vitamin D supplement
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Dr Deborah Lee of Dr Fox Online Pharmacy, highlights the importance of taking a daily vitamin D supplement following the NHS’ latest recommendation

Did you know we should all be taking a daily supplement of vitamin D?

In April 2020, the NHS issued a statement, based on recommendations from Public Health England (PHE), that we should all consider taking 10 mcg/day vitamin D as a supplement, to keep our bones and muscles healthy.

This advice has been issued now, largely because of the restrictions imposed by quarantine and lockdown. However, many people remain unaware.

The guidance is for everyone including pre-school children, and the elderly. It applies to us all, and not just to those in specific high-risk or vulnerable groups.

It also states there is no evidence taking extra vitamin D will reduce the risk of the coronavirus.

Why is vitamin D so important for our health? and why and how, should we follow this recommendation?

Facts about vitamin D

Vitamin D – ‘the sun vitamin’ – also known as cholecalciferol –  is one of 13 ‘essential vitamins’. Essential vitamins are those which are vital for your body to function properly.

There are two forms of vitamin D –

  • Vitamin D2 is ingested in your diet. It’s found in oily fish, for example, mackerel, salmon, and herring. Also, in egg yolks, red meat, liver, some fat spreads, and fortified breakfast cereals. Dietary intake of vitamin D2  is especially important because human beings cannot synthesise this in the body.
  • Vitamin D3 is produced in your skin when this is exposed to sunlight – UVB radiation.

To remain in good health, your body needs adequate levels of both vitamin D2 and D3. 

What is the function of vitamin D?

Vitamin D had two important functions –

  • Calcium and phosphorus – vitamin D is integral in calcium and phosphorus metabolism, to maintain healthy bones, teeth, and muscles.

Vitamin D facilitates the absorption of calcium and phosphorus from food in the intestines, through the gut wall and into the bloodstream. This is why you need to take in enough vitamin D in your diet.

If your vitamin D levels are too low, this reduces the absorption of calcium from the gut, by up to 90%.

  • Fighting infection – vitamin D plays an important role in defending your body against infection. It helps maintain the barrier function of your skin and mucosal surfaces. It also stimulates the cellular immune response and activates the body’s defence mechanisms to destroy bacteria and viruses.

It may not be a coincidence that most respiratory infections, including seasonal flu, are much more common in the winter months when days are short and dark, and vitamin D levels tend to be lowered.

Vitamin D deficiency – who is at risk?

Vitamin D deficiency affects a staggering 50% of the population. This means more than one billion people are affected around the world. Most of us are unaware of the ‘hypovitaminosis D pandemic.’

But why should this be? There are a number of reasons.

Firstly, this may be due to lifestyle factors. For example, more people now work indoors for longer hours, meaning there is less exposure to sunlight. In addition, our eating habits have changed, and people now have different dietary preferences.

Vitamin D deficiency is more common in the winter when the days are shorter and darker.

Vitamin D deficiency affects all age groups, races and different ethnic backgrounds.

  • People with darker skin have increased amounts of melanin in their skin. This absorbs more UVB. This then means they need longer hours of sun exposure than people with pale skin, to produce adequate vitamin D levels.
  • The elderly may not go outside for long periods and have less exposure to UVB. They may also have small appetites and eat less healthily. Older people also tend to cover their skin more with clothing. Ageing reduces your natural ability to produce vitamin D in sunlight.
  • Babies and children are at risk, as well as pregnant and breastfeeding women, and middle-aged adults.
  • Use of 30-SPF sunscreens reduces the production of vitamin D in the skin by more than 95%.
  • Obesity is known to significantly impair the production of vitamin D3 when the skin is exposed to UVB.
  • Fat malabsorption syndromesg. coeliac disease, lactose intolerance and cystic fibrosis – result in an inability to absorb vitamin D from the gut. The same problem occurs after bariatric surgery.
  • Chronic kidney disease is also associated with vitamin D deficiency as the kidney loses it’s ability to convert vitamin D to it’s active form.
  • Other medical conditions at risk of vitamin D deficiency include people suffering from certain types of
  • Primary hyperparathyroidism – an overactive parathyroid gland results in an increased break down of vitamin D.
  • Medication such as anticonvulsants, and anti-HIV drugs, also lower levels of vitamin D, as they accelerate vitamin D breakdown.
  • Vegans- as they avoid eggs, meat and fish.

Low levels of vitamin D – Health risks

In recent years, medical evidence has been accumulating which suggest that low levels of vitamin D are associated with increased mortality.

There is a recognized association between low vitamin D levels, and cardiovascular disease, cancer, and death. Also, other medical studies have shown a link between vitamin D deficiency, and heart failure, high blood pressure, and diabetes.

Vitamin D supplementation has been shown to have health benefits. For example, in a 2007 meta-analysis of 18 randomised controlled trials, conducted mostly in older people, the authors reported a significant reduction in all-cause mortality, in those taking vitamin D supplements.

Vitamin D – along with calcium supplementation – is recommended for osteoporosis prevention and treatment in older people, as a means of preventing fracture risk.

Vitamin D blood levels

An adequate blood level of vitamin D, is ≥30 ng/ml (75 nmol/L).

However, there may be additional benefits if you have levels between 90 -100 nmol/L (36-40 ng/mL).

What is the daily recommended intake of vitamin D?

The recommended adult vitamin D dosage is 400 IU (10 μg) per day.

Why take vitamin D supplements?

