What is Vitamin D and why is it so important?

The winter months bring lots of talk around Vitamin D. It can be confusing as to why this vitamin gets so much airtime and what the importance of supplementing really is, and why we discuss supplementing around this vitamin so much? Let’s take a deeper look. 

What is vitamin D? 

Vitamin D is technically not a vitamin. The true definition of a vitamin – “any of a group of organic compounds which are essential for normal growth and nutrition and are required in small quantities in the diet because they cannot be synthesized in the body” states a vitamin is something we cannot make within our body so must be consumed. However, vitamin D acts as a hormone and can be made in the body via the action of sunlight on our skin. 

Where can we find it? 

The majority of vitamin D we use is made from the sunlight, synthesised through our skin. This means how much we absorb is influenced by many external factors, for example clothing which covers large amounts of the skin, cloud cover, pigment of our skin, how long we spend indoors and location. For individuals that are located in indoor settings and get minimal outdoor exposure, for example a hospital, care home, prison or even those working shifts, exposure to vitamin D is very limited. While sun cream is important for protecting our skin from sun damage, it has been found to reduce how much vitamin D we absorb. Additionally, for those living in the northern hemisphere, a vitamin D winter occurs. Between the months of October – March the sun is not in the correct angle for us to make vitamin D from its rays, so we must obtain it from different sources. These factors increase the risk of deficiency of vitamin D. 

It is difficult to obtain sufficient vitamin D from external sources as there is limited availability from food. Foods including oily fish, egg yolks, liver, fortified cereals, fortified dairy products, and mushrooms grown under UV light provide vitamin D, but unfortunately not in sufficient quantities to meet our daily needs, they would need to be consumed in very large quantities to meet requirements. For those following restrictive diets, for example a vegan diet, this increases risk of deficiency even further. People who avoid the sun, are pregnant, smoke and have dark skin are also at an increased risk of deficiency. 

Why do we need it?

Vitamin D is known to be most important for our bone health. It is involved in a complex mechanism with other nutrients, calcium and phosphorus, within our body which helps us build and maintain healthy bones and muscles. Vitamin D is essential for the absorption of calcium. So even if we have sufficient calcium in our diet, if we do not have adequate vitamin D, the body cannot bind and absorb the calcium to reap the benefits for our bones. 

The body is very clever, so when we do have enough, it signals our body to reserve calcium for when stores are low. 

Vitamin D is also thought to have a role in reducing inflammation in the body. Vitamin D sites are found in every cell in the body and deficiency has been linked to a rise in inflammation along with increased risk of weight gain, diabetes and over time affecting our heart health. There is also on-going research into the role of vitamin D in immunity, cancer risk and benefits to our gut health. 

What can happen if we’re deficient? 

Deficiency of vitamin D in the long term can be damaging to our bones, it increases the risk of fractures and developing conditions such as rickets in children and osteoporosis in adults. 

Osteoporosis is a condition that weakens bones, making them more fragile and increasing the likelihood they will break. The condition develops slowly over several years and is often only diagnosed following a fall or sudden impact causing bone to break/fracture. Osteopenia is the stage before osteoporosis which involves lower bone density than average for your age, but not low enough for osteoporosis. There are ways to reduce the risk of osteoporosis if you have osteopenia. The similar condition in children, rickets, causes bone pain, poor growth and soft, weakened bones that can lead to bone deformities. Adults can experience a similar condition, which is known as osteomalacia or soft bones. 

What abouts supplements? 

During the winter months of October to March the UK government recommend all adults and children over the age of 1 years old should supplement 10ug per day of vitamin D and babies who are breastfed should be given a 8.5ug supplement per day. Formula is supplemented with Vitamin D so babies that are formula fed do not need additional sources as long as they are getting 500mls or more per day. From late March/early April to the end of September, the majority of people should be able to make all the vitamin D they need from sunlight on their skin. Those that are vulnerable, including children under the age of 5 and adults over the age of 65 should continue to take a supplement all year round. 

In summary, Vitamin D is a very important nutrient for bone health and other possible benefits for wider health including immunity and gut health. The vitamin, which acts as a hormone, is not widely available through food and its main route into the body is from sunlight through our skin. UK adults and children should supplement 10ug/day in the winter months and vulnerable individuals should supplement all year round.