Hundreds of people are being admitted to hospital with vitamin D deficiency at the Western Sussex Hospitals NHS Foundation Trust.
The vitamin helps people keep healthy bones, muscles and teeth, according to the NHS.
Vitamin D deficiency cases at the trust have soared over the last three years, with 240 diagnoses in the 12 months to March 2018, data from NHS Digital shows.
During the same period in 2015-16, there were just 60 cases.
Public Health England has encouraged people to consider taking a vitamin D supplement during the winter months, after a surge in diagnoses at hospitals across England.
Over the last three years, cases have increased by 84 per cent, climbing from 54,850 in 2015-16 to 101,140 in 2017-18.
The vast majority were secondary diagnoses, meaning vitamin D deficiency was not the main cause for the patient’s admission to hospital.
Vitamin D helps the body to regulate calcium and phosphate levels, which are needed to maintain healthy bones, muscles and teeth, according to the NHS.
A lack of it can lead to bone deformities in children or painful musculoskeletal conditions such as osteomalacia in adults.
Sunlight is the main source of vitamin D, but a small amount can be obtained through dietary sources.
The British Nutrition Foundation said one in four 11 to 18 year olds and one in six adults in the UK are believed to have low levels of vitamin D.
Professor Louis Levy, head of nutrition science at Public Health England, said: “Vitamin D is essential for healthy bones and most of us get enough from sunshine and a healthy balanced diet during summer and spring.
“During autumn and winter, those not consuming foods naturally containing or fortified with vitamin D should consider a 10 microgram supplement.
“Those who don’t expose their skin to the sun may not get enough vitamin D from sunlight and should take a supplement all year round.”
Black or ethnic minority people and those who spend a lot of time indoors – such as people living in care homes – could benefit from supplements throughout the year, he added.
The NHS says vitamin D is only found naturally in a small number of foods, such as oily fish, egg yolks, and liver.
It is also found in fortified foods such as low-fat spreads, cereals and fortified milk and dairy substitutes.
• Report by Harriet Clugston, data reporter