Unfortunately, everything that is good for us can also be bad if too much is taken. This is also true for the miracle vitamin that is vitamin D. If taken in too high quantities, it can raise the levels of blood calcium to such a degree that it can make people feel nauseous, constipated, confused and more. It can also cause kidney stones and abnormal heart rhythms.
Fortunately, actually having too much vitamin D is almost impossible, particularly if you rely on the sun and your food to build up levels. The exception is cod liver oil, but you would literally need to drink an entire bottle to have any negative effects. As such, people who do suffer from vitamin D toxicity do so because they overdose on supplements.
Recommendations on Vitamin D
In 1997, an official recommendation was made by the Institute of Medicine’s Food and Nutrition Board. They stated that it is safe to have up to 2,000 IU (international units) of vitamin D per day for adults, or 1,000 IU for children over the age of one. However, an update was released in 2010 that suggests levels are actually much higher. Now, it is believed toxicity won’t occur until someone has 10,000 IU per day (supplements and natural sources included).
The reality, however, is that it simply isn’t clear. The official recommendation of the Institute of Medicine is that there is an ‘upper level intake’. That refers to the level people could take before it could potentially become unsafe. The official upper level intake currently stands as follows:
• 4,000 IU for adults
• 3,000 IU for children between ages four and eight
• 2,500 IU for children aged between one and three
• 1,500 IU for infants between six and 12 months
• 1,000 IU for infants under six months
As previously said, there is now also new research suggesting that the upper level IU for adults is actually much higher, which is 10,000 IU. This was noted by the Vitamin D Council as well. They base this on the fact that the skin itself will produce 10,000 IU after just half an hour of sun exposure in summer months between 11am and 3pm. Because many people experience this without sunscreen and never experience negative effects, 10,000 IU per day must be safe.
The National Institutes of Health, however, maintain that if the levels of vitamin D are consistently higher than 200 nanograms per milliliter, this is ‘potentially toxic’. Clearly, therefore, there is no agreement on what is and isn’t safe. Further research is ongoing.
One thing all scientists do agree on, however, is that there is no evidence to suggest that taking more vitamin D is actually more beneficial as well.
Serious Consequences of Toxicity
A rare condition known as hypervitaminosis D, which basically means extremely high levels of vitamin D are present in the body, is potentially serious. In almost all cases, it is caused by an overdose of supplements. As a result, the blood starts to build up abnormally high calcium levels. This can have a negative impact on the tissues, bones and various organs. It can also raise blood pressure, lead to bone loss, and damage the kidneys if left untreated.
Because there is so much confusion about vitamin D, people often don’t know what they are doing. They may, for instance, expose themselves to the sun, drink fortified milk, eat oil fish, take a daily multivitamin and take a vitamin D supplement on top of that. Or perhaps they are taking certain medication that is negatively affected by vitamin D. Either way, these situations may lead to hypervitaminosis D.
The majority of cases of hypervitaminosis D happen in people who take vitamin D as a supplement, but also suffer from one of the following conditions:
• Liver disease
• Kidney disease
It is important to be aware of the symptoms of hypervitaminosis, which essentially means that the levels of calcium in the blood spike to dangerous levels, which is known as hypercalcemia. The symptoms to be aware of include:
• Loss of appetite
• Excessive thirst
• Weight loss
• Excessive urination
• Nervousness and irritability
• Muscle weakness
• Ringing in the ear, known as tinnitus
• Vomiting and nausea
• Disorientation and confusion
• Heart arrhythmias
• High blood pressure
If left untreated, a vitamin D overdose can lead to serious medical complications, including:
• Kidney damage
• Kidney stones
• Kidney failure
• Calcification (which is hardening) of the soft tissues and/or arteries
• Excessive bone loss
It can be difficult, however, to diagnose hypervitaminosis. It can only be done by a medical professional who will start by conducting a physical examination and a review of your medical history, paying particular attention to any prescription and over the counter drugs you may be taking. A number of tests will usually be ordered if a doctor does suspect hypervitaminosis is present. These tests include:
• Blood tests, which will measure the levels of phosphorous, calcium and vitamin D and will also determine whether there is any kidney damage.
• Urine tests, which will look specifically for high levels of calcium.
• X-rays of the bones to see whether any bone loss is present.
Specifically, the tests will look for the presence of:
• Hypercalcemia (excessive calcium levels in the blood)
• Hypercalciuria (excessive calcium levels in the urine)
• Polydipsia (excessive thirst)
• Hypertension (high blood pressure)
• Polyuria (excessive urination)
If any of these tests show abnormal results, further tests will be required in order to actually confirm the diagnoses. These tests include:
• X-rays of the bones
• Serum phosphorus
• Serum calcium
• 25-hydroxy vitamin D levels
• 1,25-dihydroxy vitamin D levels
Those who are confirmed to be suffering from hypervitaminosis D must immediately stop taking any kind of vitamin D supplementation. Additionally, they will usually have to lower their calcium intake. In very severe cases, doctors may prescribe bisphosphonates and/or corticosteroids. These will stop the bones from releasing calcium. Further monitoring will be required until levels of vitamin D are back to normal.
Clearly, it is very important to avoid hypervitaminosis D. While it is rare for it to happen, being aware of the potential risk is usually enough. Check, therefore, what the IU of vitamin D is on any and all supplements that you take (remember that it may be present in various multivitamins, for instance). The upper tolerable level is 4,000 IU and believed to actually be much higher, but it is always better to be safe than sorry. If at all possible, you should try to obtain your vitamin D from natural sources, avoiding supplements at all. The exception is if you receive supplements on prescription.
Some of the best sources of vitamin D, besides sunshine, include:
• Salmon, tuna, mackerel and other fatty fish
• Cod liver oil
• Beef liver
• Certain mushrooms
• Egg yolks
The above list does demonstrate how difficult it is for vegetarians and vegans to obtain vitamin D. Indeed, they are at an increased risk of having a deficiency. It is even more important, therefore, that they take concerted efforts to expose themselves to the sun. They may also want to consider speaking to their health care professional to ask whether they should supplement.
Vitamin D – Getting It Right
We know that vitamin D is essential to our overall health. Virtually every single cell found in the human body has a receptor to deal with vitamin D. Exposing the skin to the sun produces vitamin D naturally, meaning it is actually not a vitamin but rather a prohormone. It can also be obtained through diet, most notably fortified dairy products, juices and cereals, as well as fatty, oily fish.
Considering that some 60% of the population in this country has a vitamin D deficiency, it is clear that supplementation is hugely important. It affects the health of our bones, improves our immune system, protects against cancer, may help to prevent hair loss and much more. As such, guidelines have been directed about how many nanograms per milliliter of blood should be present. Dropping below that would point to a deficiency. The limits, as currently agreed upon, are explained in the table below.
|Range||Nanograms per milliliter of blood|
|Sufficient||20 to 30|
|Safe upper limit||60|
|Toxic||Higher than 150|
It is accepted that taking between 1,000 and 4,000 IU of supplemental vitamin D is enough for the majority pf people.
Resources and References:
Am I Getting Too Much Vitamin D? – Information on what is excessive vitamin D intake. (Vitamin D Council)
What Is Vitamin D Toxicity, and Should I Worry About It Since I Take Supplements? – Information on vitamin D toxicity. (Mayo Clinic)
Can Too Much Vitamin D Be Toxic? – Vitamin D toxicity. (Live Science)