Vitamin D (Calciferol) is a fat-soluble vitamin, found naturally in very few foods. It plays several important roles in the body. One of its primary functions is to help regulate the absorption of calcium and phosphorus, which are essential for maintaining strong and healthy bones.

Two Different Forms of Vitamin D

Vitamin D exists in several forms, the two main ones being vitamin D2 (ergocalciferol), and vitamin D3 (cholecalciferol). These are known collectively as calciferol. They are secosteroids, which are similar in structure to steroids but the second carbon ring is open.

Vitamin D2 is produced by phytoplankton, invertebrates, and fungi in the presence of UV rays. It is primarily obtained from fortified foods and supplements.

Vitamin D3 is synthesized in the skin, again in response to UV rays when skin is exposed to sunlight.

Vitamin D Production

For vitamin D production, skin must be exposed regularly to direct sunlight to achieve the necessary amounts of vitamin D. This means certain people are at risk for vitamin D deficiency, such as night shift workers and the chronically ill or bedridden. African Americans also need to monitor their vitamin D, since darker skin absorbs less sunlight.

The sunlight must be direct, so sitting by a window will not be enough. The UV rays needed to start the process of vitamin D production cannot penetrate glass. It is recommended that people expose their skin to direct sunlight as often as possible, for twenty minutes per day. This can be difficult at times for all people, but particularly the elderly. This puts the elderly in the high risk group also.

Another reason for vitamin D deficiency can be that certain medications deplete it from the body.

Here’s how the process works:

Sun Exposure: When the skin is exposed to ultraviolet B (UVB) radiation from the sun, a compound called 7-dehydrocholesterol, present in the skin, absorbs the UVB rays.

Conversion to Previtamin D3: The absorbed UVB radiation causes a photochemical reaction, converting 7-dehydrocholesterol into previtamin D3.

Thermal Isomerization: Previtamin D3 undergoes a thermal isomerization process, triggered by body heat, transforming it into vitamin D3 (cholecalciferol), the active form of vitamin D.

Transport to the Liver and Kidneys: Vitamin D3 is then transported to the liver and kidneys, where it undergoes further transformations to become the biologically active form of vitamin D (calcitriol).

It’s important to note the following considerations:

Sun Exposure: The amount of vitamin D produced through sun exposure depends on factors such as the time of day, season, latitude, skin type, and the amount of exposed skin. Generally, spending around 10–30 minutes in the sun a few times a week can be sufficient for vitamin D synthesis.

Sunscreen Use: Sunscreen with a high sun protection factor (SPF) can block UVB radiation and reduce vitamin D synthesis. However, it’s crucial to balance sun exposure for vitamin D production with the need to protect the skin from harmful UV rays.

Diet and Supplements: While sun exposure is a natural source of vitamin D, it can also be obtained from certain foods like fatty fish, fortified dairy products, and through vitamin D supplements if dietary intake or sunlight exposure is insufficient.

Activation of Vitamin D

Whatever the form of vitamin D, it is biologically inert (i.e. can’t be used by the body) and therefore has to undergo two hydroxylations (gaining an -OH group) to become active.

The first occurs in the liver and converts vitamin D to 25-hydroxyvitamin D [25(OH)D], also known as calcidiol (meaning two alcohol OH groups).

The second occurs primarily in the kidney and forms the physiologically active 1,25-dihydroxyvitamin D [1,25(OH)2D], also known as calcitriol (meaning three alcohol OH groups).

Health Benefits of Vitamin D

We all need vitamin D in order to grow and thrive. Vitamin D is unique among vitamins because our bodies can produce it in the skin when exposed to sunlight. In addition to its role in bone health, vitamin D is also believed to play a role in immune function, cardiovascular health and mood regulation. Some research suggests that adequate levels of vitamin D may help reduce the risk of certain chronic diseases, such as heart disease, cancer and autoimmune disorders.

Below we will explore some of these health benefits in more detail:

Vitamin D Helps with Calcium Absorption

Vitamin D is not just a vitamin, it is also a hormone. It assists the gastrointestinal tract to absorb calcium. In fact, vitamin D is so essential for calcium absorption that nearly all calcium supplements now contain it as a supplement. In addition to working with calcium, vitamin D as a hormone causes other minerals in the body, such as magnesium, zinc and iron, to concentrate on bone production. This is why vitamin D is absolutely essential for bone health.

Vitamin D Helps Boost the Immune System

Vitamin D plays a crucial role in the functioning of the immune system. It has various effects on both the innate and adaptive immune systems, and its deficiency has been associated with an increased susceptibility to infections and immune-related disorders.

Here are some ways in which vitamin D interacts with the immune system:

Immune Cell Regulation: Vitamin D can modulate the activity of immune cells, including T cells, B cells, and antigen-presenting cells. It helps regulate the immune response by promoting a balanced and controlled reaction to pathogens.

