Vitamin D helps to regulate the amount of calcium and phosphate minerals in the body, according to the NHS.
The nutrients help to keep bones, teeth and muscles healthy.
But, not getting enough vitamin D – also known as the sunshine vitamin – increases your risk of a number of health conditions, including cancer.
“Vitamin D is an extremely important vitamin that has powerful effects on several systems throughout the body,” said nutritionist Franziska Spritzler.
“The recommended daily intake is usually around 400-800 International Units, but many experts say you should get even more than that.”
Catching a number of cold and flu viruses could be a sign of vitamin D deficiency.
People without enough of the sunshine vitamin are more likely to develop bronchitis, pneumonia and even colds, scientists have claimed.
Spritzler said: “One of vitamin D’s most important roles is keeping your immune system strong so you’re able to fight off the viruses and bacteria that cause illness.
“It directly interacts with the cells that are responsible for fighting infection.”
Bone and back pain
Bone pain and lower back pain could be signs of vitamin D deficiency.
People with vitamin D deficiency could be twice as likely to develop bone pain in their legs, ribs or joints.
Without enough vitamin D, the body doesn’t get enough calcium, which is used to keep bones strong and healthy.
“Hair loss is often attributed to stress, which is certainly a common cause,” said Spritzler.
“However, when hair loss is severe, it may be the result of a disease or nutrient deficiency.”
Low vitamin D levels have been linked to alopecia areata – an autoimmune disease characterised by severe hair loss on the head and other parts of the body.
Feeling very tired could be a sign that you need more vitamin D.
“Excessive fatigue and tiredness may be a sign of vitamin D deficiency.
“Taking supplements may help improve energy levels.”
There may be a link between vitamin D levels and pain-sensing nerve cells in the body, scientists have revealed.
So, having a vitamin D deficiency may be causing achy muscles.
The best way to reduce the pain and sensitivity is to take vitamin D supplements, the nutritionist said.