium from food, and regulates how much calcium and phosphorus are excreted from the kidneys and released from the bones.¹

Vitamin D also promotes a healthy immune system. It supports the activity of immune cells like monocytes, macrophages, and dendritic cells.² Vitamin D also upregulates the expression of anti-inflammatory cytokines and downregulates inflammatory cytokines, thus protecting against inflammation.²

Interestingly, the majority of cells and tissues in the body have vitamin D receptors, meaning the functions of vitamin D extend throughout the entire body.³ For instance, vitamin D supports heart health, fat and glucose metabolism, and muscle growth and development, among other functions.³

Where it’s found

Vitamin D is naturally present in foods like fatty fish, egg yolks, mushrooms, and liver or organ meats.⁴ It can also be added to foods such as milk, cereal, and orange juice, through a process called fortification.

Vitamin D is known as the “sunshine vitamin” because it can be obtained through sunlight.⁵ More specifically, sunlight exposure triggers the conversion of a vitamin D precursor (called 7-dehydrocholesterol) into active vitamin D.⁵

Lastly, vitamin D may be taken in supplemental form. Most vitamin D supplements use vitamin D₃, although some use vitamin D₂. Some research suggests that vitamin D₃ may be a superior supplement form, as it may be more potent and long-lasting.¹

Daily requirements

The Recommended Dietary Allowance (RDA) for vitamin D, or the amount that is likely to meet the nutritional needs of nearly all healthy people, is 15 mcg (600 IU) for individuals between the ages of 1 and 70, and 20 mcg (800 IU) for individuals aged 70 and older.⁶

Unfortunately, many people do not consume enough vitamin D through their diet. For instance, data from the National Health and Nutrition Examination Survey (NHANES) showed that 94% of people in the United States aged 1 year and older consumed less than the recommended amount of vitamin D.⁶ Thus, supplementation may be recommended to prevent deficiency.

Vitamin D deficiency

Vitamin D deficiency can have negative consequences on bone health, immune function, and overall well-being. Severe vitamin D deficiency can cause bone diseases such as rickets (in infants) and osteomalacia (in adults).¹ Vitamin D deficiency may also weaken the immune system and increase the risk of infection or autoimmune disease.²

Some people may be at a higher risk of developing vitamin D deficiency. For instance, deficiency may be more likely in infants, elderly, people with dark skin, vegetarians, people with chronic kidney or liver diseases, and people with malabsorption syndromes.¹

The Estimated Average Requirement (EAR) for vitamin D, or the amount that is likely to meet the nutritional needs of half of healthy people, is 10 mcg (400 IU) for individuals over the age of 1.⁷ The EAR is lower than the RDA, as it serves as the minimum amount required to meet the needs of some of the population.

Can you get too much vitamin D?

Consuming excessive vitamin D can be harmful. When too much vitamin D builds up in your blood, you may experience symptoms such as nausea, vomiting, confusion, loss of appetite, or kidney stones.⁶ Vitamin D toxicity is not caused by sun exposure, since your body can limit how much vitamin D you produce from sunlight.¹ Instead, vitamin D toxicity is generally due to excessive vitamin D supplementation.¹

The tolerable upper limit for vitamin D (i.e. the maximum daily amount that is considered safe for most people) is 100mcg (4,000 IU) for adults over the age of 19.⁶

Fun facts

The ultraviolet B (UVB) rays from sunlight, which help your body make vitamin D, cannot penetrate glass, plexiglass, or plastic.⁵ This means you unfortunately cannot get vitamin D by sitting near a sunny window!

As a fat soluble vitamin, vitamin D can be stored in the body’s adipose (fat) tissue.⁴ This means that if you don’t consume enough vitamin D, your body may be able to use what it has stored to prevent deficiency. However, this also means that getting rid of excess vitamin D can be difficult, and toxicity is thus a possibility.

Vitamin D may support a good mood! Vitamin D receptors are found throughout the brain, including in areas associated with mood and depression.⁸ In fact, research shows that people with low vitamin D levels may be at a higher risk of depression.⁹ Nonetheless, there is insufficient evidence to support the use of vitamin D for preventing or treating depression.⁸