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Breastfed babies cry more than formula-fed ones, but that's normal, so stick with it. Formula-fed babies may be quieter but overfed.

That's the message the U.K. Medical Research Council wants mothers to take from a study published yesterday in the science journal  PLoS One.

The British and U.S. governments  recommend mothers exclusively breastfeed for the first six months of a child's life. They cite research showing breastfeeding is healthier for babies and mothers. Some researchers even say it makes children, especially boys,  smarter.

In both countries, official statistics show three-quarters of new mothers follow this advice, but many give up in the first few months, if not weeks. According to the latest U.S. data, 13 percent of those who tried completed the whole six months.

The most common reason given by women in Britain's 2005 Infant Feeding Survey was, "Breast milk alone didn't satisfy my baby."

This means mothers perceive irritability as "a negative signal," a Medical Research Council statement said, an interpretation perhaps few mothers would challenge.

However, "[r]ather than being a sign of stress, the researchers say irritability is a natural part of the dynamic communication between mothers and babies and should not deter women from breastfeeding," the release continued.

And formula-fed babies "may appear more content, but research suggests that these infants may be over-nourished and gain weight too quickly," wrote the study's lead researcher, Dr. Ken Ong, of University of Cambridge.

To study the link between infant temperament and feeding, the study asked mothers of 316 babies to rate their baby's behavior at age three months. Compared with formula-fed babies, exclusive breast-fed and mixed-fed babies showed "greater distress," "less smiling" and "lower soothability," according to the article.

Susan Burger, PhD, president of the New York Lactation Consultant Association, faulted the study for assessing babies' temperaments using mothers' self-reported data but agreed with the study's goal of giving mothers more realistic expectations as a way to bolster breastfeeding.

In places like the U.S. and U.K., she said, two generations' worth of public health misinformation have left behind artificial sleep and eating patterns that still pervade our culture.

"If a baby isn't drinking four ounces and then sleeping four hours, mothers think something's wrong" and may be tempted to give up on breastfeeding, she said. But it's normal for a baby to ask for milk more frequently, and to interact with the mother, she added.

She also pointed out the cultural aspect of the temparement-feeding dynamic. Breastfed babies rarely cried during her travels in Central and West Africa, she said.

"What's needed is for women to have more support," she concluded, echoing the study. "We're re-learning how to breastfeed."