All things Vitamin D – how much Vitamin D per day?

Now that the cold and dark winter months are descending, we have shorter days, less sunlight and for most us Brits, a long way to wait before we feel that sun-kissed feeling again. So how should we be getting our daily dose of the sunshine vitamin if the sun isn’t shining?

The NHS actually recommends that between the months of October to April, that everyone in the UK should consider taking the RDI of vitamin D… and with 1 in 5 of us in the UK low or deficient, this is advice well worth listening to.

But is the RDI of 10mcg really enough? And how should we get our daily Vitamin D – is a multivitamin the right choice or can we rely on food? 

Read on below for everything you need to know about supporting your Vitamin D status this winter.


Vitamin D’s primary role is in maintaining healthy bones.  Vitamin D is required for regulation of calcium and phosphorus metabolism and is therefore essential for musculoskeletal health including bone growth. With up to 300,000 people hospitalised each year because of fragility fractures, it is essential that deficiencies don’t occur in this critical nutrient.

GUT HEALTH– Vitamin D has a vital role to play in immune defence, whilst helping to optimise overall gut health. There are different genes regulated by our vitamin D receptor that has the ability to impact the integrity of the gut barrier and the immune defences in the gut. Plus vitamin D supplementation has been associated with improved diversity of gut bacteria. 

One 2020 study found that men with higher levels of the active, hormone form of vitamin D had a higher variety of gut microbes, including the forms of gut microbiota that have the ability to produce the postbiotic butyrate. (1)

ENERGY – Low energy is often a common sign of a vitamin D deficiency. Vitamin D is used by our mitochondria, the part of the cell that helps to generate ATP (energy) and poor mitochondrial function is often related to feelings of fatigue. Therefore low levels of vitamin D might impact our natural production of energy.

IMMUNE FUNCTION – vitamin D is key for the proper functioning of the immune system, and contributes to the function of our innate and adaptive immune responses. Studies have indicated that a deficiency in Vitamin D is associated with an increased risk of developing autoimmune conditions and increased susceptibaility to infections. (2) One study that involved 25,000 older individuals showed that adults who take vitamin D supplements have a lower risk of developing autoimmune disease. (3)

MOOD – Our happy hormone, serotonin, decreases with a lack of sun exposure. The human body needs vitamin D to be able to effectively make serotonin in the brain, so a lack of vitamin D could also result in low mood or an individual feeling irritable. 



A reference nutrient intake (RNI) of 10 micrograms (400IU) vitamin D per day has been set for everyone in the UK aged 4 years and older.   

Babies up to 1 years old need between 8.5-10 micrograms of vitamin D per day.

However, we are all unique, and some of us, we may have higher requirements for Vitamin D.

So, who may require high levels of vitamin D?

GENETIC VARIATIONS VITAMIN D – Recent genetic studies have associated a vitamin D deficiency with numerous candidate genes. These include:

  • Cytochrome P450
  • family 2 
  • R (CYP2R1)
  • The group-specific component (GC) gene
  • 7-dehydrocholesterol reductase/NAD synthetase 1(DHCR7/NADSYN1) gene (3)

HERITAGE – Research has shown that those who live in low latitude countries (such as south africa and brazil) are often sufficient in vitamin D. However, those who live in higher latitude countries such as the UK, are more likely to have a  Vitamin D deficiency. Research has also demonstrated that vitamin D requirements will vary between individuals living in each country, but a moderate dose of vitamin D is an effective strategy for maintaining adequate levels over the winter months. (5)

SKIN COLOUR – individuals with darker skin pigmentation need longer or more intense ultraviolet radiation exposure to synthesise sufficient levels of vitamin D. Therefore, those with darker skin tend to make less vitamin D in the sun than those with lighter skin tones. 

AGE – It can be challenging for those in the UK to reach vitamin D needs through just sunlight and diet alone, therefore it is recommended that over 65’s take a vitamin D supplement of 10 micrograms a day as they tend to get outside less. In addition, they should aim to get outside in the sun for 10.15 minutes a day without sunscreen when possible. 

OBESITY – Studies have shown that getting enough vitamin D is helpful when it comes to decreasing body fat and obesity. One study showed that obese women who took vitamin D experienced more weight loss, losing an average of 7 pounds more than the women who did not supplement with vitamin D. For those overweight or obese, increasing their daily intake of vitamin D may help promote weight loss and therefore overall health. (5)

PREGNANCY – During pregnancy, women require 10 micrograms of vitamin D daily. Vitamin D is vital as it helps to regulate the amount of calcium and phosphate in the body, which are needed to keep bones, teeth and muscles healthy. This helps support not only the mother but also her developing baby, too. 

VEGANS – Following a vegan or heavily plant-based diet, excludes natural vitamin D food sources from the diet. Therefore, supplementing will be the best option for these individuals. 

Please see below under DIETARY SOURCES OF VITAMIN D to find the richest food sources of vitamin D.  

It is never recommended to take more than 4000iu of vitamin D unless you are working under the guidance of a doctor or Nutritionist, as too much Vitamin D can be toxic and impact calcium levels in your blood.

If you are low or deficient in Vitamin D, taking the recommended daily intake may not be enough! The best thing to do is get a blood test to know what your levels are, then you can supplement appropriately to get you back up into the optimal range. 

I like the Medichecks Vitamin D test or alternatively you can run functional testing with one of the Clarissa Lenherr Nutrition team.


