Table 1.

Details of physical functioning, obesity and leisure-time physical inactivity in 1946-NSHD and 1958-NCDS

Factor	Participant age (years) at ascertainment	Ascertainment method	Description
Physical functioning (outcome)	1946-NSHD: 60–64	Self-reported	The Physical Component Summary subscale of the SF-36 survey,24 is a validated 10-item questionnaire measuring the extent to which individuals feel they are limited in physical tasks due to their health.24,25,27 The scale covers a range of severe and minor limitations, including bathing or dressing, lifting, carrying groceries, climbing stairs, bending, kneeling, stooping and walking short to moderate distances. Participants were asked to respond on a three-point scale (limited ‘a lot’, ‘a little’, ‘not at all’); scores were summed and linearly transformed to a scale ranging from 0 to 100 (lower scores represent poorer PF). As in previous work,7,26 within each cohort, poor functioning was defined as being in the lowest, gender-specific, 10th-centile of the PF scale.
	1958-NCDS: 50
Obesity (time-varying exposure)	1946-NSHD: 36, 43, 53 and 60–64	Height and weight were measured (1946-NSHD: all ages; 1958-NCDS: 33 years) or self-reported (1958-NCDS: 42 and 50 years)	BMI was calculated as weight/height² (kg/m²); obesity was defined as BMI ≥ 30 kg/m2. Three trajectories were considered as exposure groups: (i) ‘never obese’ during follow-up (i.e. 36 to 60–64 years in 1946-NSHD; 33–50 years in 1958-NCDS), (ii) ‘incident obesity’ (i.e. becoming obese; 1946-NSHD: (a) not obese at 36 years, obese 43 to 60–64 years, (b) not obese at 36 and 43 years, obese 53 to 60–64 years and (c) not obese at 36, 43 and 53 years, obese at 60–64 years; 1958-NCDS: (a) not obese at 33 years, obese 42–50 years and (b) not obese at 33 and 42 years obese at 50 years, and (iii) ‘persistent obesity’ during follow-up.
	1958-NCDS: 33, 42 and 50
Leisure-time physical inactivity (time-varying mediator)	1946-NSHD: 36, 43, 53 and 60–64	Self-reported	In 1946-NSHD, at 36, 43, 53 and 60–64 years, participants reported how often they participated in leisure-time activity. At 36 years, participants reported the number of times they took part in 27 different sports, exercise and other leisure activities during the previous month. At 43 years, information was collected on participation in sports, exercise or other vigorous leisure activities in the previous year. At 53 and 60–64 years, participants were asked how often they participated in sports, exercise or other vigorous leisure activities during the previous 4-weeks. As in previous work,8,28 at each age, participants were classed as inactive if they reported no participation in leisure-time activity (i.e. participants were considered inactive if they participated in relevant activities less than once in the previous month at 36 years, per month at 43 years, and in the previous 4 weeks at 53 and 60–64 years). In 1958-NCDS, at 33, 42 and 50 years the same questions were used to ask participants about regular leisure-time activity frequency. ‘Regular’ was defined as ≥1/month for most of the year and, to aid recall, a list of example activities (of predominantly moderate or vigorous intensity, e.g. swimming, walking) was provided. Those responding affirmatively, reported activity frequency in one of six categories (every/most days, 4–5 days/week, 2–3 days/week, once a week, 2–3 times/month or less often).29 As in previous work,30,31 inactivity was defined as low activity frequency (<1/week, i.e. those reporting activity as 2–3 times/month, less often and those reporting no ‘regular’ activity).
	1958-NCDS: 33, 42 and 50