Are you D-deficient? Why is vitamin D so important?

Vitamin D is one of the most important vitamins for the body and plays a vital role in many of its functions.


What is vitamin D?

Known as the "sunshine vitamin", most people are aware that vitamin D is critical for bone health. It's suggested that the vitamin is required for proper muscle strength (and can, therefore, indirectly increase your energy levels), adequate amounts are associated with better breast cancer prognosis, and a reduction of flu incidence and severity of symptoms.

Vitamin D also helps the body to absorb calcium and phosphate from the foods that we eat. This shows why vitamin D is so important in its role for bone health.

However, results of some studies show that those who are overweight seem to be less able to convert vitamin D to the active form, meaning that vitamin D isn’t doing its job properly in the body. As we get older, our skin is less able to convert sunlight into vitamin D, meaning deficiency is more likely as we age and supplementation is more necessary. Low levels of vitamin D have also been linked to depression.

How do I get vitamin D?

Firstly, it's important to know that dietary sources are very limited. This doesn’t mean that you can't get some vitamin D from foods, but it's unlikely to be enough to meet your biological needs. However, the following are useful sources of vitamin D and have additional benefits:

  • Fish: sardines or salmon have the added benefit of being a rich source of omega-3 fats and protein, which is very important for your health.
  • Eggs: an excellent source of protein and are a good source of other vitamin nutrients, like zinc.
  • Dairy products: yoghurt, cheese and butter, which also contain important fat-soluble vitamins and calcium.
  • The sun: this is by far the most important source, and the amount of vitamin D synthesised depends on the season (you obtain virtually no vitamin D in the UK from November to March), time of day, length of day, cloud cover, smog, skin melanin content (i.e. if you are Asian or Black, you require more sun exposure in the UK), and sunscreen are among the factors that affect UV radiation exposure and vitamin D synthesis.

Fortunately, it's easy to buy vitamin D supplements (ideally with a 2000iu content per capsule) and it's straightforward to take a blood test, via your GP or by ordering an NHS home test kit, to assess your levels. Optimal levels should be around 100nmol/s and a trained nutritional therapist would be able to advise on the dose to achieve your optimal level.

Who is at risk of deficiency?

According to the National Institute for Health and Care Excellence (NICE), you are more at risk of deficiency if you fall into the following groups:

  • Infants and children aged under five.
  • Pregnant and breastfeeding women, particularly teenagers and young women.
  • People over 65.
  • People who have low or no exposure to the sun, for example, those who cover their skin for cultural reasons, who are housebound or confined indoors for long periods (so this includes anyone who works in an office!).
  • People with darker skin, for example, people of African, African-Caribbean or South Asian family origin.

As you can see from the above, categories will include a large percentage of people living in the UK.

To obtain more information about vitamin D or if you wish to find out whether vitamin D supplementation could help with a health condition you have, please seek the advice of a trained nutrition professional.


  • Kim, Y. and Je, Y. (2014) 'Vitamin D intake, blood 25(OH)D levels, and breast cancer risk or mortality: a meta-analysis'. British Journal of Cancer, 110(11), pp. 2772–84
  • Harvard Health Publishing (2021), 'Vitamin D and your health: Breaking old rules, raising new hopes', Harvard Medical School,
  • Office of Dietary Supplements, (2022), 'Vitamin D', National Institutes of Health,

The views expressed in this article are those of the author. All articles published on Nutritionist Resource are reviewed by our editorial team.

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London SW15 & W1H
Written by Melody Mackeown, mBANT, CNHC, BSEM | Nutritional Therapist and Health Coach
London SW15 & W1H

Melody Mackeown, is a nutritional therapist who works in Putney and Earlsfield, London.

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