What the Hell is Vitamin D and Why Should I Give a Damn?

In the second entry of our "What the hell is...?" series, we are going to be looking at Vitamin D.

Humans have for millions of years lived under the sun's rays and we have always worshiped it for its life-giving powers. It has a profound and powerful relationship to our wellbeing, that has only come to light properly in the last 100 years. Every year more and more research is pointing towards how essential it is to a full and vibrant life. It has even been suggested that around ten percent of our genetic code has receptors for vitamin D, meaning that the amount of it you have in your system directly influences a whole host of bodily functions. If you're deficient in it, you could be in trouble.

The Sun: An 850,000 mile wide, 15 million degree nuclear fireball, providing free heat, light, and energy, as well as making all life on Earth possible.

- Still doesn't ask you to worship it.

The story of how Vitamin D first came into the limelight started before and during the Industrial Revolution that spread across Europe. The mechanisation of industry that took place, lead to heavily concentrated populations and the rapid expansion of cities. This high density housing in combination with massive atmospheric pollution, made an environment with few opportunities to get direct sun exposure. All this lead to a rapid increase in the incidence of conditions like osteomalacia and rickets.

For those of you who don't know, rickets is a crippling bone disease affecting children that leads to softening of bone tissue, resulting in brittle, easily broken bones and physical deformities. This is especially apparent in the child's legs, as these were the bones most likely to bear weight.


By the 1900's this condition had reached epidemic levels in European cities.

It is now well known that low vitamin D levels were to blame, and by a process of deduction whereby many researchers noticed that rural living children did not suffer from the condition at all, vitamin D as a chemical would eventually be isolated, artificially synthesised and added to certain food products such as milk, virtually eliminating the condition as a widespread health concern.

Since then, research now shows that rickets is only the most obvious condition suffered by those with low vitamin D levels; even if your levels aren't low enough to get such a crippling bone condition, they are likely low enough to cause a whole bunch of health problems.

This is important as it has been estimated that 50% of the world's population is at risk from low vitamin D levels, meaning that this could be at root with many health problems that blight the world, as well as ones that affect your life now, or in the future.


What kind of health problems?

Well apart from the aforementioned rickets and osteomalacia, the list of what conditions are associated with a lack of vitamin D is rather a long one. The Vitamin D Council, a not for profit organisation that aims to promote awareness of vitamin D, has compiled a list of the most up to date evidence here. But for those of you that have better things to do than spending the next week reading scientific reports, the list of associated conditions are the following:

That's quite a list!

It has been suggested that a lack of vitamin D has a negative effect associated on all of these ailments, the strength of evidence varies from condition to condition but research is ongoing and increasingly showing how important "The Big D" is to our wellbeing.

Furthermore a meta-analysis of randomised control trials was conducted on vitamin D research in and published in the journal Archives of Internal Medicine. The study covered 18 individual research papers, spanning 57,311 people and concluded that:

Intake of ordinary doses of vitamin D supplements seems to be associated with decreases in total mortality rates. The relationship between baseline vitamin D status, dose of vitamin D supplements, and total mortality rates remains to be investigated. Population-based, placebo-controlled randomized trials with total mortality as the main end point should be organized for confirming these findings.

Source: Autier P. Gandini S. (2008). Vitamin D Supplementation and Total Mortality A Meta-analysis of Randomized Controlled Trials. Arch Intern Med. 167 (16), 1730-1737.

The good news is that you don't need to know the ins and outs of each condition associated with Vitamin D, in order to keep yourself healthy. With a bit of knowledge it is easy to make sure you don't fall fowl of low vitamin D levels, in a simple, safe, and effective way.


So how do I see if I get enough?

The first thing you should know about Vitamin D as a chemical, is that it isn't actually a vitamin.

Vitamins are organic compounds that living creatures need to ingest because can't make enough of them on their own. Vitamin D on the other hand can be made in sufficient levels by the body by simply spending twenty or minutes outside in direct sunlight.

