Animal studies have linked obesity and other health problems with exposure to bisphenol A (BPA). That’s a common ingredient of many clear, hard plastics and the resins that line food cans. Concerns over BPA health impacts led manufacturers to start phasing out the chemical in products that make contact with foods and drinks. Now a study in children and teens suggests that even some BPA substitutes may foster weight gain.
Those substitutes — BPS (bisphenol S) and BPF (bisphenol F) — are now used as a lining in some aluminum food cans. They’re also found in the paper used to print cash-register receipts.
Melanie Jacobson works in New York City at the New York University School of Medicine. Her team’s new study finds that overweight kids tend to have higher levels of BPS and BPF in their bodies than do normal-weight kids. That would suggest that like BPA, these chemicals are obesogens (Oh-BE-suh-genz).
The group described its findings on July 25 in the Journal of the Endocrine Society.
Some pollutants act like hormones
Hormones control many of the body’s activities. At least in animals, BPA can mimic estrogens, a type of hormone. In fact, animal studies had shown BPA could cause harm by interfering with the body’s natural hormones. The new data suggest some BPA substitutes also may be hormone mimics.
“It’s not surprising,” Bruce Blumberg says of the new findings. Previous research had linked BPA to obesity in both kids and adults. A cell biologist, Blumberg studies obesogens at the University of California in Irvine. He notes that a chemical’s structure, or shape, determines how it acts. And the chemical structures of both BPS and BPF, he notes, closely resemble that of BPA.
Exposure to obesogens “make us more likely to get fat than we otherwise would,” says Blumberg. Studies in rodents, he notes, show that BPA makes fat cells larger. That can encourage the body to store more food energy as fat.
Linking chemicals and obesity
BPS and BPF have been studied far less than BPA has, notes Jacobson. For its new study, her team tapped into data from a national survey. It’s part of ongoing research to track the health and nutrition of children and adults across the United States.
Jacobson’s team focused on data for 1,831 people. All were between the ages of 6 and 19. The measured data included each person’s weight, height and distance around the waist. People who are considered overweight have a higher weight and waist circumference than will others of their height.
The researchers used these data to compare each person’s body size. A normal body size for a 19-year-old girl is very different from that of a typical 6-year-old boy. So the researchers used a special calculation to adjust for age and sex. It “puts everyone on the same playing field,” explains Jacobson.
Her team then compared each kid’s body size to the amount of bisphenols in their urine. BPA turned up in the urine of nearly every kid and teen (97.5 percent). Roughly 88 percent of them also had BPS. About 55 percent had detectable BPF.
Young people with higher levels of BPS in their urine were 16 percent more likely to be obese than were kids with lower levels. And kids with higher levels of BPF were 29 percent more likely to have abdominal obesity than were those with lower levels. Abdominal obesity is a high ratio of waist circumference to height.
The researchers found no link between BPA and obesity in the new data.
“Our findings suggest that these newer chemicals also may be a factor in child obesity,” says Jacobson. What the findings don’t mean, however, is that these chemicals are making kids fat. The study shows a correlation — or link — between two things: chemicals and obesity. That’s different from saying one caused the other. Indeed, Jacobson says, “We don’t know whether the chemicals caused the obesity.”
The national survey data provided a snapshot of kids’ body sizes and chemical exposures from a single point in time. The researchers have no way of knowing which happened first — the chemical exposure or the obesity. Future studies could look to see whether bisphenol exposures lead to weight changes over time.
Scientists know that “a good diet and getting lots of exercise still are the most important things kids can do to maintain a healthy weight,” Jacobson says. Owing to her study’s new findings, she says kids may want to cut their exposures to BPS and BPF.
How? Avoid touching store receipts and eat fewer foods that come in cans, suggests Blumberg.
“Don’t microwave plastic food containers or put them in the dishwasher,” adds Jacobson. “When heated, [any bisphenols in them] are more likely to leach out into food and drink.”
aluminum A metallic element, the third most abundant in Earth’s crust. It is light and soft, and used in many items from bicycles to spacecraft.
biologist A scientist involved in the study of living things.
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.
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. Most 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. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
circumference The size of a circle or other geometric object by measuring the distance all of the way along its outer edge.
correlation A mutual relationship or connection between two variables. When there is a positive correlation, an increase in one variable is associated with an increase in the other. (For instance, scientists might correlate an increase in time spent watching TV with an increase in rates of obesity.) Where there is an inverse correlation, an increase in one value is associated with a drop in the other. (Scientists might correlate an increase in TV watching with a decrease in time spent exercising each week.) A correlation between two variables does not necessarily mean one is causing the other.
data Facts and/or statistics collected together for analysis but not necessarily organized in a way that gives them meaning.
diet The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health. (verb) To adopt a specific food-intake plan for the purpose of controlling body weight.
endocrine A term for the system of hormones (chemicals secreted by the body) and the tissues in which they turn various cellular actions on (or off). 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 The primary female sex hormone in most higher vertebrates, including mammals and birds. Early in development, it helps an organism develop the features typical of a female. Later, it helps a female’s body prepare to mate and reproduce.
factor Something that plays a role in a particular condition or event; a contributor.
fat A natural oily or greasy substance occurring in plants and in animal bodies, especially when deposited as a layer under the skin or around certain organs. Fat’s primary role is as an energy reserve. Fat also is a vital nutrient, though it can be harmful if consumed in excessive amounts.
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.
journal (in science) A publication in which scientists share their research findings with experts (and sometimes even the public).
leach (in geology and chemistry) The process by which water (often in the form of rain) removes soluble minerals or other chemicals from a solid, such as rock, or from sand, soil, bones, trash or ash.
link A connection between two people or things.
nutrition (adj. nutritious) The healthful components (nutrients) in the diet — such as proteins, fats, vitamins and minerals — that the body uses to grow and to fuel its processes. A scientist who works in this field is known as a nutritionist.
obese Extremely overweight. Obesity is associated with a wide range of health problems, including type 2 diabetes and high blood pressure.
obesity (adj. obese) Extreme overweight. Obesity is associated with a wide range of health problems, including type 2 diabetes and high blood pressure.
obesogens Any of a host of different chemicals in the environment — many of them industrial pollutants — that appear capable of signaling the body to fatten up.
overweight A medical condition where the body has accumulated too much body fat. People are not considered overweight if they weigh more than is normal for their age and height, but that extra weight comes from bone or muscle.
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.
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.
ratio The relationship between two numbers or amounts. When written out, the numbers usually are separated by a colon, such as a 50:50. That would mean that for every 50 units of one thing (on the left) there would also be 50 units of another thing (represented by the number on the right).
resin A sticky, sometimes aromatic substance, often secreted by plants. It may also be the viscous starting ingredient for some plastics that will harden when heated or treated with light.
rodent A mammal of the order Rodentia, a group that includes mice, rats, squirrels, guinea pigs, hamsters and porcupines.
sex An animal’s biological status, typically male or female. There are a number of indicators of biological sex, including sex chromosomes, gonads, internal reproductive organs, and external genitals. It can also be a term for some system of mating between male and female animals such that each parent organism contributes genes to the potential offspring, usually through the fertilization of an egg cell by a sperm cell.
survey To view, examine, measure or evaluate something, often land or broad aspects of a landscape. (with people) 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.