Click to View Putting the Risk of Vitamin D Toxicity into Perspective
Mar 31, 2016

by Samantha Kimball, PhD, MLT

Vitamin D is unique among nutrients. Vitamin D is actually more of a hormone than a vitamin. Vitamin D is used by nearly every cell in the body. It can be obtained naturally from the sun or by ingesting it. It was named a “vitamin” when it was discovered that many people were deficient and it could be obtained from their diet, this happened because they were not getting enough from sun exposure. This is more prevalent today than ever.

If you are lucky enough to live near the equator, where you can synthesize vitamin D year-round, and you spend a minimal amount of time unprotected in the sun and fully exposed (15 minutes in a bathing suit) each day, you probably get enough vitamin D from that ball of life in the sky. However, we Canadians are not so lucky. Our northern climate means that in the winter the sun isn’t powerful enough for our bodies to make vitamin D at all and in the summer months, when it is possible to make vitamin D, most people wear sunscreen which blocks the sun and the production of vitamin D. With our extremely limited ability to obtain vitamin D naturally we need to supplement.

There is a continuous debate among vitamin D experts about how much vitamin D you need to take to be healthy. Opinions and comments like “Vitamin D has health benefits,” but “you shouldn’t take too much because it is just too risky!” are confusing and often portrayed in parallel in the media. What is missing is a little perspective.

There are so many reported associations between low vitamin D and disease, the list is lengthy and includes diseases that have a huge impact on health across Canada – diabetes, heart disease, mental health, cancer and autoimmune disease to name a few. The evidence is consistent at the level of observational studies or surveys about health and lifestyle. That is the same kind of evidence that resulted in advice to wear seat belts in cars and to stop smoking. But for vitamin D many argue that the only acceptable evidence is the ‘double blind, randomized placebo-controlled clinic trials’ which do not always agree with the wealth of observational data. So, if I am concerned that I’m not getting enough vitamin D and I want to take more than what is recommended, for example 6,000 IU/d, what does the risk really equate to?

Vitamin D toxicity is exceedingly rare. The Pure North clinic has seen over 44,000 participants and has not seen even one case of toxicity. This wouldn’t be that surprising, but Pure North recommends optimal levels of vitamin D that require intakes above the Tolerable Upper Level (UL) set at 4,000 international units per day (IU/d) by Health Canada and the Institute of Medicine (IOM). The vitamin D recommendations at the Pure North S’Energy Foundation (a health and wellness program in Calgary) align with those of the Endocrine Society and other vitamin D experts from all over the world. Pure North participants routinely take 6,000 – 15,000 IU/d, depending on their body weight. There have been no cases of toxicity in over 8 years and over 40,000 participants.

So why hasn’t there been any toxicity if the risk is so great?

Let’s back track a bit to clarify what vitamin D toxicity is. Vitamin D toxicity manifests itself as high serum calcium levels (hypercalcemia). Calcium levels in the blood are kept within a very narrow range because calcium plays a central role in normal body function. Calcium levels are important for normal cell function including muscle function, signal transduction, nerve transmission, hormone action, blood clotting and bone structure. When calcium levels get too high people experience symptoms of nausea, vomiting, abdominal pain, headache, dizziness, muscle weakness and anorexia. Left untreated, hypercalcemia can lead to kidney failure and in extreme cases eventually death. The most common causes of hypercalcemia are primary hyperparathyroidism and malignancy.

So how common is vitamin D-induced hypercalcemia?

Some researchers at the Mayo clinic decided to look at a large amount of data collected in the Olmsted County and Rochester Epidemiology Project to see how common high levels of vitamin D were and how often vitamin D toxicity was seen.[1] The data showed there were a lot more people taking vitamin D supplements in 2015 than in 2005. With more people taking vitamin D supplements and at higher levels of intake, the researchers found that more people reached 25-hydroxyvitamin D [25(OH)D] (blood serum) levels above 125 nmol/L and some reached levels above 250 nmol/L. Importantly, there was not an associated increase in serum calcium. To put these numbers into perspective, the IOM recommendations aim to reach a blood level of 50 nmol/L for vitamin D [25(OH)D], which they say is enough for bone health. No other health benefits were considered.

