# Prevalence and Associated Factors of Excessive Dietary Supplement Use Among Japanese Adults: Cross-Sectional Study

## TL;DR

This study finds that 18.5% of Japanese adults use dietary supplements above recommended doses, with factors like employment and supplement form linked to excessive intake.

## Contribution

The study identifies sociodemographic and usage factors associated with exceeding manufacturer-recommended doses of dietary supplements in Japan.

## Key findings

- 18.5% of participants consumed dietary supplements above manufacturer-recommended doses.
- 61.9% of those exceeding recommended doses surpassed tolerable upper intake levels for at least one nutrient.
- Middle-aged individuals and those in employment were more likely to exceed recommended supplement doses.

## Abstract

The use of dietary supplements (DSs) can lead to an excessive intake of certain nutrients, posing potential health risks. However, studies are scarce on whether DS users adhere to recommended doses provided by the manufacturer and what factors are associated with overconsumption of DS.

By leveraging purchase history data to estimate DS use precisely, this study aimed to investigate the factors associated with DS consumption exceeding manufacturer-recommended doses and examine the prevalence of excess nutrient intake among DS users.

An online survey was conducted from November to December 2024 among 2002 adults (aged 18‐74 years) with a history of buying one of the 25 major DS products and who had used it in the previous month or regularly. Self-reported daily DS consumption was assessed using a questionnaire and compared to the manufacturer-recommended doses indicated in the package. Using multivariate logistic regression analysis, the associations between DS consumption exceeding the manufacturer-recommended doses and sociodemographic factors were examined.

The prevalence of DS users exceeding tolerable upper intake levels (ULs), defined according to the Dietary Reference Intakes for Japanese, was calculated based on vitamin and mineral intake from DS only. Consequently, 371 (18.5%) of the 2002 participants consumed DS above the manufacturer-recommended dose. Consumption of DS above the recommended dose was associated with middle-aged, part-time or full-time employment, use of tablet-form DS, especially single water-soluble vitamin tablets, use of DS for 6 months or more, and intentional consumption above the recommended dose. For 1705 individuals consuming DS with UL nutrients, 17.4% (n=297) exceeded the manufacturer-recommended dose. Of these, 61.9% (184/297) surpassed UL by ≥1 nutrient.

Middle-aged, part-time or full-time jobs, using tablet-form DS, and using DS for 6 months or more were associated with DS consumption exceeding the manufacturer-recommended dose, which may lead to excessive nutrient intake.