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By Dr Duane Mellor RD PhD

Why is everyone talking about vitamin D?


The year 2020 has certainly been a challenging one, with the COVID-19 global pandemic. This has led to an increased interest in how our immune systems help protect us, impact on our health and how we can keep it in good shape including how diet can affect it.

Many people may think that vitamin C is the nutrient which has been most associated with coughs and colds, although the evidence is not actually that strong. This year vitamin D has emerged as a front-runner of vitamins which may help promise with respect to keeping our lungs healthy. Much of this evidence is based on other forms of infection and pneumonia and not directly linked to COVID-19. Although there is some emerging evidence that people who experience the most severe effects of COVID-19 have lower vitamin D levels. Whilst it is not proof of low vitamin D levels will prevent vitamin D or even reduce the risk of severe disease, what is known is that at least 1 in 5 people in the UK have low vitamin D levels.

Why do so many people have low vitamin D levels?


Firstly, we need to consider where we get vitamin D from. Vitamin D is not just a vitamin it is a hormone, it has many similarities to cholesterol which is also the basis of other hormones including oestrogen and testosterone. The second, factor is that although we can get it from food, as it is only naturally found in a few foods including oily fish, liver, red meat and the yolks of eggs. Additionally, it is also fortified into a number of foods including margarines and some breakfast cereals. So, if it is not that widely found in foods, why are more people not lacking in this vital nutrient? Perhaps, is that we have the ability to make vitamin D from cholesterol when our skin is exposed to ultraviolet light from the sun. This explains the problem why people are more likely to be lacking in vitamin D in the winter when there is less sunlight. Also, it explains why more people with darker skin, including individuals of Asian and African origin are more likely to be vitamin D deficient as darker skin limits the amount of ultraviolet light able to stimulate its production. The link between vitamin D and sunlight is why normally the health advice to adults (and especially older adults) should take a vitamin D supplement through the winter months. This advice has been changed this year to recommend people take vitamin D supplements all year around, as with a series of restrictions and lockdown many people have not been outside as much this year.

How much vitamin D is enough?


Although the government recommendations are to take a supplement equivalent to the reference nutrient intake of 10 micrograms per day (400 IU) many people may benefit from higher amounts due to their lower levels of the vitamin with 25 micrograms (1000 IU) being more appropriate. As well as the amount it is important to consider the type of vitamin D and where it is from. This is a concern to some people who are trying to limit the intakes of animal products. There are 2 main types of vitamin D found in supplements, Vitamin D2 (ergocalciferol) and Vitamin D3 (cholecalciferol). Recent research has shown that supplements containing the D3 variety are more effective at raising blood levels of this vitamin. However, the most sources of D3 are animal-based, where lanolin from sheep’s wool is often used, increasingly vegan sources are being developed including D3 from lichen and D2 in mushrooms which has been exposed to flashes of ultraviolet light.

So, what does vitamin D do?


Many people tend to think that vitamin D is predominantly involved with keeping our bones healthy. It does this through its role in controlling the absorption and levels of the mineral calcium in our blood. Calcium is more than what keeps our bones strong, it helps throughout our body, from controlling our muscles and heart to how our lungs work and immune system. Vitamin D has an important role in regulating how our immune cells release protective proteins and divide, helping to maintain a normal and appropriate immune response to infection.

Vitamin D we now know has a much wider role than just keeping our bones strong, helping to prevent rickets in children and osteoporosis in adults. It is key to keeping many parts of our body working properly. One area which is emerging, is how low levels of vitamin D have been linked to an unhealthy colon microbiome, meaning the balance of bacteria and the vital short-chain fatty acids they produce can negatively impact on the overall health of our colon. Although this is not causal, it suggests that there could be a link between having good vitamin D levels and having a healthy gut. Perhaps, future research should focus on the potential effects of combining vitamin D and probiotics on overall health.

Vitamin D is important for far more than just our bones, it is key for many aspects of our health including helping to maintain normal immune function. It is not the easiest vitamin to obtain from your diet, especially over winter (as well as years such as this when we might not go outside and get as much sun as normal) supplements are recommended for a number of groups of people. When choosing a vitamin D supplement, it is best to choose one containing vitamin D3 (cholecalciferol) which is the most effective form of this vitamin.