There are couple of logistical problems though. Vitamin D is only produced by using something called ultraviolet radiation, and specifically UV-B radiation, and the amount of it is highly influenced by latitude and seasonal availably of sunlight. In winter months people cover up more and do so with thicker clothes than usual, thereby limiting the amount of skin exposed to the sun's rays. On top of that, sunlight has a longer path length through the atmosphere in winter, meaning that a greater portion of it does not make it to the ground.

Shown here.

The Journal of Clinical Endocrinology and Metabolism outlines an interesting study whereby researchers looked at how much vitamin D was produced in people's skin during Winter at several different locations, one of which was the City of Edmonton in Canada (52 degrees north).

The study concluded that...

Human skin or [3 alpha-3H]7-dehydrocholesterol exposed to sunlight on cloudless days in Boston (42.2 degrees N) from November through February produced no previtamin D3. In Edmonton (52 degrees N) this ineffective winter period extended from October through March.

Source: Webb, AR. Kline, L. Holick, MF. (1988). Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. The Journal of Clinical Endocrinology and Metabolism. 67 (2), 373-78.

This is interesting if you live in London, as our city sits at 51 degrees north, almost exactly the same as Edmonton. With that in mind, and not accounting for things like average cloud cover (London isn't exactly famous for it's crystal clear skies anyway), it is reasonable to assume that between the months of October and March, people living in London get essentially no vitamin D from the sun, and this ineffective Winter period only gets more pronounced the further north you go.

South London being slightly closer to the Sun = better ;-)

Furthermore, the optimal time for getting vitamin D is at noon, when the sun is highest in the sky and sunlight has the least distance to travel to the Earth's surface. This is also precisely the time when most people are stuck indoors at work. So even in Summer, it is still unlikely that you are going to get enough exposure.

However all is not lost though for the health conscious yet office bound amongst you.


Enter vitamin D supplementation 

Vitamin D supplements are cheap and very easy to get a hold of. Pay a visit to any chemist and you should have no problem getting hold of it. What you should get a hold of are tablets or capsules that are 1000 IU (International Units) or 25μg (micrograms) each.

Like this bottle for example

The dosage that I recommend is 5000 IU per day, and for the bottle shown above that translates as five tablets. That may sound like a lot but in fact if you were to go outside in the middle of summer, at noon, with no clouds in the way, you would likely make around 20,000 to 30,000 IU of vitamin D in less than half an hour.


Can you take too much Vitamin D?

One of the big worries surrounding vitamin D is that of toxicity; how much is too much?

I don't want to end up scaring everybody, but there is a lot of confusion about vitamin D and how much you can safely take, so I need to spend some time talking about vitamin D toxicity, how it happens and what to do if you do come across it (extremely unlikely though it is).

The symptoms associated with vitamin D toxicity are as follows:

  • High amounts of calcium in the blood and urine
  • poor appetite
  • vomiting, general
  • weakness
  • tingling sensations in the mouth
  • confusion
  • constipation
  • diarrhea
  • abnormalities with heart rhythm

Not a lot of fun huh? Well thankfully, it is very difficult to achieve vitamin D toxicity.

Documented instances have only been seen in individuals taking 40,000 IU per day; in the words of the American Journal of Clinical Nutrition..

Except in those with conditions causing hypersensitivity, there is no evidence of adverse effects with serum 25(OH)D concentrations <140 nmol/L, which require a total vitamin D supply of 250 microg (10000 IU)/d to attain. Published cases of vitamin D toxicity with hypercalcemia, for which the 25(OH)D concentration and vitamin D dose are known, all involve intake of > or = 1000 microg (40000 IU)/d. Because vitamin D is potentially toxic, intake of >25 microg (1000 IU)/d has been avoided even though the weight of evidence shows that the currently accepted, no observed adverse effect limit of 50 microg (2000 IU)/d is too low by at least 5-fold.

Source: Vieth R. Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety. American Journal of Clinical Nutrition. 1999 May; 69 (5): 842-56.


Furthermore, there have been two reported instances of people poisoning themselves with daily doses of up to 2,000,000 IU (not a typo). And even with these kind of doses, nether of them died. 

