Birth order influences BMI and insulin sensitivity

Evidence that birth order influences BMI and insulin sensitivity

A study of 50 overweight middle-aged men by researchers at the University of Auckland’s Liggins Institute, suggests that first-borns may be more likely than second-borns to have a greater body-mass index (BMI).

They also found that first-borns had a lower sensitivity to the hormone insulin. Both BMI and lower insulin sensitivity are considered risk factors for type 2 diabetes, hypertension and coronary heart disease.

The research, published in the journal Scientific Reports, adds to our understanding of the potential long-term health effects of birth order, although larger studies that include sibling pairs are needed to fully evaluate this link.

Some evidence suggests that birth order may influence metabolism and body composition, from infancy to early adulthood, but the potential impacts in mid-life have not been explored previously.

The research by Professor Wayne Cutfield and colleagues studied 50 overweight, but otherwise healthy men between the ages of 35 and 55, who were recruited as part of two clinical trials at the Liggins Institute.

They report that first-borns were on average 6.9 kg heavier than second-borns and had a greater BMI. Insulin sensitivity was also 33 percent lower in first-born men than in second-borns, despite adjustment for fat mass.

The research offers a broad assessment of the possible effects of birth order on metabolic health. The authors note, however, that the participant range was rather narrow (overweight males living in a large urban centre), and because sibling pairs were not studied, the study could have underestimated the magnitude of birth order effects on insulin sensitivity and other metabolic outcomes.

BA Albert, M de Bock, JGB Derraik, CM Brennan, JB Biggs, PL Hofman, WS Cutfield, (2014) ‘Among overweight middle-aged men, first-borns have lower insulin sensitivity than second-borns’, Scientific Reports, published 06 Feb 2014 available on-line at http://dx.doi.org/10.1038/srep03906

ENDS

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