Unfortunately, it’s not possible to achieve sufficient levels of vitamin D through diet alone.

You should eat a varied, balanced diet, including foods which contain vitamin D2. However, to ensure enough vitamin D3, a daily supplement is now recommended for everyone, not just people in high-risk groups.

Are vitamin D supplements safe?

Taking vitamin D supplements is safe so long as you stick to the recommended adult dose of 400 IU (10 μg) per day.

This dose is likely to achieve a blood level of vitamin D, in the region of 30 ng/ml.

There is generally no need to have blood tests if you want to take a vitamin D supplement. However, it is possible if you have specific health concerns,  to see your GP and request a vitamin D blood test.

This can be done before you start, as a baseline, and then be repeated 3-6 months after starting treatment.

Side-effects of vitamin D

The most worrying possible side effect from high doses of vitamin D is hypercalcaemia (high blood levels of calcium). However, hypercalcaemia only occurs when blood levels of vitamin D are very high. You are most unlikely to get this if you take extra vitamin D at the recommended dose.

For the majority of adults who take vitamin D 400 IU (10μg) per day, it is highly unlikely this will cause serious side effects.

If you have any health conditions or take any other medication, it’s always advisable to check with your GP before you start regularly taking new medicines.

Other possible side effects are listed below. This list is not exhaustive –  For more information.

  • Rash
  • Urticaria
  • Vitamin D toxicity – in the rare event vitamin D toxicity should occur symptoms include –






Frequently passing urine


Who should not take vitamin D supplements?

Do not take vitamin D supplements if you have –

  • Hypercalcaemia
  • Severe kidney disease
  • Kidney stones
  • Heart disease – and/or take digoxin
  • Sarcoidosis
  • Allergy to vitamin D, or any vitamin D products
  • Other allergies – some vitamin D drops contain peanut oil, aspartame, and other substances, such as food colourings and dyes. Check the product ingredients carefully.

Drug interactions

Drug interactions may occur if you take vitamin D with –

  • Anticonvulsants – enzyme-inducing e.g. carbamazepine, phenytoin, topiramate, and non-enzyme inducing  g. gabapentin, lamotrigine
  • Benzodiazepines g. diazepam, nitrazepam
  • Steroids g. prednisolone taken by mouth
  • Digoxin – a risk of digoxin toxicity
  • Cholestyramine – this prevents vitamin D absorption
  • Actinomycin – possibly inhibits vitamin D absorption from the gut
  • Imidazole – inhibits activation of vitamin D in the kidney

This list is not exhaustive. If you take regular medication, always check with your doctor or pharmacist before you start to  take any additional medicines. 

Taking daily vitamin D – which vitamin D supplement?

Vitamin D supplements are available as tablets, soft gels, capsules, drops and injections.

Beware that not all vitamin D products contain the same amount of vitamin D – cholecalciferol. In one 2013 study, published in the Journal of the American Medical Association, researchers carried out laboratory testing on various vitamin D brands and found the potency of cholecalciferol varied from 9 – 146% of the stated dose. Only one manufacturer supplied a product within 90 – 120% of the expected potency.

When choosing a vitamin D product, always look at the back of the packaging and check the product is USP verified. This means the products have been rigorously tested and the ingredients have been verified. You can find a list of USP approved vitamins here.

Vitamin D options are available for vegans.

How to take vitamin D

For best results take vitamin D once a day, with a meal, because it is a fat-soluble vitamin. If you take it on an empty stomach it is unlikely to be absorbed.

You can take it in the morning or at night, but if you tend to skip breakfast, take it in the evening, just before your evening meal.

It may be best to take it early in the evening, as there is a suggestion vitamin D can interfere with the production of melatonin. However, there is no evidence to support the fact that vitamin D disrupts sleep patterns.

Make sure you drink plenty of fluids.

If you miss a dose, skip it, but take the next one on time.

Vitamin D and sunlight

Fair-skinned people are recommended to go outside without sunscreen, for 15-20 minutes per day, in spring and summer, to avoid vitamin D deficiency all year. In the winter there is very little UVB, and most vitamin D will be coming from the diet.

For dark-skinned people, sun exposure should be 20-40 minutes per day, but this will be beneficial in the summer only.

Vitamin D, respiratory infections, and COVID-19

UK scientists warn that you should not take high levels of vitamin D, to prevent or treat COVID-19.

In a publication (March 2020) in the journal Nutrients, the authors reviewed the current medical evidence and suggest that vitamin D supplementation could reduce the risk of influenza, COVID-19, and deaths.

The authors present evidence to suggest that higher levels of vitamin D in the population will reduce the risk of acute respiratory tract infections including influenza, COVID-19, and pneumonia. They suggest additional vitamin D should be started now, to raise levels before the onset of the winter.

The authors are suggesting a higher vitamin D dosing regime than is currently recommended in the UK. They also comment that people on vitamin D supplements should also consider taking additional magnesium because magnesium helps activate vitamin D.

However, caution is needed. The available evidence comes from observational studies only, and these do not prove causation. High levels of vitamin D can be harmful.

PHE have recommended we all take a low dose vitamin D supplement to ensure adequate vitamin D levels for our general health.

If there is an additional benefit for COVID-19 or other respiratory infections, this would be a bonus.

This new NHS advice, for the general public to take daily vitamin D supplements, is endorsed, for example, by The British Nutrition Foundation, The Nutrition Society, and the Royal Osteoporosis Society.

For more information


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