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Testing and monitoring Vitamin D levels are important if we are to supplement at high levels.

The British association of Nutrition and Lifestyle Medicine (BANT) recommends that

all adults supplement a minimum of 600-800 iu of vitamin D3 and 1000mg vitamin C

daily to give their immune system an optimum chance of fighting the Covid virus or

Flu virus. However some authorities are recommending much higher levels.

Vitamin D insufficiency is common in the northern hemisphere countries. Limited

exposure to sunlight during the winter reduces our ability to naturally synthesise it

through the skin and although there are dietary sources - oily fish, egg yolks and

mushrooms; these are not eaten in large enough quantities to make up for the

deficiency. (1)

Vitamin D is a potent immune modifying micronutrient and a deficiency has been

shown to increase the risk of respiratory tract infections, including Covid-19.  A recent, large meta-analysis (looking at 10,933 people in 25 trials), showed that vitamin D supplementation reduced the development of acute respiratory infections from 60% to 32%. (2)

Similarly, hospital data from Spain, found early intervention with Vitamin D supplementation in SARS-CoV-2 infections reduced the severity of the infection and lowered ICU admissions. (3)

So there is definitely plenty of evidence to support supplementation but I am concerned that some people are supplementing at very high levels without firstly getting a baseline measurement of their blood level.

Here is an example of advice about supplementing at high doses from the reference below:

‘ To reduce the risk of infection, it is recommended that people at risk of influenza and/or COVID-19 consider taking 10,000 IU/d of vitamin D3 for a few weeks to rapidly raise 25(OH)D concentrations, followed by 5000 IU/d. The goal should be to raise 25(OH)D concentrations above 40–60 ng/mL (100–150 nmol/L). (1)

I recently arranged for a client to have her blood levels checked before considering supplementation and her results showed an excellent level of 106nmol/l. This prevented any dangers of overdosing.

Vitamin D is a fat soluble vitamin which means that unlike water soluble vitamins it can’t be easily excreted by the kidneys. Over dosing through dietary sources is not thought to be possible but is a consideration when supplementing. It can lead to symptoms of hypercalcaemia which include nausea, loss of appetite and vomiting.


For further advice about Vitamin D supplementation and testing please contact me at the clinic.


  1. Evidence that Vitamin D Supplementation Could Reduce Risk of Influenza and COVID-19 Infections and Deaths, 2020,

  2. Vitamin D supplementation to prevent acute respiratory infections: individual participant data meta-analysis, 2019,

  3. Effect of calcifediol treatment and best available therapy versus best available therapy on intensive care unit admission and mortality among patients hospitalized for COVID-19: A pilot randomized clinical study, 2020,

  4. Vitamin C and Immune Function, 2017,

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