happy girl topping up her vitamin d, enjoying life and freedom in autumn in nature

Vitamin D: 100 years on

2022 marked one hundred years since Elmer McCollum and Marguerite Davis, two biochemists, reported their discovery of a substance they would name – vitamin D. It was also the year that the connection between sunlight and vitamin D was made. A century on, and vitamin D continues to be at the forefront of research and the science has evolved rapidly, uncovering more and more about its benefits to our health. In fact, vitamin D has become the one of the most highly researched nutrients.

As we make our transition into the autumn months, when the sunlight is not strong enough for the body to make vitamin D, we feel it is the perfect time to recap on the benefits of vitamin D and also to take a look at the very latest research, one hundred years on.

Vitamin D deficiency

Vitamin D is produced when the skin is exposed to UV radiation (from sunlight), hence giving rise to its name ‘the sunshine vitamin.’ Few foods naturally contain adequate amounts of vitamin D, so supplementation, particularly in the autumn and winter months, is important. The government advice is that everyone should consider taking a daily vitamin D supplement during these months, although a new survey commissioned by the British Nutrition Foundation revealed that almost half of British adults are not aware of this recommendation.1

Skip to Key Takeaways

Despite a large percentage of us likely having insufficient levels, those who are at an increased risk of deficiency include:

  • infants and children aged 5 and below
  • pregnant or breastfeeding women – meeting the mother’s requirements for vitamin D is important as is building adequate foetal stores for early infancy
  • those who have darker skin – e.g. people of African, African-Caribbean, or South Asian ethnic origin as the pigment melanin reduces the skin’s ability to make vitamin D in response to sunlight exposure
  • overweight or obese people – high prevalence of vitamin D deficiency in obese subjects is well-documented
  • those who have reduced exposure to sunshine – such as people who cover their skin or use high factor sunscreen
  • the elderly – particularly if they stay indoors during the winter months and especially those who are institutionalised
  • those who take certain medications – which can impair vitamin D metabolism

Vitamin D is considered to be deficient if levels are below 29nmol/l. However, optimum levels are suggested to be greater than 125nmol/L.

  • Optimal – 125-199 nmol/L
  • Sufficient – 75-124 nmol/L
  • Low – 30-74 nmol/L
  • Deficient – less than 29 nmol/L

If you are unaware of your status or fall into one of the ‘at risk’ categories, then it may be beneficial to get your vitamin D levels tested. Awareness of your vitamin D status means you can focus on attaining optimal results and better health outcomes.

Vitamin D and its benefits to health

Sufficient levels of vitamin D can bring about many health benefits to teeth, bone and muscular health. Extensive research shows that it also offers a wide range of extra-skeletal effects and has been positively associated with:

  • reduced inflammation1-3
  • improved mental and emotional health4-8
  • gut health9,10
  • allergies10
  • autoimmune disease11-13
  • hormonal health14,15
  • insulin resistance15-16
  • bone health and muscle strength
  • health in pregnancy, and much more 

Seasonal Affective Disorder (SAD)

Apt for this time of year is SAD, which is suggested to affect around 2 million of us here in the UK.1  SAD is a type of recurring major depression with a seasonal pattern and symptoms are likely to start in the autumn and continue through the winter months. Many of us can feel a bit flat after the spring/summer months but for those with SAD, symptoms such as fatigue, depression and feelings of hopelessness can really impact on life. Many people with SAD have insufficient or deficient levels of vitamin D and research investigating this association suggests that supplementing vitamin D may improve their symptoms.2

Research into vitamin D over the last 12 months

During the last 12 months alone some new and exciting research has emerged which we have summarised below.


Major depression is thought to be the second leading cause of disability worldwide.1 In a meta-analysis of random-controlled trials carried out this year it was found that vitamin D had a beneficial impact on both the incidence and the prognosis of depression.2 A further extensive meta-analysis, which included many studies from around the world, suggested that vitamin D supplementation may alleviate depressive symptoms in adults with depression.3


Globally, the numbers of people living with dementia will increase from 50 million in 2018 to 152 million in 2050, a staggering 204% increase.1  In a society ageing with dementia, research is crucial. Published this year, a world-first genetic study from the university of South Australia showed a direct link between dementia and a lack of vitamin D.2 The genetic study analysed data from 294,514 participants from the UK Biobank and found: 

  • low levels of vitamin D were associated with lower brain volumes and an increased risk of dementia and stroke
  • genetic analyses supported a causal effect of vitamin D deficiency and dementia
  • in the UK population, up to 17% of dementia cases might have been avoided by boosting vitamin D levels to within normal range


From the same genetic research, a direct link between low levels of vitamin D and high levels of inflammation were found, providing an important biomarker to identify people at higher risk of chronic illnesses with an inflammatory component. The study examined the genetic data of 294,970 participants in the UK Biobank to show the association between vitamin D and C-reactive protein (CRP) levels, an indicator of inflammation.

