If your father was overweight during puberty, your risk of developing asthma doubles
If a father is overweight during his adolescence, his future children have a more than doubled risk of having asthma, a large generational study shows.
People who are overweight are known to have an increased risk of asthma. Now, researchers have looked at the relationship between parental overweight and the prevalence of asthma and allergies in their children.
"Little is known about how being overweight affects the next generation, so we wanted to look into this," says Ane Johannessen, the lead researcher behind the new study. Johannessen is an epidemiologist and associate professor at the University of Bergen (UiB).
The researchers looked at parents’ who were overweight during childhood, adolescence and as adults. The incidence of asthma in their children was measured after the children themselves became adults.
The results were striking for one factor in particular: researchers found a strong correlation between a father’s being overweight at puberty, and an increased prevalence of asthma in his offspring. Children of a father who had been overweight at puberty were more than twice as likely to have asthma as children of a father who had normal weight during puberty.
“We were surprised that the connection was so strong. In fact, the risk of the child developing asthma is greater if the father was overweight as a youth than if children themselves are overweight,” Johannessen says.
Can leave epigenetic traces
But how can a father's weight, long before conception, affect his child?
“In the past, research has tended to focus on what we have been exposed to early in life and how it affects our health when we grow up. However, we are increasingly discovering that it may be important to look even further back in time. The lives our parents lived can leave epigenetic traces, which in turn can affect their descendants,” says Marianne Lønnebotn, a midwife and PhD candidate at UiB who was a co-researcher on the study.
Epigenetics relates to how inheritance and the environment shape our gene expression, but without changing our DNA.
“Many important processes take place in our germ cells during puberty, and these processes may be more influential during this period. It is conceivable that the germ cells are affected by a father being overweight, especially during puberty,” Lønnebotn says.
The finding that the greatest risk is found in fathers and during puberty is in keeping with an earlier study from the project. This study showed that the risk of asthma in children is higher if fathers started smoking before the age of 15.
Boys most at risk
The researchers also looked at the father's weight as a child and as an adult, and the mother's weight during these same periods, but did not find any connection between being overweight and children's risk of asthma.
Johannessen said researchers also looked at other factors that might explain the finding that a father’s being overweight during puberty has such a strong effect on his offspring.
“It’s possible to think that the family has genes that predispose them to both obesity and asthma. But we have collaborated with statisticians who have done sophisticated analyses that can actually separate these factors from one another— and it appears that a father being overweight at puberty is the cause,” she said.
She said that researchers only saw an increased incidence of asthma without allergies when a father was overweight at puberty. They did not find an association between asthma with allergies and being overweight.
More focus on young boys' health
The researchers believe the study shows that society should increase its focus on young people's health.
“So far, researchers haven’t focused on how important the health of boys and men is to their future children. There should be more attention paid to this, especially when it comes to boys at puberty, which is clearly a vulnerable phase. Some of the things that can be done are providing healthy food at school, more focus on physical activity both at school and during free time, a strengthened school health service and facilitating walking and cycling paths,” Lønnebotn said.
The data that provided the starting point for the study comes from RHINESSA, a generational study led by Cecilie Svanes, a professor at the University of Bergen.
The focus of the RHINESSA study has been lung health over generations. The project includes participants from Norway, Sweden, Denmark, Iceland, Estonia, Spain and Australia. More than 2,000 fathers and 2,500 mothers have participated, along with more than 6,000 of their descendants.
“We rarely have studies where we follow people for as long as this, which provides us a lot of opportunities,” Johannessen says.
A number of studies are currently underway based on data from RHINESSA.
Questions the accuracy of the method
Rønnaug Ødegård is senior consultant at the Regional Centre for Obesity Research and Innovation at St. Olavs Hospital. She says the new study is interesting and thorough, but believes there are questions related to how the findings have been interpreted.
“The researchers have as their starting point the fact that the mothers and fathers themselves defined their weight status when they were children, at puberty, and adults, by choosing from images of increasingly larger body silhouettes. I think this is a dicey way to define obesity. This does not mean that the results of the study are incorrect, but that the method is inaccurate, which makes the study more susceptible to random findings,” Ødegård said.
She points out that all types of exposures during our lives can affect epigenetic mechanisms.
“So I think it's not unlikely that being overweight at puberty can have consequences for asthma in that person’s children. What I have more doubts about is that a mother being overweight doesn’t matter. This may be related to the inaccurate method the researchers used to define being overweight,” Ødegård said.
While the new study suggests that the mother’s weight plays no role in her child’s asthma risk, the Danish Mother and Child Study found a connection between a mother's BMI very early in pregnancy and asthma in the child, she said.
“For me, it would have strengthened this study's results if researchers had found some of the same effects as the Danish study,” Ødegård said.
Genetics can also contribute
She notes that the researchers used advanced epidemiological statistics, where they made a strong effort to show a causal link between children's asthma and the father's being overweight at puberty.
“Nevertheless, this is an interpretation, and it cannot be excluded that shared genetics and / or a common environment may also have contributed to the results,” she said. “Dad is likely to have a genetic predisposition to obesity if he is overweight at the time when his voice changes — which is an age where boys often shoot up in height and are quite slim.”
People who are overweight have an increased risk of asthma, and it is thought to be contingent on a common genetic cause of the two diseases, she said.
"When a father has a likely genetic predisposition to obesity, it is not unlikely that he also has a predisposition to asthma — which his offspring inherit," she said.
She thinks the most interesting thing about the study is that it reinforces the importance of the father's biology in the development of his children's health.
“We already know that the mother is important, including through the Danish Mother and Child Study. But it is very likely that father is also important, as this study suggests. In addition, the study strengthens the link between being overweight and asthma,” she said.
Marianne Lønnebotn said that the findings from the new study supplement findings from the Danish Mother and Child Survey, and don’t necessarily contradict them.
“We have not analysed the effect of a mother being overweight during pregnancy, which means it’s not true that the mother is acquitted of contributing to asthma risk in our study. We are only looking at a mother being overweight before pregnancy, and not during pregnancy,” Lønnebotn said.
Ane Johannessen et al: “Overweight in childhood, puberty or early adulthood: changing the asthma risk in the next generation?”, Journal of Allergy and Clinical Immunology, September 2019. doi: 10.1016/j.jaci.2019.08.030