Vitamin D is created by the body from direct sunlight on the skin when outdoors, so people must make sure they get enough exposure to the sun to top up the vitamin. Certain groups are at risk of running a vitamin D deficiency, however, which can cause a number of bodily changes.

It is well understood that lacking the nutrient can lead to bone deformities such as rickets in children, and bone pain caused by a condition called osteomalacia in adults.

In addition to bone problems, evidence published in the International Journal of Rheumatic Diseases also revealed a strong association between low levels of the vitamin and dry eyes.

According to Mayo Clinic, dry eyes is a common condition that occurs when your tears aren't able to provide adequate lubrication for your eyes, which can cause discomfort, such as a stinging or burning sensation.

The study researchers hypothesised that the link to vitamin D levels is attributed to its anti-inflammatory properties - tear gland damage from inflammation is one of common causes of dry eyes.

In addition, the researchers proposed that vitamin D may help prevent dry eyes by inducing cathelicidin, an anti-microbial protein that can be produced by cells in the eyes and heal eye wounds.

In order to test this hypothesis, researchers compared the prevalence and symptom severity of dry eyes between 50 vitamin D deficient (levels less than 20 ng/ml or 50 nmol/l) women and 48 vitamin D sufficient (levels greater than or equal to 20 ng/ml or 50 nmol/l) women.

The researchers only included pre-menopausal women, since postmenopausal hormonal changes have been found to be associated with dry eye.

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Foods which contain vitamin D include:

As most of these foods are animal products, its harder to get vitamin D from food if you are vegan or vegetarian.

As most of these foods are animal products, its harder to get vitamin D from food if you are vegan or vegetarian, notes the NHS but calcium - the key mineral found in vitamin D - can be found in other foods.

These include:

Vitamin D can also be taken in supplement form, and the Department of Health recommends that you take a daily supplement containing 10 micrograms of vitamin D throughout the year if you:

It added: If you have dark skin for example you have an African, African-Caribbean or south Asian background you may also not get enough vitamin D from sunlight.

You should consider taking a daily supplement containing 10 micrograms of vitamin D throughout the year.

The NHS advises against taking too many vitamin D supplements a long period of time as this can cause too much calcium to build up in the body.

This can weaken the bones and damage the kidneys and the heart, so if you choose to take vitamin D supplements, 10 micrograms a day will be enough for most people, says the health body.

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Vitamin D deficiency: The sign in your eye that could signal you are lacking the vitamin - Express