BACKGROUND: Previous studies have reported an association between low birth weight and low adult lung function, but findings have not been consistent. The aim of this study was to investigate whether birth weight is associated with both the level and the decline in adult lung function in general population.

METHODS: The Danish Inter99 study is a population-based intervention study in adults aged 30-60 years, providing information on birth weight and lung function on 4428 participants. Of these, 2931 participants performed spirometry at baseline and at five-year follow-up. Multiple linear regression models were used to examine the association between birth weight and forced expiratory volume in first second (FEV1) and forced vital capacity (FVC) and age-related decline in these variables. Analyses were conducted stepwise including sex, age, adult height, abdominal circumference, birth height, mother's age at birth, parity, prematurity, multiple pregnancy, socioeconomic and lifestyle factors and lung symptoms as covariates.

RESULTS: Birth weight was positively associated with spirometric variables. For a 1 kg increase in birth weight, FEV1 increased by 86 ml (CI95%: 34-139) and FVC by 88 ml (CI95%: 27-148). No significant trend was found with regard to the FEV1/FVC ratio. In longitudinal analyses, there was a 0.2% (CI95%: 0.04-0.3) lower decline in FEV1/FVC ratio per year for every 1 kg increase in birth weight, whereas we found no significant association between birth weight and decline in FEV1 and FVC.

CONCLUSION: Low birth weight was significantly associated with lower adult FEV1 and FVC but not with the decline in these variables during a 5-year observation. Although FEV1/FVC ratio was not related to birth weight, persons with low birth weight experienced a steeper decline on this index. In general, the magnitude of the association between birth weight and adult lung function was modest.