Breastfeeding may protect against persistent stuttering
A study of 47 children who began stuttering at an early age found that those who were breastfed in infancy were more likely to recover from stuttering and return to fluent speech.
The analysis, reported in the Journal of Communication Disorders, found a dose-dependent association between breastfeeding and a child’s likelihood of recovering from stuttering, with children who were breastfed longer more likely to recover. Boys, who are disproportionately affected by stuttering, appeared to benefit the most. Boys in the study who breastfed for more than a year had approximately one-sixth the odds of developing persistent stuttering than boys who never breastfed, the team found.
The researchers, University of Illinois speech and hearing science professor emerita Nicoline Ambrose and doctoral student Jamie Mahurin-Smith (now at Illinois State University), found no evidence that income or maternal education had any influence on stuttering in their sample. The researchers questioned the mothers about their children’s willingness and ability to breastfeed, and also found no evidence of an underlying neurological problem that could have inhibited the children’s ability to breastfeed and to speak fluently later in life.
“We’ve known for years that both genetic and environmental factors contributed to stuttering, but our understanding of the specific environmental variables in play has been murky,” Mahurin-Smith said. “These findings could improve our understanding of stuttering persistence and recovery.”
Several earlier studies had found “a consistent association between breastfeeding and improved language development,” the researchers report. A 1997 study found that babies breastfed for more than nine months had a significantly lower risk of language impairment than those breastfed for shorter periods of time. A later study found that infants who breastfed were more likely to produce “variegated babbling at earlier ages,” a key marker of healthy language development.
Other studies have found associations between the duration of breastfeeding and verbal IQ or a child’s likelihood of being diagnosed with an autism spectrum disorder.
Ambrose and Mahurin-Smith suggest that essential fatty acids found in breast milk but often lacking in infant formulas may help explain why longer duration of breastfeeding is associated with better brain and language development.
“Long-chain fatty acids found in human milk, specifically docosahexaenoic acid and arachidonic acid, play an important role in the development of neural tissue,” Mahurin-Smith said. “Fluent speech requires an extraordinarily complex sequence of events to unfold rapidly, and our hypothesis was that early differences in neurodevelopment could cause difficulties with speech fluency later in life.”
The infant brain triples in size in its first year of life, and “more than half of the solid weight of that newly built tissue will be lipid,” the researchers wrote. DHA is the fatty acid most prevalent in the mammalian brain. Infants lacking adequate DHA in the diet can synthesize it from other fatty acids, but “research shows that the rate at which DHA is incorporated into brain tissue outstrips the rate at which it can be synthesized.”
Multiple studies suggest that the lack of adequate DHA in development can impair brain structure and function, Ambrose said. Fatty acids also are known to influence gene expression, she said, binding to transcription factors that can regulate the activity of many genes.
The Age Factor in Stuttering
Age is among the strongest risk factors for stuttering with several important implications. Although the disorder begins within a wide age-range, current robust evidence indicates that, for a very large proportion of cases, it erupts during the preschool period. Data obtained at the University of Illinois Stuttering Research Program revealed that for 65% of the child participants, stuttering onset occurred prior to age 3; the figure rose to 85% by 3 1/2 years of age (Yairi & Ambrose, 2005). Leaving room for some sampling errors, children past age 4 face a relatively low risk for stuttering. From clinical considerations, these statistics call for greater emphasis on preparing clinicians for working with early childhood stuttering.
Age brings out other factors. The fact that the critical age for stuttering onset parallels the age span when significant rapid developments occur in the anatomy of the speech system, as well as in complex language and articulatory skills, invites speculations that interferences in these maturational processes contribute to stuttering; hence the possibility of relations among stuttering, language, and articulation. Although our own data (Watkins, Yairi, & Ambrose, 1999), and those of our colleagues from Germany (Rommel et. al., 1999), show that the language skills of children who stutter, as a group, meet or exceed norms, we suspect that there are differences in the ways in which they process language. One research priority consequent to information about age at onset is experimental manipulation of similarities and/or differences in language processing and production between children who stutter near the onset of the disorder and normally fluent children, particularly in terms of the nature of linguistic knowledge and the time course of knowledge activation. Varied responses to semantic and phonological distracters, slower reaction time, and/or alternative activation paths may reveal differences in language processing. One of the intriguing questions is: does age at stuttering onset “prior to, or after, a certain point in language development” underlie distinct subtypes of the disorder? Currently, scientists in several laboratories are pursuing such issues.
