Vitamin D common questions answered, who, why, how much and what with?! – Barefoot Nutrition

Vitamin D common questions answered

Vitamin D Common Questions Answered

Followers ask a lot of questions to make sure they are getting the best vitamin D, in the most absorbable form, with the least additives. How much vitamin D do I need? How much vitamin D can I make in the sun? Can I get enough vitamin D from food? Aren't all vitamin D supplements the same? Do I need to take vitamin D? We do our best to answer in this blog...

Q. How much vitamin D can I make in the sun per day?(David C, from Bristol)

As mentioned on the website, you can only produce vitamin d from the sun when the UVB wavelengths are right. In the UK that is around May to September. During these productive months, if you go out in the sun, with no sunscreen on, exposing a large portion of your skin (e.g. swim shorts or bikini only) you can be expected to make anywhere from 10,000iu – 25,000iu of vitamin D (Matsuoka et al 1989).This is based on a length of time that you do not allow yourself to burn. These figures are also based on type 2 skin (white & easily burns). The darker your skin, the longer it takes to make vitamin d (Clemens,1982).


Clemens TL et al 1982. Increased skin pigment reduces the capacity of skin to synthesise vitamin D3. Lancet.

Matsuoka LY et al 1989 In vivo threshold for cutaneous synthesis of vitamin D3. J of Lab & Clin Medicine

Q. How much vitamin d does my body use every day? (Charlotte B from Derby)

A study performed in 2003 by Heaney calculated that the average human body uses between 3000-5000iu of vitamin d per day.


Heaney, R P, 2003. Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol. The American Journal of Clinical Nutrition, 77 (1), 204-210

Q. Can I not just get enough vitamin d from food? (Leo C, from Newcastle)

A short answer to that would be no. The amount of vitamin d you can get from the richest sources, such as cod liver oil, eggs and salmon will still only be in the 100s of iu’s of vitamin d rather than the 1000s that your body uses on a daily basis.

Q. Aren’t all vitamin d supplements the same? How do I know which one is best? (Martha H, from Swindon)

Vitamin d comes regularly in 2 forms, d2 which is synthetic and d3, which is extracted. Some supplements just contain vitamin d, others contain d with k for example. Research has shown that if you are deficient in any of the co-factor nutrients associated with vitamin d (K2, Magnesium, Zinc & Boron), your body will not be able to use it properly. For example a study by Reddy et al (1974) showed that people with rickets, given vitamin d, did not respond to treatment until their magnesium levels were normalised. It may be a surprise that 75% of the population don’t get their daily recommendation of magnesium! (World health organisation).

Vitamin k works with vitamin d to deposit calcium in the bones and make sure it doesn’t settle in your arteries (Spronk et al, 2003). It has even been shown that K2 can reduce calcium deposits in soft tissues and blood vessels (Kurnatowska, et al, 2015)and even modestly reverse it! (Schurgers, et l, 2007).

Boron is thought to influence the metabolism of vitamin d (Devirian & Volpe, 2003). It also thought to increase blood levels of calcium absorption and increase vitamin d stimulation by as much as 24%! (Hegsted et al 1991).

Finally, sufficient levels of zinc are also required for vitamin d to do it’s job properly. It influences the activity of vitamin d dependent genes (Craig et al, 2001).

So simply, no, not all vitamin d supplements are the same. Making sure you are sufficient in the co-factor nutrients is just as important as taking the vitamin d itself. The nutrients we have combined with our vitamin d will ensure you have all the co-factors for vitamin d to do it’s job properly!


Craig TA et al 2001. Modulation effects of zinc on the formation of vitamin D receptor and retinoid X receptor alpha-DNA transcription complexes: analysis by microelectrospray mass spectrometry. Rapid Common Mass Spectrom;15(12):1011-6.

Devirian, T A & Volpe, S L, 2003. The Physiological Effects of Dietary Boron Critical Reviews in Food Science and Nutrition, (2003), 43(2):219–231

Hegsted M, Keenan MJ, Siver F, Wozniak P, 1991. Effect of boron on vitamin D deficient rats. Biol Trace Elem Res. Mar;28(3):243-55.

Kurnatowska I,et al, 2015. Effect of vitamin K2 on progression of atherosclerosis and vascular calcification in nondialyzed patients with chronic kidney disease stages 3-5. Polish Archives of Internal Medicine.

Reddy V, Sivakumar B, 1974. Magnesium-dependent vitamin-D-resistant rickets. Lancet. May 18;1(7864):963–5.

Schurgers et al, 2007. Vitamin K2 improves bone strength in postmenopausal women. International congress series. Vol 1297, pp 179-187

Spronk HM et al 2003. Tissue-specific utilization of menaquinone-4 results in the prevention of arterial calcification in warfarin-treated rats. J Vasc Res;40:531–537.

Q. Do I really need to take vitamin D? (Liam E, from Southend)

Everyone is different and have different needs. There are a lot of different variables that can dictate how much vitamin d you produce naturally. Skin tone, where you live, whether you go out in the sun in the producing months, whether you wear sunscreen or cover your skin up, how much of your skin you expose to the sun.

Lets do a calculation based on some averages:

-Lets say your body uses 4000iu vitamin d per day.

-Lets say your body makes 15,000iu per day of sunbathing without sunscreen (no burning!)

-Lets say in the UK you’ve managed to sunbathe for 30 consecutive days (unlikely!)

so 15,000iu x 30 days = 450,000iu stored vitamin d

We know you use 4000iu per day so your stores will last 112 days (including the 30 days of sunbathing).

So even if you manage to get out in the sun for 30 days of sunbathing, which is unlikely at best in the UK, you’ll only have enough stored vitamin d to last you 3 and a half months, leaving you deficient for the other 8 and a half months!

So the answer would be, if you do go out in the sun regularly without sunscreen in the producing months (May-September) then there is no need to supplement in those months. But then it would be wise to supplement September /October to April/May. If you have dark skin, don’t expose large areas of your skin, cover up or wear sunscreen in the sun, then year round supplementation is recommended.

Summing Up

Remember that vitamin d is a vital nutrient that is responsible for hundreds of chemical processes in the body. It also has the potential, directly and indirectly to regulate more than 200 genes.

Government guidelines of 400iu / day is woefully inadequate in our opinion which is why over half the UK population is deficient and 90% insufficient in vitamin d.

A dose of 4000iu / day with the right co-factor nutrients such as Barefoot nutrition D3 complete should keep your blood levels at around 100nmol/l (Moyad, 2009) which is a level comparable with hunter gatherer tribes (luxwolda et al, 2012),a healthful level, not just to stave off rickets which is all the government is bothered about but to enable your body to complete all required processes for health systems which use vitamin d.

Our Vitamin D3 Complete that not only delivers optimal amounts of vitamin D3 in the most effective form but also includes the important nutrient co-factors for superior absorption and utilisation.

We do all of this without any of the artificial ingredients, bulking agents, flow agents, anti-caking agents, artificial colourings and additives found in so many of our competitors products.

It is for this reason that we believe we provide the UK’s (maybe even the world’s) best Vitamin D supplement


Luxwolda et al, 2012. Traditionally living populations in East Africa have a mean serum 25-hydroxyvitamin D concentration of 115 nmol/l. British Journal of Nutrition.Nov 14;108(9):1557-61

Moyad, M A, 2009. Vitamin D: A Rapid Review. Dermatology Nursing. (1), 21

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