National nutrition data: contributions and challenges to monitoring dietary supplement use in women.

Survey data from three nationally representative surveys--the National Health and Nutrition Examination Survey, National Health Interview Survey and Continuing Survey of Food Intakes by Individuals--indicate that, in general, women are greater consumers of dietary supplements than men in terms of overall prevalence of use and number of supplements taken. However, monitoring dietary supplement use over time and aggregation or comparison of findings over different surveys is hampered by a lack of comparability between survey data collection and analysis. Differences exist in the types of dietary supplements queried, use of a referent time frame, specificity regarding the supplement taken and level of detail collected relating to personal usage. Some comparability in supplement data collection may be possible but some inconsistencies may persist because of differences in survey goals or collection procedures. Collection of data on dietary supplement use is challenging and collection of very detailed and precise data are time consuming and expensive. Consequently, the level of detail and precision necessary for monitoring, research, and policy uses is an issue that should be addressed in view of the high monetary and time costs of detailed dietary supplement data collection, as well as increased demands on survey respondent time.