Source:  Koutkia, P. Chen, T. C. Holick, M. F. Vitamin D intoxication associated with an over-the-counter supplement. New England Journal Of Medicine. 2001 Jul 5; 345 (1): 66-7.

Source: Los Angeles Times Supplements guru sues over his own product. 29/4/2010;

To put that in perspective, achieving that with the 25μg tablets I recommended before, you would need to consume two thousand tablets a day, every day!

Just try and imagine that for a moment

Before you go running to the supplement shop however, there is one more thing that needs to be considered.


Vitamin D + Magnesium

Let me reiterate again that 5000 IU is not enough to induce toxicity in normal circumstances.

That being said, in the unlikely event you do experience some or all of the symptoms associated with vitamin D toxicity, while on 5000 IU supplementation, or even simply by sun exposure without supplementing, you may have exposed a big problem you have in another area.

Magnesium is one of the most abundant elements in the body and a key ingredient that allows the body's enzymes to metabolise vitamin D into it's biologically active form 1,25(OH)2D (calcitriol). Having low levels of it can manifest symptoms that look like vitamin D toxicity.

If you experience the symptoms of toxicity, the first thing you should do is stop taking any further supplementation, go to the doctor, and request a blood test looking at "25(OH)D" levels. This will establish if you have toxic levels of vitamin D in your blood. If the results sit below 140 nmol/L, then you are almost certainly not toxic. The symptoms you experienced may be due to one of the following factors.

1) Vitamin D hypersensitivity as a result of already present high blood calcium levels. This is otherwise known as hypercalcemia, and it is a very rare condition.  It is normally the result of:

Hypercalcemia can be misdiagnosed as vitamin D toxicity, as vitamin D toxicity also produces high blood calcium levels. The aforementioned blood test should clear up any confusion.

2) An underlying deficiency in magnesium - This is by far the most common reason, and taking supplementary magnesium with your vitamin D will largely circumvent this problem. Vitamin D needs magnesium to work properly. It's a bit like a buddy cop movie.

Vit-D man you CRAZY!!!

Good sources of magnesium from food include:

  • Spinach - 79mg per 100g
  • Haddock - 39mg per 100g
  • Brazil nuts - 375mg per 100g
  • Almonds - 275mg per 100g

If none of those tickle your fancy, then you can Google "Magnesium rich foods" for more examples.

If making sure you eat certain foods is too much of a pain in the ass, then supplementation of magnesium tablets is another option. Be sure however to get a high quality one as the common magnesium oxide supplements have been shown to only have a 4% uptake rate, meaning that they are almost completely ineffective at raising the body's magnesium levels.

Better alternatives include.

  • Your food (Just saying)
  • Magnesium malate (Considered by many to be the most effective supplement)
  • Magnesium glycinate (Also very effective)
  • Magnesium citrate
  • Magnesium gluconate
  • Magnesium taurate


Can you take too much Magnesium?

Like vitamin D, magnesium is difficult to overdose on. Provided that you do not have any problems with them, your kidneys are highly efficient at removing excess amounts of the mineral, and keeping serum levels (in your blood) in the normal range.

Optimal intakes of magnesium per day have been established as 7-10 mg/kg. This means that for a 75Kg individual somewhere around 525-750 mg would be about right as a total daily intake from all sources.

Source: The Vitamin D Council. (2011). Vitamin D Cofactors - Magnesium. Accessed 20th Nov 2012.

Furthermore there is no known adverse effects from supplemental intakes of 375mg per day. With this in mind I recommend having around this amount with your daily 5000 IU vitamin D dose as an effective precaution.



Don't let all that talk about toxicity detract from the fact that vitamin D is very safe, and hugely important for preventing a wide range of medical problems. Many medical professionals believe that maintaining sufficient levels of it, is the single best thing you can do for your health.

The amount 0f 5000 IU is well within the safe limits according to what the evidence on the subject says and you shouldn't worry about taking it at that level, especially if you supplement an additional 375mg of magnesium as suggested.

Okay... now you can go running to the supplement shop.



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