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Vitamin D tabletes are photographed in the Globe studio on March 26 2015. (Fred Lum/The Globe and Mail)
Vitamin D tabletes are photographed in the Globe studio on March 26 2015. (Fred Lum/The Globe and Mail)

The vitamin D dilemma: How much should we be taking? Add to ...

True, it was a painful winter. We were stuck in a cocoon of cold (some of us still are) with limited daylight to lift our winter-weary spirits. So maybe we shouldn’t be surprised that vitamin D has emerged as a central point of controversy. In a country with little, if any, opportunity to synthesize the vitamin in fall and winter, the seasons with the least amount of sunlight, we should know just how much of the sunshine supplement we really need.

Enter the latest debate about vitamin D, sparked by a series of advertisements in newspapers across the country (including this one) claiming that none of us are getting anywhere near the amount our bodies require if we adhere to Health Canada’s recommended intakes. Osteoporosis experts are being inundated with calls from confused patients. Dietitians of Canada has expressed its concern in a letter to Health Canada. And Canadians are wondering what to make of the bold assertion that Health Canada was wrong and that we actually need more – a whole lot more – vitamin D to ward off disease. Do we?

Root of the controversy

It seems that every few years vitamin D steals the spotlight, as researchers learn more about its possible link to various conditions and diseases.

This latest controversy was prompted by an analysis by Paul Veugelers and John Paul Ekwaru, biostatisticians from the School of Public Health at the University of Alberta in Edmonton. Published last October in the online journal Nutrients, their work concluded that the U.S.-based Institute of Medicine (IOM) – the organization that develops Recommended Dietary Allowances (RDAs) for Canadians and Americans – made a serious calculation error in determining the RDAs for vitamin D. That error, the scientists asserted, has serious public health implications.

The report might have languished in the journal’s archives had it not been for Pure North S’Energy Foundation. The Calgary-based organization offers a nutrition and supplement-based health prevention program, and provides research funding to U of A’s School of Public Health, where Veugelers is a research chair. Since January, the foundation has paid for national newspaper advertisements alerting Canadians to the “vitamin D mistake.”

Pure North contends that healthy individuals need much more than 600 international units (IU), the official daily recommended amount, advising at least 5,000 IU each day and, in the case of obese Canadians, as much as 15,000 IU – nearly quadruple Health Canada’s recommended safe upper limit.

Earlier this month, researchers from the University of California at San Diego and Creighton University in Omaha added fuel to the fire. In a letter published in the same online journal, the scientists presented their own data, which they claimed confirmed the Institute of Medicine’s miscalculation noted by the Canadian investigators.

In a press release dated March 17, the American researchers stated that their work showed the current RDAs for vitamin D are “only about one-tenth those needed to cut incidence of diseases related to vitamin D deficiency.”

Why do we need vitamin D?

Vitamin D’s best-known role is helping the body absorb calcium and phosphorus from foods, nutrients critical for building and maintaining bone. Low levels of vitamin D can speed up bone loss and increase the risk of fractures.

Many different tissues in the body have vitamin D receptors, including the heart, kidneys, colon, brain, muscle and immune cells, which indicates that they need vitamin D to function properly. Some, but not all, studies have found that higher blood levels of vitamin D are associated with a lower risk of colorectal cancer, multiple sclerosis, lupus, high blood pressure, cardiovascular disease and Type 2 diabetes.

Even so, these observations don’t prove that taking a vitamin D supplement will lower your risk of cancer, heart attack or multiple sclerosis. Some experts believe low vitamin D stores are a consequence, not a cause, of illness.

Researchers hope that answers will come from the VITAL study, a randomized controlled trial in 25,875 men and women across the U.S. investigating whether taking 2000 IU of vitamin D3 supplements daily reduces the risk for developing cancer, heart disease and stroke in healthy people. The first results are expected in late 2017.

An evolving field

As they await the results of large randomized controlled trials, researchers are constantly evaluating new evidence to determine if dietary recommendations need tweaking or an overhaul. The latest came in 2011 when the IOM increased the recommended daily intake for vitamin D to 600 IU for most adults.

Fast forward to 2014 and the University of Alberta report. Veugelers told The Globe the analysis by his team sought to understand why, in two studies, Canadians who used vitamin D supplements were still vitamin D deficient. They wondered if the recommendation set by Health Canada and the IOM was too low.

“A closer look at the IOM report confirmed what we suspected: a statistical error. In their calculations, the IOM had used ‘standard error’ where they should have used ‘standard deviation,’ ” Veugelers explained.

To prove their point, Veugelers says he and his colleagues used the IOM data, conducted the same analyses using standard deviation (instead of error) and found the recommendation was, in fact, too low. “It explained why Canadians who follow the Health Canada recommendation and supplement with vitamin D may still be vitamin D deficient,” he said.

Considering the financial relationship between Pure North and the university he works for, does Veugelers believe there’s a conflict? He thinks not. “There is no profit to be made on vitamin D. You can get it for free by exposing yourself to the sun, or for $30 you buy an annual supply of supplements,” he said. “I acted from the perspective of my ‘academic duty’ to publish this error as it is essential to the health of Canadians. I was/am aware that this publication is not going to make me popular.”

The problem, says Dr. Stephanie Atkinson, a professor in pediatrics at McMaster University and researcher on bone and mineral metabolism, is that the data was misconstrued.

Atkinson, who sat on the technical expert committee that guided the 2011 review of vitamin D RDAs, argues that the approach taken by Veugelers and his team “grossly overestimated” daily vitamin D recommendations – to the point that it increases the risk of adverse health effects.