Researchers concluded that the observed association between 25(OH)D and CRP is likely to be caused by vitamin D deficiency and that correction of low vitamin D status may reduce chronic inflammation.1 High levels of CRP have also been linked to depression2, schizophrenia3, Covid-19 severity4, risk of cardiovascular disease5 and more.


Atopic eczema is a chronic inflammatory condition that can have a large impact on sufferers, and it is estimated that one in six children up to the age of five suffer from it. Research published in the British Journal of Dermatology this year revealed that infants had a lower risk of developing atopic eczema in their first year if their mothers took 1000 international units of Vitamin D a day from when they were 14 weeks pregnant until they delivered. Over 700 pregnant women took part in the research – with 352 taking the supplements from 14 weeks until they gave birth and 351 taking a placebo.1,2 


In one study published this year, researchers showed a correlation between vitamin D deficiency and Covid-19 severity and mortality. The study was among the first to analyse vitamin D levels prior to infection, which facilitates a more accurate assessment than during hospitalisation, when levels may be lower secondary to the viral illness. The records of 1,176 patients with positive PCR tests were searched for vitamin D levels measured two weeks to two years prior to infection. Patients with vitamin D deficiency (less than 20 ng/mL) were 14 times more likely to have severe or critical case of Covid-19 than those with more than 40 ng/mL. Furthermore, mortality among patients with sufficient vitamin D levels was 2.3%, in contrast to 25.6% in the vitamin D deficient group.1,2 

D2 and D3

New research has found significant differences between the two types of vitamin D, with vitamin D2 not faring as well. The study found that vitamin D3 could balance the immune system and help strengthen defences against viral infections such as Covid-19. The study found that gene expression associated with type I and type II interferon activity, critical to the innate response to bacterial and viral infections, differed following supplementation with either vitamin D2 or vitamin D3, with only vitamin D3 having a stimulatory effect.1

The majority of the population are not obtaining adequate levels of vitamin D and epidemiological studies suggest that suboptimal levels and deficiency is common in the UK. It is therefore important to ensure adequate intake is met for all individuals and particularly when supporting clients with a range of disorders. It is possible however to have excessive and therefore toxic levels of vitamin D, so we would suggest that if taking more than 5000 IU per day for more than 3 months, then vitamin D levels should be checked regularly, especially during the summer months. 

Vitamin D contributes to:

  • The absorption and utilisation of calcium and phosphorus
  • Normal blood calcium levels
  • The maintenance of bones and teeth
  • The maintenance of normal muscle function
  • The normal function of the immune system
  • Vitamin D has a role in the process of cell division
  • Vitamin D is needed for normal growth and development of bone in children
  • Vitamin D helps to reduce the risk of falling associated with postural instability and muscle weakness. Falling is a risk factor for bone fractures among men and women 60 years of age and older

Key Takeaways

  • 100 hundred years since the connection was made between sunlight and vitamin D
  • Few foods naturally contain adequate amounts of vitamin D, so supplementation is important
  • Increased risk groups include pregnant women, children under 5, those with darker skin, the elderly and those on certain medications
  • Vitamin D is considered to be deficient if levels are below 29nmol/l. However, optimum levels are suggested to be greater than 125nmol/L.
  • vitamin D can bring about health benefits to teeth, bone and muscular health and also a wide range of extra-skeletal effects
  • Many people with SAD have insufficient or deficient levels of vitamin D
  • An extensive meta-analysis suggested that vitamin D may alleviate depressive symptoms in adults
  • A world-first genetic study showed a direct link between dementia and a lack of vitamin D
  • An observed association between 25(OH)D and CRP is likely to be caused by vitamin D deficiency
  • A study revealed that babies had a lower risk of developing atopic eczema in their first year if their mothers took 1000 international units (IU) of Vitamin D a day
  • Researchers showed a correlation between vitamin D deficiency and Covid-19 severity and mortality
  • A study found that vitamin D3 could balance the immune system and help strengthen defences against viral infections such as Covid-19, but D2 could not



  1. 49% adults unaware of vitamin D recommendation – British Nutrition Foundation (2021). (Accessed: 13 September 2022).
  2. Ismailova, A. and White, J.H. (2022) ‘Vitamin D, infections and immunity’, Reviews in endocrine & metabolic disorders, 23(2), pp. 265–277.

