Teenagers who are either underweight or obese are likely to have fewer children in adulthood, a study has found.
It’s known that both obesity and abnormally low body weight are related to reproductive difficulties, and that obesity raises the risk of a number of pregnancy complications. However, it has not been clear whether underweight and obese teenagers go on to have fewer children than their normal-weight peers.
For the new study, researchers used data on nearly 1,300 Finnish men and women who were part of a larger study that has tracked their health since 1980. All were between the ages of 3 and 18 at the study’s outset, and had their body mass index (BMI) measured in adolescence.
The researchers report the findings in the medical journal Epidemiology. Overall, adults who had been underweight as teenagers had 10 percent to 16 percent fewer children, compared with those who had a normal BMI in adolescence. Men and women who’d been obese as teens had 32 percent to 38 percent fewer children.
“We know a lot about (the) correlation between BMI and fertility in adulthood,” study co-author Dr. Liisa Keltikangas-Jarvinen, of the University of Helsinki, told Reuters Health.
In this study, she explained, there was a long-term effect of teenage BMI, independent of adulthood BMI. This was particularly true of women.
For women, an abnormally low BMI can disrupt the menstrual cycle, while obesity can lead to fertility problems. Obesity can, for example, contribute to polycystic ovary syndrome, a cause of infertility.
A man’s reproductive health can also be affected by weight. Both obesity and a low BMI have been linked to poor sperm quality, and obesity can raise the risk of erectile dysfunction.
In this study, underweight and obese teenagers were also less likely than their normal-weight peers to live with a partner in adulthood — a difference that partially explained why they had fewer children.
Given the increase in obesity rates around the world, the researchers note, the current findings suggest there could be widespread effects on adults’ reproductive health.
In particular, Keltikangas-Jarvinen said, the results ”stress” the potential long-term effects of obesity at a young age — offering one more reason to prevent excessive weight gain in childhood.