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Does eating liquorice in pregnancy raise the risk of ADHD?

3:45pm Monday 6th February 2017 content supplied byNHS Choices

"Avoid liquorice while pregnant: Scientists find one of its ingredients can affect a child's IQ, memory and even cause ADHD," the Mail Online reports.

Researchers found eating liquorice in pregnancy is linked to a range of developmental issues.

The news is based on Finnish research on almost 400 young adolescents with an average age of 12.5.

Liquorice consumption is thought to be higher in Finland than in the UK thanks to the popularity of salmiakki, a popular salty liquorice snack.

Researchers found girls whose mothers had consumed high amounts of liquorice during pregnancy were more likely to go through puberty at a younger age.

And girls and boys whose mothers consumed high amounts scored seven points lower on intelligence tests, and higher for attention deficit hyperactivity disorder (ADHD).

But, as with many other diet studies, the picture is too complex for us to assume a direct cause and effect relationship.

The component in liquorice thought to cause damage is called glycyrrhizin. But it's also found in a range of other foods, drinks and medicines.

Only liquorice intake was measured in the study, so the actual level of glycyrrhizin the women ate is merely an estimate.

Many other factors influence cognitive development, and it's not clear if the researchers fully adjusted for all possible factors.

There are currently no UK guidelines suggesting pregnant women should avoid all liquorice.

But, as a precaution, it's advised pregnant women avoid the herbal remedy liquorice root, as it has a particularly high concentration of glycyrrhizin.

Where did the story come from?

The study was carried out by researchers from the University of Helsinki in Finland.

It was funded by a range of academic and governmental institutions, including the Academy of Finland, the National Doctoral Programme of Psychology, and the Finnish Ministry of Education and Culture. The sponsor had no role in the study design.

The study was published in the peer-reviewed American Journal of Epidemiology on an open access basis, so it's free to read online. The authors declared no conflicts of interest.

The Mail generally covered the study accurately, acknowledging that the results need to be interpreted with caution as researchers "said it was impossible to say whether it was directly responsible for the development of a child".

But, as is so often the case, the headline let the story down with the unproven statement that, "Scientists find one of its [liquorice's] ingredients [glycyrrhizin] can affect a child's IQ, memory and even cause ADHD".

What kind of research was this?

This was a longitudinal cohort study of Finnish mothers and children.

The study previously looked at the children when they were eight years old and found those whose mothers reported high liquorice consumption during pregnancy scored lower on tests of intelligence and memory, and had a higher risk of behavioural problems.

The researchers aimed to follow up on this cohort of children again, now with a mean age of 12.5 years, to explore associations with puberty maturation and cognitive and behavioural factors.

A cohort study can show links between factors - in this case, liquorice consumption in pregnancy and later outcomes in childhood and adolescence - but cannot show that one factor causes another.

What did the research involve?

The study looked at 378 children born in 1998, now with a mean age of 12.5 years, whose mothers had either consumed large amounts of glycyrrhizin, a natural constituent of liquorice, of more than 500mg a week, or a low amount of less than 249mg a week.

While on the maternity ward, mothers reported the brand and how much liquorice they ate on a weekly basis during pregnancy. The researchers used this amount to calculate the quantity of glycyrrhizin consumed a week in mg.

Of the 378 children, 327 children were exposed to low amounts of glycyrrhizin in the womb and 51 were exposed to high amounts.

At follow-up, children were assessed for:

  • stages and signs of puberty, based on three measures of growth and development - this included height, weight, body mass index (BMI) for age, and the difference between current and expected adult height; the researchers also looked at Tanner staging for pubertal stage and the Pubertal Development Scale, both well-validated ways of measuring pubertal development
  • cognition - based on tests of intelligence, memory and learning, social perception, attention and executive function
  • psychiatric problems - based on their mother's completion of the Child Behaviour Checklist
  • neuroendocrine function - studying how hormones like cortisol could affect the function of the nervous system and, in turn, other functions, such as the metabolism

Confounding variables were adjusted for, including:

  • child's age
  • educational level of either parent
  • maternal age and BMI
  • maternal smoking and alcohol intake
  • coffee, tea and chocolate consumption
  • stress during pregnancy

What were the basic results?

