What you need to know about Vitamin D

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Copyright © Leslie Beck, 2015.

Leslie Beck, Registered Dietitian, is the best-selling author of 12 books on nutrition and health, writes a weekly column in The Globe and Mail, and is a regular contributor to CTV News. Based at the Medisys clinic in Toronto, Leslie offers one-on-one diet coaching, personalized meal plans and evidence-based recommendations on the use of nutritional supplements.www.lesliebeck.com

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In a country with little, if any, opportunity to synthesize vitamin D in fall and winter, the seasons with the least amount of sunlight, Canadians have been advised to turn to supplements to ensure they’re getting enough of the bone-building nutrient.

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.

How much vitamin D do you need?

As we await the results of large randomized controlled trials, researchers are constantly evaluating new evidence to determine if dietary recommendations need tweaking or an overhaul. 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 who have or are at high risk for osteoporosis, get 800-2,000 IU daily. The organization advises routine vitamin D supplementation for all Canadian adults year round.

 

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.

 

Can you get it all from 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 about sun exposure?

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 should you look for in a supplement?

It is typically recommend that you take a 1,000 IU vitamin D supplement year round, although some individuals may need a higher dose to achieve a sufficient blood level. 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.

 

Can you get too much of a good thing?

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.

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.

 

How do I know if I am getting enough?

The best indicator of your vitamin D status is a blood test called 25-hydroxyvitamin 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 is 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.


Copyright © Leslie Beck, 2015.

Leslie Beck, Registered Dietitian, is the best-selling author of 12 books on nutrition and health, writes a weekly column in The Globe and Mail, and is a regular contributor to CTV News. Based at the Medisys clinic in Toronto, Leslie offers one-on-one diet coaching, personalized meal plans and evidence-based recommendations on the use of nutritional supplements.www.lesliebeck.com

 

 

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