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Sugary fruit juices and drinks linked to childhood asthma

"Children who drink fruit juice have a higher risk of developing asthma," reports the Mail Online.

Researchers in the US say children whose mothers drank more sugary drinks while pregnant, and children who drink a lot of fruit juice in early childhood, are more likely to be diagnosed with asthma by mid-childhood (around age 7 to 8).

We know people who are overweight are more likely to have asthma, and sugary drinks can contribute to being overweight. 

But this study suggests the sugar contained in drinks (specifically fructose) may be contributing directly to the asthma risk. 

Previous studies have speculated that a high-fructose diet may contribute to inflammation of the airways and disrupt the normal immune response. 

The research is based on questionnaires filled in by 1,068 women, from early pregnancy until their child was aged around 7 or 8. 

Researchers found the children of women who drank more sugary drinks while pregnant were more likely to develop asthma later on. 

And children who consumed more fructose from sugary drinks in early childhood were also more likely to develop asthma later on. 

But drinking fruit juice alone didn't seem to be linked to asthma. 

On its own, this study isn't enough evidence to prove sugary drinks increase asthma risk. 

But it does make sense to limit children's intake of sugary drinks, particularly young children. 

While it may be tricky to convince them otherwise, especially at Christmas, plain water and milk are healthier options. 

Where did the story come from?

The researchers who carried out the study were from Brigham and Women's Hospital and Harvard Medical School in the US. 

The study was funded by the US National Institutes of Health and the United States Environmental Protection Agency. 

It was published in the peer-reviewed journal Annals of the American Thoracic Society. 

The Mail Online provided a reasonably balanced overview of the study, and discussed the limitations of the methods. 

But the article didn't point out that the analysis of fruit juice consumption alone (as opposed to total fructose from juice and sugar-sweetened drinks) for women in pregnancy or children didn't show a link with asthma. 

What kind of research was this?

This was a cohort study that followed a group of women and their children over time. 

Researchers wanted to see if diet during pregnancy, and the child's diet at a young age, was linked to their chances of having asthma. 

This type of study is the best way of looking at how diet or other lifestyle factors affect people's health. 

But people who have the behaviours of interest (in this case, drinking more sugary drinks) may also have other behaviours and characteristics that might influence their health (confounding factors). 

There are accepted methods to try to remove the impact of these other factors, but it's likely to be difficult to do this completely.

For this reason, a single study like this can't prove that one factor (such as sugary drinks containing fructose) is a direct cause of another (asthma). 

Researchers need to build a broader picture of supporting evidence from different types of studies before this is generally considered an accepted truth.

What did the research involve?

Researchers recruited more than 2,000 women in early pregnancy. They filled in questionnaires about their diet twice during pregnancy, then about their child's diet at ages 3 to 4. 

They then checked whether the children had been diagnosed with asthma at age 7 to 8. They had full data from 1,068 mother and child pairs. 

After adjusting their figures to take account of potential confounding factors, they looked at whether consumption of fruit juice, sugar-sweetened drinks, or total fructose intake (a type of sugar found in fruit juice and sugar-sweetened drinks) was related to the child's chances of having been diagnosed with asthma. 

The researchers focused on fructose as a study in mice suggested a diet high in fructose did have some effect on their lungs. 

The researchers assessed whether a child had asthma by asking whether the child had ever been diagnosed by a doctor as having the condition and was also either taking medication for the condition or had been wheezing in the past year.

The researchers used standard food frequency questionnaires to assess how many sugar-sweetened drinks, and how much fruit juice and fructose from juice and sugar-sweetened drinks, the women and children consumed. 

They took account of the following potentially confounding factors:

  • mothers' education (one way of measuring socioeconomic status) 
  • smoking during pregnancy
  • mothers' weight before pregnancy
  • household income
  • sex, age and ethnicity of the child

Some of the factors they thought might be important, such as whether the parents had asthma, didn't affect results, so they didn't take them into account.

For the analyses of children's diet, the researchers adjusted their figures to account for the mothers' sugary drink intake during pregnancy. 

They also looked at whether the children's body mass index (BMI) explained the results. 

What were the basic results?

Around 1 in 5 (19%) children had been diagnosed with asthma by the end of the study. 

The researchers found:

  • Women who drank sugar-sweetened drinks during pregnancy were likely to be less educated, younger and have a higher BMI. But this didn't explain away their results. 
  • After taking account of these factors, children of women who drank the most sugar-sweetened drinks during pregnancy had 70% higher odds of having asthma than children of women who drank little or none (odds ratio [OR] 1.70, 95% confidence interval [CI] 1.08 to 2.67). Women's total consumption of fructose in pregnancy showed a link to asthma in their children, but these links disappeared once other factors were taken into account.
  • Children's consumption of sugar-sweetened drinks (or fruit juice specifically) in early childhood wasn't linked to asthma. But children who had the highest total intake of fructose sugar from juice or sugar-sweetened drinks in early childhood had 79% higher odds of having asthma than children with the lowest total intake of fructose (OR 1.79, 95% CI 1.07 to 2.97). 

How did the researchers interpret the results?

The researchers said their findings "contribute to the literature that should be considered when developing recommendations regarding consumption and availability of these drinks during pregnancy and early childhood".

Conclusion

This study adds to previous research suggesting there may be a link between the high consumption of sugary drinks (or the sugar in these drinks) in pregnant women, or in early childhood, and asthma in later childhood. 

It doesn't prove these drinks cause asthma. 

We already know eating and drinking too much sugar (including in the form of sugary drinks) contributes to our risk of being overweight or obese, and being obese increases the chances of breathing problems like asthma. 

This study has explored whether they also might have a separate – direct – effect. 

It did find this might be a possibility, as taking account of children's and women's weight didn't explain away the association between sugary drinks and asthma.

But the study has some limitations: 

  • The main limitation is that there are likely to be other factors contributing to the results. The researchers did try to account for some factors, but there may be others. 
  • The results weren't entirely consistent. There was a link with mother's – but not children's – consumption of sugar-sweetened drinks, and a link with children's consumption of fructose that disappeared for mothers' consumption after adjustment for other factors. Also, the researchers noted that another study from Denmark didn't find a link between maternal sugar-sweetened drink consumption in pregnancy and a child's asthma, so not all the evidence is pointing in the same direction.
  • The study relies on women accurately reporting what they ate and drank during pregnancy and what their child ate and drank in early childhood. Their responses may have had some inaccuracies. 
  • The women and children were from relatively well-off, educated families, so the results might not apply to all sections of society. And the consumption of fruit juice alone didn't seem to affect asthma risk. 

The researchers will need to confirm their findings in other groups of people and get a better understanding of how fructose consumption might affect the lungs.

It's important to know it's not just artificially sweetened drinks such as cola, lemonade and sweetened fruit drinks that include a lot of sugar. 

Fruit juice is naturally very high in sugar, and drinking a lot of fruit juice can be bad for teeth, as well as increasing weight. 

Advice in the UK is to drink no more than one portion of fruit juice a day. 

But it makes sense to limit your or your child's intake of sugary drinks, including fruit juice. The best drinks for children are plain water and milk. 

Find out more about squash and fruit drinks for children.

Analysis by Bazian 
Edited by NHS Choices

Links to the headlines

Children who drink fruit juice have a higher risk of developing asthma

Mail Online, December 19 2017

Links to the science

Wright LS, Rifas-Shiman SL, Oken E, et al Prenatal and Early-Life Fructose, Fructose-Containing Beverages, and Mid-Childhood AsthmaAnnals of the American Thoracic Society. Published online December 8 2017