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"Should I take vitamin D?" An evidence-based guide.

Updated: Sep 20, 2021

Vitamin D Evidence based guide


Nowadays it seems like everyone is taking vitamin D. So... should you?

Vitamin D has been linked to different conditions from mood disorders like 'winter depression'[1], to having healthy bones and preventing osteoporosis [2]. It's also quite important for the immune system. Vitamin D is also currently used in the treatment of some COVID-19 cases [3].

But while it's quite an essential nutrient, about 20-25% of people in the UK are vitamin D deficient [4].

So what exactly is vitamin D? And how do you know if you should be taking it?

What is vitamin D

Vitamin D is a fat-soluble vitamin that we need regularly in order to… well, stay alive.

If that sounds worrying - it shouldn’t. We've evolved to get vitamin D from the sun, as well as some foods and, in more recent years, supplements.

Weirdly, vitamin D is the only thing we classify as a vitamin but is actually a hormone. Vitamin D has dozens of functions, from maintaining appropriate calcium levels for strong teeth & bones, to ensuring that our immune system is in working order, so it can fight off foreign invaders. It also helps regulate our blood pressure and glucose levels.

But "vitamin D" is not just this one molecule. Rather, it’s a group of a few similar compounds.

The two main types of vitamin D found in nature are:

  • Vitamin D2 (ergocalciferol) - mainly found in plants (e.g. mushrooms)

  • Vitamin D3 (cholecalciferol) - mainly found in animals (such as humans)

Interestingly, we have vitamin D receptors in many different parts of our body: bones, liver, kidneys, muscles, parathyroid glands and skin. Once vitamin D binds to these receptors, it activates a whole array of processes that help the body maintain homeostasis.

So vitamin D is pretty important. This is why we need to make sure we always have good levels of vitamin D in order to stay healthy and well-functioning.

Am I deficient in vitamin D?

Vitamin D deficiency

This depends on a few factors.

On average, between 20-33% of the UK population are vitamin D deficient. However, this number is much higher for people from ethnic minorities, such as mixed ethnicity (43%) and Asians (66%) [5].

You might also be more likely to be deficient if you’re pregnant and breastfeeding and/or if you have a darker skin tone. This is because pregnancy & breastfeeding increase your needs for vitamin D, and darker skin has more melanin, which is thought to interfere with vitamin D production.

Other high-risk groups are children <5 years and elderly >65 years.

The signs & symptoms of vitamin D deficiency are:

  • Muscle pain

  • Bone loss (brittle bones)

  • Hair loss

  • Depression & mood changes

  • Hypertension

Vitamin D deficiency has also been linked to developing certain types of cancers, multiple sclerosis and thyroid problems [6].

The best way to find out if you are vitamin D deficient is to get tested. Ideal levels of vitamin D are above 30ng/ml or 75nmol/l (this is the same amount but different units of measurement).

Vitamin D from sunshine

Okay, everyone knows that you get vitamin D from the sun, right?

Well, kind of.

Sunshine and vitamin D

We don't necessarily "get" vitamin D from the sun, because sunlight doesn't carry any vitamin D inside of it.

Instead, once the correct wavelength of sunlight (UV-B light) hits our skin, it triggers a chain of reactions causing us to produce vitamin D3, which is later converted in the liver & kidneys into its active form 1,25-dihydroxivitamin D (yep, it's a mouthful).

If you want to get enough vitamin D from the sun, you need to spend 15-20 min a day in the midday sun with your face, forearms and legs uncovered and without sunscreen. After that, feel free to apply SPF as per advice from dermatologists.

Sadly, many countries don’t get the right sunlight all year round.

Generally, the further away from the equator you live, the less vitamin D you produce year-round. People living in latitudes above 35°N or below 35°S of the equator, are NOT getting enough vitamin D in the colder half of the year (October-March), and should therefore be taking additional vitamin D.

So go ahead and look up your house on Google Maps to find out if you need additional vitamin D.

Other factors that play a role in how much sunshine vitamin D you produce are:

  • Wearing sunscreen and clothing that covers most of the skin

  • Having a darker skin tone, which has more melanin that reduces vitamin D production

  • Spending time at home (sorry, standing next to the window doesn't count)

How much should I take per day?

As you’ve just discovered from the previous section, how much vitamin D you should take depends on how far from the equator you live.

If you're a healthy adult living in a country with not enough sunshine (described above), then approx. 600-800 IU (15-20mcg) daily should help you to maintain appropriate vitamin D levels [7]. This can come from both food and supplements. In the UK, the NHS recommends taking a minimum of 400 IU (10mcg) of vitamin D every day between October and early March [8].

If you’re deficient in vitamin D, you may want to speak to your GP for a specific dose you should be aiming for. Overall, a daily dose between 1000-4000 IU (25-100mcg) would be appropriate to get your levels in the adequate zone.

As with everything, there is an upper tolerable limit of 4000 IU (100mcg) per day, above which vitamin D may be toxic. So too much of a good thing is a not-so-good-anymore thing.

Food sources

"Always choose food first."

This is great advice when trying to have a good intake of specific nutrients, like vitamins, minerals and antioxidants.

Sadly, this isn't the case for vitamin D. It's a practical eating challenge to get your daily intake of vitamin D solely from food every day.

However, you can seriously bump up your daily intake by having a healthy diet rich in animal-based products like fatty fish and liver, as well as some wild mushrooms, such as maitake.

Here's an example of how to get 800 IU of vitamin D from food:

  • 85g of cooked wild-caught salmon - 570 IU

  • 3 large whole eggs (cooked) - 120 IU

  • 85g beef liver - 40 IU

  • 2 sardines canned in oil - 40 IU

  • 85g tuna from a can - 30 IU

Salmon high in Vitamin D

In addition, cod liver oil has a lot of vitamin D and can be enough to hit your daily target, so please check the label if you're already taking cod liver oil.

