Vitamin D is getting a lot of press.  Once a supplement only considered in winter – self-isolation and its links to help the fight against Covid-19 has seen significant growth in its popularity.  Here, Aimée Benbow, BSc (Hons), MSc, ANutr at Viridian Nutrition answers the most commonly asked questions surrounding Vitamin D including, does SPF prevent you from absorbing vitamin D? Can too much of the supplement cause harm? And what food sources are high in Vitamin D?

What is vitamin D?
Vitamin D is a nutrient that is supplied either through the diet or summer sun exposure.  What makes vitamin different from other vitamins is the fact it works within the body as a hormone.  Subsequently, it is intricately involved in immunity, in fact, vitamin D is necessary for every immune cell.  This may explain the association between lowered vitamin D status in those with chronic health conditions.  Additionally, research shows that supplemental vitamin D can improve mood in those who suffer from seasonal affective disorder, colloquially referred to as the winter blues.  Vitamin D has been shown to work with lactic acid-producing beneficial bacteria (probiotics) to drive down inflammation and contribute to improved gastrointestinal health.  In fact, vitamin D receptors are found within all the human organs that include, the heart, kidney, bone and skin, which means that adequate vitamin D is necessary for those organs to function normally.

Although Public Health England recommends that all adults and children supplement with 400iu of Vitamin D from October through to March, a larger dose may be necessary for those with a diagnosed vitamin D deficiency.  

Does SPF prevent the body from absorbing vitamin D?
Sunscreens containing skin protection factors (SPF) work by blocking ultraviolet (UV) rays from the sun, particularly UVB the rays which cause sunburn. However, it is also UVB rays which when in contact with our skin, initiates the process that leads to our body manufacturing vitamin D. Therefore, we can see that the strict use of sunscreen can, in fact, lead to poor vitamin D status.

Why is it particularly important for the UK to take a vitamin D supplement now?
New guidance in 2016 from Public Health England (PHE), advises that throughout autumn and winter people should consider taking a daily supplement of vitamin D at 10micrograms (400IU). However, updated governmental advice released in April last year suggests that everyone should now consider taking vitamin D supplements throughout spring and summer. With prolonged lockdowns over the last year and a half and many still working from home, a large proportion of the population may have experienced reduced exposure to the sun since COVID first arrived and hence have lower than normal circulating levels of vitamin D in the body.

It’s also recently been reported that vitamin D levels could be key when predicting and treating those with long COVID. It’s still early days but since vitamin D is so important for inflammation, it’s understandable why medical professionals are starting to look at the link since long COVID is thought to be caused by excess inflammation in the body.

What are the symptoms/indicators that you are experiencing vitamin D deficiency?
A variety of factors may affect vitamin D status, but symptoms of vitamin D inadequacy can be subtle, hard to identify, or even symptomless.  In fact, a recent trial showed 3 out of 5 adults in the UK during winter are deficient in vitamin D.  However, an increased frequency of infections, ongoing fatigue, unexplained back or lower body pain, poor wound healing and low mood can be general indications, subsequently these aspects may be more pronounced in the winter months when the sun is too low in the sky for vitamin D metabolism to occur in the skin.  Those at risk of lowered vitamin D status include those who follow a diet that is low in vitamin D, have limited skin exposure to summer sunlight, have dark skin, are obese or have issues with malabsorption, a digestive issue that reduces nutrient absorption.

If you are not deficient in vitamin D and add a supplement into your routine, can it cause harm?
Vitamin D is a fat-soluble vitamin which means it is stored by the body. As with other fat-soluble vitamins, if consumed in excess, long term this can lead to toxicity. It is important, therefore, that if you have not been tested and do not know if you are deficient that you only supplement with 400IU of vitamin D as recommended by Public Health England. Supplementing with 400IU of vitamin D daily, even with adequate levels of vitamin D will not pose harm. Higher dose supplements are available on the market up to 2000IU which are advisable for those who have known vitamin D deficiency. 

What sources are high in vitamin d?
The best and most efficient natural source of vitamin D is through controlled sun exposure, this can range from 20 minutes for those with fair skin to 40 minutes daily for those with darker skin.  Once vitamin D stores are fulfilled by sun exposure the mechanism halts and so levels will not achieve toxicity.  This gives the reasoning that even the best food sources of vitamin D are low and limited to oily fish such as salmon, mackerel and sardines besides dairy, eggs, and mushrooms, especially sun-exposed or ultraviolet light-exposed mushrooms. Consequently, vitamin D is often fortified into foods, for example, to milk alternatives.

READ MORE: 7 Easy Ways To Diversify Your Microbiome For Better Gut Health