Weight loss on stimulant medication: how does it affect body composition and bone metabolism? - A prospective longitudinal study

Abstract

Objective: Children treated with stimulant medication for attention deficit hyperactivity disorder (ADHD) often lose weight. It is important to understand the implications of this during growth. This prospective study was designed to quantify the changes in body composition and markers of bone metabolism on starting treatment.

Methods: 34 children (29 boys) aged 4.7 to 9.1 years newly diagnosed with ADHD were treated with dexamphetamine or methylphenidate, titrating the dose to optimise the therapeutic response. Medication was continued for as long as clinically indicated. Body composition and bone density (dual-energy X-ray absorptiometry) were measured at baseline, 6 months and 3 years; changes were analysed in Z-scores based on data from 241 healthy, local children. Markers of bone turnover were measured at baseline, 3 months and 3 years.

Results: Fat loss of 1.4±0.96kg (total fat 5.7±3.6 to 4.3±3.1kg, p<0.001) occurred in the first 6 months. There were significant reductions over 3 years in the sex and height corrected Z-scores for lean tissue, bone mineral content, bone mineral density and ratio of central to total fat (-0.84±0.86, p=0.003; -0.55±0.31, p<0.0001; -0.41±0.28, p<0.0001 and -0.55±0.62, p=0.006 respectively). Propeptide of type I collagen indicated a significant reduction in bone turnover after 3 months (564±202 to 458±96ng/ml, p=0.019), which was fully recovered after 3 years (619±276ng/ml).

Conclusions: Stimulant medication was associated with early fat loss and reduced bone turnover. Lean tissue including bone increased more slowly over 3 years of continuous treatment than would be expected for growth in height. There was long-term improvement in the proportion of central fat for height. This study shows that relatively minor reductions in weight on stimulant medication can be associated with long-term changes in body composition. Further study is required to determine the effects of these changes on adult health.

Figure 1

Number of subjects and attrition in each part of the study.

Figure 2

Growth chart showing the average height and weight calculated from the changes in Z-scores. The error bars denote the standard deviation of the change in Z-scores going forwards and backwards from the baseline data, standardised for the average baseline age. The data show initial weight loss with simultaneous slowing of the height velocity on starting stimulant medication. Reference data: Centres for Disease Control and Prevention (CDC) 2000; mean ± 2SD.

Figure 3

Percentage change in components of body composition. BMC: bone mineral content; BMD: bone mineral density 6 months n=23; 3 years n=14 *** p<0.001; ** p<0.01; * p<0.05 from baseline, paired t-test. There was a significant reduction in fat mass and significant increases in lean tissue and BMC in the first 6 months. Over 3 years there were significant increases in lean tissue, BMC, BMD and fat.