Figure 1.

Study design for analysis of incident arthritis conditions (n= 13,669)

Figure 1 shows how cross-sectional, recall questions on weight history and age at arthritis diagnosis were leveraged to create a retrospective cohort of US adults. We studied individuals who participated in the NHANES III (1988–1994) or NHANES continuous (1999–2016) cross-sectional survey at ages 50–79 years. As part of the survey, individuals reported their recalled weight at age 25 (young adulthood) and at 10 year prior to survey (age 40–69 years, midlife), which were used to create a measure of weight change between young adulthood and midlife. We then investigated the association between this weight change and subsequent risk of developing an arthritis condition. ‘Follow-up’ for incident arthritis began at the midlife weight measure, which was 10 years prior to survey. Individuals who reported receiving a first diagnosis of arthritis more than 10 years prior to survey were considered prevalent cases and, thus, were excluded from the analysis of incident arthritis. Individuals who reported receiving a first diagnosis of arthritis during the follow-up period between midlife and time of survey were considered to have experienced incident arthritis over follow-up.