Everything You Need To Know About: Vitamin D

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What Is Vitamin D?

Vitamin D is a fat-soluble vitamin that can be found in a few foods, supplemented or produced by the body. Being fat-soluble means that the body can store any excess within its fat cells, for use at a later time if needed.

It is also known as calciferol and once it is activated it becomes either 25-hydroxyvitamin D (25(OH)D) or calcidiol if it was converted by the liver or 1,25-dihydroxyvitamin D (1,25(OH)2D) or calcitriol if converted in the kidneys.

vitamin d bones

What Does Vitamin D Do?

Vitamin D has many roles within the body. One of the main roles is promoting calcium absorption in the gut and ensuring that adequate levels of that and phosphate are in the bloodstream. This ensures normal bone mineralisation and prevents muscle cramping/spasms. It’s vital for bone growth and remodelling.

Vitamin D also helps with reducing inflammation, cell management, immune functions, and glucose metabolism.

Why Is Vitamin D Important?

As mentioned above, vitamin D plays a number of important roles in the body. Without sufficient vitamin D, the body would become deficient which can cause many issues.

Without vitamin D, bones can become brittle, thin or misshapen leading to rickets in children, osteomalacia in adults, and osteoporosis in older adults.

Vitamin D has also been linked to potentially helping with cancer prevention, depression, type 2 diabetes, cardiovascular disease, weight loss, and multiple sclerosis.

Symptoms Of Vitamin D Deficiency

There are several signs and symptoms of vitamin D deficiency you should be aware of, it is VERY important to contact your doctor should you suspect a deficiency.

vitamin d illness

Regular Illness

One of vitamin D’s roles is to aid with immune function so if you are deficient then your body may struggle to fight off bacteria and viruses.

If you become sick regularly with colds or the flu, then a deficiency in vitamin D might be a factor.

Fatigue and Tiredness

If you find yourself regularly exhausted with no real reason to be so then it could be low levels of vitamin D in your bloodstream. Case studies have shown that low levels of this vitamin can cause fatigue and that supplementing with vitamin D could reduce the severity of fatigue in people with a deficiency.

Weight Gain

Being overweight or obese is one risk factor for vitamin D deficiency, however, there is research to suggest that a vitamin D deficiency may also increase the risk of weight gain too.

vitamin d depression

Anxiety & Depression

There are some observational studies that suggest a link between vitamin D levels and anxiety or depression, stating that there is a relationship between either of them and low levels in the blood. However, many controlled trials suggest there is no link. Although the controlled trials are technically higher up on the hierarchy of evidence, a review of these trials found limitations in these studies such as low doses of vitamin D and/or short trial durations.

Bone Loss

As mentioned previously, vitamin D plays a vital role in calcium absorption and the metabolism of bone. Without it, the body is at risk from bone loss which increases the risk of fractures.

Symptoms Of Vitamin D Toxicity

While deficiency is extremely common, estimated at 1 billion people worldwide, the toxicity of vitamin D is also a risk which is why you should seek medical advice before you supplement anything more than the recommended amounts.

Toxicity can result in elevated blood calcium levels called hypercalcemia, which can present symptoms including:

  • Digestive issues – vomiting, nausea, and abdominal pain
  • Dizziness, fatigue, and confusion
  • Excessive thirst
  • Frequent urination

It can also result in bone loss, having the opposite effect of deficiency where the body has too much which may result in too low a level of another vitamin, K2. It is recommended that high doses of vitamin D also take with a K2 supplement.

Vitamin D toxicity may also result in kidney failure, even in people with healthy kidney function.

Where Do You Get Vitamin D From?

There are three sources of vitamin D; food, sunlight and supplementation.

vitamin d foods

Food Sources Of Vitamin D

There aren’t many naturally occurring food sources of vitamin D. Fatty fish such as salmon, trout, tuna and mackerel, as well as fish oils, are some of the best sources. Beef liver, egg yolks, and cheese have small amounts of the D3 form. Mushrooms provide a variable amount of the D2 form and certain mushrooms receive UV treatment to increase their levels. Selected food products may also be fortified with vitamin D such as plant-based milk.

vitamin d sunlight


Our body is able to make its own vitamin D with the UV rays of the sun. However, many factors can reduce the amount your body is able to produce.

Your geographical location, skin colour, and age are all factors that can influence the amount of vitamin D your body makes. For example, those with darker skin tones produce less than those with lighter skin tones. People closer to the equator have more opportunities for sunlight than those closer to the poles.

Wearing sunscreen also prevents your body from making vitamin D as it puts a protective layer over your skin to stop the UV rays from penetrating it. Sunscreen is needed as protection against skin cancer, so going without it completely isn’t safe.

vitamin d supplements


It is easy to supplement vitamin D into your diet and there are many different manufacturers of the supplement. You can get it in tablet, drops, and spray form making it very easy to take.

There are two forms of vitamin D supplement you can buy, D2 and D3. D2 is always suitable for vegans as it is derived from plants whereas D3 is often derived from animal sources such as sheep’s wool. If you require a vegan vitamin D supplement then make sure you check where it is derived from.

Many general multivitamin tablets already contain vitamin D so it is worth checking how much you get from that before adding any more to your diet.

Should You Supplement Vitamin D?

It is thought that one billion people are deficient in vitamin D. So, with how minimal we get from our food, plus the limited exposure to the sun, almost everyone should be supplementing in some form or another.

If you are worried about your levels of vitamin D then you should talk to your doctor who will give you a blood test. Alternative, you can pay for private testing done through a company such as LetsGetChecked, a company I’ve personally used.

How Much Vitamin D?

The current guidelines are that everyone over the age of five years old should be taking 10 micrograms (μg) of vitamin D a day – especially through the winter months, from April to October.

During the summer months, the majority of the population should receive sufficient amounts of sunlight to maintain their serum levels. However, those who work indoors, night workers, and those who cover up during the summer months are at risk of not producing enough so should continue to take 10 micrograms throughout the year.

It is recommended that babies from birth to one year of age should have a daily supplement containing 8.5 to 10 micrograms of vitamin D throughout the year if they are:

  • breastfed
  • formula-fed and are having less than 500ml (about a pint) of infant formula per day, as infant formula is already fortified with vitamin D
vitamin d

Children aged one to four years old should be given a daily supplement containing 10 micrograms of vitamin D throughout the year.

You can buy vitamin D supplements or vitamin drops containing vitamin D (for under 5s) at pharmacies, supermarkets or online *from Amazon. Women and children who qualify for the Healthy Start scheme can get free supplements containing vitamin D.

Those who are obese with lower levels of vitamin D will need a higher dose to achieve the same blood levels as someone who is at a normal weight.


Vitamin D is a very important nutrient that many people are deficient in. Although we can get some from our diet and our bodies can make it, it is still recommended to take a 10 microgram supplement daily but especially between October and April when our sun exposure is reduced.

If you have any questions about vitamin D then please don’t hesitate to ask.

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Everything You Need To Know About Vitamin D

1 thought on “Everything You Need To Know About: Vitamin D”

  1. Fantastic coverage of Vit D, Chammy, and it’s good you’ve included the point on toxicity, even if it is rare. I was actually found to have almost non-existent vit D levels a couple of years ago, something no doc had ever bothered to check before. I’ve got osteoporosis as a result and it’s not cool. It’s taught me a thing or two though, like how important vitamin D is – I make sure my parents take daily supplements now too!


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