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Sorting Out Supplements

One day the news media are reporting that dietary supplements don’t prevent disease and may actually threaten our health; the next day another study says supplements can help to thwart disease or fill nutrient gaps in our diets. What should health and wellness professionals tell clients when asked about supplements?

This article will review the evidence for three popular supplements—vitamin D, magnesium and omega-3-fatty acids (or “fish oil”)—and will provide a bottom-line answer on whether people need these supplements and who would benefit most from taking them. Note: A registered dietitian nutritionist is your best resource for information on dietary supplements and can guide clients on whether they need to take them.

Supplement Usage Overview

Use of supplements has been on the rise since the early 1980s, according to the Nurses’ Health Study, which tracked about 74,000 female registered nurses, and the Health Professionals Follow-Up Study, which tracked about 50,000 male health professionals (Kim et al. 2014). The studies noted a steady decline in the use of vitamin A, beta carotene, vitamin C and vitamin E, and an increase in the use of multivitamins, calcium, vitamin D, folic acid, magnesium and omega-3 fatty acids. The authors suggested that these shifts reflect changes in dietary guidance and/or government policies, updates to science and research findings, and the growth of the dietary-supplement industry (Kim et al. 2014).

Let’s take a look at three of the most popular supplements:

Vitamin D

Vitamin D is a media darling—for good reason. Vitamin D promotes calcium absorption and maintains adequate serum calcium and phosphate levels. It is also important for cell growth, neuromuscular and immune function, and inflammation reduction. Researchers are still learning about the health benefits of vitamin D, so there continues to be debate about what the ideal blood levels of the vitamin are and when supplementation is needed. The recommended intake is 600 International Units for most adults, though some researchers believe that this is not high enough to support all of the benefits of vitamin D (Heaney & Holick 2011).

When you consider that food sources of the vitamin are limited and that wearing sunblock with an SPF higher than 8 prevents the body from making vitamin D in the skin, it is easy to understand why people are swallowing vitamin D supplements. For now, clients should have their blood levels checked before supplementing at high doses. Most multivitamin-and-mineral products contain at least 400 IU of vitamin D, and many women’s formulas contain as much as 1,000 IU (Consumer Reports 2013). At those levels vitamin D is safe, but again, more isn’t better; clients should avoid taking more than 4,000 IU a day (NIH 2011) unless prescribed by their doctor.

Those at risk for vitamin D deficiency include

  • people with dark skin;
  • people with limited sun exposure (some athletes who train exclusively indoors have been found to have low levels of vitamin D);
  • people who have had gastric bypass surgery for obesity; and
  • older adults.

Most commonly, the vitamin D in supplements is either D2 (ergocalciferol) or D3 (cholecalciferol). Vitamin D2 is slightly less potent than D3, but D3 is made from lanolin, which many vegetarians consider an animal product (Larson-Meyer 2012).


About half of the body’s magnesium is found in bones, which is why this often-overlooked nutrient is critical to bone health. Research has also shown that magnesium is important in preventing and managing hypertension, diabetes and cardiovascular disease.

Though magnesium is common in many foods, people’s intake of the mineral typically falls below the recommended amounts (Moshfegh et al. 2009). Foods with dietary fiber are good sources of magnesium. Refining grains by removing the bran and germ lowers the magnesium content, so whole grains are better sources than refined grains.

The recommended intakes for adults aged 19–30 are 400 mg for men and 310 mg for women; the guidelines are slightly higher for over-30 men (420 mg) and women (320 mg) (NIH 2013b). Getting magnesium from food is definitely preferred over supplements, because high doses can cause nausea, cramping and diarrhea. After all, magnesium is the key ingredient in Milk of Magnesia, the popular laxative.

Those at risk for magnesium deficiency include

  • individuals with malabsorption problems related to gastrointestinal disorders such as Crohn’s disease or celiac disease;
  • those who have undergone gastric bypass surgery for obesity (especially if the small intestine and/or ileum was resected);
  • those with type 2 diabetes; and
  • older adults.

Omega-3 Fatty Acids

The key omega-3 fatty acids are EPA and DHA, two long-chain polyunsaturated fats often called “fish oil”; and alpha-linolenic acid (ALA), found in walnuts, flaxseed and chia seeds. EPA, DHA and (to a lesser extent) ALA get converted in the body to compounds called eicosanoids, which dilate blood vessels, lower blood pressure, and reduce blood clotting and inflammation. Americans are not consuming the recommended amounts for omega-3s, according to a recent analysis of NHANES data (Papanikolaou 2014).

The American Heart Association recommends eating two servings of fatty fish (a serving is 3.5 ounces of cooked fish) each week to get the recommended intake of 250–500 mg of omega-3s per day (AHA 2014a). People with heart disease should aim for 1 gram of EPA + DHA per day (AHA 2014b).

While dietary sources are preferred, it can be a challenge to get the recommended amounts of healthy fats without supplementation. Some of us just don’t like fatty fish, so supplemental fish oil may be a good addition to the diet. Look for supplements that provide about 500 mg of EPA + DHA.

Those at risk for low intakes of omega-3 fatty acids include

  • individuals who restrict dietary fat; and
  • those who do not eat fatty fish.

Choosing Dietary Supplements

With so many varieties of dietary supplements on the market, how do you choose a good one? The laws governing dietary supplements make it a buyer-beware market. The U.S. Food and Drug Administration does not test dietary supplements for safety or effectiveness, and manufacturers are responsible for providing a good product. Use these tips when picking a supplement:

Buy from a reputable supplement maker. Beware of Internet sales of supplements or bargain-basement prices; with supplements you get what you pay for.

Read labels closely. Packaging may look similar on the outside, but the nutrients in the bottle can differ in purity and potency. One way to know if a supplement delivers quality ingredients and proper potency and contains no contaminants is to look for the “USP-verified” symbol. The U.S. Pharmacopeia is a nonprofit scientific organization that has been setting pharmaceutical quality standards since 1820 (USP 2014). It is the gold standard for supplements.

Know what you really need, and take only enough to supplement your diet. Rarely do you need the recommended serving size as listed by the manufacturer on the supplements fact panel to meet the entire Recommended Dietary Allowance from supplements. For example, I take 500 mg of omega-3 fatty acids per day because I don’t eat fatty fish—but I don’t take more, whatever the label says. I choose a variety that is “burpless” to eliminate an often-complained-about side effect (“fish burps”).

Be realistic about claims. If a supplement sounds too good to be true, it probably is.

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