Vitamin D: Why Is It Important For Overall Health?

Health organisations all over the world recommend taking a vitamin D supplement between October and March, when sunlight is scarce in the Northern hemisphere. Here we’ll take a look at why Vitamin D is so important for our overall health.

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Everybody is familiar with vitamins, either as food supplements or as dietary essential factors.

We’re also aware that some ailments and diseases are caused by vitamin deficiency and can be treated by adding these vitamins to our diet – this is especially true in regards to vitamin D.

However, a thorough understanding of how vitamins work is essential to beat the deficiency once and for all.

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What is Vitamin D?

Vitamin D is not a single substance. Vitamins come about in several related forms known as vitamers.

A vitamer of a specific vitamin is one of many chemically similar compounds that display biological activity against a specific vitamin deficiency. 

Research has shown that all vitamers manifest biological activity against their specific vitamin deficiency, although different vitamers show different power against those ailments.

When it comes to Vitamin D, the most common forms are Ergocalciferol (vitamin D2) and Cholecalciferol (vitamin D3).

The latter is generated in the skin after exposure to ultraviolet light including sunlight.

It is transformed in the liver to calcifediol which is then converted in the kidney to calcitriol.

Calcifediol is a non-active form of vitamin D, and only calcitriol can be used by the human body. 

Factors Affecting Vitamin D Levels

Exposure: Vitamin D is produced by the skin from exposure to direct sunlight or even artificial UVB light.

This endogenous way of producing vitamin D is somewhat hindered by changes in lifestyle as people spend more time indoors and are less exposed to sunlight. 

Concerns related to the adverse effects of exposure to sunlight or UV-B light, such as skin cancer and photo-ageing have further expanded the prevalence of vitamin D deficiency.

Other factors may affect levels of vitamin D, such as season and time of the day, race, latitude, exposure to sun, and the use of sun cream.

Skin Colour: People who live further north are more susceptible to Vitamin D deficiency as they have reduced levels of vitamin D in their bodies.

People with lighter skin tones have been shown to have higher levels of vitamin D compared to people with darker skin tones as melanin acts like a shade. 

Recent research has found that despite having lower levels of vitamin D, people with darker skin tones don’t have either hyperparathyroidism or hypocalcaemia, two diseases associated with the deficiency of Vitamin D.

A possible explanation for this is that the bioavailable vitamin D is equivalent to those with lighter skin due to a genetic polymorphism that results in lower levels of vitamin D-binding protein. 

Liver and Kidney Functions: Studies have found that the production of circulatory active forms of vitamin D is dependent on good liver and kidney function.

An increased incidence of vitamin D deficiency is found with many types of liver disease, including non-alcoholic fatty liver disease (NAFLD), Hepatitis C virus (HCV) and autoimmune liver disease such as primary biliary cirrhosis (PBC). 

People with chronic kidney disease (CKD) are also more prone to Vitamin D deficiency, as the condition affects Vitamin D homeostasis. 

For patients who suffer from these issues, dietary supplementation of Vitamin D is highly recommended by many health organisations.

Symptoms of vitamin D deficiency may include:

• Depression or feelings of sadness.
• Sleeping issues.
• Fatigue
• Hair loss.
• Bone pain or achiness.
• Loss of appetite.
• Getting sick more easily.
• Muscle weakness.

Vitamin D: The Impact On Health

There are more than 36 organs biologically influenced by the Vitamin D receptors that bind Vitamin D down-regulating or up-regulating different genes on a cellular level.

Bone Health

Probably the most important role of vitamin D is in calcium and bone homeostasis.

Calcium is absorbed by the intestine and Vitamin D is the main regulator of the active transcellular absorption pathway in the intestine, affecting not only bone homeostasis and calcium absorption, but also having a direct effect on osteoblasts, promoting differentiation and mineralisation of bones. 

Children with vitamin D deficiency are at risk of developing hypocalcaemic rickets, a terrible yet preventable disease.

The NHS Digital data shows that in 2017-2018, there were 101,136 hospital admissions having vitamin D deficiency as a factor; a rise of 34 per cent in a year. 

Low Vitamin D levels leave these children at risk of developing seizures and cardiomyopathy as well. 

Post-menopausal women are at elevated risk of osteoporosis and subsequent bone fractures.

Vitamin D supplementation reduces the risk and some research studies suggest that vitamin D supplementation might also decrease the risk of early menopause.

Autoimmune Conditions

Vitamin D may also have an effect on the immune system and consequently on the development of autoimmune disease.

Its effect has been proven on both B cells and T cells.

Treatment with vitamin D inhibits the maturation and differentiation of dendritic cells, resulting in increased tolerance for autoimmune diseases.

Vitamin D can also reduce cancer cell growth and decrease inflammation in several types of arthritis.

There’s also plenty of data relating low levels of vitamin D to the development of Multiple Sclerosis (MS), tuberculosis and respiratory infections such as flu and Covid-19.

Which Foods Contain Vitamin D?

Despite being bioavailable, it’s hard to get enough Vitamin D through food.

As a rule of thumb, foods rich in both protein and fatty acids, such as fish, meats, eggs and dairy are good sources of Vitamin D as well.

For vegans and vegetarians, certain types of mushrooms are known to contain high amounts of Vitamin D2 due to their purposeful exposition to ultraviolet light.

There are also foods fortified with Vitamin D, but those must be consumed with discretion as most of them are highly processed – always give preference to whole foods!

Final Thoughts

All the benefits and mechanisms mentioned about Vitamin D are probably only the tip of the iceberg.

Despite all the accumulated evidence regarding the positive effects of this vitamin, there’s still a lot more to be discovered.

In places where sunlight is not available all year round, vitamin D supplement use or fortifying foods with vitamin D may be a good option, as they are easily available in the market.

For those suffering from a chronic disease, Vitamin D supplementation may represent a great relief but it should always be advised by a health practitioner.

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