The sparse sunshine we get in the UK does more than negatively affect your mood and shorten the cricket season – it also results in many Brits being deficient in vitamin D.

This essential vitamin is produced by the body when we soak up the sun’s rays and is vital to healthy bones, teeth and muscles. The lack of sun in the UK means that around 30% of Brits have low levels of vitamin D in the winter and 10% are deficient in the summer.

The problem is severe enough that the government advises adults to consider taking a 10microgram supplement of vitamin D daily between from October and March.

If you’re not already clued-up on vitamin D supplements, here’s all the info you could possibly need on sunshine pills, as absolutely no-one calls them.

What is it?

Despite its name, vitamin D is not technically a vitamin, but actually a fat-soluble, pre-hormone compound that plays an essential role in a huge number of biological functions, including improving cognition and reducing the risk of certain cancers, cardiovascular disease and dementia. As well as being produced by your body when your skin is exposed to direct, strong sunlight, it’s is also found in low doses in certain foods, such as fish and eggs.

Do you need a vitamin D supplement?

If you live in the UK, or other high-latitude regions of the northern hemisphere, then the chances are that you will have some level of vitamin D deficiency. One of vitamin D’s main roles is to regulate the amount of calcium and phosphate in the body, so a severe deficiency can result in bone pain and tenderness from a condition called osteomalacia, as well as contributing to many other health issues. Supplementation can keep your levels in the ideal range to help prevent these problems, but be aware that taking high doses can deplete levels of other essential nutrients, including vitamin K.

When should you take vitamin D supplements?

The government recommendation is for all adults in the UK to consider taking vitamin D supplements from October until March, but if you’re at particular risk of a deficiency then you might need them all year round.

Who is most at risk? Well, if you don’t spend much time outdoors or tend to not expose much skin when you do go outside – favouring long sleeves and a hat, perhaps – then it’s worth weighing up the benefits of taking year-round vitamin D supplements. The government also suggest that babies and children under five take daily supplements all year round.

People with dark skin (particularly those with African, African-Caribbean and south Asian backgrounds) might also struggle to get enough vitamin D from sunlight, so they should consider taking a supplement all year round.

What are the best dietary sources of vitamin D?

Oily fish – such as salmon, sardines and mackerel, rather than white fish like cod – bolsters its already impressive heath credentials by being a good source of vitamin D.

Other good food sources of vit D include red meat, liver and egg yolks. Not necessarily all at the same time, but we won’t judge you if that’s your favourite breakfast.

It’s common in some other northern hemisphere countries to find foods that are fortified in vitamin D, including cereals and spreads, and these are found on UK supermarket shelves with increasing regularity now too.

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How much do I need?

In the UK, the government recommendation is 10mcg (400 IU) a day for adults and children over five. Infants’ and babies’ intake will vary depending on whether or not they are fed baby formula, because that contains vitamin D.

Can you take too much vitamin D?

The government recommendation of 10mcg of vitamin D a day is lower than you’ll find in many supplements. That doesn’t mean they are necessarily dangerous, but there is a point at which the amount of vitamin D you take leads not to better health, but to too much calcium in the body, which can weaken your bones, and damage your heart and kidneys. For adults that amount is a hefty 100mcg (4,000 IU) a day, so you’d have to be going some to take that much, but it’s something to bear in mind.

For kids, the recommended maximum is lower – 50mcg in children aged one to ten and 25mcg in infants of 12 months and under.

Which supplements should I buy?

Supermarkets like Tesco and Sainsbury’s sell own brand tubs of vitamin D, as do specialist health food stores like Holland & Barrett. These normally come in at around £3 for 100 tablets that either hit the 10mcg-a-day guidelines, or offer slightly more at 12.5mcg. You can save money by buying in bulk on Amazon, but be sure to check the amount of vitamin D in the supplements available online so you’re not overdoing it.

If you don’t get on with tablets, then Solgar’s Softgels might be a better bet, although the capsules themselves are easier to swallow than the price, which is over £7 for 100.

How should I take it?

You should take a vitamin D supplement after a meal that contains high-quality fat because it’s fat-soluble, which means it’s better absorbed by your body in the presence of dietary fat.

What other benefits of vitamin D are there?

A 2017 study suggested that bread and milk should be fortified with vitamin D, saying that this could stop 3.25 million a year suffering from colds and flu.

Researchers from Queen Mary University of London analysed data from more than 11,000 participants in previous studies and found that one person in every 33 taking vitamin D supplements would be spared a respiratory tract infection (ranging from the sniffles to the flu or pneumonia) as a result.

Lead researcher Professor Adrian Martineau said, “Assuming a UK population of 65 million, and that 70% have at least one acute respiratory infection each year, then daily or weekly vitamin D supplements will mean 3.25 million fewer people would get at least one acute respiratory infection a year.”

The team also suggested that expecting everyone to take supplements was unrealistic, and that the UK should consider fortifying foods like bread and milk with vitamin D. This is already done in several other countries such as the USA, Canada, Australia and Sweden.

“Vitamin D fortification of foods provides a steady, low-level intake of vitamin D that has virtually eliminated profound deficiency in several countries,” said Martineau.