The best known way to get your daily dose is through sunlight, but that's not always easy to come by in the UK. So how much vitamin D do you really need, and which foods could help you to top up?
Why do you need vitamin D?'Vitamin D is required for the normal function of the immune system, absorption of calcium and phosphorus, contributes to normal blood calcium levels and to the maintenance of normal bones, teeth and muscle function and is required for cell division,' says Ella Allred, nutritonist at nutricentre.com.
Studies have also shown that vitamin D can help to improve your sleep quality, and may reduce the risk of developing certain cancers, including breast cancer and pancreatic cancer.
How much vitamin D do you need per day?According to the NHS, most people should be able to get all the vitamin D they need by eating a healthy balanced diet and by getting some sun. However, pregnant and breastfeeding women, children under the age of five or adults over the age of 65, and people who do not spend much time outside, could all need to give their vitamin D levels a boost.
The amount of melanin you have in your skin can also affect the amount of vitamin D you produce. 'White skin also requires less sunlight than darker skin tones to create the same amount of vitamin D, meaning that people with black or brown skin need to spend even more time in the sunlight,' Ella explains.
What's the best way to get vitamin D?'Most of our vitamin D comes from our body's synthesis in response to sunlight. Modern lifestyle however, has it that most people work inside and are not exposed to adequate levels of sunlight to produce enough vitamin D in the UK,' says Ella.
A lack of vitamin D can lead to bone deformities like rickets in children, and a condition called osteomalacia, which causes bone pain and tenderness in adults. If you are concerned that you are deficient in vitamin D, you can top up your vitamin D by taking a supplement. These can come in many different forms, such as tablets, capsules or sprays, but the Vitamin D Council states that 'it doesn't matter what form you take, or what time of the day you take it.'
Which foods contain the most vitamin D?Although you can't get your recommended amount of vitamin D from food alone, there are certain foods that are high in vitamin D and can help you to maintain your health.
Oily fish isn't just rich in vitamin D; it's packed with omega-3 fatty acids, protein, some B vitamins and selenium, all of which are essential for good health. Salmon, sardines, tuna, mackerel and swordfish are some of the best choices for vitamin D intake.
Low in fat and high in protein, eggs have long been known as a nutritional powerhouse, and they're a great source of vitamin D as well. Try them scrambled, poached or, rather appropriately, sunny side up, to give your vitamin D levels a boost.
Pork is pretty high up the vitamin D scale, beaten only by options like beef liver. Add pork chops or steaks to your regular dinner rotation and you'll get a nutritious hit of the vitamin (even better, cook them on a barbecue in the sunshine!)
You probably already know that milk is good for your bones, but it's not just because of its calcium content. Whether you pour it over your cornflakes, stir it into your tea or blend it with fruit to make a smoothie, you're adding a little extra vitamin D to your day.
Yogurt has many of the same health benefits as milk, and many brands are fortified with additional vitamin D as well. Because vitamin D helps you to absorb calcium into your bones, choosing a yogurt that's rich in both could be doing your skeleton some serious favours.
They count as one of your five-a-day, with good reason - mushrooms are on the list of vitamin D foods too. Shitake and button mushrooms are your best bets for getting the greatest dose.
Great news, vegetarians and vegans - it's not just meat and dairy that can improve your vitamin D levels. Soy-based tofu is full of protein, zinc, calcium and cholesterol lowering omega 3 fatty acids, so it's worth addding to your diet even if you do eat animals.
It's high in fat, so you shouldn't go too crazy on the Babybels, but cheese is also a decent provider of vitamin D. Ricotta and swiss are top choices, so enjoy a portion of either stirred into pasta or melted onto wholegrain toast or crackers.
It's not always easy to know how to choose a healthy cereal, but if you've selected one that's fortified with vitamin D, you could be onto a winner. All Bran, Cheerios, Cornflakes and various oatmeals all typically pack an extra vitamin D punch - it's only a small amount, but every little helps.
Supplement your cereal with a glass of OJ and you'll be getting an even greater helping of vitamin D. Just be sure to check the label to check that your chosen brand has extra vitamin D included - some bottles have far more than others.
Butter and margarine
Butter is usually championed as the superfood, but both spreads are often enriched with extra vitamins, including vitamin D. Again, it's a case of choosing a brand that's richest in the nutrient, but once you've done the research, you can buy the same tub again and again.
Cod liver oil
Vitamin D foods are all well and good, but if you're after a powerful dose in a small package, you'll find it hard to do better than cod liver oil. They're also a brilliant supplier of vitamin A, and contain those all-important Omega 3s as well, supporting your bones, immune system function and skin simultaneously.