Brain imaging studies of children should also enhance understanding of this issue. Our team members, Chang, Erickson, and Ambrose (2005) successfully obtained high resolution structural MRI data from stuttering and control children ages 8-13. Initial results indicate significant group differences in white and grey matter volume in brain areas involved in integrating sensory and motor aspects of speech. Testing younger children closer to onset should advance our knowledge.
Evidence is also accumulating that age at onset may bear a relation to genetic factors, in particular, it appears there may be a trend for persistent stuttering to have a slightly later onset than recovered stuttering (Yairi & Ambrose, 2005). As the Illinois team continues to uncover possible interactions among different genetic loci (Cox, et al., 2005), the age factor should become more clear.
Age is also a risk factor in regard to children’s awareness of disfluent speech. The belief that preschoolers who stutter lack in such awareness played a major role in theories and developmental models of the disorder. For many years, clinicians’ assumption that awareness would trigger strong emotions (e.g., anxiety) in children was the main reason for shunning direct speech therapy for preschoolers. Whereas some three-year olds are either clearly, or
appear to be, aware of stuttering, available experimental data show a very large increase in awareness between ages 4 and 5, including normally fluent children (Ambrose & Yairi, 1994; Ezrati, Platzky, & Yairi, 2001). This information would seem to justify direct intervention techniques as well as provide clues for the timing of intervention and should be considered in counseling of parents and teachers about reactions of normally fluent children to their stuttering peers.
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Ehud Yairi, Ph.D.
University of Illinois
“It may be that fatty acid intake affects the expression of genes responsible for stuttering,” Ambrose said.
“Our study adds to the evidence suggesting that human milk can exert a significant influence on neurodevelopment,” Mahurin-Smith said. “Although it’s not a magic bullet, it can make an important difference for children, even years after weaning.”
Although past research has provided evidence of a genetic component to the transmission of susceptibility to stuttering, the relationship between the genetic component to stuttering and persistence and recovery in the disorder has remained unclear. In an attempt to characterize this relationship, the immediate and extended families of 66 stuttering children were investigated to determine frequencies of cases of persistent and recovered stuttering. Pedigree analysis and segregation analysis were used to examine patterns of transmission. The following questions were investigated:
1. Is there a sex effect in recovery from stuttering? Here, we sought to test the hypothesis that females are more likely to recover than males, leading to the change in sex retio from approximately 2:1 males to females close to onset of the disorder, to 4 or 5:1 in adulthood.
2. Is persistence/recovery in stuttering transmitted in families? If recovery/persistence appears to be transmitted, (a) are recovered and persistent stuttering independent disorders?; (b) is recovery a genetically milder form of persistent stuttering?; or (c) is persistence/recovery transmitted independent of the primary susceptibility to stuttering?
Results indicated sharply different sex ratios of persistent versus recovered stutterers in that recovery among females is more frequent than among males. It was found that recovery or persistence is indeed transmitted, and further, that recovery does not appear to be a genetically milder form of stuttering, nor do the two types of stuttering appear to be genetically independent disorders. Data are most consistent with the hypothesis that persistent and recovered stuttering possess a common genetic etiology, and that persistence is, in part, due to additional genetic factors. Segregation analyses supported these conclusions and provided statistical evidence for both a single major locus and polygenic component for persistent and recovered stutterers.
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By Nicoline Grinager Ambrose, University of Illinois at Urbana-Champaign,
Nancy J. Cox, University of Chicago School of Medicine,
Ehud Yairi, University of Illinois at Urbana-Champaign.
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