Total | Two years of follow-up | Four years of follow-up | Follow-up time until next DSA† | Full follow-up time | |||||
CHD Events | CHD Events | CHD Events | CHD Events | ||||||
N | N | HR (95% CI) | N | HR (95% CI) | N | HR (95% CI) | N | HR (95% CI) | |
DSA1 (1993–1998) | 22 035 | 71 | 174 | 872 | 1562 | ||||
NSU | 13 444 | 47 | 1.00 | 113 | 1.00 | 580 | 1.00 | 1012 | 1.00 |
SU-n3 | 3263 | 9 | 1.24 (0.60 to 2.56) | 20 | 1.17 (0.73 to 1.90) | 101 | 1.06 (0.85 to 1.31) | 178 | 0.96 (0.82 to 1.13) |
SU+n3 | 5328 | 15 | 0.95 (0.53 to 1.72) | 41 | 1.05 (0.73 to 1.52) | 191 | 0.86 (0.73 to 1.02) | 372 | 0.94 (0.83 to 1.06) |
DSA2 (2002–2004) | 15 937 | 75 | 171 | 527 | 742 | ||||
NSU | 8353 | 53 | 1.00 | 115 | 1.00 | 346 | 1.00 | 475 | 1.00 |
SU-n3 | 2665 | 10 | 1.01 (0.51 to 2.02) | 25 | 1.24 (0.79 to 1.93) | 61 | 0.94 (0.71 to 1.24) | 81 | 0.84 (0.66 to 1.07) |
SU+n3 | 4919 | 12 | 0.55 (0.29 to 1.04) | 31 | 0.64 (0.43 to 0.96) | 120 | 0.75 (0.61 to 0.93) | 186 | 0.81 (0.68 to 0.97) |
DSA3 (2004–2011) | 10 120 | 59 | 125 | 241 | |||||
NSU | 5029 | 44 | 1.00 | 82 | 1.00 | 148 | 1.00 | ||
SU-n3 | 1610 | 6 | 0.60 (0.25 to 1.42) | 19 | 1.01 (0.61 to 1.67) | 35 | 1.00 (0.69 to 1.45) | ||
SU+n3 | 3481 | 9 | 0.38 (0.18 to 0.78) | 24 | 0.52 (0.33 to 0.83) | 58 | 0.70 (0.52 to 0.95) | ||
Time-varying | 24 330 | 205 | 470 | 1640 | |||||
NSU | 144 | 1.00 | 310 | 1.00 | 1074 | 1.00 | |||
SU-n3 | 25 | 0.93 (0.61 to 1.43) | 64 | 1.13 (0.86 to 1.49) | 197 | 0.91 (0.78 to 1.06) | |||
SU+n3 | 36 | 0.59 (0.41 to 0.85) | 96 | 0.73 (0.58 to 0.92) | 369 | 0.74 (0.66 to 0.84) |
The follow-up time in the EPIC-Norfolk study was from 1993 to 2015.
We performed the analysis in two ways. First, in separate analyses using DSA1, DSA2 and DSA3 as the time origins, such that a single DSA was used to predict future CHD mortality (top three sections). Second, we performed an analysis which combines the three DSA into a single analysis. In more detail, we used the most up-to-date exposure and covariate measures for each individual at each time they were at risk, that is, time-varying covariates modelling. In the ‘time-varying’ approach, the follow-up time is divided by the dates of the respective DSA measures. Each participant is allocated to an exposure group (‘NSU’, ‘SU-n3’ or ‘SU+n3’), but only for that section of the follow-up time in which they belonged to that group. If they changed supplement use (ie, ‘varied’ by stopping a supplement or changing the type of supplement) the next section of the follow-up time (until the next DSA) was allocated to the exposure group they changed to. This type of analysis reduces misclassification of the exposure and any other confounders over time in a single analysis. Please note, the variables in this analysis do not explain what the associated risk is when changing from a specific supplement user category to another, this is shown in table 3. The reshaped dataset for time-varying analyses contains a larger number of participants (n=24 330) than available at DSA1 alone since 2295 participants did not complete DSA1, but did complete DSA2 and/or DSA3; equally, some participants were excluded from DSA1 due to missing covariate data when these covariates were available at DSA2 and/or DSA3 and so the participant contributed follow-up time from DSA2 and/or DSA3 only.
*Using adjustment model 3: time-point specific age, smoking, BMI, alcohol consumption, physical activity, season of questionnaire completion, marital status and self-report of myocardial infarction, stroke or diabetes; as well as: sex, social class and education measured at DSA1.
†In case of DSA3, the censor date was the date of administrative follow-up (31 March 2015).
DSA, Dietary Supplement Assessment; EPIC, European Prospective Investigation into Cancer; NSU, non-supplement users; PUFA, polyunsaturated fatty acids; SU+n3, n-3 PUFA supplement users (mainly cod liver oil); SU-n3, non-n-3 PUFA supplement users.