Background: There is inconsistent evidence on the optimal time after standing to assess for orthostatic hypotension. We determined the prevalence of orthostatic hypotension at different time points after standing in a population of older adults, as well as fall risk and symptoms associated with orthostatic hypotension.

Methods: We performed a secondary analysis of the Study to Understand Fall Reduction and Vitamin D in You (STURDY), a randomized clinical trial funded by the National Institute on Aging, testing the effect of differing vitamin D3 doses on fall risk in older adults. STURDY occurred between July 2015 and May 2019. Secondary analysis occurred in 2022. Participants were community-dwelling adults, 70 years or older. In the orthostatic hypotension assessment, participants stood upright from supine position and underwent six standing blood pressure measurements (M1-M6) in two clusters of three measurements (immediately and 3 min after standing). Cox proportional hazard models were used to examine the relationship between orthostatic hypotension at each measurement and subsequent falls. Participants were followed until the earlier of their 24-month visit or study completion.

Results: Orthostatic hypotension occurred in 32% of assessments at M1, and only 16% at M5 and M6. Orthostatic hypotension from average immediate (M1-3) and average delayed (M4-6) measurements, respectively, predicted higher fall risk (M1-3 = 1.65 [1.08, 2.52]; M4-6 = 1.73 [1.03, 2.91]) (hazard ratio [95% confidence interval]). However, among individual measurements, only orthostatic hypotension at M5 (1.84 [1.16, 2.93]) and M6 (1.85 [1.17, 2.91]) predicted higher fall risk. Participants with orthostatic hypotension at M1 (3.07 [1.48, 6.38]) and M2 (3.72 [1.72, 8.03]) were more likely to have reported orthostatic symptoms.

Conclusions: Orthostatic hypotension was most prevalent and symptomatic immediately within 1-2 min after standing, but more informative for fall risk after 4.5 min. Clinicians may consider both intervals when assessing for orthostatic hypotension.