Vitamin D Toxicity
Vitamin D is toxic in excess, but for most people, that excess could only result from getting huge doses – and that means more than 20,000 IU of vitamin D daily – for several weeks or months.
Sunlight alone never causes vitamin D toxicity, and we know that just 20 minutes of full body exposure to sunlight can produce the equivalent of 10 000 to 20 000 IU of vitamin D3 in fair-skinned people.
Lifeguards, and many other people who spend day after day in full sun, sometimes with little protection, do not suffer from vitamin D excess.
(Sure, we need to avoid over-exposing our skin to the sun, but the harm we might do to ourselves would not be from too much vitamin D.)
Vitamin D toxicity from food
The amount of vitamin D in natural foods is relatively small, and from fortified foods somewhat greater, but this is not even enough to prevent vitamin D deficiency, let alone cause toxicity.
The only toxicity issue related to food arises when a food manufacturer accidentally overdoses the food with huge quantities of vitamin D, while creating a fortified food. (This happens extremely rarely. Nevertheless, it seems to be one of the more common causes of vitamin D toxicity!)
But when people think about vitamin D toxicity, their concern is usually that they might take too many vitamin D supplements.
Toxicity from vitamin D supplements
The amount of supplemental vitamin D3 that would produce toxicity in healthy individuals cannot be stated exactly, because it would vary from individual to individual.
Evidence from accidental overdose of vitamin D in individuals and communities has given some indications.
It appears from this evidence that human toxicity starts at around 40,000 IU per day, taken continuously for at least three months. But smaller doses, for even longer periods, might have the same effect.
Some people have taken even more than 40 ooo IU per day, for even longer periods of time, without experiencing toxicity.
But it is now possible to buy vitamin D capsules with 50,000 IU per capsule. so taking even one of these mega-doses per day on an ongoing basis could eventually result in vitamin D toxicity in susceptible people.
Protection against vitamin D toxicity
If you are taking less than 10 000 IU of vitamin D per day in supplementation, you do not need to worry about vitamin D toxicity. It will not happen.
The same is true if you are taking 50 000 IU of vitamin D every week. That is equivalent to 7000 IU of vitamin D daily, and will not cause toxicity. (But these are not dosage recommendations!)
The only exception is if you are suffering from one of those rare medical conditions which causes vitamin D hypersensitivity. See below for more info on this.
If you are still concerned, the best way to be sure of your vitamin D status is by taking a 25(OH)D blood test.
A periodic vitamin D blood test (every 6 months or so) also helps to protect you against toxicity that could arise if you were accidentally taking more vitamin D than you thought.
This has occurred in a handful of cases of vitamin D toxicity reported in recent years, where huge doses of vitamin D were mistakenly included in supplements by the manufacturer.
Testing for vitamin D toxicity
When we take vitamin D supplements, the vitamin D is converted by the liver into calcidiol, also known as 25-hydroxyvitamin D, or 25(OH)D for short.
That’s the form of vitamin D which is stored in the body (in fat, muscle and blood) and also the form measured by the 25(OH)D blood test.
Unless you have a rare medical condition causing vitamin D hypersensitivity, vitamin D toxicity is only possible if your 25(OH)D blood level goes above 100 ng/ml.
|Vitamin D Status||25(OH)D Blood Level|
|High but not Toxic||66-100||164-250|
|Toxicity Possible||Above 100||Above 250|
Although toxicity is considered possible above 100 ng/ml, most cases of vitamin D toxicity occur at even higher levels than this, usually above 200 ng/ml.
See vitamin D testing for more information on how to order your vitamin D blood test.
If a test shows that a person’s vitamin D level is in the possibly-toxic range, the doctor will order further tests (including active vitamin D, calcium urine levels and calcium blood levels) to determine if vitamin D toxicity is actually present.
Vitamin D hypersensitivity
There are some conditions which render a person hypersensitive to vitamin D (for example, primary hyperparathyroidism, sarcoidosis, granulomatous diseases, and some cancers).
Such people should be under their doctor’s care, and should only take vitamin D if it is prescribed for them.
But most people with a medical condition, including many cancer patients, can benefit greatly by having their vitamin D levels optimized. Just check with your doctor first.
Symptoms of vitamin D toxicity
Vitamin D toxicity manifests as too much calcium in the blood (hypercalcemia) and urine.
There are often NO symptoms of this condition, but it is very serious, because the body is continually losing its calcium through urination.
Or as Dr Cannell puts it, with a delightfully deadpan expression on his face, you urinate out your bones!
But in some cases there may be symptoms, eventually, and they can be any, or all of these-
- dehydration (frequent thirst and urination)
- muscle aches
- poor appetite
- slurred speech.
Some of these symptoms could be mistaken for gastroenteritis, in the absence of laboratory tests. Bear in mind, vitamin D toxicity is extremely rare, so most doctors will never come across a case.
If the condition is not treated, excess calcium may also be deposited inside kidneys, heart and other organs, which could be life-threatening.
Treatment of vitamin D toxicity
The treatment of vitamin D toxicity should be under the direction of a knowledgeable physician. Treatment generally comprises:
- stopping vitamin D supplements
- restriction of calcium intake
- total sun avoidance
until serum 25(OH)D level is back into the normal range. This may take several months.
In most cases, appropriate treatment leads to a full recovery.
- Vitamin D Safe Upper Limit
- Optimum Vitamin D
- Vitamin D RDA
- Vitamin D Co-factors
- Who Should Not Take Vitamin D
- Before You Buy Vitamin D