 Benefits to Health

  1. Filgueiras, M.S. et al. (2020) ‘Vitamin D status, oxidative stress, and inflammation in children and adolescents: A systematic review’, Critical reviews in food science and nutrition, 60(4), pp. 660–669.
  2. Jani, R. et al. (2021) ‘Circulating 25-hydroxy-vitamin D and the risk of cardiovascular diseases. Systematic review and meta-analysis of prospective cohort studies’, Nutrition, metabolism, and cardiovascular diseases : NMCD, 31(12), pp. 3282–3304.
  3. Mansournia, M.A. et al. (2018) ‘The Effects of Vitamin D Supplementation on Biomarkers of Inflammation and Oxidative Stress in Diabetic Patients: A Systematic Review and Meta-Analysis of Randomized Controlled Trials’, Hormone and metabolic research = Hormon- und Stoffwechselforschung = Hormones et metabolisme, 50(6), pp. 429–440.
  4. Aghajafari, F. et al. (2018) ‘Vitamin D Deficiency and Antenatal and Postpartum Depression: A Systematic Review’, Nutrients, 10(4).
  5. Cheng, Y.C., Huang, Y.C. and Huang, W.L. (2020) ‘The effect of vitamin D supplement on negative emotions: A systematic review and meta-analysis’, Depression and anxiety, 37(6), pp. 549–564.
  6. Głąbska, D. et al. (2021) ‘The Influence of Vitamin D Intake and Status on Mental Health in Children: A Systematic Review’, Nutrients, 13(3), pp. 1–22.
  7. Silva, M.R.M. et al. (2021) ‘Relationship between vitamin D deficiency and psychophysiological variables: a systematic review of the literature’, Clinics (Sao Paulo, Brazil), 76.
  8. Guzek, D. et al. (2021) ‘Influence of Vitamin D Supplementation on Mental Health in Diabetic Patients: A Systematic Review’, Nutrients, 13(11).
  9. Charoenngam, N. et al. (2020) ‘The Effect of Various Doses of Oral Vitamin D 3 Supplementation on Gut Microbiota in Healthy Adults: A Randomized, Double-blinded, Dose-response Study’, Anticancer research, 40(1), pp. 551–556.
  10. Yamamoto, E.A. and Jørgensen, T.N. (2020) ‘Relationships Between Vitamin D, Gut Microbiome, and Systemic Autoimmunity’, Frontiers in immunology, 10.
  11. Głąbska, D. et al. (2021) ‘Vitamin D Supplementation and Mental Health in Multiple Sclerosis Patients: A Systematic Review’, Nutrients, 13(12).
  12. Wang, S. et al. (2018) ‘The effect of vitamin D supplementation on thyroid autoantibody levels in the treatment of autoimmune thyroiditis: a systematic review and a meta-analysis’, Endocrine, 59(3), pp. 499–505.
  13. Bae, S.C. and Lee, Y.H. (2018) ‘Association between Vitamin D level and/or deficiency, and systemic lupus erythematosus: a meta-analysis’, Cellular and molecular biology (Noisy-le-Grand, France), 64(1), pp. 7–13.
  14. Łagowska, K. (2018) ‘The Relationship between Vitamin D Status and the Menstrual Cycle in Young Women: A Preliminary Study’, Nutrients, 10(11).
  15. Łagowska, K., Bajerska, J. and Jamka, M. (2018) ‘The Role of Vitamin D Oral Supplementation in Insulin Resistance in Women with Polycystic Ovary Syndrome: A Systematic Review and Meta-Analysis of Randomized Controlled Trials’, Nutrients, 10(11).
  16. Yu, L. et al. (2020) ‘Association between vitamin D and prediabetes: A PRISMA-compliant meta-analysis’, Medicine, 99(8).

Seasonal Affective Disorder

  1. Beating the winter blues | NHS inform (2022). (Accessed: 13 September 2022).
  2. Melrose S. Seasonal Affective Disorder: An Overview of Assessment and Treatment Approaches. Depress Res Treat. 2015;2015. doi:10.1155/2015/178564

Depression and Mood

  1. Whiteford, H. A. et al. (2013) Global burden of disease attributable to mental and substance use disorders: findings from the Global Burden of Disease Study 2010. The Lancet. 382 (9904). pp. 1575-1586.
  1. Xie, F. et al. (2022) ‘Effect of vitamin D supplementation on the incidence and prognosis of depression: An updated meta-analysis based on randomized controlled trials’, Frontiers in public health, 10.
  2. Mikola, T. et al. (2022) ‘The effect of vitamin D supplementation on depressive symptoms in adults: A systematic review and meta‐analysis of randomized controlled trials’, Critical Reviews in Food Science and Nutrition [Preprint].


