Over the past two decades, the share of children with defective tooth enamel has been rising. And BPA, a chemical used to make many plastics, could be partly to blame. That’s the finding of a new study in rats. It showed that this pollutant can trigger the same problem in lab animals that had been showing up in the kids.
Enamel is the hard substance that covers a tooth. If it does not form properly, a child can develop cavities and other problems. A dentist can repair these defects. But there is no way to fix the altered gene instructions responsible for making the enamel weak in the first place.
This enamel defect “now affects 15 to 20 percent of children six to nine years old,” says Sylvie Babajko. She is a molecular biologist at INSERM. It’s the National Institute for Health and Medical Research in Paris, France. This defect affects different numbers of children in different places. In some parts of the world, as many as 40 percent of children may have this weakened enamel, she notes. But where it’s been studied well, about 1 in 6 kids (18 percent) are affected.
Babajko, Katia Jedeon and their team are studying this failure of kids’ tooth enamel to form correctly. The problem affects both molars and incisors (teeth in both the back and front of the mouth). The teeth end up with white milky spots. They are caused when the mineral structure of the teeth develop weakened regions. These are defects.
The problem develops when teeth are first forming, Babajko notes.
The problem is not new. But it has been showing up in more and more kids. And the increase emerged at the same time as did other health problems linked to a specific group of chemicals, she notes. Such chemicals are known as endocrine disruptors.
In their new study, the researchers traced the weakened enamel in their rats to pollution-altered genes. Those genes instruct cells on how to build a tooth. Babajko’s group reported its findings on May 31 at the 18th Congress of European Endocrinology. It was held in Munich, Germany.
Confusing the body’s hormone system
Hormones are part of the body’s endocrine (EN-doh-krin) system. They control the timing of pivotal actions — from how organs form and how cells use energy to how the brain works and how the body prepares for reproduction. In some cases, pollutants can block or slow the action of hormones. Other times, these pollutants can masquerade as hormones. Either way, these endocrine disruptors can do a lot of damage by throwing off the timing of when the body turns important actions on or off.
Two types of hormones — estrogens and androgens — play a role in directing the cells that make tooth enamel. Estrogens are known as female sex hormones. Androgens are male sex hormones. Both types of hormones play important roles in how the bodies of all young mammals develop. Their effects start in the womb and continue on through puberty and adulthood.
Over the past few years, Jedeon and her colleagues found evidence that two pollutants could promote defects in enamel. Both were androgen disruptors.
One chemical was vinclozolin (Vin-KLOH-zuh-lin), a fungi-killing chemical. It can block the action of the androgen known as testosterone. But aside from farm workers, most people don’t encounter this chemical.
The other pollutant, BPA, is far more common. Short for bisphenol (Bis-FEE-nawl) A, this chemical can mimic the action of estrogen. It also can disrupt the action of testosterone. Manufacturers use BPA to make everything from eyeglasses and kitchen bowls to dental sealants. A coating on many papers, BPA rubs onto hands from the paper used to print many store receipts. BPA also coats the inside of many food and drink cans and jar lids. Some 16,000 different food and drink products use BPA in their packaging. Most people have broad exposure to this chemical.
Although the INSERM studies had linked exposures to both chemicals with impaired enamel formation, the researchers did not know precisely what was going wrong. So for their latest study, they decided to home in on genes of enamel-making cells.
Of genes and androgens
Kids may be most vulnerable to BPA very early in life, Babajko says. This would be from when their baby teeth first begin to form until about age four or five. So for its new study, Babajko’s team exposed pregnant rats to either BPA or vinclozolin. Once the babies were born, those pups were exposed for another month. The researchers then examined cells and their genes in those pups.
BPA and vinclozolin both altered a small group of genes, the data show. These genes are directly involved in the enamel-making of teeth. What’s more, these genes are especially vulnerable to changes in androgens. As a result, Babajko now concludes, BPA and such androgen-disrupting chemicals may be “leading to the weakening of enamel quality.”
The results also suggest these tooth defects could be used as a signal that a child has been exposed to a hormone-disrupting chemical, she adds.
Many cells and body parts that these chemicals might affect have not yet been studied, says Andrea Gore. This is because they’re not usually considered to be part of the endocrine system, she explains. Gore is an endocrine expert at the University of Texas at Austin. The new study, she says, suggests that hormone-disrupting chemicals may be affecting parts of the body that have not yet been studied for these effects.
“Teeth certainly fall into that category,” she says. If tooth development involves these hormones, then they may be vulnerable to impacts from chemicals like BPA, she says.
