What is Vitamin D deficiency? Symptoms, causes - and best food sources and supplements according to experts

Covid-19 and flu infections are expected to increase over the winter, but the colder months also brings with it another health concern - lack of vitamin D.

Vitamin D is crucial for good bone, teeth and muscle health, and can help stimulate the immune system against infections.

Known as the “sunshine vitamin”, the body usually gets all of the vitamin D it requires from sunlight on the skin when outdoors.

However, between October and early March sunlight does not contain enough UVB radiation for the skin to be able to make enough of the vitamin, which can lead to a deficiency.

A lack of vitamin D can cause bones to become weak and soft, resulting in bone deformities. In children this can lead to rickets, while in adults it will cause osteomalacia, which causes pain and tenderness in bones, and weaker immunity.

Dr Sarah Schenker, dietitian and nutritionist, explained: “We have an essential requirement for vitamin D for many processes in the body, in particular for good bone health as it aids the absorption of calcium from the diet, and it also plays a key role in the immune system.

“It is important for innate immunity, which is the way the body prevents the entry and

spread of pathogens (including viruses that can cause disease), and it stimulates the production of powerful substances in the cells that line the respiratory tract and protect the lungs from infection.”

How much vitamin D does the body need?

From early April to the end of September, most people should be able to make all of the vitamin D that their body needs from sunlight on their skin.

However, supplements may be needed from October through to March to meet the recommended dose of 10 micrograms per day.

Dr Schenker added: “It is recommended that vulnerable people, including older, black and Asian people who avoid or do not have access to sun exposure,  pregnant women, breastfeeding women, babies and young children take a 10mcg supplement.

“I would recommend that most people consider taking a supplement.”

What are the symptoms of vitamin D deficiency?

A lack of vitamin D can cause some unpleasant symptoms, but these can be relieved by boosting your intake.

Rupal Joshi, Clinical lead at online health clinic Numan, said the most common symptoms of vitamin D deficiency include:

• Muscle weakness
• Fatigue
• Aches
• Bone pain
• Mood changes and depression

Severely low vitamin D levels can also cause rickets in children, which causes the bones to soften and bend, and osteoporosis in adults, which means bones weaken and break more easily.

Nutritionist Dr Federica Amati, Chief Nutrition Scientist for Indi Supplements, added: “As vitamin D is so integral to so many functions, a lack of vitamin D can have different effects for different people.

“One of the key effects is on our immune system, which is especially important in winter when we are exposed to more viruses.

“As our body isn’t very efficient at storing and releasing vitamin D to keep levels constant, it’s important to ensure we take an effective dose of vitamin D supplement in the winter months.

“In less severe deficiency we can become more susceptible to viral infections and there are some studies that suggest an increased risk of depression and anxiety.”

How can I boost my vitamin D intake?

Vitamin D does not occur naturally in many foods, so the Department of Health recommends taking a supplement containing 10 micrograms (μg) of vitamin D each day.

The following groups of people are considered to be most at risk vitamin D deficiency and should take daily supplements to ensure they get enough:

• all babies from birth to one year old
• all children aged between one and four
• people who are not often exposed to the sun, such as those who are frail, housebound, in a care home, or usually wear clothes that cover up most of their skin when outdoors

Eating oily fish, red meat and eggs can also help to boost vitamin D levels, so it is worth incorporating more of these foods into your diet over the winter months.

Dr Schenker said: “There are very few food sources, but foods that do provide some vitamin D include oily fish, such as salmon, tuna, and mackerel, and fish liver oils which are among the best sources.

“Small amounts of vitamin D are also found in beef liver, cheese and egg yolks. Vitamin D in these foods is primarily in the form of vitamin D3.

“Some mushrooms provide vitamin D2 and levels can be enhanced by leaving them exposed to sunlight.”

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