• Rado

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

Updated: Sep 20, 2021

Vitamin D Evidence based guide


What is vitamin D | Am I deficient? | Vitamin D from sunshine | How much do I need | Food sources | Best supplements | Vitamin D and other nutrients

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.