Some pollutants mess with the thyroid | Science News for Students

Some pollutants mess with the thyroid

Teens may be most susceptible to a chemical in food packaging that affects hormones
May 19, 2017 — 7:10 am EST
thyroid gland

The thyroid is a butterfly-shaped gland in the neck. It makes hormones that help with growth and development.

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There’s a butterfly-shaped gland in your neck that makes hormones — chemicals that signal when certain cells of the body should turn on. One hormone made by this thyroid gland directs several key body processes. These include brain development, bone strength and growth. The hormone even helps to control appetite and weight gain. But certain pollutants can interfere with the production of this hormone. And a new study finds that teens are particularly sensitive to the effects of one of these pollutants.

Called perchlorate (Pur-KLOR-ayt), this chemical is used to make explosives, fireworks and rocket motors. The solid booster rocket on the space shuttle, for instance, contained a lot of perchlorate. Manufacturers also add the chemical to some food packaging. Why? Perchlorate controls static electricity. So spraying it onto paper, cardboard and plastic containers can keep crumbs and bits of food from clinging.

The problem is that some of that perchlorate can rub off. And it can get into the food we eat, explains Tom Zoeller. He works at the University of Massachusetts in Amherst. There he studies how chemicals can block the production or action of thyroid hormones. He wasn’t involved in the new research.

Hormones are major players in the body’s endocrine (EN-doh-krin) system. But pollutants can mess with them. Because of that, such pollutant chemicals are known as endocrine disruptors. They can cause problems in people and animals.

“It’s hard to find a bodily function that isn’t influenced by thyroid hormone,” says Leonardo Trasande. He’s a pediatrician at New York University in New York City. He studies how pollution in the environment can affect a child’s health.

Past research had suggested that in people, perchlorate might be linked to lower-than-normal levels of the thyroid hormone known as thyroxine (Thy-ROX-een). So Trasande led a group of researchers to see if his team could predict a person’s tthyroxine levels based on how much perchlorate was in their body.

And they could, they reported April 20 in the Journal of Clinical Endocrinology & Metabolism. What’s more, their data show for the first time that teens may be especially vulnerable to the pollutant’s effects.

What they did

Trasande’s team had a hunch perchlorate could mess with the thyroid. That’s because the chemical blocks this gland's uptake of iodine. This chemical element is an important component of a healthy diet. It occurs naturally in some foods. Iodine is also added to table salt. That’s fortunate, because without it the thyroid cannot make thyroxine.

food packaging
Perchlorate is a chemical used to prevent static electricity. Sometimes it’s added to food packaging so crumbs won’t stick.
Picsfive/iStockphoto

To probe a possible link between perchlorate and thyroxine, the researchers analyzed urine samples. How much of the pollutant is found in a person’s pee can give scientists a measure of their exposure to perchlorate. The urine came from more than 3,000 people across the United States, all between 12 and 80 years old. The researchers compared the perchlorate levels of urine to the amount of thyroxine in each person’s blood.

The researchers also measured two other chemicals that can block the body’s use of iodine. These were thiocyanate (THY-oh-SY-uh-nayt) and nitrate. Cigarette smoke contains high amounts of thiocyanate. Nitrate is in many plant fertilizers. Each of these chemicals can enter the body through air, water or food.

People exposed to the most perchlorate had about 4 percent less thyroxine in their blood than did people exposed to the least perchlorate. Adolescent girls who were exposed to the most perchlorate saw an even bigger thyroid hormone drop. They had about 8 percent less thyroxine than did people with low perchlorate exposures.

That’s important because people between the ages of 12 and 21 showed the highest exposure to perchlorate. The researchers don’t know why. It might simply be that growing kids eat a lot. “We know adolescents eat more food per body weight than adults,” says Trasande. And, he adds, “Food contamination is a major route of exposure.”

The researchers didn’t measure perchlorate in foods for this study. They also didn’t survey what each of the recruits typically ate. That may be part of some follow-up work.

What it means

Trasande calls his team’s new findings “concerning.” Puberty is a really important period of growth and development.

And, adds Zoeller, “The human body is especially vulnerable to hormonal disruption during periods of rapid change.” Puberty is one of those periods. Kids typically experience their final growth spurt at this time. It’s also when their reproductive organs mature. At the same time, their brains are rewiring themselves to an adult configuration. Thyroxine plays a role in all of these processes.

It’s not clear what the new perchlorate findings mean for thyroid health, says Zoeller. “We don’t know if teens with lower thyroid-hormone levels experience any kind of negative long-term health impacts.”

That’s why he argues that more research and longer-term studies are needed. Researchers need to better understand the relationship between levels of thyroxine and health in pre-teens and teens.

Until then, there are steps teens can take to limit any effects of perchlorate.

They should make sure their diet contains iodine, says Zoeller. Getting enough of it may help counter any iodine-blocking effects of perchlorate and other chemicals. Seafood, dairy products and eggs contain a lot of iodine. Iodized salt — table salt treated with added iodine — does too.

