Vitamin D, How much is too much?

Vitamin D, How much is too much?

Combating recent claims that 5,000iu of supplemental is too much, it begs the most important question, 'Vitamin D, How much is too much?'

It has been understood that as much as 40% of the population in the US and Europe are Vitamin D deficient1. Therefore it does not come as much of a surprise that Vitamin D3 supplementation has been a popular choice recently. With thousands of different supplements on the market, how do you know how much you need to take?

Cholecalciferol, known more commonly as Vitamin D, is an essential fat soluble vitamin that can be found in foods, such as dairy products2. However, people normally associate Vitamin D with the sun because upon contact with the skin the production of this vitamin is increased significantly. Stored as 7-dehyrocholecalciferol, the vitamin must be converted to its active form, cholecalciferol, to be of benefit. With the lack of sun in the UK during the winter months, people have turned to supplementation as a more convenient way of avoiding deficiencies. Yet, the recommended strength of this supplement is highly debated.

What are the National Recommendations?

Vitamin D3 is measured in the blood in nano grams per millilitre (ng/mL). An individuals Vitamin D status can fall into 1 of the following 4 categories3:

  • Deficient: <12ng/mL
  • Insufficient: 12-20ng/mL
  • Adequate: 20-50ng/mL
  • High: >50ng/mL

Public Health England recommends 10 micrograms (approximately 400 IU) to be taken every day4. Vitamin D3 is not as readily absorbed in the body requiring some other factors, such as some other vitamins, to increase absorption. One study performed showed that supplementation with a dose of 1000 IU per day meant that only half of the population reached the recommended blood level of 30ng/mL5. The dose in this study was over 2 times the suggested dose from Public Health England and still proved to raise blood Vitamin D levels inadequately.

But how much is too much?

There has been concern that prolonged use with high doses of Vitamin D can cause abnormally high blood calcium levels which can lead to kidney stones and weaker bones. This claim has been tested in many groups of people with various supplement strengths. Interestingly, there seems to be little solid scientific evidence that higher doses or 10,000 IU can have a negative impact on health6. In fact, in one large study with over 17,000 adults, a daily dose of 20,000 IU for several months showed no signs of any toxicity7. From other reviews, it is clear that toxic amounts of Vitamin D3 can only be achieved in doses way above 20,000 IU8 with this still happening very rarely.

With this being said, it has been shown that there is no need to take more than 10,000 IU9. At this point, the body is not able to produce the active form any more so than at a lower level of around 5,000 IU. Another study confirmed this, stating 3 month supplementation with 5,000 IU may be more efficient than lower doses for those who display Vitamin D deficiencies10. For this reason, don’t be tempted by the companies offering mega-doses of Vitamin D3. Stick to the range of 1,000-5,000 IU.

To maximise absorption, Vitamin D3 is best taken with a meal. Despite being a fat soluble vitamin, the most significant increases in absorption were found when taken with a low-fat meal11. Try to aim for 11 grams of fat to see the best results. Examples of this much fat include half an avocado or a tablespoon of olive oil.

Nadia Farrugia | Oxford Vitality Nutritionist 



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