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March 15, 2001 -- What's a mother to do? A new study in this week's issue of the British Medical Journal suggests that young adults who were breastfed for at least four months as infants are more likely to have stiffer, less expandable blood vessels -- a risk factor for heart disease later in life.
And although the researchers don't advocate that mothers switch to formula when they can breastfeed their babies, they do raise questions about the optimal time to wean kids from breast to bottle.
In a study of more than 300 adults in their 20s, C.P.M. Leeson and colleagues from the Institute of Child Health and Great Ormond Street Hospital for Children in London found that the longer they had been breastfed as children, the stiffer were there arterial walls as adults.
But the study also found that there was no difference in arterial expandability between adults who had been bottle-fed with formula or breastfed for less than four months.
But a physician who studies blood vessel health as it relates to high blood pressure cautions that the study flies in the face of conventional wisdom about the benefits of mother's milk.
"I would be very skeptical of that conclusion, because it goes against everything we've ever learned about breastfeeding," Stanley S. Franklin, MD, clinical professor of medicine at the University of California at Los Angeles, tells WebMD. "If you told me there was a correlation with heavy cow's milk use during infancy, childhood, and adolescence, I might say that there might be something there [because of the fat], but breast milk is something that has evolved over the millennia for the benefit of the species."
In an editorial accompanying the study, Ian Booth, MD, professor of pediatrics and child health at the University of Birmingham, U.K., cautions that the results need to be confirmed in other studies, and even then the well-established health benefits of breastfeeding "will probably never be outweighed by considerations of ... heart disease 50 years later."
So what gives? By most accounts, breastfeeding in infancy is good for the heart in adult life, not the other way around. For example, in a study published last year, researchers from the Netherlands reported that middle-aged men and women who had been breastfed as infants in the first weeks after birth had lower blood sugar levels following a special sugar test, lower levels of bad cholesterol and higher levels of good cholesterol levels, and a more favorable ratio of good-to-bad cholesterol than adults who had been bottle-fed immediately after birth.
But Leeson and colleagues point to a study published in the British Medical Journal in 1992 indicating that men in their 60s and 70s who had been breastfed for at least one year had significantly higher rates of heart disease and higher levels of LDL, the bad cholesterol, than men who had been fed a combination of breast and bottle in the first year.
In the current study, to test whether breastfeeding duration might have an influence on blood vessel health later in life, the authors studied 160 men and 171 women aged 20 to 28 years. The subjects were evaluated for heart disease risk with questionnaires, blood samples, physical measurements and imaging studies.
They found that people who had been breastfed for more than four months were more likely to have stiff, inflexible arteries, which could put them at risk for heart disease or stroke later on. The researchers also looked for but could not find any evidence of a relationship between duration of breastfeeding and other possible explanations for heart disease, such as cholesterol levels, body size or mass, smoking status, blood pressure, social status, birth weight or family history of early heart vessel disease.
"It's prolonged breastfeeding followed by a Western-style diet full of fat that is the culprit here," speculates co-author Alan Lucas, MD. "If that theory is correct, that the Western-style diet is really to blame, then that's where the public health intervention should be." Lucas is professor and director of the Childhood Nutrition Research Center at the Insitute of Child Health in London.
The researchers caution that the findings, while deserving further study, should not be cause for alarm among parents, new or old, or among people who were breastfed as children.
"There are so many good things about breastfeeding that have to be set against any possible adverse effects," Lucas says.
"At this stage, our findings should not influence current advice on the importance of breast feeding," Leeson and colleagues write. "Even if prolonged breastfeeding were confirmed to have disadvantages, these would need to be carefully weighed against the advantages. For example, in developing countries, the benefit of prolonged breastfeeding in infants and toddlers would be an overriding consideration. Nevertheless, there is an urgent public health need to study further the possible influence of a longer period of breastfeeding on the evolution of arterial disease."