Hormone-impairing substances make daughters fat
Pregnant women with high levels of hormone-impairing substances in their blood have a three times higher risk than other women of giving birth to daughters who will be overweight at the age of 20.
Wrong eating habits and too little exercise are usually blamed for the growth in numbers of overweight children and adults over the past decades. But they may not be the only cause of the current obesity epidemic.
A new study strongly suggests that increasing levels of perfluorooctanoate (or perfluorooctanoic acid, PFOA – see Factbox) in the environment can be a contributory factor to obesity. PFOA, which has a number of hormonal effects, persists indefinitely in the environment and has been found in low levels in the blood of a large part of the US population.
The results of the new study are very similar to results from other studies showing that mouse embryos exposed to PFOA had a higher risk of becoming obese later in their lives.
“There seems to be a relatively strong connection between the amount of PFOA in the blood of pregnant women and increased body mass index (BMI) and waist measurement in their daughters 20 years later,” says Thorhallur I. Halldorsson. A PhD in public health, Halldorsson is an associate professor at the Centre for Fetal Programming at the State Serum Institute (SSI) in Copenhagen; he is also affiliated with the Unit for Nutrition Research, Faculty of Food Science and Nutrition at the University of Iceland in Reykjavik.
PFOA belongs to a group pf hormone-impairing substances known as per- and polyfluorinated compounds (PFCs).
Many PFCs are non-degradable and are considered as pollutants in the environment as they can damage living organisms.
These substances are nevertheless used in many different products and industrial processes, such as surface treating and water- and fire-proofing various materials.
Food is the largest source of hormone-impairing substances for most people, but the indoor environment is also important.
PFCs are also transferred from mother to child through the placenta during pregnancy, and through the mother’s milk after birth.
“In fact, the risk of overweight in daughters seems to be tripled if the mother had a high level of PFOA in her blood during pregnancy,” he adds.
Twenty-year-old blood samples
Halldorsson and his colleagues measured the PFOA level in blood samples from about 1,000 pregnant Danish women. The samples came from another study from 1988-1989, taken when the women were in the 30th week of pregnancy, and then frozen.
The PFOA measurements were correlated with other measurements, from 2008-2009, taken of the 20-year-old children of the women sampled in 1988-1989. Some 650 of the offspring agreed to participate in the follow-up study, with 420 taking part in clinical examinations, while the rest answered questionnaires.
The researchers registered the BMI and waist measurements of the young people and correlated these data with the respective mother’s PFOA level.
Body Mass Index (BMI) is the official method of estimating overweight and underweight.
BMI is defined as the individual's body weight divided by the square of their height.
35+: Severely obese
A person’s BMI score is an indication of the relationship between height and weight, and doesn’t say anything about how much of the weight comes from fat and how much from muscle.
Factors such as the mother’s weight and level of education, as well as whether she smoked during the pregnancy, were taken into consideration. But the calculations were not adjusted for the offspring’s lifestyle factors, as the researchers saw no relationship between the children’s behaviour and their mothers’ PFOA levels 20 years earlier.
High level of PFOA increased BMI
The correlation of PFOA levels in the blood of the mothers with data from the 20-year-old offspring showed that:
- On average, three times as many daughters of mothers with the highest concentrations of PFOA in their blood during pregnancy were overweight compared with daughters of mothers with the lowest PFOA levels.
- The BMI of daughters of mothers with the highest concentrations of PFOA in the blood during pregnancy rose on average 1.6 kg/m2 and their waist circumference was 4.3 cm greater on average.
- There was no risk of developing obesity among the sons of mothers with a high PFOA level.
Only daughters affected
As in the study with mice, it was only the female offspring whose BMI and waist measurement were affected by the mothers’ PFOA level. Halldorsson offers a couple of explanations:
“We know from other studies that hormone-impairing substances work differently in the two genders, and the one gender is often affected more than the other,” he says. “We don’t know why that is. But in our study the difference can be due to the age of the subjects: biologically, boys and girls are at different stages of development when they are 20 years old.”
Higher insulin level as well
Halldorsson and his colleagues also found a relationship between a high PFOA level in pregnant women and a higher level of insulin and leptin – hormones that are associated with obesity – in the blood of the offspring. This applied to boys as well as girls, although the level in boys was somewhat lower.
“Finding higher levels of insulin and leptin was interesting, as they underline what the BMI tells us – but they can be a more certain indicator that a higher level of PFOA leads to obesity,” says Halldorsson. “The insulin and leptin levels rise as the fat depots increase, while the BMI index is calculated on the basis of body weight.”
Further studies needed
The study conducted by Halldorsson and his colleagues indicates that hormone-impairing substances play a role in the obesity epidemic – and that they may have other negative effects than previously thought.
“We have suspected for a long time that hormone-impairing substances damage the health, but there’s a need for further studies to determine the magnitude of this problem,” says the researcher.
“Our study and the mice trials show a correlation between PFOA levels and obesity, but we still need to determine the concentration levels more precisely.”
Translated by: Michael de Laine
- Prenatal Exposure to Perfluorooctanoate and Risk of Overweight at 20 Years of Age: A Prospective Cohort Study, Environmental Health Perspectives, doi.org/10.1289/ehp.1104034
- Phenotypic dichotomy following developmental exposure to perfluorooctanoic acid (PFOA) in female CD-1 mice: Low doses induce elevated serum leptin and insulin, and overweight in mid-life, Molecular and Cellular Endocrinology, doi.org/10.1016/j.mce.2009.02