Vitamin D – what you need to know

Vitamin D – what you need to know

What is vitamin D?

Vitamin D is a fat-soluble vitamin; meaning it is dissolved and stored within our fat cells in our bodies. Importantly, it requires fat to be absorbed (think: olive oil, avocado, nuts, seeds, oily fish, meat).

Why do we need vitamin D?

Vitamin D is actually better classified as a HORMONE as it plays a crucial role in many body systems from bones, cardiovascular, gastrointestinal, endocrine (hormonal health), immunity, fertility and more.1

While the main role of this vitamin is to maintain normal levels of calcium and phosphorus within the blood2, many scientific studies have shown other areas and systems that vitamin D plays a significant role in:

  • The immune system3 – research has shown that vitamin D deficiency may increase susceptibility to infections
  • Mental health conditions – research has shown that vitamin D deficiency is more common amongst those suffering with anxiety and depression
  • Gut barrier function5
  • Sleep6

About 90% of vitamin D is synthesised through our skin when exposed to UV light from the sunshine, leaving the remaining 10% from food rich in the vitamin1.

So, you can see why getting out in the sunshine is so vital. As our sunlight hours decline at this time of the year, the government recommends that EVERYONE in the UK supplements with 10µg or 400 IU every day from September to March. This recommendation includes breastfed babies, however babies who are receiving more than 500ml of formula milk per day do not need the extra supplement.

Vitamin D goes through a few conversion processes in our bodies (in the liver and the kidneys) before it enters its active form, called Calcitritiol (vitamin D3). Supplementing with the active form, D3, is always preferable, so look out for this when purchasing your supplements.

Our main source of vitamin D is the sunlight*, however food sources such as full fat dairy products, eggs, beef liver, fatty fish and sun exposed mushrooms will contain small amounts.


Testing your levels of Vitamin D is essential, as many of the government nutrient recommendations may be too low for some subsets of people (such as those with deficiency) and the research also suggests a safe upper intake for vitamin D3 supplementation is 10,000 IU.7

There are at-home finger prick tests available which are super easy and simple to arrange, so please get in touch if you are interested.

*Our skin colour (amount of melatonin in our skin) can influence the amount of vitamin D we make from sunlight exposure. Typically, fairer skinned people need to spend less time in the sun than those with darker skin.8

As always, I recommend getting advice from a qualified nutritionist regarding vitamin D supplements, especially if you find out you are deficient. Not all supplements are equal, so ensuring you are using reputable brands is vital.

*** This blog post is not intended or implied to be a substitute for seeking professional medical advice, diagnosis or treatment. Information provided here is general and is not intended to treat, diagnose, prevent or cure any diseases or conditions. Please contact your GP or private health consultant if you have any personal health concerns, or consult a registered nutritional therapist for personalised dietary and lifestyle advice and guidance.



  1. Pludowski, P., Holick, M.F., Pilz, S., Wagner, C.L., Hollis, B.W., Grant, W.B., Shoenfeld, Y., Lerchbaum, E., Llewellyn, D.J., Kienreich, K. and Soni, M., 2013. Vitamin D effects on musculoskeletal health, immunity, autoimmunity, cardiovascular disease, cancer, fertility, pregnancy, dementia and mortality—a review of recent evidence. Autoimmunity reviews12(10), pp.976-989.
  2. Holick, M.F., 2004. Vitamin D: importance in the prevention of cancers, type 1 diabetes, heart disease, and osteoporosis. The American journal of clinical nutrition79(3), pp.362-371.
  3. Martineau, A.R., Jolliffe, D.A., Hooper, R.L., Greenberg, L., Aloia, J.F., Bergman, P., Dubnov-Raz, G., Esposito, S., Ganmaa, D., Ginde, A.A. and Goodall, E.C., 2017. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. bmj356, p.i6583.
  4. Jorde, R., Sneve, M., Figenschau, Y., Svartberg, J. and Waterloo, K., 2008. Effects of vitamin D supplementation on symptoms of depression in overweight and obese subjects: randomized double blind trial. Journal of internal medicine264(6), pp.599-609.
  5. Raftery, T., Martineau, A.R., Greiller, C.L., Ghosh, S., McNamara, D., Bennett, K., Meddings, J. and O’Sullivan, M., 2015. Effects of vitamin D supplementation on intestinal permeability, cathelicidin and disease markers in Crohn’s disease: results from a randomised double-blind placebo-controlled study. United European gastroenterology journal3(3), pp.294-302.
  6. Majid, M.S., Ahmad, H.S., Bizhan, H., Mohammad Hosein, H.Z. and Mohammad, A., 2017. The effect of vitamin D supplement on the score and quality of sleep in 20–50 year-old people with sleep disorders compared with control group. Nutritional neuroscience, pp.1-9.
  7. Heaney, R.P., 2008. Vitamin D in health and disease. Clinical Journal of the American Society of Nephrology3(5), pp.1535-1541.
  8. Libon, F., Cavalier, E. and Nikkels, A.F., 2013. Skin color is relevant to vitamin D synthesis. Dermatology227(3), pp.250-254.


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