Frederick vom Saal studies hormone-mimicking pollutants such as BPA at the University of Missouri in Columbia. Androgens and estrogens are involved in how the body uses calcium to make bone, he explains. Similar processes are involved in producing tooth enamel. So it is possible that a hormone-disrupting chemical such as BPA could disrupt enamel-making in teeth. And the cells Babajko’s study examined do interact with such hormones, he adds.
“One of the things we know about these [hormones] is that they are involved in all kinds of stuff you wouldn’t necessarily expect,” says vom Saal. What’s more, these hormone-mimicking pollutants can affect people and lab animals in very similar ways. So, what was seen in this study could “point us to [the cause behind] something that is a significant public health issue for a substantial number of children,” he says.
It is not yet possible to know for sure if BPA is responsible for weakened tooth enamel and resulting cavities. But scientists say that there is enough evidence to make further research important.
(for more about Power Words, click here)
androgens A family of powerful male sex hormones that includes testosterone.
biology The study of living things. The scientists who study them are known as biologists.
bisphenol A (BPA) A building block of polycarbonate plastics and many commercially important resins. This chemical gained widespread public attention when research showed it could mimic the activity of estrogen, a female sex hormone.
cavity (in geology or physics) A large open region surrounded by tissues (in living organisms) or some rigid pocketlike structure. Or (in dentistry) a tiny hole in a tooth that develops over time. Cavities are more likely to happen when a person eats a lot of sugar or does not brush and floss regularly.
cell The smallest structural and functional unit of an organism. Typically too small to see with the naked eye, it consists of watery fluid surrounded by a membrane or wall. Animals are made of anywhere from thousands to trillions of cells, depending on their size. 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 (become bonded together) in a fixed proportion and structure. For example, water is a chemical made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O. Chemical can also be an adjective that describes properties of materials that are the result of various reactions between different compounds.
diabetes A disease where the body either makes too little of the hormone insulin (known as type 1 disease) or ignores the presence of too much insulin when it is present (known as type 2 diabetes).
enamel The glossy, hard substance that covers a tooth.
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.
endocrine system The hormones (chemicals secreted by the body) and the tissues in which they turn on (or off) cellular action. Medical doctors who study the role of hormones in health and disease are known as endocrinologists. So are the biologists who study hormone systems in non-human animals.
estrogen A type of hormone associated with the development of female characteristics.
gene (adj. genetic) A segment of DNA that codes, or holds instructions, for producing a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.
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. (in botany) A chemical that serves as a signaling compound that tells cells of a plant when and how to develop, or when to grow old and die.
incisor A type of narrow-edged tooth that is found at the front of the mouth and adapted for cutting. Humans have four of these teeth.
metabolism The set of life-sustaining chemical reactions that take place inside cells and bigger structures, such as organs. These reactions enable organisms to grow, reproduce, move and otherwise respond to their environments.
molar A type of grinding tooth found in the back of a the mouth of a mammal, such as a human.
molecular biology The branch of biology that deals with the structure and function of molecules essential to life. Scientists who work in this field are called molecular biologists.
obesity Extreme overweight. Obesity is associated with a wide range of health problems, including type 2 diabetes and high blood pressure.
pesticide A chemical or mix of compounds used to kill insects, rodents or other organisms harmful to cultivated plants, pet or livestock, or unwanted organisms that infest homes, offices, farm buildings and other protected structures.
plastic Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation.
testosterone Although known as a male sex hormone, females make this reproductive hormone as well (generally in small quantities). It gets its name from a combination of testis (the primary organ that makes it in males) and sterol, a term for some hormones. High concentrations of this hormone contribute to the greater size, musculature and aggressiveness typical of the males in many species (including humans).
Original Meeting Source: K. Jedeon et al. Systemic enamel pathologies may be due to anti-androgenic effects of some endocrine disruptors. European Congress of Endocrinology. May 31, 2016. Munich, Germany. Endocrine Abstracts, Vol. 41, May 2016.
Original Meeting Source: K. Jedeon et al. Bisphenol A affects amelogenesis by modulating enamel key genes expression. Endocrine Abstracts (2015) 37 GP08.06. doi:10.1530/endoabs.37.GP.08.06.
Original Meeting Source: K. Jedeon et al. Estrogen and bisphenol A affect enamel formation by different signaling pathways. Endocrine Abstracts (2014) 35 P509. doi:10.1530/endoabs.35.P509
Original Meeting Source: K. Jedeon et al. Hypomineralized teeth as biomarkers of exposure to endocrine disruptors. Endocrine Abstracts (2013) 32 OC2.6 doi:10.1530/endoabs.32.OC2.6.