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NEW YORK (Reuters Health) - Middle-aged adults who were born at a relatively low weight may have more breathing difficulties than those who were bigger newborns, a new study suggests.
In a study of 627 Chinese men and women in their 40s, researchers found that participants' scores on standard lung-function tests generally lined up with their birth weights. The lowest average scores were recorded among adults who had been born weighing less than 5.5 pounds, while the highest scores were seen among those whose birth weights topped 7 pounds.
The findings do not prove that low birth weight itself is the reason for the discrepancy, the researchers note in the journal Pediatrics.
But they do support the so-called "fetal origins hypothesis" that impaired growth in the womb might ultimately affect adult lung function, write Dr. Lijun Pei and colleagues at Peking University in Beijing. According to that theory, environmental factors during early development -- particularly poor maternal nutrition -- might help "program" a person's risks of various health problems later in life, Pei and senior researcher Dr. Xiaoying Zheng told Reuters Health in an email.
The findings are based on birth records and lung-function tests for 627 adults born in Beijing between 1948 and 1954.When the men and women were between the ages of 41 and 47, they underwent a standard test of lung function called spirometry -- which measures the amount of air that moves in and out of the lungs with each breath, as well as the speed at which it flows.
Lower scores can indicate airway obstruction, possibly from lung diseases like asthma or emphysema.In this study, the average lung-function score in the group with the lowest birth weights was within normal range. But Pei and Zheng said that past studies have found associations between low birth weight and higher risks of childhood asthma and, in adulthood, chronic obstructive pulmonary disease -- a group of lung diseases that includes emphysema and chronic bronchitis.
The researchers found that lower birth weight was related to poorer lung function even when they accounted for a number of other factors that affect birth weight and adult lung health. Those included prematurity, participants' history of childhood respiratory illnesses, adulthood weight and smoking habits. Smoking during pregnancy is a known risk factor for low birth weight, and there is evidence that children born to smokers have smaller lung volumes and higher risks of asthma and respiratory infections.
Pei's team lacked information on whether participants' mothers smoked during pregnancy. They also had no information on mothers' diets during pregnancy, so the extent to which poor nutrition in the womb might account for the link between birth weight and adulthood lung function in unknown.
However, Pei and Zheng pointed out, malnutrition was common in Beijing at the time study participants were born. A study of Chinese schoolchildren of that era, for example, found that more than two-thirds were deficient in vitamin C -- which offers clues to their overall nutritional status. It's "plausible," according to Pei and Zheng, that poor fetal nutrition and subsequent underdevelopment of the lungs could affect lung function into adulthood.