Health Canada, too, arrived at the same conclusion. Having taken note of the paper by Veugelers and his colleagues, the agency formally asked the IOM to review and respond to the assertion that a statistical error was made when deriving the recommended daily allowances for vitamin D. After formal reviews, both Health Canada and the IOM concluded that no statistical error was made.

Furthermore, Health Canada noted that “there was no evidence that increases in vitamin D intake for obese persons beyond the requirements for non-obese individuals affect bone health or other health conditions.”

According to Health Canada, “the analysis by Veugelers and Ekwaru greatly overestimates the amount of vitamin D needed for most people and intake at these levels would increase the risk for adverse health effects for some people.”

Too much of a good thing

“It is irresponsible to recommend such high [vitamin D] levels that potentially put Canadians at risk,” says Karen Boyd, Dietitians of Canada regional executive director for Alberta and the Territories.

While it’s tempting to take extra vitamin D in the hopes that it may reduce cancer risk or ward off a heart attack, you can get too much of a good thing. Because vitamin D is stored in fat cells, excess doses can build up to harmful levels, causing high blood calcium and damage to the heart, blood vessels and kidneys.

And while vitamin D toxicity is unlikely at daily intakes below 10,000 IU, evidence suggests that some people are more sensitive to the adverse effects of too much vitamin D, and that these adverse effects can occur at lower vitamin D blood levels than in less sensitive people.

Emerging evidence also suggests there may be adverse health risks associated with blood vitamin D levels that are higher than recommended, but not yet at the point where they would be considered toxic. These are the reasons behind setting the daily upper limit at 4,000 IU.

So the recommended daily allowance for vitamin D stays – at least for now. While findings from observational studies suggest higher doses of vitamin D have benefits beyond bone health, we will have to wait for more definitive answers from randomized controlled trials, the gold standard for generating valid evidence on the effectiveness of an intervention such as vitamin D supplements.

Unless you are vitamin D deficient, which can be determined by a blood test, at this point there is no conclusive evidence that taking vitamin D in excess of the recommended daily amount is better for your bones or guards against cancer, heart disease or other chronic diseases.

Because Canadians aren’t getting enough from the sun and our food, everyone agrees that a vitamin D supplement is necessary. But taking megadoses is not only unwarranted, it may be unsafe.

How much do you need?

Health Canada’s daily recommended intakes (RDAs) for vitamin D, updated in 2011, are 400 international units (IU) for infants, 600 IU for children aged one to adults aged 70, and 800 IU for adults over 70. Health Canada’s safe upper limit is 4,000 IU per day. Osteoporosis Canada advises healthy adults aged 19-50 consume 400-1,000 IU daily, and those over 50, or younger adults at high risk, get 800-2,000 IU daily. The organization advises year-round vitamin D supplementation for all Canadian adults.

Can’t I just bask in the sun?

Even though sunlight may be a major source of vitamin D for many people, the RDAs are based on getting minimal sun exposure. It’s estimated that up to 15 minutes of daily sun exposure on the hands, arms and face around 12 p.m. during the spring, summer and early fall can provide light-skinned Canadians with 1,000 IU of vitamin D. However, people with dark-coloured skin and older adults make considerably less vitamin D from the sun’s ultraviolet B rays, the portion of sunlight that stimulates our skin to produce the vitamin. And even in the summer, you may be making less vitamin D than you think: Correctly applied sunscreen reduces your ability to produce vitamin D by more than 90 per cent. Don’t ditch the sunscreen though, since UV radiation is known to cause skin cancer. Diet and supplements are safe ways to get vitamin D.

What about food?

Foods that provide vitamin D naturally, which are few and far between, include salmon (447 IU per 3 ounces), tuna (154 IU per 3 ounces), eggs (41 IU per yolk) and cheese (14 IU per 2 ounces of cheddar). Fluid milk, many non-dairy beverages and some brands of orange juice are fortified with vitamin D (100 IU per one cup). So if you drink two or more servings (1 cup each) of milk or vitamin D-fortified non-dairy milk, a 400 IU supplement of vitamin D may suffice.

What should I look for in a supplement?

If you don’t drink cow’s milk or fortified non-dairy beverages, I recommend taking a 1,000 IU vitamin D supplement year round. Most multivitamins contain 400 IU of vitamin D, but some manufacturers have started upping that to 1,000 IU. Single supplements of vitamin D typically come in 400 and 1,000 IU doses. Choose a supplement that contains vitamin D3, the form that is more efficient in raising vitamin D levels, not D2.

Are some people at risk for low vitamin D?

Older adults and people with dark-coloured skin are less efficient at making vitamin D in their skin from the sun’s UVB rays. People with limited sun exposure – for example those who spend most of their time indoors or cover themselves up – are also at risk for low vitamin D. So are people who are obese, since fat cells hold on to the nutrient and alter its release into the bloodstream. Individuals who have a medical condition that reduces the intestinal tract’s ability to absorb dietary fat and fat-soluble vitamins, such as vitamin D, must also pay close attention to their vitamin D intake. Crohn’s disease, ulcerative colitis and celiac disease are associated with fat malabsorption.

How do I know if I am getting enough?

The best indicator of your vitamin D status is a blood test called 25-hydroxy vitamin D, which reflects the amount of vitamin D you produce from sunlight in the skin and how much you consume from foods and supplements. According to a 2013 report by Statistics Canada, one-third of Canadians aged 3 to 79 years have insufficient vitamin D levels. One in 10 are considered vitamin D deficient. If you are concerned you are getting too little – or too much – vitamin D, speak to your doctor about getting tested.

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