Children of pregnant women smokers have more bone fractures at 5–14 years old

Diet and lifestyle 11. jan 2024 2 min Research Manager Eero Kajantie Written by Kristian Sjøgren

A new study shows that mothers smoking during pregnancy increase their children’s risk of having a broken bone at 5–14 years old. A researcher says that the reasons could be that the children of mothers who smoked during pregnancy have more fragile bones or that they are more willing to take risks and get more easily injured.

Mothers in Finland who smoked while pregnant had children with a slightly increased risk of bone fractures at 5–14 years old.

This is the conclusion of a new study in which researchers investigated the association between mothers’ smoking during pregnancy and children’s bone fractures.

“Our study suggests the need to further investigate why the children of mothers who smoked during pregnancy have an increased risk of bone fractures. These investigations will elucidate the connection, so that we can better understand how smoking during pregnancy affects the bone health of the unborn child,” explains a researcher behind the study, Eero Kajantie, Professor, Finnish Institute of Health and Welfare, Helsinki, Finland.

The research has been published in the Journal of Bone and Mineral Research.

Data on bone fractures for 220,699 children

The researchers reviewed registry data on 220,699 children born in Finland from 1 January 1987 to 30 September 1990.

The researchers used Finland’s health registries to identify the children who had hospital treatment for a bone fracture before the age of 15 years.

Then the researchers investigated whether the children of mothers who had smoked during pregnancy had a greater risk of bone fracture than the children of nonsmoking mothers.

To identify differences, the researchers divided the children into three age groups: 0–1 year, 1–4 years and 5–14 years.

In addition, the researchers adjusted their data for factors that could affect the risk of bone fractures. These included sex of the child, parity, child’s year of birth, mother’s age at childbirth, mother’s and father’s educational level and mother’s fracture status.

“Some previous studies have indicated that smoking during pregnancy increases the risk while others show that it does not increase the risk. This study is one of the largest of its type, and previous research shows that when mothers say that they smoked during pregnancy, it is usually correct,” says Eero Kajantie.

Increased risk of bone fractures among children 5–14 years old

The study found that 18,857 (8.5%) of the 220,699 children had at least one bone fracture before the age of 15 years.

The researchers found no statistically significant association between the mother’s smoking status during pregnancy and increased risk of bone fractures among children 0–1 year or 2–4 years old.

Conversely, for mothers who smoked during pregnancy, the risk of bone fracture increased among children 5–14 years old.

The researchers divided the fractures into three groups: all fractures, non-high-energy fractures (such as stress fractures) and high-energy fractures (such as from a fall).

Children whose mothers had smoked during pregnancy had an elevated risk of all three types of fractures.

The risk increased by 12% for all fractures, 13% for non-high-energy fractures and 15% for high-energy fractures.

“Since the risk of experiencing a fracture is relatively low, the increased risk is also very low and does not mean much for each individual. But for society, all mothers smoking during pregnancy versus none smoking during pregnancy would mean many more bone fractures among children. This makes determining the underlying mechanisms relevant,” explains Eero Kajantie.

Several possible explanations

Eero Kajantie says the association between a mother’s smoking during pregnancy and her child’s risk of bone fracture may have several explanations.

Smoking during pregnancy could affect the child’s bone development and could influence bone density or bone strength, with the child developing weaker bones that fracture more easily.

Another possibility is that smoking during pregnancy may affect the child’s behaviour in potentially high-risk situations.

For example, previous studies have shown that smoking may affect the child’s risk of developing attention-deficit/hyperactivity disorder (ADHD), and since ADHD is associated with more high-risk behaviour, mothers’ smoking could indirectly lead to more bone fractures.

The researchers aim to investigate whether the children of mothers who have smoked during pregnancy develop ADHD more often and thereby have more bone fractures.

Another possibility, according to Eero Kajantie, is to examine the bone density of the children of mothers who smoked during pregnancy to determine whether their bones are less strong than the children of nonsmokers and whether this could be the explanation.

“Another major study from Sweden found the same evidence as in our study. This confirms that there is an association, and learning more about this will be in society’s interest and not only contribute to fewer children having bone fractures but also elucidate the mechanisms behind the increased risk for bone fractures,” Eero Kajantie concludes.

I am a researcher in lifecourse health. I divide my time as a Research Manager at National Institute for Health and Welfare (THL) and Professor of Lif...

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