Scientists who conducted a study of 11,000 British children found no reliable association between breastfeeding and higher IQ at age two.
Nor was breastfeeding related to improvements in IQ after the age of two, indicating that it did not help young brains develop better over time.
The children were taking part in the Twins Early Development Study (Teds) set up to disentangle the impact of “nature and nurture” on growing children - that is, the relative effects of genes and the environment.
Some of the twins were identical, sharing all their genes, and others non-identical. Only identical twins would be expected to respond the same way to a purely genetic influence.
Breastfeeding was associated with a small IQ advantage for girls at age two, but by 16 this had disappeared.
Writing in the online journal Public Library of Science ONE, the scientists concluded: “Breastfeeding has little benefit for early life intelligence and cognitive growth from toddlerhood through adolescence.”
Study co-leader Dr Sophie von Stumm, from Goldsmiths, University of London, stressed that breastfeeding had other benefits, such as helping to build a child’s immune system, but added: “That said, mothers should be aware that they are not harming their child if they choose not to, or cannot, breastfeed. Being bottle fed as an infant won’t cost your child a chance at a university degree later in life.”