Although many epidemiologic studies ask about current use of vitamin s
upplements, long-term use is usually the exposure of etiologic interes
t. We conducted a mailed survey to investigate the relation between cu
rrent and long-term (10-year) supplement use (N = 325 adults). Estimat
es of current daily intake for supplemental micronutrients were roughl
y twice that of average daily intake over the past 10 years. Correlati
ons between current intake and long-term intake from supplements alone
were 0.77, 0.75, and 0.65 for vitamin C, vitamin E, and calcium, resp
ectively. A measure of supplement use at one point in time incorporate
s measurement error that will attenuate measures of association.