Vitamin D: what you need to know

Experts agree vitamin D is the one supplement we should all be taking during autumn and winter in the UK. 

This is because vitamin D plays a key role in immune and bone health, and between October and March in the UK the sun isn't strong enough for our bodies to produce what we need. It's also hard to get enough from diet alone. 

Vitamin D: key facts

• Everyone is advised to take a vitamin D supplement containing at least 10 micrograms (400IU) a day during winter months, and those more at risk of deficiency should take it all year round.
• Don't overdo it as vitamin D can build up in the body - 100mcg (4000IU) is the maximum safe daily dose for adults.
• Tablets are the cheapest option, particularly own-brand or generic versions. 
• Gummies and chews are popular, but watch out for added sugar, and for high salt levels in soluble versions.

Read on for advice on how much to take and when, who's more at risk of deficiency and the cheapest places to buy vitamin D tablets, sprays and gummies. 

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Why is vitamin D important?

Vitamin D is important for the health of your bones, muscles and teeth. This is because it helps you absorb calcium and phosphorous from food. 

A deficiency can cause weakened bones – this can lead to rickets in children and osteomalacia in adults. Vitamin D and calcium, together, protect older adults from osteoporosis and reduce the risk of falls related to balance and muscle weakness. 

Vitamin D also plays an important role in keeping your immune system functioning properly. This is especially key during winter, when there are more colds and bugs going around. 

How much vitamin D should you take?

Vitamin D is sometimes referred to as the 'sunshine vitamin' as your body makes it when exposed to the sun. 

Five to 15 minutes in the sun before 11am or after 3pm, without sunscreen, and with forearms and lower legs uncovered, should be enough exposure in the summer months. But during the winter there isn't enough sun (or the correct wavelength of UV radiation) to make vitamin D this way in the UK. 

This is why the NHS recommends that between October and March, everyone above the age of one takes a daily supplement containing 10mcg (micrograms) of vitamin D (confusingly, sometimes also written as 10μg), or 400IU – International Units. 

This includes pregnant and breastfeeding women.

Breastfed babies should also have between 8.5-10mcg a day. Babies on formula milk don't need an additional supplement as formula already contains vitamin D. You can find out more in our guide to vitamin D supplements for babies and children.

Some foods, such as cereals and yoghurt drinks, are also fortified with vitamin D, but these usually contain low amounts, so it's still worth opting for a supplement to ensure you get enough.

Vitamin D is a fat-soluble vitamin, so it's best to have your supplement with food for optimum absorption.

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Can you take too much vitamin D and what are the risks?

Many supplements contain much higher doses than the NHS-recommended 10mcg.

25mcg is a common 'high-strength' option from supermarkets, discounters and pharmacies, but supplements containing 50 or even 100mcg are also widely available.

Taking a supplement containing between 10 and 50mcg a day is unlikely to cause harm, but bear in mind more is not necessarily better. Remember you'll also be getting some vitamin D from the foods you eat.

Taking too much vitamin D over a long period of time can cause calcium to build up in the body, which can actually weaken bones and damage your heart and kidneys. This is known as hypercalcaemia. 

The NHS advises the following upper safety limits for vitamin D:

• Adults – max 100mcg (4000IU) a day
• Children aged 10 and under – max 50mcg (2000IU) a day
• Babies under one – max 25mcg (1000IU) a day.

If you have a diagnosed deficiency (often an incidental finding on a blood test), your doctor might prescribe you a course of high-dose vitamin D, but only for a short period. 

Cod liver oil naturally contains vitamin D so if you're taking a cod liver oil supplement check how much vitamin D it contains before adding an extra supplement.

Where to buy the cheapest vitamin D supplements

Prices vary from less than 2p to more than 30p per dose depending on what type of supplement you pick. Easy-swallow formulations are typically pricier.

Own-brand vitamin D tablets from pharmacies, discount stores and supermarkets are usually cheapest, and buying larger packs or multi-buy offers (Boots, Superdrug, Holland & Barrett and supermarkets often have vitamins on this kind of offer) can also help keep costs down.

Cheapest vitamin D supplements:

• Cheapest tablets: Boots vitamin D 10mcg, 180 pack - £4.00 (2p per daily dose) - often on '3 for 2' offer, making it £2.67 per pack (less than 1p per dose). 

• Cheapest spray: Holland & Barrett Vitamin D spray 1000IU/25mcg, 15ml bottle - £4.69 (100 sprays - 5p per daily dose). Or BetterYou D1000 (25mcg)  vitamin D oral spray, 15ml - £7.95 (100 doses, 8p per daily dose) also at Holland & Barrett. Both are these are available on a '3 for 2 offer'.

