While some of the health claims around vitamin D might have been exaggerated, the buzz around this nutrient isn't without reason. Experts agree it's the one vitamin we should all be taking in the UK, especially during the winter months.
This is because vitamin D plays a key role in immune and bone health, and you can't get enough from the sun between October and March in the UK. It's also hard to get enough from diet alone.
Read on for advice on how much to take and when, who's more at risk of deficiency, whether you really need vitamin K as well, the facts on vitamin D and Covid, and the cheapest places to buy vitamin D tablets, sprays and gummies.
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 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.
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 includes pregnant and breastfeeding women.
Some foods, such as cereals, yoghurt drinks and mushrooms are also fortified with vitamin D, but these are usually 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.
The NHS says 10mcg a day is enough for most of the population to avoid a deficiency, but many supplements contain much higher doses.
25mcg is a common 'high-strength' option from supermarkets, discounters and pharmacies, but supplements containing 50 or even 100mcg are also widely available.
Taking between 10 and 50mcg a day is unlikely to cause harm, but bear in mind more is not necessarily better. 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:
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.
Otherwise, you're best sticking to less than 50mcg a day.
There are many different forms of vitamin D supplement available, from tablets and capsules to sprays, gummies and even teas.
Prices vary from less than 1p to more than 30p per dose depending on what format you pick.
Own-brand vitamin D tablets from pharmacies, discount stores and supermarkets are usually cheapest, and buying larger packs or multi-buy offers (Boots, Wilko, supermarkets etc often have vitamins on this kind of offer) can also help keep costs down.
We've rounded up the cheapest prices we could find for vitamin D supplements in a 'high strength' 25mcg format, as this is one of the most commonly available high-street doses:
Prices correct as of 26 November 2021. Price per dose rounded up to nearest pence.
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 £1.15, whereas with the cheapest gummy it would be around £12 total. Opting for big brand formulations will be even pricier.
There's no evidence to suggest this is a more effective way to absorb vitamin D, despite what some companies' marketing implies.
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 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.
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.
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:
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.
At the start of the pandemic there was a lot of buzz around whether vitamin D could be helpful for preventing or treating coronavirus.
However, we do know that vitamin D is important for our bone, muscle and immune health and that it's common for people to be deficient in the UK – something likely to have been exacerbated by long periods of lockdown and limits on movement, so it's still important to ensure you get enough.
Video - Vitamin D and Covid: expert view
We spoke to Martin Hewison, Professor of Endocrinology at the University of Birmingham, and specialist in vitamin D research, to find out how vitamin D helps your immune system:
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.
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.
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.
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.