Can I test my Vitamin D & should I supplement?

Once again there are stories in the press regarding Vitamin D especially in relation to a certain virus. So I wanted to take the chance to give you the low down on some factors you may need to consider for your individual situation. Understanding your Vitamin D levels, by getting a Vitamin D test is one way to understanding more about your individual situation.

NOTE: I’m not saying supplements absolutely should or shouldn’t be used, in some cases supplements (including Vitamin D) provide a crucial intervention, but for some, they may not be necessary, hopefully, the information below will give you some insight.

What is Vitamin D & why do we need it?

Vitamin D is actually strictly a hormone (but that’s a whole other conversation for me to get my geek on with), so for the purposes of this blog, I’ll call it a vitamin. It is fat-soluble, and the body uses it to support bone health by aiding the absorption of Calcium, and alongside other nutrients plays a role in cardiovascular health, immune and mood modulation.  There are two forms; D2 and D3. Vitamin D2 is produced by plants after being exposed to UV light, whilst D3 is the biologically active form we (and animals) make in our bodies when the skin is exposed to UV light (i.e. sunshine), hence why Vitamin D is often referred to as the ‘sunshine vitamin’.

How do we get Vitamin D?

Our bodies are able to make Vitamin D, as skin exposure to sunshine (specifically UVB rays) triggers the chemical reaction for Vitamin D production. As you can see from the figure below, the process starts in your skin, then through the liver and finally your kidneys produce ‘active Vitamin D’.

Figure 1: Factors that affect the synthesis of vitamin D3 from 

Vitamin D goes through several steps and has a different name at each step, cholecalciferol, calcidiol and calcitriol (amongst others!), of those, calcidiol is the form doctors most commonly focus on when measuring Vitamin D levels in the blood.

We can and usually do obtain small amounts of Vitamin D from dietary sources such as oily fish, butter, egg yolks (D3 form), mushrooms and some fortified foods (D2 form) but let’s put that into context against what is often considered a ‘maintenance’ dose of supplemental Vitamin D and dose received from 15 minutes in the Berkshire UK midday sun for someone with fair skin, wearing shorts and t-shirt in full sun (i.e. no clouds) not using sunscreen in January, April, July and October :

Figure 2: Sun exposure Vs 1000iu supplement Vs dietary sources 

The ‘dosages’ via sun exposure were calculated using the D Minder app, for dates in 2020, with a location of Newbury, West Berkshire (51.406°N 1.324°W). Whilst a little Vitamin D is shown to be possible in January, in reality, you wouldn’t be wearing shorts and t-shirt in January and it’s more likely to be cloudy meaning little to no Vitamin D can be made. Using the D Minder app, it suggests in Newbury the first day of Vitamin D in 2020 was 26th Feb, and the last day will be 13th Oct, subject to weather conditions i.e. cloudy or not!

What does this tell us?

The diagram below is taken from this detailed scientific look into sun exposure (UV levels) and Vitamin D levels2 it shows the range of exposure times required for optimal UV (white region), plotted as a function of UVI. Your skin tone plays a role in the amount of Vitamin D you can make from UV rays, the paler your skin usually the more prone you are to burning, and the darker the skin the less prone, but darker skin also means it is harder to get the UV rays to trigger Vitamin D production. The chart below is based on ‘type II – pale burns easily’.



Figure 3: 

The upper right shaded area represents times when you have received too much UV, leading to erythema (skin reddening).




The lower left shaded region represents the time when you do not receive enough UV to maintain an intake of 1000IU for full body exposure




What impacts our ability to make Vitamin D?

As shown in Figure 1, there are a number of variable external factors that can influence our ability as individuals to make Vitamin D, including but not limited to, health status, geographic location, weather, time of day, skin tone and exposure time, wearing of clothes and sunscreen. Of course, acting responsibly with our sun exposure so covering up, using sunscreen and being aware of exposure times, including the time of day must all be monitored to care for skin and overall health. But if you work night shifts, or spend large amounts of sunlight hours inside your opportunity to make meaningful levels of Vitamin D is likely to be significantly compromised3. In addition, certain medications or health conditions may influence your Vitamin D levels.