• Cheapest gummy vitamins: Superdrug Vitamin D gummies, strawberry flavour 25mcg, 30 pack - £4.94 (16p per daily dose), Boots Vitamin D gummies, blackcurrant flavour 25mcg, 30 pack - £5.50 (18p per daily dose) and Holland & Barrett Vitamin D1000 IU (25mcg), 30 pack - £5.49 (18p per daily dose). These are also all available on a multibuy offer making the daily dose cheaper.

Prices correct as of 14th October 2024. Price per dose rounded up to nearest pence.

Gummies vs sprays vs tablets: what's the best way to get your daily dose?

Vitamin sprays and gummies have gained popularity in recent years as they can be more palatable and convenient, especially if you struggle with swallowing pills.

They tend to be more expensive, which can really add up when you're taking daily supplements for a number of months. 

If you opt for the cheapest tablets we've found, taking a daily supplement from October to March will cost you just £3.64 (excluding special offer prices), whereas with the cheapest gummy it would be around £30.94 total. Opting for big brand formulations will be even pricier.

Are sprays better than tablets?

There's no evidence to suggest this a spray is a more effective way to absorb vitamin D, despite what some companies' marketing implies.

A randomised, controlled trial (the gold standard of testing whether treatments work) published in the European Journal of Clinical Nutrition in 2019, concluded that sprays are just as effective as tablets, but not better. 

Many of the volunteers did say that they preferred the spray to taking a tablet, which is understandable - supplement fatigue can kick in if you're having to take other medicines in tablet form daily.

If you're more likely to stick to taking vitamin D regularly if it's in spray or gummy form it might be worth forking out the extra cost - you can shop around for the cheapest deals using our pricing tips above.

Watch out for added sugar and salt

Gummies and chewables often contain added sugar. In fact, many samples we looked at had sugar listed as the main ingredient. 

There have been reports of children over-consuming gummy vitamins as they view them as sweets, so be sure to keep tasty versions of vitamins well out of reach once you've doled them out.

Effervescent tablets, which you dissolve in water and drink, are also one to watch out for. These tend to contain sodium, too much of which increases your risk of high blood pressure. 

If you have high blood pressure you should avoid all effervescent tablets that list sodium in the ingredients.

Who is particularly at risk of vitamin D deficiency?

Some people are at higher risk of vitamin D deficiency. If you are in one of these groups the NHS recommends you take a vitamin D supplement all year around.

Those at higher risk include:

• People with dark skin – melanin reduces the skin's ability to make vitamin D and people with dark skin have more melanin.
• People who cover their skin – people who cover up when outside are unable to make enough vitamin D as their skin isn't exposed to sunlight.
• People who stay indoors a lot – people who are frail, housebound or live in a care home may not get enough exposure to sunlight.

Symptoms of vitamin D deficiency

It's not easy to spot vitamin D deficiency. Some people might feel tired or get aches and pains.

But others may not have any symptoms until it's too late, for example bowed legs or poor growth in children.

Your doctor can carry out a blood test to check your levels, but if you're worried about your exposure to the sun or it's winter you should start taking a supplement.

Which foods contain vitamin D?

Oily fish such as salmon, mackerel and sardines, egg yolks, red meat, liver and certain mushrooms that have been grown in sunlight or UV light all contain vitamin D. 

Egg yolks and cheese contain a small amount. 

Other foods are fortified with vitamin D, such as some breakfast cereals, yoghurt drinks and fat-based spreads.

But it's hard to get enough from food alone – a salmon fillet contains around 13mcg vitamin D (but you're unlikely to eat one every day), boiled eggs only have 1.6mcg, and a bowl of fortified cereal around 2.5mcg.

What's the difference between vitamin D2 and D3?

There are two forms of vitamin D in supplements: D2 (ergocalciferol) and D3 (cholecalciferol).

D2 is found in plants whereas D3 is in animal foods and what we synthesise from sunlight.

Both are absorbed in the small intestine, although some studies have shown vitamin D3 supplements are better at raising vitamin D levels compared with D2 supplements.

You can get vegan supplements containing either D2 or D3.

Do I need to take vitamin D and vitamin K together?

Some supplements contain both vitamins D and K together. This is because both are needed for calcium metabolism: vitamin D promotes calcium absorption and vitamin K promotes the calcification of bones and reduces the calcification of soft tissues such as blood vessels (which is a risk with very high vitamin D and calcium intake).

However the current evidence doesn't suggest you need to take supplements that combine vitamin D and vitamin K for optimal absorption, especially as it's easy to get enough vitamin K from your diet.

Vitamin K is found in leafy, green vegetables such as spinach, kale and broccoli. It's also in vegetable oils, dairy products, meat and eggs.