Quantitative assessment of dietary supplement intake in 77,000 French adults: impact on nutritional intake inadequacy and excessive intake.

backgroundDietary supplements (DS) are largely consumed in Western countries without demonstrating their nutritional benefits and safety in the general population. The aims, in a large population-based study of French adults, were: (1) to compare the prevalence of nutrient intake inadequacy and the proportion of individuals exceeding tolerable upper intake levels (UL) between DS users and non-users, and (2) to quantify the extent of potentially "at-risk" DS use practices (e.g., DS/drugs contraindicated association or use of beta-carotene DS in smokers).

methods76,925 participants, 47.6% men and 52.4% women, mean age 46.9 ± 16.3 years were enrolled to the NutriNet-Santé cohort and they completed a quantitative DS questionnaire and three 24 h dietary records. A composition database including > 8000 DS was developed. Variance reduction was applied to estimate usual intakes and analyses were weighted according to the French census data.

resultsAmong DS users of the specific nutrient, DS contributed to 41% of total intake for vitamin D in men, 55% in women; and to 20% of total intake for pyridoxine in men, 21% in women. Compared to dietary intakes only, their prevalence of inadequacy was reduced by 11% for vitamin C, 9% for magnesium, 6% for pyridoxine in men, and 19% for calcium, 12% for iron, and 11% for magnesium in women (p < 0.0001). The proportion of subjects exceeding UL reached 6% for iron and 5% for magnesium in men, and 9% for iron in women. 6% of DS users had potentially "at-risk" practices.

conclusionWhile DS use contributed to decrease the prevalence of insufficient intake for several nutrients, it also conveyed excessive intake of iron and magnesium. Besides, a substantial proportion of potentially "at-risk" DS use practices was reported.