Which vitamin D supplement should I take?

We’re all advised to take a vitamin D supplement in the UK, but how do you know which supplement is best? Should you take vitamin D in summer? And how quickly can you boost your vitamin D levels? We answer these questions and more.

This article covers:

• Vitamin D₂ vs. D₃: what’s the difference?
• Top tips for maximum vitamin D absorption
• Which vitamin D supplement is best?
• Vitamin D FAQs

Vitamin D2 vs. D3: what’s the difference?
 

When wandering the supplement aisles you might have noticed two types of vitamin D: D₂ and D₃. They come from different sources. Vitamin D₃ (also known as cholecalciferol) is usually derived from sheep’s wool or fish oils, while vitamin D₂ (ergocalciferol) supplements are plant-based.

That’s because plants and animals produce vitamin D through slightly different mechanisms. Animals have a compound 7-dehydrocholesterol in their skin, which reacts with UVB rays to produce vitamin D₃. Meanwhile, the plant and fungi version of this compound is ergosterol, the precursor to vitamin D₂.

What form of vitamin D is most effective?

Both forms are good for boosting your vitamin D levels. But vitamin D₃ tends to be better absorbed, as the enzymes and proteins in our bodies evolved to process it.

Vitamin D₂ still works as a vitam in D source. It just has less bioavailability and the effects might not last as long. Some studies suggest vitamin D₂ doesn’t possess the same immune-boosting capabilities as vitamin D₃, but more research is needed [1].

Is there a vegan form of vitamin D₃?

As animals produce vitamin D₃ most vegan forms of vitamin D tend to be vitamin D₂. But there is one organism that produces both forms of the sunshine vitamin – lichen.

Lichens are small plant-like photosynthesisers consisting of symbiotic colony of fungi and bacteria. You might have seen them growing on trees in pale green clumps, or as yellow and black splodges on rocks at the beach. The fungal part of a lichen colony is responsible for producing vitamin D₂, and the cyanobacterial part of the colony produces D₃.

So if you’re looking for vegan vitamin D₃, try a lichen-based supplement.

Top tips to get the most out of your vitamin D supplements

Take vitamin D with meals

Some supplements, like iron, are best taken without food. But vitamin D is a fat-soluble vitamin, which means the best way to get it into your bloodstream is by taking it with high fat foods [2]. Not all fats are healthy though, opt for whole food fats such as avocados, nuts and seeds to make your nutrition as optimal as can be.

Look for vitamin K combinations

Vitamin D is vital for healthy bones, and combining vitamin D with vitamin K can maximise calcium absorption. You should get enough vitamin K from your diet, 1 mg or less is all you need in a supplement.

Choose vitamin D supplements containing oils

If taking your supplements with food doesn’t work for you, don’t worry – just check for vitamin D supplements formulated with oils (olive oil or sunflower seed oil). The fats from the oils will support optimal absorption.

Which vitamin D supplement is best?
 

First, let's take a look of the pros and cons of each type of vitamin D, and then explore the advantages and disadvantages different delivery methods of vitamin D supplements.

So, which vitamin D supplement is best for you? We'll let you decide.

Vitamin D FAQs

How long do vitamin D supplements take to work?

The effects of vitamin D supplementation vary from person to person depending on how severe your deficiency is. But you should feel the effects within a few weeks to a few months.

How much vitamin D should I take per day?

If you have a vitamin D deficiency (you can check with a Vitamin D (25 OH) Blood Test), supplementing 100 μg (micrograms) / 4000 IU a day for 10 weeks should bring your levels back to a healthier range. If your vitamin D levels are just insufficient you’re advised to take 20-50 μg per day for 12 weeks. You can then retest after 12 weeks and see where your levels are at [3]. 

Do I need to take vitamin D supplements during summer?

Despite the British weather, if you’re able to spend time outside in the sun between 11am and 3pm, from April to September (10 minutes a day with your legs and forearms uncovered ought to do it) you shouldn’t need to take a vitamin D supplement.

However, if you live in Scotland you may want to consider a 10 μg supplement all year round [4]. The best thing to do is check with your GP to be certain.

Do vitamin D supplements help you tan?

Vitamin D supplements will not help you tan. Tanning is the production of melanin to protect your skin from UV rays, so while you may tan from topping up on your vitamin D levels outside, there’s no research to show the two are linked. Wear suncream!

Are there side effects to taking vitamin D supplements?

Vitamin D supplements are generally safe, but as with all supplements taking too much can have detrimental health effects. Hypercalcaemia is the build-up of too much calcium in the body which can weaken the bones and heart. Take care to follow the dosage guidelines.

References

1. Durrant LR, Bucca G, Hesketh A, Möller-Levet C, Tripkovic L, Wu H, et al. Vitamins D2 and D3 Have Overlapping But Different Effects on the Human Immune System Revealed Through Analysis of the Blood Transcriptome . Front Immunol. 2022;13: 790444.
2. NIH, Office of Dietary Supplements - Vitamin D . [cited 16 Apr 2025].
3. NHS, Vitamin D . In: nhs.uk [Internet]. 23 Oct 2017 [cited 16 Apr 2025].
4. NHS Inform, Vitamin D . In: NHS inform [Internet]. [cited 10 Apr 2025].