Finally, avoiding packaged foods when possible might also help reduce perchlorate exposures, says Trasande. Indeed, he says, “It may be one more good reason to maintain a healthy diet full of fresh and non-processed foods.”

Power Words

(for more about Power Words, click here)

adolescent     A transitional stage of physical and psychological development that begins at the onset of puberty, typically between the ages of 11 and 13, and ends with adulthood.

cell     The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Some organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O.

clinical     (in medicine) A term that refers to diagnoses, treatments or experiments involving people.

component     An item that is part of something else.

dairy     Containing milk or having to do with milk. 

development     (in biology) The growth of an organism from conception through adulthood, often undergoing changes in chemistry, size and sometimes even shape.

diet     The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health.

electricity     A flow of charge, usually from the movement of negatively charged particles, called electrons.

element     (in chemistry) Each of more than one hundred substances for which the smallest unit of each is a single atom. Examples include hydrogen, oxygen, carbon, lithium and uranium.

endocrine disruptor     A substance that mimics the action (sometimes well, sometimes poorly) of one of the body’s natural hormones. By doing this, the fake hormone can inappropriately turn on, speed up or shut down important cellular processes.

gland     A cell, a group of cells or an organ that produces and discharges a substance (or “secretion”) for use elsewhere in the body or in a body cavity, or for elimination from the body.

hormone     (in zoology and medicine) A chemical produced in a gland and then carried in the bloodstream to another part of the body. Hormones control many important body activities, such as growth. Hormones act by triggering or regulating chemical reactions in the body.

iodine      An element needed for the thyroid to produce the hormone used in growth, development and more. Some foods naturally have plenty. Others, principally table salt, may be fortified with this nutrient.

mature     (noun) An adult individual. (verb) The process of growth and development that occurs as an individual moves toward adulthood.

nitrate     An ion formed by the combination of a nitrogen atom bound to three oxygen atoms. The term is also used as a general name for any of various related compounds formed by the combination of such atoms.

organ     (in biology) Various parts of an organism that perform one or more particular functions. For instance, an ovary is an organ that makes eggs, the brain is an organ that makes sense of nerve signals and a plant’s roots are organs that take in nutrients and moisture.

pediatrician     A field of medicine that has to do with children and especially child health. A doctor who works in this field is known as a pediatrician.

perchlorate     This naturally occurring chemical is a potentially cancer-causing component of certain jet fuels, explosives and fertilizers. In animals, this pollutant can perturb levels of thyroid hormones. It also appears capable of acting like an androgen (a male sex hormone).

pollutant     A substance that taints something — such as the air, water, our bodies or products. Some pollutants are chemicals, such as pesticides. Others may be radiation, including excess heat or light. Even weeds and other invasive species can be considered a type of biological pollution.

processed foods     Foods purchased from a grocery story that are substantially different from the raw materials that went into them. Examples include most foods that come in cans, bottles, boxes or bags. Examples include breakfast cereals, frozen pizzas, canned tuna, jars of spaghetti sauce and dill pickles.

puberty     A developmental period in humans and other primates when the body undergoes hormonal changes that will result in the maturation of reproductive organs.

recruit     (in research) New member of a group or human trial, or to enroll a new member into a research trial. Some may receive money or other compensation for their participation, particularly if they enter the trial healthy.

reproductive organs     The organs in a creature’s body that allows it to make and deliver eggs or sperm, and where appropriate, to nurture developing eggs and fetuses.

smoke     Plumes of microscopic particles that float in the air. They can be comprised of anything very small. But the best known types are pollutants created by the incomplete burning of oil, wood and other carbon-based materials.

static electricity     The buildup of excess electric charge on some surface instead of flowing through a material. This charge buildup tends to develop when two things that are not good conductors of electricity rub together. This allows electrons from one of the objects to be picked up and collected by the other.

survey     (v.) To ask questions that glean data on the opinions, practices (such as dining or sleeping habits), knowledge or skills of a broad range of people. Researchers select the number and types of people questioned in hopes that the answers these individuals give will be representative of others who are their age, belong to the same ethnic group or live in the same region. (n.) The list of questions that will be offered to glean those data.

thyroid     A gland in the neck that releases hormones, which play a pivotal role in directing development and metabolism (the use of food as fuel). The gland is relatively small, with two lobes separated by a bridge-like structure. Some therefore refer to its shape as resembling a butterfly.

thyroxine    Also known as T4, it's a hormone made by the thyroid gland. This hormone plays a pivotal role in the growth and development of many organisms, including humans.

Citation

Journal: J. McMullen et al. Identifying subpopulations vulnerable to the thyroid-blocking effects of perchlorate and thiocyanate. The Journal of Clinical Endocrinology & Metabolism. Posted online April 20, 2017. doi:10.1210/jc.2017-00046.