Where do we get Vitamin D from?
A small number of foods such as egg yolks, oily fish (salmon, sardines, herring, tuna and mackerel) cod liver oil, shiitake mushrooms and liver contain vitamin D but the major source of vitamin D in our body is from direct sunlight (UVB) exposure. Vitamin D3 is the form found in fish and animal sources and is the form that is also made in our skin.
Vitamin D is a fat soluble vitamin that can be stored in the body. This is just as well as we rely on creating a good reserve in the summer to get through the winter. Vitamin D3 that is made in the skin enters the bloodstream and undergoes hydroxylation in the liver to 25-hydroxyvitamin D (25(OH)D). This is the major circulating form of vitamin D in the blood and is what is used when we measure vitamin D status.
At UK latitudes, weaker winter sunlight with lower UVB intensity together with frequent cloud cover, means that only a negligible amount of Vitamin D can be produced. Surveys show that in the UK, 39% of 19-64 year olds may have Vitamin D insufficiency in the winter. That means a blood serum level that is lower than 25 nmol/L.(1)
Obtaining sufficient Vitamin D from food sources is difficult which is why Public Health England (PHE) and National Institute for Care and Excellence (NICE) are recommending that everyone should take a daily vitamin D supplement through the winter months (2). Children over 1 year and adults are recommended to take 10μg (400IU) daily.
Is the UK recommendation, the right amount for you?
UK recommendations are set for the avoidance of insufficiency, but some studies suggest that higher levels would be more appropriate for the avoidance of chronic inflammatory diseases (3), which are what so many of us now ‘expect’ to get as we get older. The UK recommendation does not take into account individual differences of vitamin D production or status. Knowing what your current Vitamin D levels are, is the starting point for thinking about supplementation.
Who may be more risk of Vitamin D insufficiency?
- Older adults are less efficient at producing Vitamin D3 in their skin. This pandemic year they may also have spent more time sheltering indoors as well.
- Those with limited sun exposure, because of having to work indoors through the summer, or wearing long robes or coverings for religious reasons. UK staycations this year may mean that you are starting the autumn with less than usual
- Darker skin: people who have higher levels of the pigment melanin in the epidermal layer may have reduced ability to produce vitamin D on exposure to UVB rays
- Those with problems with fat digestion or absorption, Vitamin D is made from a form of cholesterol (7-dehydrocholesterol) and therefore requires the absorption of dietary fat
- Obese individuals: larger amounts of subcutaneous fat may sequester vitamin D that has been made in the skin, making less available in the general circulation for use in the body (3)
Why is Vitamin D important?
Receptors for Vitamin D are found on many cells and tissues in the body so we can infer from this that it likely has many different functions, a lot of which are not yet well understood.
- Vitamin D is mostly widely known and accepted for its function in controlling calcium and phosphate levels in the body and for its role in bone health. Vitamin D controls the intestinal absorption of calcium from food and helps to regulate calcium levels in the blood stream. This is important if you know there is a family history of osteoporosis
- Vitamin D is important for the functioning of our immune system including our response to infectious disease. In this pandemic year, one study demonstrated a significant correlation between lower death rates from Covid 19 and proximity to the equator (4) which could be related to Vitamin D status. There are other emerging studies of Vitamin D that suggest that low vitamin D status may be linked with worse Covid 19 outcomes (5). Vitamin D has an important role in regulating the immune response suppressing autoimmunity and exerting a beneficial anti-inflammatory effect.
- Vitamin D status and IBS (6) there are some limited studies that find an association between low Vitamin D status and IBS, although it cannot be suggested from these that low vitamin D may cause IBS. One study reports that Vitamin D supplementation may improve severity of IBS symptoms, which would be consistent with the observed anti-inflammatory role of vitamin D.
What can I do if I am concerned about my Vitamin D levels?
When we are talking about supplementing, it’s important to get the right amount. Just taking loads of it because it’s ‘good for you’ is not necessarily the right approach. The best thing to do is to test serum Vitamin D levels and to supplement accordingly.
My Vitamin D check includes an initial 30 minute consultation before I arrange for a testing kit to be sent to you at home to do at your leisure. Once we have your results, I will advise you on what to do.
- Webb AR, Kazantzidis A, Kift RC, Farrar MD, Wilkinson J, Rhodes LE. Meeting Vitamin D Requirements in White Caucasians at UK Latitudes: Providing a Choice. Nutrients [Internet]. 2018 Apr 17 [cited 2021 Oct 8];10(4). Available from: /pmc/articles/PMC5946282/
- Statement from PHE and NICE on vitamin D supplementation during winter – GOV.UK [Internet]. [cited 2021 Oct 8]. Available from: https://www.gov.uk/government/publications/vitamin-d-supplementation-during-winter-phe-and-nice-statement/statement-from-phe-and-nice-on-vitamin-d-supplementation-during-winter
- Nair R, Maseeh A. Vitamin D: The “sunshine” vitamin. J Pharmacol Pharmacother [Internet]. 2012 Apr [cited 2021 Oct 8];3(2):118. Available from: /pmc/articles/PMC3356951/
- Whittemore PB. COVID-19 fatalities, latitude, sunlight, and vitamin D. Am J Infect Control [Internet]. 2020 Sep 1 [cited 2021 Oct 8];48(9):1042. Available from: /pmc/articles/PMC7319635/
- R K, H R, A H, SJ W, A S. Putative roles of vitamin D in modulating immune response and immunopathology associated with COVID-19. Virus Res [Internet]. 2021 Jan 15 [cited 2021 Oct 8];292. Available from: https://pubmed.ncbi.nlm.nih.gov/33232783/
- CE W, EA W, BM C. Vitamin D status in irritable bowel syndrome and the impact of supplementation on symptoms: what do we know and what do we need to know? Eur J Clin Nutr [Internet]. 2018 Oct 1 [cited 2021 Oct 8];72(10):1358–63. Available from: https://pubmed.ncbi.nlm.nih.gov/29367731/