Best supplements

Since getting enough vitamin D from food isn't always easy, you can also take a supplement.

Vitamin D supplements can be in the form of tablets, capsules, soft gels, liquid oils, sublingual sprays or even gummy vitamins.

You can choose whichever form you like or are most likely to remember to take every day. For example, you might prefer to use a sublingual spray each morning after breakfast, or you could add a vitamin D-rich oil to your daily salad.

Unless you're strictly plant-based, you're better off taking vitamin D3 (cholecalciferol), which is better at increasing your serum vitamin D levels.

However, keep in mind that vitamin D3 supplements are usually animal-based, so vegetarians and vegans can choose

plant-based D2 supplements.

The following are three high-quality vitamin D supplements you can try (these are NOT affiliate products, just genuine recommendations):

  • Solgar vitamin D3 15mcg softgels (from an established manufacturer with good standards)

  • Better You DLux vitamin D3 oral spray (a tasty and easy-to-use oral spray)

  • Pharma Nord Bio-Vitamin D3 pearls (this supplement is pharmacologically tested to have the exact dose claimed)

Of course, there are also many other brands on the market that produce high-quality vitamin D supplements, so make sure you choose an established brand that you can trust.

Finally, make sure to take your vitamin D supplement with a meal, usually breakfast or lunch, to help its absorption (remember, vitamin D is fat-soluble).

Note: Taking large doses of vitamin D when you're NOT deficient is unlikely to be beneficial. Our bodies, these smart wonders of nature, are able to absorb more vitamin D if our levels are low, and absorb less if we already have good vitamin D levels.

It can also be harmful to take too much vitamin D if you're not deficient (there is some suggestive link to an increased risk of stroke [9]).

Vitamin D with other nutrients

Some of the nutrients we take usually interact, either supporting each other's functions or having a friendly "competition".

Vitamin D enhancers

Vitamin D has several "colleagues" that, when taken together, enhance each other's roles. These are:

  • Calcium - You may know that calcium is needed for bone structure and integrity, as well as for the signalling of nerve cells. However, absorption of calcium from the diet tends to be fairly low (around 30%) [10]. Vitamin D helps us absorb calcium better, so they both work together to make sure we have healthy bones. However, taking higher doses of calcium can be harmful as it may be deposited where it shouldn't be, such as the kidneys and arteries. This is where vitamin K2 can help.

  • Vitamin K2 - Vitamin K2 helps us avoid calcium deposits in the blood vessels and other soft tissues by directing it to the bones. This is why healthy bone supplements usually include a combination of calcium, vitamin D and vitamin K2.

  • Magnesium - Magnesium appears to regulate our vitamin D levels by increasing absorption when we need more and reducing it when we need less. It also helps us regulate our levels of other nutrients, such as calcium, which is why it can be a good addition to the combination of vit D, calcium and vit K2.

  • Dietary fat - Vitamin D is a fat-soluble vitamin. Therefore, in order to be absorbed, it needs to be dissolved in some amount of fat. This is why you should try to take your vitamin D supplement with a meal containing fat (e.g. eggs, milk, cheese, flax seeds, spread). There's no need to change what you eat, though, as chances are you're already having enough fat in your breakfast for the most optimal absorption of vitamin D.

Vitamin D "competitors"

There are some nutrients that "compete" with vitamin D for absorption. These are:

  • Vitamin A - As a fellow fat-soluble vitamin, Vitamin A competes with vitamin D for absorption. However, this can also be beneficial, since this friendly "competition" can prevent the body from absorbing toxically high levels of either vitamin.

  • Vitamin E - Similarly to vitamin A, vitamin E is a fat-soluble vitamin that competes for absorption with vitamin D, and this can also be helpful for avoiding toxically high levels of both nutrients.

  • Fibre - Dietary fibre gives vitamin D a hard time getting absorbed because it inhibits one of the main mechanisms for its absorption. With that in mind, you don't have to try eating less vegetables in order to boost your vitamin D levels because, like we mentioned, your body can regulate its absorption of vitamin D by your needs.

  • Certain medications - There are interactions between vitamin D and some medications, such as antacids, heart medications, water pills and others [11]. If you're currently taking medicine regularly, check the medication’s guide or speak with your GP to discuss how and when to take vitamin D.

Once again, the fact that these nutrients "compete" isn't necessarily bad. Most often, this healthy "competition" can be the reason for having optimal levels of all nutrients.

Overview: next steps with vitamin D

  1. Firstly, make sure to expose your skin (safely) to sunlight every day. Aim for 15-20min in midday at direct sunlight on your arms, legs and face, before you put sunscreen on. This amount varies depending on where you live, the season and your vitamin D needs.

  2. Get your blood vitamin D levels tested if you (or your GP) suspect that you're deficient. The healthy levels are set at 30ng/ml or 75nmol/l.

  3. Try to get some vitamin D from foods, such as wild-caught salmon, whole organic eggs, sardines, grass-fed beef liver and low-mercury tinned tuna.

  4. If you decide to take a supplement, choose an appropriate vitamin D supplement based on your current levels. You can take 400-800 IU/day for normal levels, or up to 1000-4000 IU/day for serious deficiency. Please speak to your GP before taking high doses as vitamin D is known to interact with certain medications.

  5. You can also combine your vitamin D supplement with calcium, vitamin K2 and magnesium for better absorption and improved bone health. Some nutrients that can compete with vitamin D's absorption are vitamins A & E, and dietary fibre.

If you want to lose weight or you're trying to achieve optimal nutrition and you want personalised dietary advice, you can book your initial consultation.

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