The NHS suggests:

  • Levels of below 25 nomol/L indicate a deficiency 
  • 50 nmol/L and above is sufficient
  • 75 nmol/L and above is optimal

Functional medicine suggests optimal levels of vitamin D range 100-200 nmol/L


Vitamin D2 and D3 are the main forms of Vitamin D and whilst both play a role in our health, studies have suggested that D3 is the best-absorbed version of Vitamin D.

When it comes to supplements, a recent review suggested that vitamin D3 supplements may increase serum levels of Vitamin D for longer than supplementing with D2 (10). Some studies have shown that D2 is more sensitive to humidity and temperature fluctuations, therefore vitamin D2 supplements are more likely to degrade over time. (7)

Vitamin D3 is only found in animal food sources, but D2 is mainly found in plant sources and fortified foods. D2 is less impactful than D3 at helping to raise overall blood levels of vitamin D. 



Vitamin D is produced by the body in response to sunlight on our skin. Midday during the summer is the best time to get natural sunlight, due to the sun being at its highest point, and the UVB rays being most intense. (8) However, the further you live from the equator, the less vitamin D you will produce during the winter months. 

For those of us who live here in the UK, it is a struggle to make any vitamin D from natural sunlight between the months of October to March, therefore supplementation is a must. 

When it comes to wearing sunscreen, the skin is exposed to lower levels of harmful UV rays BUT these rays are also essential for making vitamin D. Therefore, sunscreen can prevent the skin from producing natural vitamin D. Some studies have shown that sunscreen of SPF 30 or more can reduce natural vitamin D production in the body by 95-98%. (9)


Whilst there are a number of foods that do contain Vitamin D, it is quite hard to get ample Vitamin D through diet alone.

Vitamin D3 (the active form) containing foods include:

  • Egg yolks – one egg provides 1/10 of our daily intake of 400iu
  • Fatty fish – salmon and mackerel
  • Organ meats such as liver
  • Cheese

Some foods contain Vitamin D2, which is the less active form of vitamin D, is found in:

  • Activated mushrooms
  • Fortified foods
  • Supplements

D2 is much cheaper to produce which is why you will find it in cheaper supplements and foods.


As you will see, it is very hard for vegans/ plant-based eaters to get adequate vitamin D from their diet, as the only sources available to them contain D2, which has been shown to be less effective at raising blood levels of Vitamin D. Vegans are at at increased risk of vitamin D deficiency for this reason, and may require supplementation.


HOW TO TAKE- Vitamin D is a fat-soluble vitamin, therefore it is best absorbed into the bloodstream when paired with high fat foods. Therefore it is recommended to take your vitamin D supplement with a meal to enhance absorption and always opt for the form vitamin D3.  

Some research has shown that taking vitamin D at night could potentially negatively influence sleep quality by interfering with melatonin production. Therefore I always recommend my clients take vitamin D with their breakfast or lunch.

D3, MAGNESIUM AND K2 – The bioavailability of vitamin D depends on magnesium, which helps to convert it into its active form, calcitriol. Research also suggests that combining vitamin D3 and K2 together may help support absorption of calcium and integration of calcium into the bone.

WHAT ABOUT VEGANS? Not all forms of vitamin D are vegan-friendly. Vitamin D2 is always suitable for vegans however D3 is often derived from animal sources, however some vegan options exist. Always make sure to read the label to ensure they come from non-animal sources such as from Lichen.

VITAMIN D & CALCIUM – For those with osteoporosis or other musculoskeletal disorders, taking calcium and vitamin D together may be just what you need to protect your bones. Calcium helps to build and maintain bones, whilst vitamin D helps the body effectively absorb calcium. Therefore, even if you are taking enough calcium this could be going to waste if you are deficient in Vitamin D. 


  • Feel Immune- use code NUTRI-CLARISSA here
  • Feel Multi- use code NUTRI-CLARSSA here
  • Nutri Advanced D3 drops with K2 here


*Food supplements are not a replacement for a varied and balanced food intake and a healthy lifestyle. Please note that if you are breastfeeding, pregnant, on any medication or have any health concerns please check in with your health care provider before taking any supplements.


https://www.nature.com/articles/s41467-020-19793-8?utm_medium=affiliate&utm_source=commission_junction&utm_campaign=CONR_PF018_ECOM_GL_PHSS_ALWYS_DEEPLINK&utm_content=textlink&utm_term=PID100064639&CJEVENT=0ecb6dbb43e711ed83017f360a18050d (1) 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3166406/ (2)

https://pubmed.ncbi.nlm.nih.gov/30415629/ (3)

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5791363/ (4)

https://pubmed.ncbi.nlm.nih.gov/34255034/ (5)

https://pubmed.ncbi.nlm.nih.gov/24622804/ (6)

https://pubmed.ncbi.nlm.nih.gov/17023693/ (7)

https://pubmed.ncbi.nlm.nih.gov/24494051/ (8)

https://pubmed.ncbi.nlm.nih.gov/17634462/ (9)

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3349454/#:~:text=Vitamin%20D3%20was%20shown,combined%20(P%20%3D%200.01).&text=Vitamin%20D3%20was%20calculated,raising%2025(OH)D. (10)

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Hi there

London Nutritionist Clarissa Lenherr

I’m Clarissa, a registered nutritionist (mBANT) and workplace wellness expert. In my practice, I have helped hundreds of clients reach optimal health through creating sustainable, effective habits and dietary adjustments. My aim is to empower people with the skills, tools and knowledge to take their health into their own hands and feel the happiest, healthiest versions of themselves. Featured in The Daily Mail, Women’s Health, The Telegraph, and more.




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