Vitamin D has an adventurous history. Following its discovery in the first half of the 20th century doctors began using it in massive doses for multiple maladies.
As the dosage was extensive (hundreds of thousands of IUs through several weeks), vitamin D use did sporadically lead to adverse reactions but combined with vitamin A even these symptoms diminished and it became more effective against infection. (4) Instead of slightly decreasing the doses of vitamin D used, it was declared dangerous and the daily recommended intake was determined at 400 UIs. Unfortunately, such a low dose isn’t even enough to cure severe vitamin D deficiency.(5) This amount didn’t change for decades, even though it was later discovered that by sunbathing we produce 10000-25000 IUs of vitamin D in our skin in 15-20 minutes. (1)
Varying the doses
25-OH-D3 levels, which can accurately determine the body’s vitamin D supplies, were discovered much later. Prior to the discovery, doctors were only guessing the efficient doses. Fortunately, nowadays the recommended daily intake of vitamin D has been augmented, but there’s an ongoing debate about the ideal amount. The current, official recommendation is 4000 IUs for the maximum amount of daily intake that is considered safe, however, as the following study proves, this isn’t based on a solid scientific foundation either.
An extensive study
Vitamin D deficiency affects countless people all over the world and it increases the chances of chronic illness. Proper vitamin D levels, on the other hand, decrease mortality by 50%. (6) Doctors at an American hospital followed vitamin D research on a regular basis. Once they were convinced of the importance of having good vitamin D levels, they began prescribing vitamin D as part of standard therapy for all consenting patients. They documented the results and then published their findings in a scientific journal. (7)
How were the effects of vitamin D examined?
Most consenting patients at the above-mentioned hospitals received 5000-10000 IUs of vitamin D every day. The researchers measured the patients’ 25-OH-D3 levels as well as the level of calcium in their blood since one symptom of vitamin D overdose is said to be a higher level of calcium.
The researchers then compared the data of the patients who received vitamin D supplements with the results of those who did not consent to the experiment or were newly admitted to the hospital.
Besides these groups, there were some participants who supplemented 20000-60000 IUs of vitamin D for 2-8 years. They successfully treated their health issues with the aid of this much higher dosage of vitamin D. The study examined the same levels as it did for the other patients.
What were the results?
As expected, as a result of vitamin D supplementation vitamin D levels multiplied. Vitamin D3 supplementation increased levels from 25 ng/ml to 68 ng/ml if patients received 5000 IUs of vitamin D3, and to 96ng/ml if they were given 10000 IUs per day. Despite the high dosage calcium levels did not increase in the blood, even in the long run, after years of taking supplements. The patients experienced no negative symptoms that would point to increased calcification.
Those patients who used a significantly higher dose, 50000 Ius per day, to control their asthma or skin disease, sometimes ended up with their 25-OH-D3 levels being over 300ng/ml, but for most of them, it was around 200ng/ml. This is way above the officially determined daily intake that’s recognized as safe. Even so, their calcium levels were still within the healthy range, and they did not experience any other symptoms indicative of an overdose.
Summary
The study revealed that the long-term use of 10000 IUs of vitamin D3 was safe, and even a daily dose of 40000-50000 IUs of vitamin D3, which is ten times the recommended amount, caused no negative symptoms, and neither did it increase calcium levels in the blood.
Errors in the dosage?
Of course, like everything else, vitamin D3 can overdose too, but this is very rare and only happens when applied incorrectly. For instance when as a result of some mistake many times more is consumed than the intended amount.
In two documented cases, a manufacturing defect led to customers taking 1000 times the daily amount of vitamin D3 than what the label said. (9) In the first case, 1860000 IUs of vitamin D3 were supplemented daily for two months, while in the second case, a man accidentally supplemented 970000 IUs of vitamin D3 for two non-consecutive months. Both were hospitalized with acute symptoms; their 25-OH-D3 levels were 1220 ng/ml and 645 ng/ml, respectively. Thankfully both made a full recovery and once their vitamin D levels got below 400 ng/ml (four times the maximum reference range) their calcium levels were normalized, too.
Interaction with other vitamins
Other studies have found that vitamins A and K, which are in synergy with vitamin D, increase the beneficial effects of vitamin D while simultaneously protecting against its potential negative effects.(10, 11,4,12) Although as the above study shows, detrimental effects are pronouncedly rare to begin with.
The combined use of vitamins A and D supplements raises vitamin D levels in the blood much more effectively; besides, vitamin A helps prevent calcification caused by vitamin D overdose. (11)
There’s no reason to be afraid of vitamin D. Let’s take it in an effective and safe dose, along with vitamins and dietary minerals that are in synergy with it.
https://vitaverse.co.uk/news-notes/163/should-we-worry-about-vitamin-d-overdose
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