medwireNews: The uncertain effect of metformin on children’s body mass index (BMI) may be down to an unappreciated effect on growth, say the authors of a meta-analysis.

The recognised ability of metformin to reduce BMI in children should therefore “be interpreted to reflect not only decreased body mass or adiposity but also increased height”, say Normand Boulé (University of Alberta, Edmonton, Canada) and co-researchers.

The team notes that metformin is increasingly used off label in children for conditions including polycystic ovary syndrome, impaired glucose tolerance and obesity, making it “important to parse out the effect of metformin on BMI into its height and weight components.”

Their meta-analysis, which is published in JAMA Pediatrics, included 10 randomised trials that assessed metformin use in patients younger than 19 years, and reported height changes. Among the 477 participants overall, those taking metformin had a reduction in BMI, by a significant weighted mean difference of 1.0 kg/m2 relative to controls, but no relative change in height.

However, when the studies were divided into those that used a high cumulative metformin dose (≥274 g; n=286) or a lower dose (≤186 g; n=191), the team found that children given metformin in the high-dose studies had a significant 1.0 cm increase in height relative to controls. They also had a significant 1.3 kg/m2 reduction in BMI but no change in weight, suggesting that the BMI reduction was largely caused by the height increase.

In the lower-dose studies, patients given metformin had no significant changes in height, weight or BMI relative to controls.

Boulé et al comment that a 1.0 cm change in height “may seem small, but the findings may still be clinically meaningful.”

They note that the effects of metformin could have been diluted by the presence of older study participants who may already have had epiphyseal growth plate closure “and therefore would be unlikely to have additional growth from metformin treatment”.

“It is possible that longer treatment periods or treatments concentrated at times of greater growth may lead to even greater height changes”, they conclude.

By Eleanor McDermid, Senior medwireNews Reporter

JAMA Pediatr 2015; Advance online publication

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