Parsons T J, Power C, Manor O
Department of Paediatric Epidemiology and Biostatistics, Institute of Child Health, London, UK.
Int J Obes (Lond). 2005 Oct;29(10):1212-21. doi: 10.1038/sj.ijo.0802932.
To investigate relationships between frequency of physical activity or television viewing and body mass index (BMI) cross-sectionally at six ages from childhood to adulthood, to better understand longitudinal relationships. To investigate how the relationships vary with age and gender and whether any relationships are due to confounding factors.
The 1958 British birth cohort includes all births (approximately 17 000) in one week in March 1958. BMI and physical activity frequency were recorded at 11, 16, 23, 33 and 42 y and television viewing frequency at 11, 16 and 23 y. A total of 11 109 subjects provided BMI and activity data at 42 y. Relationships between BMI and (in)activity were investigated using linear regression.
At ages 11, 33 and 42 y in both sexes and at 23 y in female subjects, those who were more active had lower BMIs, and the relationships strengthened with age. At 42 y, the most active had a lower mean BMI than the least active, by 0.83 kg/m2 in men, and 1.03 kg/m2 in women. BMI and activity were unrelated at 16 y in female subjects, and 23 y in male subjects. At 16 y in males, the most active males had a mean BMI 0.25 kg/m2 higher than the least active. At 11 y in female subjects and 23 y in both sexes, those who watched television most frequently had higher BMIs. BMI and television viewing were unrelated at 11 y in males and at 16 y in both sexes. Relationships between BMI and activity or television viewing were largely unexplained by potential confounding factors.
The relationship between BMI and physical activity changes with age. In early adolescence and in adulthood, a higher activity level, or lower frequency of television viewing was associated with a lower BMI. In later adolescence (16 y), television viewing and activity were unrelated to BMI, except for an unexpected BMI-activity relationship in males. We suspect this relationship in males is primarily due to selection effects, whereby physically bigger boys, with a larger BMI, are more likely to take part in exercise activity, and possibly also to BMI being a less accurate predictor of fatness in adolescent boys.
横断面研究从儿童期到成年期六个年龄段的身体活动频率或看电视时间与体重指数（BMI）之间的关系，以更好地理解纵向关系。研究这些关系如何随年龄和性别变化，以及是否存在由混杂因素导致的关系。
1958年英国出生队列包括1958年3月某一周内的所有出生人口（约17000人）。在11岁、16岁、23岁、33岁和42岁时记录BMI和身体活动频率，在11岁、16岁和23岁时记录看电视频率。共有11109名受试者在42岁时提供了BMI和活动数据。使用线性回归研究BMI与（不）活动之间的关系。
在11岁、33岁和42岁的男性和女性以及23岁的女性受试者中，身体活动较多者的BMI较低，且这种关系随年龄增强。在42岁时，最活跃者的平均BMI比最不活跃者低，男性低0.83kg/m²，女性低1.03kg/m²。在16岁的女性受试者和23岁的男性受试者中，BMI与活动无关。在16岁的男性中，最活跃的男性平均BMI比最不活跃者高0.25kg/m²。在11岁的女性受试者以及23岁的男性和女性中，看电视最频繁者的BMI较高。在11岁的男性以及16岁的男性和女性中，BMI与看电视无关。BMI与活动或看电视之间的关系在很大程度上无法用潜在的混杂因素来解释。
BMI与身体活动之间的关系随年龄变化。在青春期早期和成年期，较高的活动水平或较低的看电视频率与较低的BMI相关。在青春期后期（16岁），看电视和活动与BMI无关，但男性存在意外的BMI-活动关系。我们怀疑男性中的这种关系主要是由于选择效应，即体型较大、BMI较高的男孩更有可能参加体育活动，也可能是因为BMI在青少年男孩中作为肥胖预测指标不够准确。
