After a follow-up time of 547
312 person years (mean 11.6 years), there were 812 cases of diverticular disease (806 of these were from hospital admissions data and six from causes of death). In most cases (>95%) the diagnosis was “diverticular disease without perforation or abscess” either of the large intestine (n=560, 69.0%) or the part of the intestine was not specified (n=221, 27.2%).
Tables 1 and 2 show the characteristics of the 47
033 participants by sex for non-vegetarians and vegetarians. Of all the participants, 76% were women, and 35% of men and 32% of women reported consuming a vegetarian diet. Among both men and women, vegetarians were younger than non-vegetarians; about 80% of the vegetarian men and women were younger than 50 at recruitment compared with around 50% of the non-vegetarian men and 60% of the non-vegetarian women. There was a low prevalence of smoking, ranging from 10% of vegetarian women to 15% of non-vegetarian men. Both the median intake of alcohol and the median BMI were highest among the non-vegetarian men and lowest among the vegetarian women. The proportion of non-vegetarians who reported a previous diagnosis of diabetes, hypertension, or hyperlipidaemia was about two to three times higher than among the vegetarians. Over 25% of non-vegetarians reported receiving some type of long term medical treatment at recruitment compared with less than 20% of vegetarians. The proportion who reported current or previous use of oral contraceptives was slightly higher among vegetarian women, whereas the use of hormone replacement therapy was almost three times higher among non-vegetarian women.
Table 1 Baseline characteristics of EPIC-Oxford participants for men and women by diet group. Figures are numbers (percentage) of participants unless stated otherwise
Table 2 Dietary characteristics at baseline in EPIC-Oxford participants for men and women by diet group at baseline and follow-up. Figures are numbers (percentage) of participants unless stated otherwise
About two thirds of the vegetarians had been adhering to their diets for more than five years at the time of recruitment, and in the first follow-up questionnaire mailed about five years later, 90% of male and 84% of female vegetarians reported that they were still consuming a vegetarian diet (table 2). Among non-vegetarians, the median intake of meat was higher in men than women. Women had a higher intake of fruits and vegetables than men, and vegetarians consumed slightly more fruit and vegetables than non-vegetarians. Among the non-vegetarians, the median intake of dietary fibre (18 g/day for both men and women) was lower than in vegetarians (22 g/day and 21 g/day for men and women, respectively).
Compared with non-smokers, there was a 31% higher risk of diverticular disease among former smokers and a 34% and 86% higher risk for light (<15 cigarettes/day) and heavy (≥15 cigarettes/day) smokers, respectively (table 3). After adjustment for smoking, there was no significant association between the consumption of alcohol and risk of diverticular disease. There was a significant positive relation between BMI and risk of diverticular disease; compared with those with a BMI of 20.0-22.5, the risk was 37% lower among participants with a BMI <20 and 67% higher among participants with a BMI ≥27.5. The risk for diverticular disease was lower in participants with higher than with lower educational attainment, and risk was higher also in those with low rather than with high socioeconomic status. Participants who reported having hypertension or hyperlipidaemia had a 44% or 47% greater risk of developing diverticular disease, respectively, compared with those who did not report having the condition. There was also a significantly greater risk of diverticular disease among participants who reported receiving long term medical treatment and among women who had used oral contraceptives or hormone replacement therapy.
Table 3 Relative risk of diverticular disease by certain demographic variables in EPIC-Oxford study
Results in table 4 show that after adjustment for a range of confounding variables including BMI, vegetarians (vegetarian or vegan) had a 30% lower risk of developing diverticular disease than non-vegetarians (those who eat meat or fish, or both). In analyses that subdivided the non-vegetarian group, those who do not eat meat but eat some fish did not have a significantly lower risk of developing diverticular disease than meat eaters (relative risk 0.91, 95% confidence interval 0.71 to 1.16); however, risk of diverticular disease was 31% lower among vegetarians or vegans (0.69, 0.55 to 0.86). In analyses that separated vegans from vegetarians, there was an even lower risk among the vegans (four cases); compared with meat eaters the risk of diverticular disease was 0.28 (0.10 to 0.74).
Table 4 Relative risk of diverticular disease by diet group in EPIC-Oxford study
Using the absolute rates of admission to hospital or death from diverticular disease, the cumulative probability of diverticular disease between ages 50 and 70 for meat eaters was 4.4% and the cumulative probability in vegetarians or vegans was 3.0%.
Vegetarians and vegans also had a significantly lower risk of diverticular disease than meat eaters after adjustment for sex specific fifths of dietary fibre intake (relative risk 0.79 (0.63 to 1.00) and 0.32 (0.12 to 0.87), respectively). There was no evidence that the association between vegetarianism and diverticular disease differed according to duration of adherence to a vegetarian diet. In the fully adjusted model, the risk among vegetarians who had followed a vegetarian diet for more than five years was 0.72 (0.57 to 0.92) and for all other vegetarians the relative risk was 0.64 (0.42 to 0.97) compared with non-vegetarians.
In the fully adjusted model the association between the quantity of meat consumed and risk of diverticular disease was not significant (table 5); compared with those with the highest intake of meat (≥100 g/day), the risk of diverticular disease for those with an intake less than 50 g/day was 0.95 (0.76 to 1.18). There was, however, a significant inverse dose-response relation between the intake of dietary fibre and risk of diverticular disease. Participants in the highest fifth of dietary fibre (≥25.5 g/day for women and ≥26.1 g/day for men) had a 42% lower risk (relative risk 0.58, 0.46 to 0.73) compared with participants with the lowest intake of fibre (<14 g/day for both women and men). Adjustment for confounding variables made little difference to this association. After further adjustment for diet group, the association was slightly attenuated but remained significant (0.66, 0.50 to 0.86; P=0.002 for trend). There was also a significant inverse association between the intake of dietary fibre and risk of diverticular disease among meat eaters only; compared with meat eaters in the lowest fifth of dietary fibre intake, those in the highest fifth had a 26% lower risk of developing diverticular disease (0.74, 0.54 to 1.00; P=0.018 for trend).
Table 5 Relative risk of diverticular disease by intake of meat and dietary fibre in the EPIC-Oxford study
There was no evidence of heterogeneity in the association between diet group or fibre intake and risk of diverticular disease between men and women (table 6) or between older and younger participants (table 7). In a sensitivity analysis that excluded the first two years of follow-up (752 cases of diverticular disease included), the associations of diet group and dietary fibre with risk of diverticular disease remained significant; the relative risk for vegetarians or vegans compared with meat eaters was 0.72 (0.57 to 0.90) and the risk for the highest versus the lowest fifth of dietary fibre intake was 0.62 (0.47 to 0.82; P<0.001 for trend). In analyses where cases were restricted to participants for whom diverticular disease was the primary diagnosis or underlying cause of death (n=531 cases included), the relative risk for vegetarians or vegans versus meat eaters was 0.72 (0.55 to 0.95), and the risk for the highest versus the lowest fifth of dietary fibre intake was 0.61 (0.44 to 0.84; P=0.002 for trend).
Table 6 Association between diet group and intake of dietary fibre and risk of diverticular disease stratified by sex
Table 7 Association between diet group and intake of dietary fibre and risk of diverticular disease stratified by age