There are constantly reports of new scientific studies in the news.
Every week we hear about how chemicals might be “linked” to health problems.
“A New Study Shows…”
But is there science behind these claims? And what do they actually mean for your health? Here, we lay out the ways scientists test for chemical toxicity.
1. Studies Using Chemical Structures
Scientists can use computers to analyze chemical shapes, or “structures.” They can then predict how toxic the chemicals might be based on the structure. This is called in silico.
By looking at how the atoms of a chemical are arranged, experts can compare them to chemicals that are known to be toxic. They can also use scientific models to predict how the chemical shapes might interact with the body.
While this type of research doesn’t provide definite results, it does have a major benefit. Chemicals can be ruled as potentially dangerous before they are mass produced and put on the market.
This scenario relies on something called “the precautionary principle.” That is, even if a chemical might be safe, we err on the side of caution if its structure indicates it might be toxic.
2. Studies Using Cells
Studies using cells are called in vitro studies. In some cases, cells are taken directly from live animals. Yeast or bacteria cells are often used. For many studies, cells have been grown and multiplied in petri dishes and can be many generations old.
Human cells can also be used. These are typically cancer cells, which can live for many generations.
Cell studies have the benefit of using few or no animals. Scientists can also genetically alter cells to show us exactly how a chemical might be causing bad effects.
For example, these types of cells are altered to emit light when in contact with chemicals that act like estrogens. This makes it easy to visualize how “estrogen-like” a chemical is.
However, studies using only cells do not always accurately tell us how a chemical might affect a whole animal or human. There are a lot of additional factors and processes that happen with a live animal or human, including:
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Metabolism
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Hormone or enzyme activity
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Diet
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Level of stress
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Outer environments (air, water, etc.)
All these can change how a chemical affects health.
Thus, cell studies cannot show the whole picture of how a chemical affects health.
3. Studies Using Animals
Many people, including some scientists, are opposed to animal testing. Aside from the moral arguments against it, it is expensive and labor intensive. Animals are also not always the best substitutes for humans. So why do we do it?
“Controlled” Environment
With animal studies (also known as in vivo), scientists can control an animal’s environment. They can directly compare animals that were exposed to a chemical with animals that weren’t exposed.
This is very powerful, because the scientist can then use statistics to come to a definite result. They can pinpoint the effects of a potentially toxic chemical.
Unethical to Test on Humans
Some research uses controlled studies in humans--think drug groups and “placebo” groups in clinical trials.
But when talking about potentially harmful chemicals, it is unethical to purposely expose humans. This is especially true if a chemical has an effect on pregnancy or fetuses.
With animal testing, effects on offspring can be studied without harming human babies.
Easier and Faster Than Human Studies
Animals age and breed much faster than humans. Because of this, it is quicker to look at long term effects of a chemical in animals. It is also easier to look at effects across generations.
4. Studies Using People
Testing chemicals directly on humans can be unethical. But there are other ways to study the health effects of chemical exposures. These include observing large populations in the real world, with real-life chemical exposures. This is known as epidemiology.
There are several types of human studies, including:
Cross Sectional--A large group of people are studied, usually at a snapshot in time. Scientists can measure their chemical exposures by testing urine or blood. Then, they can measure health effects (such as diabetes or high blood pressure). They can then link chemicals to health outcomes at that moment.
Cohort (Longitudinal)--People are studied over time. Scientists measure an exposure that is happening as a young adult, child, or even before birth (by measuring the pregnant mother). These people are then followed over several years and even generations. This can show the long-term health effects of earlier chemical exposures.
Case-Control--Sick people (case) are compared to healthy people (control), and their exposures are measured. For example, a group of people with diabetes is compared to a similar group without. Their chemical exposures are measured through blood or urine. Then statistics can be used to see if the sick people have higher chemical exposures than the healthy people.
Occupational--People in jobs with specific chemical exposures are compared to people without those jobs. The health effects of each group can be compared to see if high chemical exposures are linked to health outcomes.
Many people assert that these types of human studies are not accurate because they often rely on correlation. They also state that there are many outside factors that could change results (such as individuals’ smoking habits or diet).
However, there are many advanced statistical methods that account for these factors. And while human studies cannot show as strong connections as animal studies, the calculations can show very real effects.
What Does This Mean for My Health?
There are a few take-aways from looking at these types of experiments.
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Looking at the results of just one study does not always reflect the truth. The news often sensationalizes or downplays certain specific studies. But because of the shortcomings in each type of study, it is hard to see the big picture with just one study.
Many scientists are now using something called “systematic review” to combine cell, animal, and human evidence to find big picture conclusions.
It is also important to look at the source of a particular study. Companies (such as food or chemical companies) pour millions of dollars into studies that might be rigged to show that their product is safe.
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If a study shows a health effect, precaution should be taken. Even though one study might not be perfectly accurate, it still indicates that there might be a problem. Thus, precautions should be taken, such as avoiding exposure.
This goes back to the “precautionary principle.” It is better to avoid a chemical that turns out to be safe than the other way around.
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The precautionary principle should be applied to consumer products. With this overarching idea, testing could be streamlined. In some cases, chemicals could be banned early, before they are put on the market.
For example, if a chemical has a toxic structure, it could be banned outright. If it doesn’t have a toxic structure, it could be tested in cells. If it ‘passes’ in cells it could then be tested in animals, and on. If at any stage it shows toxic effects, it should be banned.
This is not currently how chemicals or products are regulated or certified. However, we can encourage this type of regulation by supporting sensible chemical testing. We can also vote with our pocketbooks by supporting responsible companies and products (click here for some suggestions).
It can be overwhelming to follow all the scientific studies that come out in the news. But knowing a little bit about the science behind the studies can help you to make the best choices for yourself and your loved ones.