Researchers examined health data from 10,500 American adults and found that those with low birth weight and those who had little or no breast-feeding had higher levels of C-reactive protein (CRP), an indicator of inflammation.
Chronic inflammation is associated with health risks such as diabetes and heart attack, the study authors noted.
The study did not find a cause-and-effect relationship, however.
The researchers explained that it can be difficult to determine how birth weight and breast-feeding affect long-term health because these problems are more common among children whose parents have lower levels of education and income. This means it's unclear if other factors play a role.
But this study included a large number of siblings and the researchers found that even within the same family, birth weight and breast-feeding influenced the risk of inflammation in adulthood.
The findings will be published in the journal Proceedings of the Royal Society B.
"There were good reasons to hypothesize that breast-feeding was important to influencing levels of inflammation in adulthood," study author Thomas McDade, a Canadian Institute for Advanced Research Fellow in the child and brain development program at Northwestern University, said in an institute news release.
"[Breast-feeding] promotes development of the immune system. Children who are breast-fed get fewer infectious diseases and are less likely to become overweight," he noted.
The U.S. National Library of Medicine has more about breast-feeding.