Out of 1,714 patients in Mayo clinic study who had vitamin D levels above 250 nmol/L, they found only one case of clinical vitamin D toxicity. The woman was taking 50,000 IU of vitamin D, in combination with 3,000 mg of calcium, every day for more than three months. She was treated and her symptoms went away. There were 20,308 patients in the Mayo clinic data set. Overall, unless you decide to take 100 times what the upper limit is currently set at, you don’t have to worry. In fact, since the upper limit was set at 4,000 IU/d in 2010 many vitamin D experts have called for the upper limit to be increased to at least 10,000 IU/d, which has been demonstrated to be completely safe and is a level that is equivalent to what can be obtained from sunlight in 10 minutes under optimal conditions.[2],[3],[4]

There are several reasons someone would want to get their vitamin D levels above 125 nmol/L [25(OH)D]. The natural physiological level obtained from sunlight is around 120 nmol/L.[5],[6],[7] The scientists at Grassroots Health combined the risk of several diseases to determine what level of vitamin D was associated with reduced risk for all of them. The diseases studied included cancers, type 1 diabetes, fractures, multiple sclerosis and heart attacks. They found that a vitamin D level above 100 nmol/L [25(OH)D] was associated with a combined risk reduction of these diseases.

More interesting is a recent report that looked at vitamin D exposures in the National Poison Data System in the United States[8] – over 15 years of data. While this report does not look at toxicity explicitly, it does give us an idea of how prevalent the issue really is. The report shows a significant increase in the number of people reporting a perceived concern of vitamin D intake; up to 4,535 per year in 2014. Of the reports 4 per cent were associated with a “serious outcome.” Serious outcomes were the presence of symptoms of hypercalcemia and include: nausea (1.5%), vomiting (0.7%), abdominal pain (0.7%), diarrhea (0.7%), headache (0.5%), drowsiness (0.4%), dizziness (0.4%), constipation (0.2%), muscle weakness (0.2%), anorexia (0.2%) and rash (0.2%). These are all symptoms common for many illnesses including the flu and the common cold.

Over the 15-years there were five people who had serious outcomes that were associated with vitamin D intake, two of which were choking incidents which can happen taking any pill, so these were not vitamin D-related. There were three, or 0.07 per cent of cases over 10 years, serious cases involving kidney failure that were related with chronic ingestion of vitamin D. There were no cases of mortality. Unfortunately, the doses and duration of ingestion were not reported. However, the report also included information on the number of people who tried to commit suicide by overdosing on vitamin D. Of the 106 attempts, none were successful.

What are the key facts from the report?

Despite a 1,600 per cent increase in reports of vitamin D exposures to the US poison centers, there was no increase in illness and no mortality associated with vitamin D supplementation.

So what are the risks of vitamin D toxicity in relation to other risks we accept every day?

If you live in the United States, your risk of getting hit by lightning is 0.02, per 100,000 deaths; Dying from an overdose of Acetaminophen is 0.05 in 100,000; Getting hit by a car when crossing the road is 1.5 in 100,000; Overdosing on prescription opioids is 5.1 in 100,000 and dying from a heart attack is 143 in 100,000.

Your risk of dying from vitamin D poisoning is 0.0000000002 per 100,000.

The list of health problems associated with low vitamin D is long and included: hypertension, type 2 diabetes, depression, asthma, cancer, dementia, heart disease, multiple sclerosis, schizophrenia, autism, psoriasis, neuromuscular disease and infertility.

The hyperbole of too much vitamin D is inhibiting people from achieving the benefits of having an optimal level of vitamin D. Ultimately the decision is yours but I hope this article helps provide the facts to help make an informed decision about how much vitamin D you and your family should be getting.

According to William Sloane Coffin “all of life is the exercise of risk.” But which risk is greater, being vitamin D deficient and being at risk for a myriad of chronic health consequences, or taking too much vitamin D? Which risk is really erring on the side of caution?

In Health,

[1] Dudenkov DV., et al. 2015. Changing Incidence of Serum 25-Hydroxyvitamin D Values Above 50 ng/mL: A 10-year population-based study. Mayo Clin Proc 90:577-86.

[2] Hathcock JN., et al. 2007. Risk Assessment for Vitamin D. Am J Clin Nutr 85:6-18.

[3] Vieth R. 1999. Vitamin D Supplementation, 25-Hydroxyvitamin D Concentrations, and Safety. Am J Clin Nutr 69:842-56.

[4] Heaney RP., et al. 2003. Human Serum 25-Hydroxycholecalciferol Response to Extended Oral Dosing with Cholecalciferol. Am J Clin Nutr 77:204-10.

[5] Heaney RP. 2014. Toward a Physiological Referent for the Vitamin D Requirement. J Endorinol Invest 37:1127-30.

[6] Vieth R. 1999. Vitamin D Supplementation, 25-Hydroxyvitamin D Concentrations, and Safety. Am J Clin Nutr 69:842-56.

[7] Luxwalda MF., et al. 2012. Traditionally Living Populations in East Africa Have a Mean Serum 25-Hydroxyvitamin D Concentration of 115 nmol/L. Br J Nutr 108:1157-61.

[8] Spiller HA., et al. 2015. Vitamin D Exposures Reported to US Poison Centers 2000-2014: Temporal trends and outcomes. Hum Exp Toxicol 0960327115595685.