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The Best Vitamin D Supplement


In my profession I see many people being prescribed vitamin D supplements. I also see many customers buying vitamin D supplements. Some of them ask ‘what is the best vitamin D supplement’ others specifically ask for vitamin D3 as this was recommended form of vitamin D supplement.

In this short post, I will explain why we need Vitamin D, the difference between Vitamin D and D3 and consequently try to answer what the best Vitamin D supplement is, or rather what to look for when buying Vitamin D supplement.

Why Vitamin D?


In a nutshell, Vitamin D helps to regulate calcium and phosphate in our body and consequently is responsible for the health of our bones, teeth, and muscles.

Certain foods (oily fish, red meat, egg yolks) contain Vitamin D, however, generally.

It is difficult to get the required Vitamin D from diet alone. The main source of Vitamin D is through production by our bodies when our skin is exposed to direct sunlight.

This, of course, can be difficult, and generally, in the UK between October and March, we can’t get enough sunlight in order to produce enough Vitamin D (NHS, 2018).

You May ask ‘How Much Sunlight Do I Need?’

British Medical Journal (BMJ) advises as follows:
Exposure of the arms and legs (with sun protection on the face) for about 5 to 30 minutes (depending on the degree of skin pigmentation, time of day, season, latitude, and age of the person) between 10 am and 3 pm twice a week is sufficient for Vitamin D synthesis (BMJ, 2016).

Difference Between Vitamin D2 And D3 

The two most common forms of Vitamin D are D2 and D3.

  • Vitamin D2 is known also as Ergocalciferol is made by plants
  • Vitamin D3 is as Colecalciferol / Cholecalciferol is made in our body (exposed to the sunlight)
  • Vitamin D3 is the preferred form of Vitamin D as you get significantly more into your body when you take this form of Vitamin D
  • If you want to choose the best Vitamin D supplement, make sure you choose a product containing the D3 form of Vitamin D

Vitamin D Units v/s Micrograms


Vitamin D Units v/s Micrograms

Vitamin D content is measured in two forms: units and micrograms (written as mcg or µg).

Most products provide information on Vitamin D content in both forms.


  • 400 units = 10 mcg (µg)
  • 600 units = 15 mcg (µg)
  • 1000 units = 25 mcg (µg)

To get measurement in ‘mcg’ divide ‘units’ by 40. e.g. 1000 units / 40 = 25 mcg (µg).

How Much Vitamin D Do I Need?

NHS recommends that all adults should consider taking a daily supplement containing 400 international units (10 micrograms) of Vitamin D  during the autumn and winter and those at risk of Vitamin D deficiency (have very little or no sunshine exposure), should take a daily supplement containing 10 micrograms of Vitamin D throughout the year.

How To Choose The Best Vitamin D Supplement?

  • Look for Vitamin D3 supplements or one containing optimum of both forms of Vitamin D2 and D3
  • Look for supplements containing 400 units (10 micrograms) of Vitamin D
  • For more information (dosage by age group) visit the NHS website.

Quick FAQ

What is the best form of vitamin D to take?
Vitamin D3 or cholecalciferol is the recommended form of vitamin D. It is the natural form of Vitamin D which comes from exposure to sunlight.
Why do doctors prescribe vitamin D instead of D3
Many doctors prescribe vitamin D2 because it is easier to find. However you can buy vitamin D3 without prescription at the same dosage if you want.
Does taking vitamin D have side effects?
Yes, some common side effects of taking Vitamin D include; nausea, dry mouth, weakness, vomiting, and others.