SPONSORED
We hear it all the time from lifestyle gurus and healthy living blogs: avoid chemicals, stick with what’s natural. But trying to divide the world into 'natural' and 'chemical' betrays a misunderstanding of what those words mean. Many products that people consider natural are highly processed and laden with chemicals (See ‘Making an Ounce of Rose Oil.’).
For a quick tour of some of the compounds found in nature, we turn to Lee Dyer, a professor of biology and director of the ecology, evolution and conservation biology graduate program at the University of Nevada, Reno. Dyer studies so-called secondary metabolites, which are compounds that plants make as byproducts of normal metabolism. Some of these compounds are effective at fending off herbivores.
Dyer’s realm is the battle between plants and herbivores. The world’s plants produce tens of thousands of different chemicals, many to defend against animals and insects that want to eat them. “Plants produce natural mixes of secondary metabolites that are insecticidal. Otherwise the world wouldn’t be green,” says Dyer.
The battle ploys are effective. For example, many plants — including foods from apples to almonds — contain a compound that can produce cyanide to ward off chomping insects. “Cyanide is incredibly toxic to anything that breathes,” Dyer points out. But, plants store cyanide with a sugar attached to it, which makes it safe. Some of these plants also store a protein that can cut off the sugar from the cyanide, which makes it dangerous. When an herbivore starts chomping leaves, the cyanide-sugar component is mixed with the enzyme, breaking it off from the sugar molecule, and releasing pure cyanide.
In short, nature creates the world’s largest collection of chemicals. There is no natural-chemical divide; natural is chemical (See ‘A Chemical Look at Lemons.’). Moreover, the level of exposure to something makes all the difference (See ‘Concentrate on Concentration.’).
Measuring risk
Though most people are not aware of the diversity of chemicals in the natural world, they are aware that there is significant complexity, and that X-factor can cause uncertainty. One reason many people prefer 'natural' to 'chemical' is that humans do a poor job of identifying relative risks, and it seems easier to lump things into simple categories. In his book Getting Risk Right: Understanding the Science of Elusive Health Risks, Geoffrey Kabat, a cancer epidemiologist at Albert Einstein College of Medicine in New York City, outlines some of the reasons people worry about the threat to health posed by various substances.
“In general,” Kabat writes, “threats that are invisible and not under our control (such as ionizing radiation or trace amounts of chemicals in food and water) tend to elicit a strong reaction from the public. Strikingly, other exposures that are much more important at the population level, such as cigarette smoking, weight gain, excessive alcohol consumption, and excessive sun exposure, do not elicit anywhere near the same reaction. This may be because we have the illusion that they are under our control but also because they are widespread and familiar—they have been ‘domesticated,’ so to speak.”
Kabat lays out a number of ways in which scientists and the media contribute to public misunderstanding of risk. Scientists, in searching for impacts on human health, often start by looking for correlations between exposure to some substance and subsequent development of disease. Decades ago, for instance, scientists noticed that people who had regular exposure to cigarette smoke had an increased incidence of lung cancer. But, while the link between smoking and cancer was confirmed, it took years of research, approached in different ways and eliminating confounding factors, to affirm the connection.
Many other correlations between a substance and a disease are also found, but further study disproves the connection. Those early correlations can stick in people’s minds, so they continue to believe that there’s a causal connection long after science has moved on and proved otherwise.
Some people, for instance, continue to believe that the measles vaccine causes autism, even though the original study suggesting the link has been shown to be fraudulent, and subsequent studies didn’t bear out the hypothesis.
Another problem is that people — scientists, the press, government regulators, journal editors — tend to prefer studies that have positive results. That can skew the picture of just how prevalent threats are in the environment, because many of the negative results get ignored. Kabat cites the work of John Ioannidis, a statistician and professor of medicine at Stanford University, who found that medical journals contain more positive findings than would be expected if publications reflected the total number of studies done.
“It is simply human nature that positive findings get more attention than findings of no relationship obtained in studies of comparable quality,” he writes. “Positive associations appear more psychologically satisfying than studies that show no effect.”
For science to uncover risks takes dedicated effort by researchers, Kabat writes. “Progress can come only from excluding alternative hypotheses and forging strong links in the chain of causation.”
As we learn to better assess the chemical risks in our world, we find that the danger depends more on the level of exposure than the source, whether it’s a living plant or a production lab. To keep people safe and healthy, we must objectively study the risks of substances, regardless of where they come from.
This article was created for SC Johnson by Scientific American Custom Media, a division separate from the magazine’s board of editors.
More in this Report
 |
 |
||
 |
 |
||
 |
 |
||
 |
 |
