A lack of sunshine during the Great British Winter isn't just problematic for your skin (patchy dry spots anyone?) or for your tolerance of others on the tube.

It can also be responsible for long-term health problems such as a vitamin deficiency, which can lead to bigger problems later on. Not ideal.

According to national surveys, a fifth of adults in the UK have a Vitamin D deficiency, and if that's not a sign to go on holiday, what is?

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Also known as the 'sunshine vitamin', as it is best absorbed through the skin from exposure to sunlight, vitamin D is essential for calcium absorption and for strong bones as we age. Oh, and science shows this affects women in particular as our bones degrade quicker than men's. Also brilliant news.

Andrew Thomas, founder and managing director at BetterYou, said: 'Our modern indoor lifestyles, processed foods and the overuse of sun creams in the Northern Hemisphere are resulting in a dramatic rise in vitamin D deficiency, which can cause fatigue, aches and pains, and frequent infections.' Not good.

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Five signs to look out for that could mean you have a vitamin D deficiency:

1. You feel sad

Serotonin is the hormone is your brain that is associated with mood elevation, it has been found to raise with exposure to bright light and lessen with decreased sun exposure. According to a study by the American Journal of Geriatric Psychiatry, participants with the lowest levels of vitamin D were 11 times more prone to depression.

2. You have stomach troubles

Vitamin D is fat soluble so if you have issues in your gut, you may have a limited ability to absorb vitamin D.

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3. Your bones ache

A deficiency of Vitamin D can result in osteoporosis and weakened bones. Therefore feelings of aching bones is commonly associated with this deficiency.

4. You feel weak

Researchers at Harvard have linked vitamin D supplementation with increased muscle control. Vitamin D helps you to maintain control of your muscles.

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5. You are sweating more than usual

A sweaty head has been reported to be one of the first signs of a vitamin D deficiency. Researchers at the Mayo Clinic report this to be one of the first ways to spot this in babies.

How can you keep your vitamin D levels in check?

Go on a sunny holiday! Most of our vitamin D comes from direct contact with sunlight on our skin. We don't need to be told twice.

Take a supplement. Experts from the Science Advisory Committee on Nutrition, who led a five-year study into vitamin D absorption, concluded that vitamin D rich foods and supplements are beneficial.

The NHS recommends looking out for a supplement containing 10 micrograms of vitamin D. There are a number of vitamin D supplements on the market which come in capsule form or you can opt for a oral spray such as BetterYou Dlux 3000 Vitamin D Oral Spray - £7.99 SHOP

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Ensure you include good sources of vitamin D in your diet. The best sources are oily fish and red meat – yet another argument for making room for more protein in your diet. Vegetarians can look to eggs and fortified cereals and breads to (literally) fortify your bones.

As vitamin D is fat soluble, getting your fix alongside high-fat foods will further support your bone health. That means eating both the egg whites and the yolks, and mixing your cereals with good fats.

Skip the skimmed milk and go for minimum 2%, or tuck into your fortified toast with a healthy dollop of smashed avocado.

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