The aetiology of ulcerative colitis (UC) is largely unknown, although it is plausible that dietary n-3 polyunsaturated fatty acids (PUFAs) may be protective. Metabolites derived from n-3 PUFAs are less proinflammatory than those from n-6 PUFAs. Earlier, no prospective cohort studies have investigated this hypothesis, using dietary information collected from food diaries. The aim of this study was to investigate the total dietary intake of n-3 PUFAs and the specific n-3 PUFAs, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on the risk of developing incident UC.
Twenty-five thousand six hundred and thirty-nine participants, living in Norfolk UK, aged 45–74 years (median age at recruitment of 59.2 years), completed 7-day food diaries. These were interpreted using a computer programme, which converted food items into nutrients, including n-3 PUFAs. The cohort was monitored for participants who developed UC. Each case was matched with four controls and an analysis performed using conditional logistic regression.
In the cohort, 22 incident cases of UC were identified after a median follow-up time of 4.2 years (range 1.8–8.3 years). A statistically significant protective odds ratio (OR) for the trend across tertiles was found for DHA [OR = 0.43, 95% confidence interval (CI)=0.22–0.86, P = 0.02] and borderline statistically significant differences for trends for total total n-3 PUFAs (OR = 0.56, 95% CI=0.28–1.13, P = 0.10) and EPA (OR = 0.53, 95% CI=0.27–1.03, P = 0.06) after adjusting for age, sex, total energy intake, smoking, and other fatty acids.
Total dietary n-3 PUFAs, EPA, and DHA, particularly DHA were associated with protection from UC in a cohort aged over 45 years. If the association is causal, then increasing the population's intake of n-3 PUFAs from oily fish may help prevent UC.