Four signs you should start taking vitamin D and who is most at risk of deficiency

Research suggests that over a third of US adults have a vitamin D deficiency, with doctors warning people to look out for four key signs they may be running low.

Generally speaking, most of us can keep our vitamin D levels healthy during the summer months, when there is plenty of sunlight to keep things cruising.

But sluggish skies and colder, cloudier months can make maintaining healthy levels much harder during winter.

This is because vitamin D, often dubbed the 'sunshine vitamin', is produced directly from sunlight and is scarce in food alone, making it near impossible to reach the required 10 micrograms (mcg) a day from sunlight between October and March.

According to the Cleveland Clinic, as many as 35 percent of Americans and one billion people globally are deficient in vitamin D.

Moreover, a whopping 50 percent of the world's population is said to be vitamin D 'insufficient'.

This can lead to a range of symptoms, including muscle weakness and cramps, fatigue, and depression. Severe vitamin D deficiency can even result in rickets in children. Symptoms include incorrect growth patterns due to bowed or bent bones, muscle weakness, bone pain, and joint deformities.

In adults, meanwhile, vitamin D deficiency can reveal itself through four main symptoms. According to the Cleveland Clinic, these can include fatigue, bone pain, muscle aches, and mood changes such as depression.

Who is at higher risk of developing vitamin D deficiency?

Those at more risk include people with higher skin melanin (darker skin) and those who wear clothing with a lot of coverage.

Medical conditions, including cystic fibrosis, Crohn's disease, and celiac disease, are also at higher risk of becoming deficient since they make it harder for individuals to absorb enough vitamin D through the intestines.

Obesity is another risk factor, with a BMI higher than 30 typically associated with lower levels of vitamin D. This is because fat cells isolate the vitamin, meaning it is not released and can't be absorbed as easily.

Those with kidney or liver disease are also said to have a higher chance of being deficient since these conditions reduce the levels of enzymes required by the body to turn it into a usable form.

Additionally, the Cleveland Clinic explains that those who have undergone weight loss surgery, such as a gastric bypass, are more at risk since their bodies can less easily absorb the nutrient.

Meanwhile, the BBC reports that older people, those who are breastfeeding, and people who have experienced multiple short-term pregnancies are also more likely to struggle absorbing vitamin D.

Why do we need vitamin D?

The impact of vitamin D deficiency is not to be overlooked. It plays a crucial role in maintaining calcium balance in the blood, which is then used to support bone health.

Humans need calcium and phosphorus to build bones and support healthy tissues. A decline can result in hypocalcemia, which lowers calcium levels in your blood and can then lead to secondary hyperparathyroidism, as the parathyroid glands work overtime to keep calcium levels normal.

Doctors advise taking vitamin D supplements during the colder months, especially for people living in areas with little sunlight, though to be wary of one of four symptoms.

The NHS recommends that everyone over the age of five consider taking a daily supplement of 10 mcg of vitamin D between October and March.