Longitudinal and secular trends in dietary supplement use: Nurses' Health Study and Health Professionals Follow-Up Study, 1986-2006.

Most studies on the prevalence of supplement use in the United States were cross-sectional or evaluated trends in limited variety of supplements. The objective of this study was to describe the longitudinal and secular trend of dietary supplement use over the past 20 years in health professionals using data from two large prospective cohorts. We analyzed cohort data from 1986 to 2006 in the Nurses' Health Study (NHS) and the Health Professionals Follow-Up Study (HPFS). In 1986, 74,194 women aged 40 to 65 years in the NHS and 50,497 men aged 40 to 75 years in the HPFS were included. Use of dietary supplements including multivitamins, vitamins, and minerals was repeatedly asked every 4 years. Generalized estimating equation models were used for repeated analysis. Prevalence of use of any supplement increased among both women (71.3% to 88.3%) and men (56.4% to 80.7%) from 1986 to 2006. Notably, longitudinal increases in the prevalence of use of vitamin D (2.2% to 32.2% for women and 1.1% to 6.7% for men), folic acid (0.8% to 10.7% for women and 1.1% to 13.8% for men), and fish oil (1.6% to 18.1% for women and 3.3% to 22.2% for men) supplements were observed from 1990 to 2006. However, the use of vitamin A, beta carotene, vitamin C, and vitamin E supplements peaked in 1994 or 1998, then declined steadily. A secular increase in use of multivitamins, vitamin D, folic acid, and fish oil across same age group was noted. In conclusion, the use of many types of dietary supplements has increased over time, but the use of antioxidant supplements has declined. The secular increase in the prevalence of use of supplements across the same age group suggests that aging of the population is not the primary reason for the increase. These findings in health professionals need to be replicated in the general populations.