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If you can’t meet nutritional requirements from food, supplements may seem like a solution. But do they work?Getty Images/iStockphoto

It’s well-established that eating a healthy diet helps guard against chronic disease.

Studies have consistently found that a diet based on vegetables and fruit, whole grains, a variety of proteins and healthy fats is tied to a lower risk of heart disease, stroke, Alzheimer’s disease and certain cancers.

If your diet is less than stellar, though, you might lean toward taking a daily vitamin supplement to protect your long-term health.

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If that’s the case, an updated review of evidence suggests you’re wasting your money.

Here’s what to know about supplementing with vitamins and minerals.

Updated supplement guidelines

To update its 2014 supplement recommendation statement, the U.S. Preventive Services Task Force (USPSTF) commissioned an independent panel of experts to review of 84 studies, including 52 new studies published since 2014.

The researchers sought to determine if taking single nutrient supplements (e.g., folic acid, vitamin D, vitamin E), paired-nutrient supplements (e.g., calcium + vitamin D, folic acid + B12) or multivitamins reduced the risk of cardiovascular disease, cancer or early death.

According to the new USPSTF guidelines, published June 21 in the Journal of the American Medical Association, there’s no evidence that multivitamins, single supplements or paired supplements help prevent cardiovascular disease or cancer in otherwise healthy nonpregnant adults.

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For most of the supplements reviewed, there was little to no evidence of serious harms.

However, the USPSTF specifically recommends against taking a beta-carotene supplement because of possible increased risk of lung cancer and cardiovascular death. The updated guidelines also advise against the use of vitamin E, presumably because vitamin E supplements showed no benefit for protecting against cardiovascular disease, cancer or early death.

These findings aren’t at all surprising to me.

Whole foods contain a mixture of vitamins, minerals, phytochemicals, fibre and other nutrients, dietary components thought to work together to offer health benefits. This orchestrated web of beneficial compounds doesn’t exist in isolated vitamin and mineral pills.

Even so, this doesn’t mean that nutrition supplements are useless. In the right circumstances, they can offer benefits.

When supplements are helpful

While I recommend trying to meet daily nutrient requirements from whole foods, in some cases this isn’t always feasible.

Certain supplements are useful to bridge dietary nutrient gaps. They’re also needed to treat vitamin and mineral deficiencies.

Women who are planning to become pregnant or who could become pregnant should take a daily multivitamin that provides 0.4 mg of folic acid to help prevent neural tube defects, birth defects that affect the brain and spinal cord.

If you follow a vegan diet, taking a multivitamin and mineral supplement is an important way to get your daily iodine, a mineral found in dairy and seafood that’s needed to make thyroid hormones, as well as vitamin B12.

Naturally-occurring B12 is found only in animal foods. It’s needed to maintain healthy nerve function and to make red blood cells and DNA.

Vegetarian or not, it’s recommended that adults over 50 get most of their daily B12 from a supplement, like a multivitamin or B complex, or fortified foods. That’s because many older adults don’t produce enough gastric (stomach) acid needed to absorb B12 from foods.

I also recommend a daily multivitamin for individuals who take a medication that can reduce the absorption of vitamin B12 from diet (e.g., gastric acid inhibitors and Metformin).

If you follow a low-calorie diet to lose weight or you eat a very narrow diet, a multivitamin and mineral supplement can provide some nutrient coverage.

A daily vitamin D supplement is necessary to maintain a sufficient level of the vitamin in the bloodstream. Osteoporosis Canada recommends vitamin D supplementation for adults year-round since it’s nearly impossible to get enough of the nutrient from foods alone.

Vitamin D plays a major role in calcium absorption, bone health, muscle performance and balance.

Bottom line

Vitamin supplements are often viewed as being completely benign. That’s not always the case, however. When taken in high doses, many nutrients can have adverse effects.

For example, in moderate doses vitamin A can reduce bone density and high doses of it may be toxic to the liver. Taking too much iodine can cause some of the same symptoms of an iodine deficiency, including an enlarged thyroid gland (e.g., goiter).

Supplementing with too much zinc can lead to consequences such as impaired immune function, reduced levels of HDL (“good”) cholesterol, loss of appetite, diarrhea, headaches and abdominal pain.

To supplement appropriately and safely, consult your health care provider.

Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan. Follow her on Twitter @LeslieBeckRD

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