Health experts testify that the use of vitamin tablets can help maintain the level of vitamin D in the body, but too much can lead to serious health problems and sometimes even lead to death.

Vitamin D, an essential nutrient for a healthy body helps to improve health and boost immunity.

People who stay indoors or work in offices may not get enough vitamin D from sunlight, which is the important source of vitamin D. Such people may need to eat foods rich in vitamin D or use vitamin tablets.

Study reports suggest that approximately 1 billion people worldwide are affected with vitamin-D deficiency and around 50% of the global population have vitamin D insufficiency

In Australia where a recent study was conducted, nearly one quarter of people suffer from Vitamin- De deficiency.

"For most vitamins and minerals, people can get them in sufficient quantities from a healthy balanced diet," said Elina Hyppönen, a nutritionist at The University of South Australia who was not involved in the study.

"Vitamin D is one of the exceptions to that rule. It's very difficult to get enough from diet."

As a result, popping a daily vitamin D pill has become a common way to keep levels healthy, particularly among those who don't spend much time out in the sun.

But while vitamin D supplements are generally safe, it's possible to take too much.

According to the National Academy of Medicine in the US, the safe upper limit for vitamin D intake is 4,000 IU, or 100 micrograms, though higher doses may sometimes be used to treat health issues like deficiency, cardiovascular disease and diabetes over short periods.

Studies have shown that taking between 40,000 to 100,000 IU (1,000-2,500 micrograms) each day for several months can cause vitamin D toxicity.

This causes a build-up of calcium in the blood, a condition known as hypercalcemia, which leads to a wide variety of symptoms.

Some of these include nausea, vomiting, diarrhoea, fatigue, weight loss and excessive thirst.

In February this year, a middle-aged man in the UK was admitted to hospital with symptoms of vitamin D toxicity — hypervitaminosis D — a rare but serious condition resulting from "overdosing" on the vitamin.

The man had been taking a cocktail of more than 20 over-the-counter supplements every day, including a whopping 150,000 international units (IU) of vitamin D — almost 400 times higher than the recommended daily dose, according to the report published today in BMJ Case Reports.

After one month on the regimen, the man ended up in hospital with vomiting, abdominal pain, leg cramps and increased thirst. He'd also lost close to 13 kilograms.

While the man stopped taking the supplement cocktail as soon as symptoms appeared, they hung around for almost three months.

Alamani Alkadi, lead author and endocrinologist at East Kent Hospitals University NHS Foundation Trust in the UK, said that the man had heard about the benefits of vitamin D supplements on a radio show and wanted to see if it could improve his wellbeing.

This prompted the man to seek out the advice of a nutritionist, who recommended he also take extremely high doses of other vitamins, minerals, nutrients and probiotics, according to the report.

"At that time, he was not feeling great in himself. feeling very low in energy," Dr Alkadi said.

Also known as the "sunshine vitamin", vitamin D isn't technically a vitamin but a prohormone — a substance your body converts into a hormone.

Vitamin D is converted into calcitriol, a hormone that helps you absorb calcium and maintain healthy bones and muscles.

Getting out in the sun is the best way to give yourself a vitamin D boost, but you can also get a small amount from foods like fatty fish, mushrooms and fortified milk and cereals.

Just how much vitamin D you should be getting each day depends on your age: the older you are, the more you need.

The National Health and Medical Research Council recommends 5-15 micrograms (200-600 IU) of vitamin D each day.

While vitamin D toxicity is rare, studies have shown that it could become more common as more people rely on supplements as a boost.

A 2017 study on nearly 40,000 people in the US found that the number of people taking 1,000 IU or more of vitamin D had grown between 1999 and 2014.

About 18 per cent of the study participants took more than 1,000 IU of the vitamin each day, while another 3 per cent ingested over 4,000 IU daily.

And in 2019, an elderly woman in the UK died after taking 40,000 IU of vitamin D each day.