I didn't know I was lacking in vitamin D until I collapsed at work

"I just felt really dizzy, really nauseous, was having heart palpitations and was really hot," she says.

Saskia, a special educational needs teacher, was a keen goalkeeper who played football four times a week and felt fit and healthy. While her symptoms are not directly linked to vitamin D deficiency - she realised something was wrong.

In the UK, low vitamin D rates are increasing in some age groups, external - particularly in girls and young women.

Vitamin D can come from our diet, in foods such as oily fish and meat, or supplements.

But most is made by our body when UV light in sunlight hits the skin. Lower levels of sunlight - depending on where in the world you live or the time of year - decrease the body's ability to produce it.

Those with darker skin need exposure to stronger light to produce the same amount of vitamin D as lighter skin.

Doctors don't routinely offer blood tests to check for vitamin D deficiency, but will offer a supplement if a patient is concerned they might be high risk.