Another factor is our genetics; specific genes code for how much Vitamin D our cells have available for them to use. Obviously, we can’t change our genetics, they are a pre-determined recipe, however, for some, specific genes e.g. Vitamin D Receptor (VDR) may have a variation in their ‘code’ meaning they may work less efficiently and impacting an individuals response to Vitamin D. This change in a gene is known as a Single Nucleotide Polymorphism (SNP), it doesn’t mean the gene is faulty or not working, just the capacity or efficiency changes, up or down. In the diagram below, featuring an infographic from Lifecode Gx4 the green and blue circles show two genes that can impact Vitamin D availability. We offer testing via Lifecode Gx, including their Nutrient Core Report to help you understand your genetics including those elements that can be influenced by diet and lifestyle choices. Want to know more – Contact Us and arrange a free introductory 20-minute session with our Registered Nutritional Therapist.


Does Vitamin D help my immune system?

Research indicates that those with lower Vitamin D levels may be at a greater risk of respiratory tract infections5, this is in part due to the modulating role Vitamin D plays in the immune system. As SARS-CoV-2 is a new virus, research is only starting to emerge and whilst there is more coming through large-scale studies are still low in number. However, one large meta-analysis (10,933 people across 25 trials), indicated Vitamin D supplementation lowers the risk of cold and flu patients developing acute respiratory infections (ARIs) from 60% to 32%6.

Vitamin D also plays a role in other areas of the body such as in bone health, helping you absorb and use Calcium more effectively. In addition, Vitamin D alone will not allow your immune system to work optimally, nutrients such as Vitamin C and Zinc play an equally important role in keeping bugs at bay. However, typically these nutrients are more abundant in food sources we eat on a regular basis, whereas only small amounts of Vitamin D are obtained typically eaten as we talked about earlier, therefore lifestyle factors and the consideration around supplements can be more important.

If you’ve made it this far you may now be asking, how much Vitamin D do I need? 

As there are so many influencing factors and we are individuals there is no guaranteed one size fits all, when it comes to a ‘dose’ of Vitamin D, and that goes for all nutrients, energy requirements as well as other influencing diet and lifestyle choices. To help understand if you need to supplement Vitamin D or not, a simple Vitamin D blood test will show you blood (serum) Vitamin D levels.

This can be via your GP or here at Spriggs Nutrition we offer a straight forward finger prick at-home test that you post to and is assessed by an NHS lab, a prepaid envelope is provided. The lab send you your results and we help you interpret those results alongside reviewing your diet and lifestyle to understand if you would benefit from a top-up supplement. This service is £49, this includes:

  • Your test kit with prepaid postage to sent blood spot sample to the lab
  • Interpretation of your lab results by our Registered Nutritional Therapist
  • Review of health status & lifestyle questionnaire
  • Tailored recommendations for supplements (if applicable)
  • 10% discount on supplements via practitioners’ dispensary accounts.

Want to get your Vitamin D tested?

If you want a Vitamin D test to understand your levels and therefore if supplementing is right for you, Contact Us and state ‘Vitamin D test’ and our team will send you the online form to complete, alternatively call the clinic 01635 432383 and speak to one of the team.



References & Sources:

  1. Passeron, T., Bouillon, R., Callender, V., et al. 2019. ‘Sunscreen photoprotection and vitamin D status’, British Journal of Dermatology, vol. 181, no. 5, pp. 916-931. (Accessed 5th November 2020)
  2. McKenzie, RL, Liley, JB & Björn, LO 2009, ‘UV Radiation: Balancing Risks and Benefits’, Photochemistry and Photobiology, vol. 85, no. 1, pp. 88-98. (Accessed: 4th November 2020)
  3. Webb, A., Kazantzidis, A., Kift, R., et al. 2018. ‘Meeting Vitamin D Requirements in White Caucasians at UK Latitudes: Providing a Choice’, Nutrients, vol. 10 (4), no. 497, pp 1-13. (Accessed 5th November 2020)
  4. Lifecode Gx – Professional Genotype Analysis
  5. Grant, W., Lahore, H., McDonnell, S., et al, 2020. ‘Evidence that Vitamin D Supplementation Could Reduce Risk of Influenza and COVID-19 Infections and Deaths’, Nutrients, vol. 12(4), no. 988, pp. 1-19. (Accessed 8th November 2020)
  6. Martineau, A., Joliffe, D., Greenbery, L. et al. 2019. ‘Vitamin D supplementation to prevent acute respiratory infections: individual participant data meta-analysis’, Health Technology Assessment’, vol. 23, no. 2 (Accessed 6th November 2020)
UPDATE: 21st Nov 2020
For a comprehensive list of papers discussing the role and use of Vitamin D and COVID-19 this is a helpful resource to review data.
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