Anti-Inflammatory Effects: Vitamin D has anti-inflammatory properties and can help reduce the production of pro-inflammatory cytokines. This anti-inflammatory effect is important for preventing an overactive immune response, which could lead to chronic inflammation.

Antimicrobial Activity: Vitamin D has been shown to exhibit antimicrobial properties. It can enhance the production of antimicrobial peptides, which are small proteins that play a role in the body’s defense against infections.

Immune System Maturation: Vitamin D is involved in the maturation and differentiation of immune cells. It contributes to the development of a well-functioning immune system, especially during early life.

Autoimmune Diseases: There is evidence to suggest that vitamin D may play a role in preventing or modulating autoimmune diseases by regulating the immune response and reducing inflammation.

Respiratory Infections: Adequate levels of vitamin D have been associated with a lower risk of respiratory infections. Deficiency in vitamin D has been linked to an increased susceptibility to respiratory tract infections.

Health Problems Caused by Vitamin D Deficiency

Individuals with limited sun exposure, those with darker skin tones, and those living in regions with little sunlight may be at a higher risk of vitamin D deficiency and may need to consider dietary sources or supplements.

Rickets and Osteoporosis from Low Vitamin D

The most common result of vitamin D deficiency is bone loss and skeletal problems. Rickets, once a common disease among the poor, was eradicated completely when physicians learned that regular sun exposure promotes production of vitamin D, which in turn promotes healthy bone growth. When sun exposure is not possible, supplements must be given.

The most prevalent health risk today that is associated with low levels of vitamin D, is osteoporosis. Osteoporosis is a condition that thins the bones causing them to become weak, brittle, and prone to breaking. Along with aging, particularly in women, osteoporosis is responsible for as many as 70 percent of broken hips that occur in falls, and even spontaneously. In the elderly, a broken hip often marks the beginning of a decline that leads death.

Other Health Effects of Low Vitamin D

Some other health problems often seen in correlation with low levels of vitamin D are; psoriasis, Crohn’s disease and multiple sclerosis (MS). Healthy levels of Vitamin D improve; blood pressure, osteoarthritis, and even help fight against cancer. Vitamin D has been proven to reduce tumours. In laboratory experiments, vitamin D supplementation caused a reduction of 50% in cancerous growths.

How to Obtain Vitamin D

Vitamin D can be obtained through sunlight exposure, dietary sources or supplements. Food sources of vitamin D include; fatty fish (such as salmon and mackerel) and egg yolks. Vitamin D is also added to other foods, such as milk, orange juice and cereal. These are known as fortified foods.

It can be challenging to obtain enough vitamin D from food alone, particularly for individuals who have limited sun exposure or who live in regions with long winters and limited sunlight. Therefore, some people may need to take vitamin D supplements to maintain optimal levels.

Vitamin D Supplements

Vitamin D supplements typically contain either vitamin D2 (ergocalciferol) or vitamin D3 (cholecalciferol). Among these, vitamin D3 is more commonly used in supplements because it is the form of vitamin D that is synthesized in the skin in response to sunlight exposure. Additionally, vitamin D3 is believed to be more effective at raising and maintaining blood levels of vitamin D compared to vitamin D2.

However, both vitamin D2 and D3 can be effective in raising blood levels of vitamin D when taken as supplements, though some research suggests that vitamin D3 may be more effective at maintaining these levels over the long term.

When choosing a vitamin D supplement, it’s important to check the label to see which form of vitamin D it contains. Many supplements will specify whether they contain vitamin D2 or D3.

Vitamin D Recommended Daily Amount (RDA)

Vitamin D content is stated in either micrograms (µg or mcg) of cholecalciferol or International Units (IU). One IU equals 0.025 µg cholecalciferol, therefore to convert IUs of vitamin D into µg, multiply the number of IUs by 0.025 and that will give you the number of µg. To convert µg to IUs, multiply the number of µg by 40 and that will give you the number of IUs.

The recommended daily amount (RDA) for most adults and children is 5µg (200 IUs). If you’re between 51 – 70 years the RDA is 10µg (400 IUs). Over 70 the RDA is 15µg (600 IUs).

Vitamin D is tolerated well in dosages over this. The LOWEST tolerable Upper Limit (maximum amount that can be tolerated without harm) is 25 micrograms(µg) per day (1000 IU) for infants under 12 months. For those aged between 9 – 71+ years (including pregnant or lactating women) the tolerable upper limit is 100µg per day (4000 IUs).

A daily supplement of between 10µg (400 IUs) and 20µg (800 IUs) should therefore be suitable for most people.

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Vitamin D Notes / Side Effects

Certain medications can deplete Vitamin D in the body. If you are taking any medication it may be worth asking your Doctor if you require Vitamin D supplements.

It’s important to note that while vitamin D is essential for immune function, excessive supplementation may not provide additional benefits and could have adverse effects. The optimal levels of vitamin D can vary among individuals, and it is advisable to maintain levels within the recommended range.

Individuals with concerns about their vitamin D status should consult with healthcare professionals for guidance on appropriate supplementation.