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Despite its name, vitamin D is more than a vitamin - it's closer to a hormone that the body can synthesise under the right conditions. Regardless, we need to produce it regularly in order to maintain overall health and wellbeing.
The trigger for vitamin D synthesis is the sun, which emits UVB light that hits our skin. The UVB light reacts with a type of cholesterol found in the deeper layers of the skin, which produces a vitamin D precursor called pre-vitamin D. This is then converted to active vitamin D (calcitriol) by the liver and kidneys, and it's this form that travels around the body to interact with cells.
In the UK, even in the summer, it is difficult to get adequate vitamin D levels from sun exposure because of the inconsistencies in weather. We can also get small amounts from our diet: foods that contain vitamin D include eggs, oily fish, mushrooms and foods fortified with vitamin D, such a milk and breakfast cereals.
Vitamin D has many functions within the body, including:
This list isn't at all exhaustive and, in fact, scientists are only just scratching the surface of what vitamin D may help with.
As we've already said, the sun is the trigger for vitamin D synthesis, but does this mean we get enough from sun exposure? Well, it depends. Everyone produces vitamin D at different rates, and many are at risk of vitamin D deficiency.
Dr Sarah Brewer says: 'Public Health England recommends that everyone over the age of one year should take a daily supplement providing 10mcg vitamin D during autumn and winter. This is very much a minimum to prevent deficiency diseases - I believe that most adults would benefit from taking 25mcg (1,000 IU) per day, increasing to 50 mcg (2,000 IU) per day from the age of 50 onwards, when your ability to synthesis vitamin D in the skin starts to decline. Choose a vitamin D3 (cholecalciferol) supplement which is the same form made in the skin by the body on exposure to sunlight, and which is more effective in producing active vitamin D3 (calcitriol) than the plant-based vitamin D2 (ergocalciferol) form.'
In April 2020, this advice was updated to recommend that anyone spending a large amount of time indoors should take a vitamin D supplement during the spring and summer, too.
Those who are most vulnerable to vitamin D deficiency include:
There are also suggestions that the reason a disproportionate number of people from BAME communities have experienced serious COVID-19 infections may relate to vitamin D levels. This is because a higher level of skin melanin pigment reduces the skin's ability to synthesise vitamin D when exposed to the sun.
Research commissioned by the UK Government is exploring whether vitamin D deficiency and coronavirus severity are linked, but nothing is confirmed as yet.
However, everyone is at high risk of becoming vitamin D deficient, especially during winter. In fact, low vitamin D levels might explain why we're more prone to becoming sick during flu season - another reason why you should get your levels checked at the start of each winter1. Even living in a city instead of the countryside may induce the risk of becoming deficient.
There's also a lot of emerging research to suggest vitamin D may help in specific health conditions.
Cardiovascular disease is a massive health issue, causing more than a quarter of all deaths in the UK.2 However, recent studies are suggesting that there's a hidden superstar when it comes to heart health: vitamin D.
Vitamin D contributes to the maintenance of cardiovascular function and one study found that men who were vitamin D deficient had a significantly higher risk of a heart attack, even after controlling for known risk factors.3
Another study suggested that there was a strong link between vitamin D deficiency and increased risk of heart failure, but specifically in elderly people. This is particularly concerning, as 65% of the participants were vitamin D deficient, indicating that such deficiency is common among older adults.4
Although vitamin D is essential for every age, it may be especially important for babies and children to get a sufficient amount. This is because vitamin D can helps maintain optimal calcium levels to support the growth and development of healthy teeth and bones in young children.
Children who don't get enough vitamin D may be at risk of developing softening of the bones, which in turn can lead to bowing of larger bones, such as the legs.5
Making sure you get enough vitamin D for bone health isn't limited to just children, it is also important for the elderly. One study looked at the effects of vitamin D supplementation in combination with low-level exercise among the elderly and found that this combination was effective at reducing falls in the elderly participants.6
When a woman becomes pregnant, vitamin D is essential in helping the baby remain healthy. The Department of Health and Social Care recommends that pregnant women take a daily supplement containing 10ug of vitamin D, although it's important to always consult your doctor before taking any new supplements.
Nothing beats a healthy, balanced diet to provide all the nutrients we need. But when this isn’t possible, supplements can help. This article isn’t intended to replace medical advice. Please consult your healthcare professional before trying supplements or herbal medicines.
1Alvarez‐Rodriguez, L., Lopez‐Hoyos, M., Garcia‐Unzueta, M., Amado, J.A., Cacho, P.M., and Martinez‐Taboada, V.M. (2012). Age and low levels of circulating vitamin D are associated with impaired innate immune function. Journal of leukocyte biology, 91(5), pp.829-838.
2Heart statistics British Heart Foundation
3Giovannucci, E., Liu, Y., Hollis, B.W., and Rimm, E.B. (2008). c Archives of internal medicine, 168(11), pp.1174-1180.
4Porto, C.M., Silva, V.D.L., Luz, J.S.B., and Silveira, V.M. (2018). Association between vitamin D deficiency and heart failure risk in the elderly. ESC heart failure, 5(1), pp.63-74.
5Radhakrishnan K (2015). Vitamin D Deficiency in Children, U.S News
6Imaoka, M., Higuchi, Y., Todo, E., Kitagwa, T., and Ueda, T. (2016). Low-frequency Exercise and Vitamin D Supplementation Reduce Falls Among Institutionalized Frail Elderly. International Journal of Gerontology, 10(4), pp.202-206.