  1. Statistics about dementia – Dementia Statistics Hub (2022). (Accessed: 12 September 2022).
  2. Navale, S.S. et al. (2022) ‘Vitamin D and brain health: an observational and Mendelian randomization study’, The American Journal of Clinical Nutrition, 116(2), pp. 531–540.


  1. Zhou, A. and Hyppö Nen, E. (2022) ‘Vitamin D deficiency and C-reactive protein: a bidirectional Mendelian randomization study’, International Journal of Epidemiology [Preprint].
  2. Osimo, E.F. et al. (2019) ‘Prevalence of low-grade inflammation in depression: a systematic review and meta-analysis of CRP levels’, Psychological medicine, 49(12), pp. 1958–1970.
  3. Orsolini, L. et al. (2018) ‘Protein-C reactive as biomarker predictor of schizophrenia phases of illness? A systematic review’, Current Neuropharmacology, 16(5), pp. 583–606.
  4. Mosquera-Sulbaran, J.A. et al. (2021) ‘C-reactive protein as an effector molecule in Covid-19 pathogenesis’, Reviews in medical virology, 31(6).
  5. Yang, X. et al. (2021) ‘Association between serum level of C-reactive protein and risk of cardiovascular events based on cohort studies’, Journal of human hypertension, 35(12), pp. 1149–1158.


  1. El-Heis, S. et al. (2022) ‘Maternal antenatal vitamin D supplementation and offspring risk of atopic eczema in the first 4 years of life: evidence from a randomized controlled trial’, The British journal of dermatology [Preprint].
  2. Taking Vitamin D During Pregnancy Could Lower The Risk Of Eczema In Babies | University of Southampton (2022). (Accessed: 15 September 2022).


  1. Dror, A.A. et al. (2022) ‘Pre-infection 25-hydroxyvitamin D3 levels and association with severity of COVID-19 illness’, PLoS ONE, 17(2 February).
  2. Pre-infection deficiency of vitamin D is associated with increased disease severity and mortality among hospitalized COVID-19 patients: Study affirms that sufficient vitamin D levels may positively influence the outcome of infection — ScienceDaily (no date). (Accessed: 15 September 2022).

D2 and D3

  1. Durrant, L.R. et al. (2021) ‘Vitamins D2 and D3 have overlapping but different effects on human gene expression revealed through analysis of blood transcriptomes in a randomised double-blind placebo-controlled food-fortification trial’, medRxiv, p. 2020.12.16.20247700.

Last updated on 3rd January 2024 by cytoffice


8 thoughts on “Vitamin D: 100 years on

  1. Vitamin D is an excellent vitamin that I and my family have been taking daily over the past three years. It has boosted our immune system and has kept colds and flu at bay and I believe kept our symptoms of Covid very mild indeed.
    The government levels of vitamin D are well below what we should be taking daily, so I have been taking an optimum level of Vitamin D instead and it has kept me in excellent health. I recommend that everyone should take a vitamin D especially during the autumn and winter months.

  2. A well-researched and referenced article but there was not enough attention to the need to differentiate and emphasise the importance of D3 and D and hence the synergy between D3 and K2. Since you are one of the few brands that do a combined capsule, I felt that this would have been useful.

  3. Hello,
    I am a disabled lady, and I have been taking your junior vitamin D tablets for a while. Now I’m wondering if I increase the amount of the vitamin D, will that be beneficial to me?
    But I can’t take capsules cos they stick in my throat and I can’t swallow them all that easily.
    Thanking you for your time,

    1. Hello Anna,

      It would be useful for you to have a Vitamin D test and from that you can know if you need to take more. It is likely you will need more, particularly in the winter months. You could take our new daily K2/D3 as that will give you a good dose of Vitamin D and also some Vitamin K2 which is important for helping the uptake of Vitamin D. But the only definitive way to know how much you need is to do a blood test and measure your blood level. These are tablets but they can be crushed and mixed into juice or yoghurt with little taste.

      If you require any further help, please do feel free to contact us at nutrition@cytoplan.co.uk

      Thank you

  4. Excellent article and references. I’m 76 yrs old and keep very active/walking, swimming… for fitness also painting/politics plus reading … every day for my brain!. Although I have AF and RLS which are expected as the body starts to disintegrate with old age. I expect it to get worse so I’m tough with my attitude. I have an annual blood test and my Vitamin D was low to my surprise as I always took a Vit D3 Supplement. My graph showed 75 but after taking 2,500perday it’s now 112 so slowly creeping up. I take fatty food for absorbance?! I will be buying your Vitamin D testing kit to keep a check for myself and my family.

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