The sun might be a distant memory but you don't have to board a flight to keep your vitamin D levels ticking over.

One of the more unenjoyable elements of modern life is that we spend so much time cooped up in offices. While we know this can wreak havoc on your posture (and probably doesn't do much for your mental wellbeing either), you might have a bigger issue to worry about - vitamin D deficiency.

According to data published by Public Health England, more than one in five people have low levels of vitamin D, which is essential for keeping teeth and bones healthy, regulating mood and improving resistance against winter bugs.

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The best source of this vital vitamin is getting out in the sunshine; when the sun's UVB rays hit our skin, a reaction takes place that enables the cells to manufacture it.

The problem is, all those hours squirrelling away at your keyboard mean many of us rarely see daylight during the colder months. Booking a two-week holiday to the Bahamas would be ideal, but in reality, few of us have the time or money to jet off so close to Christmas.

Regardless, now winter's here, it means fewer sunny days, so you need to be extra-vigilant about getting enough of the good stuff. Here's how to combat bleaker days and up your vitamin D intake during the big chill.

Bake some fatty fish

Next time you're stuck for ideas for a quick and healthy dinner, head to the fish aisle. Salmon, mackerel, herring, trout and kippers are all brilliant sources of vitamin D that many of us don't eat often enough. In fact, just half a fillet of salmon has over 1,000 IU of vitamin D, which is more than the daily recommended allowance for a person (according to government advice, we should all be aiming for 1000 IU in the winter months). Fresh fatty fish also supplies iron, zinc, niacin, vitamin B6 and vitamin B12, in addition to a whole host of other nutrients you need for good health.

Glug on a pint of fortified milk

Got milk? Then get swigging. According to research, an 200ml glass of whole milk contains at least 100 IU of vitamin D, a quarter of your daily optimum vitamin D intake. Not all milk products contain this essential vitamin, so make sure you're looking out for fortified varieties.

Order eggs at brunch

Dippy eggs and soldiers are more than just homely comfort food - they're also great for, you guessed it, vitamin D. All the goodness in an egg comes from its yolk, so it's important to use the whole egg and not just the whites. One egg will give you about 40 IU, which is a brilliant excuse to get stuck into this teatime treat.

Add Shiitake mushrooms to your stir fry

In a similar way to humans, certain varieties of mushrooms can produce vitamin D when exposed to sunlight. Research has uncovered that shiitake 'shrooms are the best at mimicking the process. There are thought to be 40 IU in 120 grams of the potent fungi, which might not sound like a huge amount, but when it comes to staying healthy - every little bit helps.

Take a supplement

Let's face it, we're all busy people, and one of the easiest ways to win at winter health is to simply take a supplement. Healthspan have a Super D Vitamin Gummy (£9.95 for 90, healthspan.co.uk) that has a pleasant apple and blackcurrant flavour and is slightly more palatable than swallowing a capsule. Each of the sugar-free sweets contains 1,000 IU of Vitamin D, helping you to easily hit the recommended winter intake. Just don't snack on them like Fruit Pastilles; taking high doses of the vitamin for long periods of time can lead to excessive build up in the body, so keep a close eye on your numbers.