Vitamin D is crucial for the body, as it helps to keep your bones, teeth and muscles healthy. You could be at risk of a deficiency if you develop any of these four common symptoms.
During the winter months, when daylight hours are reduced, it may be difficult to get all of the vitamin D you need from sunlight.
Without enough vitamin D - which is also known as the ‘sunshine' vitamin - it's difficult to regulate the amount of calcium and phosphate in the body.
A severe lack of vitamin D may even lead to bone deformities, rickets, or osteomalacia.
But, it's not always easy to know if you're at risk of the condition, as the symptoms can be very sneaky.
A lack of vitamin D isn't always obvious, meaning it can often go undiagnosed for long periods of time.
One of the most common signs of the condition is persistent tiredness or fatigue, according to the Cleveland Clinic.
Unexplained tiredness is one of the most popular reasons for visiting your local GP surgery.
Other patients have also reported a dull pain in their bones, muscle aches, and even mood changes.
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"Severe lack of vitamin D causes rickets, which shows up in children as incorrect growth patterns, weakness in muscles, pain in bones and deformities in joints," it said. "This is very rare.
"However, children who are deficient in vitamin D can also have muscle weakness or sore and painful muscles.
"Lack of vitamin D is not quite as obvious in adults.
"Signs and symptoms might include fatigue, bone pain, muscle weakness, muscle aches, muscle cramps, [and] mood changes, like depression."
There are, however, a number of less common signs of a vitamin D deficiency.
Patients have previously reported losing their hair, and difficulty falling asleep.
You may find you often wake up in the night for no obvious reason, leading to poor quality sleep, as well as a reduced duration of sleep.
It's crucial that you speak to a doctor if you think you may be at risk of the condition.
The best food sources of vitamin D include oily fish, eggs, mushrooms, and some fortified products.
You could also top up on vitamin D by spending more time in direct sunlight. The sun prompts the body to naturally produce vitamin D3.
But, during the autumn and winter months, the body struggles to produce enough vitamin D, due to the axis of the earth and reduced daylight hours.
It's therefore recommended that everyone takes a 10mcg vitamin D supplement to prevent a deficiency.