Dietary Supplements – (In)Accuracy of Manufacturers’ Dosing Instructions

The consumption of dietary supplements (DS) is widespread in competitive sport. Manufacturers provide information on their packaging regarding recommended daily intake or serving size. Preparations in powder form are usually accompanied by a measuring spoon, which should correspond to a specific dosage. The aim of this study was to compare the “Labelled Weight (LW)”, quantities per serving stated by the manufacturer, with the quantities weighed out per serving. In the period Oct 2023-Oct 2024, DS (n=194) in powder form were examined. The enclosed measuring spoons were filled three times with the powder in accordance with the manufacturer’s instructions on the packaging. The quantities were weighed using a laboratory balance (sartorius precision balance - measuring accuracy 0.01 g). The mean value of the 3 measurements was defined as the “Measured Weight (MW)”. The dosage recommendations of the manufacturers for the filling quantity of the measuring spoons differed in the indications - number of measuring spoons: levelled (18%), slightly heaped (8%), heaped (6%) and without specific instructions (67%). In total, the mean MW was higher (8±20%; p<0.01; range -59% to +80%) than LW, with 65% of the DS above (35% below) the LW. A deviation of ±<10%, ±10-30% and ±>30% was found for 47%, 38% and 15% of the analysed DS, respectively. Protein powders (n=50) had a mean deviation of 7±18% (range -35% to +65%), carbohydrate powders (n=35) 12±19% (range -45% to +62%) and creatine powders (n=11) -1±20% (range -25% to +32%). DS with the instruction heaped and without specific instruction showed higher deviations compared to the indication levelled and slightly heaped (MW 11±22% vs. MW 1±12%; p< 0.01). In our survey, the dosage recommendations for the measuring spoons are partly unspecific and the deviations between LW and MW are not negligible. Unintentional overdosing of DS could cause gastrointestinal complaints or lead to undesired energy intake. Consumers of powdered DS should be advised to weigh the serving according to individual requirements. Manufacturers should standardise the dosage information, use more precise instructions regarding the degree of spoon filling level and control the enclosed measuring spoons for dosage weight.