Girls whose mothers consumed high amounts of liquorice during pregnancy, compared with those whose mothers consumed low amounts:

  • were 3cm taller on average (mean difference [MD] 0.4 standard deviations [SD], 95% confidence interval [CI] 0.1 to 0.8)
  • were 8kg heavier on average (MD 0.6 SD, 95% CI 0.2 to 1.9)
  • had BMIs 2.2 higher (MD 0.6 SD, 95% CI 0.2 to 0.9)
  • 37.9% scored "development definitely under way" on the Pubertal Development Scale Score, compared with 10.4%

For boys, there were no consistent associations between maternal liquorice consumption during pregnancy and pubertal maturation at this age.

Girls and boys whose mothers consumed high amounts of liquorice during pregnancy, compared with those whose mothers consumed low amounts:

  • scored seven points lower on tests of intelligence quotient on a scale of 100 points (95% CI 3.1 to 11.2)
  • had threefold greater odds of attention deficit hyperactivity disorder (ADHD) problems (95% CI 1.4 to 7.7)

No difference was found in cortisol levels.

How did the researchers interpret the results?

The authors concluded that, "Nutritional recommendations of various expert organisations do not mention glycyrrhizin use during pregnancy.

"The present findings suggest that pregnant women should be informed that consumption of liquorice and other food products containing glycyrrhizin may be associated with harm for their developing offspring." 

Conclusion

This study provides evidence of some link between how much liquorice a pregnant woman eats and earlier puberty in girls, but not boys.

It also shows some association between pregnant women eating liquorice and their children scoring lower for intelligence and being more likely to have ADHD.

However, this study has some limitations to consider:

  • Glycyrrhizin is found in other food products, such as chewing gum, sweets, cookies, ice creams, herbal teas, and herbal and traditional medicines, as well as alcoholic and non-alcoholic drinks.
  • The amount of these products the women ate was not reported, which means their intake of glycyrrhizin may not have been measured accurately.
  • Although the study accounted for some confounding variables, there are other factors that might have affected the results that were not reported - for example, income or social class.
  • The study was carried out on healthy babies all born in Helsinki, Finland. People in this region may consume larger amounts of liquorice than people in other countries, especially a salty liquorice called salmiakki, so the results may not be generalisable to women in the UK or elsewhere.
  • There were only 51 children in the group who had mothers who consumed large amounts of liquorice. This is a fairly low number, and a bigger study may have shown less difference between the groups.

There are currently no UK guidelines suggesting pregnant women should avoid all liquorice.

But, as a precaution, it's advised they avoid the herbal remedy liquorice root, as it contains high levels of the active ingredient glycyrrhizin.

There's also evidence that all people - not just pregnant women - should avoid regularly eating very high levels of liquorice of more than 57g (two ounces) a day for more than two weeks as this could lead to potentially serious health problems, such as increased blood pressure and an irregular heart rhythm (arrhythmia).

Read more advice about healthy eating in pregnancy and what foods to avoid in pregnancy.  

Summary

"Avoid liquorice while pregnant: Scientists find one of its ingredients can affect a child's IQ, memory and even cause ADHD," the Mail Online reports. Researchers found eating liquorice in pregnancy is linked to a range of developmental issues.

Links to Headlines

Avoid liquorice while pregnant: Scientists find one of its ingredients can affect a child's IQ, memory and even cause ADHD. Mail Online, February 3 2017

Links to Science

Räikkönen K, Martikainen S, Pesonen A, et al. Maternal Licorice Consumption During Pregnancy and Pubertal, Cognitive, and Psychiatric Outcomes in Children. American Journal of Epidemiology. Published online February 3 2017

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