Skip to content

Vitamin D

TL;DR

something.

Fat soluble so take with food containing fat. If you have a low body fat percentage you may become deficient very quickly and conversely, if you have a high body fat percentage you may experience toxicity if ...???

If supplementing, should be taken with vitamin K2 to aid absorption.

Helps with calcium absorption.

Something about bones.

D3 seems to be the one

Biotin supplementation may cause incorrect levels of this vitamin to be recorded in blood tests.

D3 Is found in cod liver oil. Based on UK recommendations (which are wrong) two typical doses of cod liver oil will provide your RDA.

Avoid taking vitamins, minerals (such as calcium) and other supplements for 30-60 minutes after consuming coffee - it contains compounds (polyphenols) that limit the absorption of many micronutrients.

Food Sources

  • egg yolks (not much)
  • mushrooms (d2 rather than d3 though)
  • fatty fish
  • cod liver oil
  • canned tuna

Forms/Types

Quality

As with all supplements - buyer beware. It's quite common for supplements to be contaminated with a variety of impurities, often in the form of heavy metals, and/or contain far more or less of the ingredients stated on the label. There's no simple rule of thumb to avoid this, such as avoiding cheap or imported products; expensive or well-known brands produced in-country may be just as bad. Ideally you should take some time to find products (if you can) that;

  • have been laboratory tested on behalf of the manufacturer by a reputable body or company that operates in your country or region (here's an example of a Peak Supps creatine supplement available on Amazon in the UK which has been tested by Eurofins: Creatine Monohydrate Powder 1Kg | Pure Micronised | Packaging May Vary - see pictures 3 & 4)
  • in the UK & EU, are manufactured in facilities that meet the minimum standards of good manufacturing practice (GMP) in their production processes (for medicines).12 Facilities are inspected for compliance and manufacturers' product(s) must:
    • be of consistent high quality
    • be appropriate to their intended use
    • meet the requirements of the marketing authorisation (MA) or product specification

Be wary of any manufacturers or brands making claims around these valid but irrelevant standards;

  • HACCP: this standard relates to food safety which indicates that the seller is claiming their supplement is a food; whilst meeting this standard is worthwhile, GMP (detailed above) would be a more appropriate standard
  • ISO22000: same as HACPP
  • ISO9001: this standard is focussed on quality control management systems in the context of managing a business or organisation, not directly on the the quality of the products that business produces (although it may have a beneficial impact)

Dosage - How Much?

The ideal blood levels of vitamin d are 100 nmol/L or above, but under 140 nmol/L. 3

RDA is wrong!!!!

The UK's NHS recommends 400 IU/10micrograms for adults from October to late March/early April as of late 2025.4 The British Heart Foundation also recommends this amount.5 This, despite research conducted 11 and 8 years ago respectively, in 2014 and 2017, that demonstrates that 8000IU is required.34

Found in cod liver oil. Based on UK recommendations two typical doses of cod liver oil will provide your RDA of vitamin d.7 This should not be an issue considering the low recommended dose in the UK and elsewhere.

Deficiency - Too Little

Rickets - 400-600 IU is enough to prevent that, but not enough for the immune system benefits.

Toxicity - Too Much

Side Effects

When to Avoid Use - Interactions/Contraindications

Random Facts

  • Many countries fortify milk with vitamin d - this has lead to a decrease in type 1 diabetes in Finland

References

  1. Medicines: good manufacturing practice and good distribution practice ↩

  2. Good manufacturing practice ↩

  3. Veugelers PJ, Ekwaru JP. A statistical error in the estimation of the recommended dietary allowance for vitamin D. Nutrients. 2014 Oct 20;6(10):4472-5. doi: 10.3390/nu6104472. PMID: 25333201; PMCID: PMC4210929. ↩↩

  4. Vitamin D - retrieved 2025-09-30 ↩↩

  5. Do I need to take vitamin D?- retrieved 2025-09-30, page states it was updated 1 December 2020 ↩

  6. Papadimitriou DT. The Big Vitamin D Mistake. J Prev Med Public Health. 2017 Jul;50(4):278-281. doi: 10.3961/jpmph.16.111. Epub 2017 May 10. PMID: 28768407; PMCID: PMC5541280. ↩

  7. Cod Liver Oil 1000mg, 360 Capsules of High Strength Fish Oil, Rich in Omega 3. Supports Heart Health, Brain Health, Eye Health and Normal Blood Pressure - retrieved 2025-09-30, the brand is Zipvit ↩