Explainer: Some supplements may not have what it takes

Environment and growing conditions can vary the amounts of useful chemicals in a plant’s tissues


Many studies have shown diets rich in pomegranates or their juice can be healthy for the heart. Yet some supplements that claim to be made from this fruit appear to lack the heart-healthy chemicals.

Samantha Forsberg/Flickr (CC-BY 2.0)

Some dietary supplements are made in a lab, like drugs. Others are derived from plants. But there’s another big difference between these supplements than just where they came from. Those plant-based ones may sound healthier, because they have a natural source. But there’s no guarantee that plant-based supplements contain the chemicals that are supposed to make them healthful.

If a drug says it contains 200 milligrams of the pain-reliever ibuprofen, it should have exactly that amount. If a company sells you more — or less — than the labeled amount, they’re breaking the law. But supplements that are made from plants don’t contain an exact amount of some chemical. Instead, their labels usually say the pills contain a certain amount of the starting plant, such as ginseng or ginger. These plants have chemicals that can be helpful to the human body. But there’s a problem: The amount of those chemicals can vary widely from plant to plant and, thus, from one package of some supplement to another.

A plant is made of more than a single chemical. Its tissues contain many chemicals, sometimes thousands of them. And the amounts of each can vary greatly between any two plants — even if grown on the same farm.

Many of the plant chemicals sought by the makers of diet supplements are defense compounds. They may be poisons that plants make to deter predators. Others may be compounds — such as antioxidants — that the plants make to protect or repair damaged tissues. If a plant is very stressed, it may make more of these chemicals. If it isn’t, it may make few of them.

Many fruits and veggies naturally come in a broad range of colors, such as these carrots. The ingredients that give them color can also make them especially helpful — delivering natural versions of chemicals present in many dietary supplements. Ausmus/USDA
The amount of nutrients in the soil also can affect a plant’s chemical content. When the proportion of nutrients is wrong, a plant may not be able to to make or use the chemicals it needs to grow — including the chemicals that diet studies have shown to be healthy for people.

Supplements may lack healthy chemicals

Science News published a big story on the problem back in 2003. Then it published a follow-up story six years later. Back then, the magazine asked: “How do we know what’s in those [food] supplements?” The answer, it found: “We don’t.”

This can prove especially true for supplements that are not made from recipes that include well-defined chemicals, such as creatine or magnesium citrate.

For instance, in one study, researchers at the Geffen School of Medicine at the University of California, Los Angeles, looked at supplements containing chemicals from pomegranates. A host of studies had found that eating this fruit or drinking its juice could lower the risk of heart disease. This benefit showed up both in lab animals and in people. Many studies had linked the health benefits from pomegranates to chemicals called tannins.

But fresh pomegranates can be expensive. They also are not in season all year round. So some supplement companies began offering capsules, tablets and soft gels claiming to hold pomegranate chemicals. However, the UCLA study found that of the 27 pomegranate supplements it tested, 17 (roughly two-thirds) had no tannins in them. And five more that did had just tiny traces. Some supplements either contained no pomegranate or had lost vital parts of the fruit as it was processed to make a food supplement, the researchers concluded.

Be careful what you ask for 

Sometimes even when a product contains exactly what it claims to, a user may still lose out. Consider the case of vitamin E.

Many studies have shown that foods rich in this vitamin can help reduce tissue damage (and perhaps disease) in the lungs and other tissues. It’s supposed to do this by quashing molecules known as free radicals. Chemicals that fight free radicals are known as antioxidants. They fight oxidation. This a potentially damaging reaction that can destroy cells. And vitamin E is known to be a very effective antioxidant.

In plants, vitamin E tends to occur as a mix of several related types of tocopherols and tocotrienols (Toh-koh-TRY-eh-nawls). These chemicals come in what are known as alpha-, beta-, gamma- and delta forms. Because alpha-tocopherol tends to occur in the highest amounts, some companies have sold it alone as vitamin E.

Yet several studies have suggested that alpha-tocopherol doesn’t have the same properties when consumed on its own that it may have when accompanied by the other forms. So people who want the benefits of vitamin E may need to make sure the supplement they buy has the entire mix of related compounds. And it may help if the chemicals are consumed in the proportions that tend to occur naturally in a plant.

That’s why many doctors and food chemists now argue that the safest way to build a healthy body is to get your nutrition from eating a variety of whole foods. And here’s an interesting fact: Many of the healthiest compounds in plant-based foods come from the pigmented molecules in them. That’s why nutrition experts recommend eating a diet rich in colorful fruits and veggies.


Janet Raloff is the Editor, Digital of Science News Explores. Prior to this, she was an environmental reporter for Science News, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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