Wednesday March 18 2015
Breastfeeding helps protect against infection
"Breastfed babies grow up smarter and richer, study shows," The Daily Telegraph reports. A study from Brazil that tracked participants for 30 years found a significant association between breastfeeding and higher IQ and income in later life.
This study followed almost 3,500 infants from birth to adulthood in Brazil. It found babies who were breastfed longer had higher IQs at the age of 30, as well as higher incomes. The authors say this is the first study to directly assess the impact of breastfeeding on income.
Another novel feature of the study was that the majority of the mothers were from low-income backgrounds. Studies in developed countries, such as the UK, may be skewed by the fact there is a trend for breastfeeding mothers to come from medium- to higher-income backgrounds.
The study used a good design and had a relatively high follow-up of participants (almost 60%) given how long it was. Although factors other than breastfeeding may have been influencing the results, the researchers did try to reduce their impact by making adjustments. The results for income may also not be as representative of more developed countries.
While it's difficult to conclusively state that breastfeeding itself definitely directly caused all of the differences seen, overall this research supports the view that breastfeeding can potentially benefit children long-term.
Current UK advice is that exclusive breastfeeding for around the first six months of life provides a range of health benefits for babies.
Where did the story come from?
The study was carried out by researchers from the Federal University of Pelotas and the Catholic University of Pelotas in Brazil.
It was funded by the Wellcome Trust, the International Development Research Center (Canada), CNPq, FAPERGS, and the Brazilian Ministry of Health.
The study was published in the peer-reviewed medical journal Lancet Global Health on an open-access basis, so it is free to read online or download as a PDF.
The majority of the UK media provided a very balanced report of this study, noting the results and their implications, as well as the study's limitations.
What kind of research was this?
This was a prospective cohort study looking at whether breastfeeding was associated with higher IQ and income in adulthood. The short-term benefits of breastfeeding on a baby's immunity are well known.
The researchers also report that a meta-analysis of observational studies and two randomised controlled trials (RCT), which looked at the promotion of breastfeeding or compared breast milk versus formula in preterm babies, found longer-term benefits on IQ in childhood and adolescence.
There have been fewer studies looking at the effect on IQ in adults, all from developed high-income countries, but none looking at income.
Although two out of these three studies found a link with higher IQ, there is concern that this may at least in part be related to the fact that mothers of higher socioeconomic status in these countries tend to breastfeed for longer.
In the UK, women from a middle or upper class background are more likely to breastfeed than women from a working class background, so the researchers wanted to look at the link in a lower-income country (Brazil) where this pattern does not exist.
This is likely to be the best study design for assessing this question, as randomised controlled trials allocating babies to be breastfed or not are unlikely to be unethical.
As with all observational studies, the main limitation is that factors other than the one of interest (breastfeeding in this case) could be having an impact on the results, such as socioeconomic status.
Researchers can reduce the impact of these factors (confounders) by using statistical methods to take them into account in their analyses.
In this study, they also chose to analyse a population where a major confounder was thought to have less impact. There may still be some residual effect of these or other unmeasured factors, however.
What did the research involve?
The researchers recruited 5,914 babies born in 1982 in Pelotas, Brazil and their mothers, and recorded whether the babies were breastfed or not. They then followed them up and assessed their IQ, educational achievements and income as 30 year olds in 2013.
The researchers invited all mothers of babies born in five maternity hospitals in Pelotas in 1982 and who lived in the city to take part in their study, and almost all agreed.
When the babies were infants (19 months or 3.5 years old) the researchers recorded how long they were breastfed and whether they were mainly breastfed (that is, without foods other than breast milk, teas or water).
Researchers who did not know about the participants' breastfeeding history assessed their IQ using a standard test when they reached about 30 years of age. They also recorded the highest level of education participants had reached and their income in the previous month.
The researchers then compared outcomes in those who were breastfed longer against those who were breastfed for a shorter period of time or not at all.
They took into account a large range of potential confounders assessed around the time of the baby's birth (such as maternal smoking in pregnancy, family income, and baby's gestational age at birth) and during infancy (household assets).
What were the basic results?
The researchers were able to follow-up and analyse data for 59% (3,493 individuals) of the participants they recruited.
About a fifth of babies (21%) were breastfed for less than a month, about half (49%) were breastfed for between one and six months, and the rest (about 30%) for longer than this. Most babies were mainly breastfed for up to four months, with only 12% mainly breastfed for four months or longer.
Longer duration of any breastfeeding or mainly being breastfed was associated with higher levels of education, adult IQ and income.
For example, compared with those who were breastfed for less than one month, those who had received any breastfeeding for a year or longer had:
- IQ scores 3.76 points higher on average (95% confidence interval [CI] 2.20 to 5.33)
- 0.91 more years of education on average (95% CI 0.42 to 1.40)
- a higher than average monthly income (95% CI 93.8 to 588.3) – this was equivalent to around an extra 30% of the average income in Brazil
The researchers carried out a statistical analysis that suggested the difference seen in income with longer breastfeeding was largely a result of differences in IQ.
How did the researchers interpret the results?
The researchers concluded that, "Breastfeeding is associated with improved performance in intelligence tests 30 years later, and might have an important effect in real life by increasing educational attainment and income in adulthood."
This large long-term study found an association between being breastfed for longer and subsequent educational attainment, IQ and income at the age of 30 in participants from Brazil.
The authors say this is the first study to directly assess the impact of breastfeeding on income. The study used a good design and had a relatively high follow-up of participants (almost 60%) given its duration.
However, there are some points to note:
- As with all observational studies, factors other than breastfeeding may have been influencing the results. The researchers did try to reduce their impact by making statistical adjustments, but some residual impact may remain.
- There was less awareness of the benefits of breastfeeding in Brazil when the study started, so less association with socioeconomic status and education was expected. However, researchers did find that women who had the least, as well as the most, education and those with a higher family income tended to breastfeed more, although the differences tended to be small (less than 10% difference in frequency of breastfeeding at six months).
- The results for IQ support those seen in higher-income countries, but there have not been any direct assessments of the effect of breastfeeding on income in these countries so far, and these may differ from lower-income countries.
While it's difficult to conclusively state that breastfeeding itself definitely directly caused all of the differences seen in this study, this research supports the belief that breastfeeding potentially has long-term benefits.
Breastfeeding is known to bring health benefits, and current UK advice is that this can be achieved through exclusive breastfeeding for around the first six months of life.
However, as experts noted on the BBC News website, breastfeeding is only one of many factors that can contribute to a child's outcomes, and not all mothers are able to breastfeed.
For more advice on breastfeeding, visit the NHS Choices Pregnancy and baby guide.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.