How Vitamin D deficiency affects the body and causes sudden collapse

A growing number of young people in the United Kingdom are being found with low levels of vitamin D, raising concerns among health professionals about the potential long-term consequences of the deficiency.

The issue has gained attention following the experience of 23-year-old Saskia Reeves-Priestley, who discovered she had a severe vitamin D deficiency after collapsing while at work.

Reeves-Priestley, a special educational needs teacher and keen football goalkeeper, said she suddenly experienced dizziness, nausea, heart palpitations and excessive sweating before falling ill.

Despite regularly playing football four times a week and considering herself physically fit, subsequent blood tests revealed that her vitamin D levels were extremely low.

Her experience highlights a nutritional problem that experts say can remain undetected because its symptoms are often difficult to recognise.

According to the UK’s National Diet and Nutrition Survey, published in June 2025, approximately 23 per cent of children aged between 11 and 18 had low vitamin D levels.

The survey also found that 18 per cent of adults aged 19 to 64 were affected.

Vitamin D plays an essential role in regulating calcium and phosphate levels, which help maintain healthy bones, teeth and muscles.

The body produces most of its vitamin D when the skin is exposed to ultraviolet B radiation from sunlight, although it can also be obtained through certain foods and supplements.

Oily fish, egg yolks, red meat and fortified breakfast cereals are among the dietary sources.

However, limited sunlight exposure, darker skin pigmentation and covering most of the skin outdoors can increase the risk of deficiency.

Health experts warn that prolonged vitamin D deficiency can cause serious bone-related conditions.

In children, it can lead to rickets, which weakens developing bones, while adults may develop osteomalacia, a condition associated with bone pain and muscle weakness.

Other possible symptoms include persistent tiredness, muscle cramps, difficulty climbing stairs and increased susceptibility to fractures.

Dr Suma Uday, a paediatric endocrinologist, is among clinicians advocating for greater awareness and earlier intervention.

She has joined other medical professionals and researchers through the ACT NOW Vitamin D campaign, which is calling for a review of the threshold used to identify vitamin D deficiency.

Professor Martin Hewison of the University of Birmingham has also raised concerns about the continued occurrence of rickets, despite vitamin D having been discovered more than a century ago.

He supports exploring wider food fortification to improve vitamin D intake across the population.

In the UK, fortification of foods such as breakfast cereals and fat spreads is currently voluntary, according to the Scientific Advisory Committee on Nutrition.

The NHS advises people to consider taking a daily supplement containing 10 micrograms of vitamin D during autumn and winter, while certain higher-risk groups are advised to take supplements throughout the year.

Following her diagnosis, Reeves-Priestley began taking vitamin D supplements regularly and has since returned to playing football.