The incidence of diverticular disease has increased over the past century (
2,
5,
6). Autopsy studies from the early part of the 20th century reported colonic diverticula rates of 2% to 10% (
6). This has increased dramatically over the years. More recent data (
5) suggest that up to 50% of individuals older than 60 years of age have colonic diverticula, with 10% to 25% developing complications such as diverticulitis. Hospitalizations for diverticular disease have also been on the rise. According to an American study evaluating hospitalization rates between 1998 and 2005 (
2), rates of admission for diverticular disease increased by 26% during the eight-year study period. Similar trends have been observed in Canadian and European data over the same time period (
5,
7).
Diverticular disease has traditionally been believed to be a disease affecting the elderly (
8). The prevalence of diverticular disease is as high as 65% by 85 years of age and estimated to be as low as 5% in those 40 years of age or younger (
8). However, more recent literature has reported an increase in the incidence of diverticular disease among younger patients. For example, a large review of the Nationwide Inpatient Sample (NIS) of 267,000 admissions for acute diverticulitis between 1998 and 2005 (
2) showed that the average age of patients decreased over the study period from 64.6 to 61.8 years. Incidence rates increased most dramatically among groups 18 to 44, and 45 to 64 years of age (incidence per 1000 population: 0.151 to 0.251, and 0.659 to 0.777, respectively). In contrast, incidence remained stable over the study period in persons between 65 and 74 years of age, and actually decreased in persons 75 years of age or older. Moreover, a very high incidence of diverticular disease in young patients was reported in a review of 238 patients admitted with diverticulitis to the surgical service at the Medical Center Hospital in San Antonio, Texas (USA) between 1981 and 1990 (
9). In this review, 26% of patients were 40 years of age or younger. These patients had a more aggressive form of disease, requiring more surgical intervention than older patients, and they exhibited a five-fold increase in the risk of complications, such as fistula, compared with their older counterparts. Given the presumption of the low incidence of diverticular disease in young patients, nearly one-half of these patients were often misdiagnosed at presentation – most commonly with appendicitis.
Sex differences among patients with diverticular disease have also been noted throughout the literature, with more recent data showing a change in sex demographics. For example, early reports (
10) suggested a higher incidence of diverticular disease among men. A review of all patients admitted to Massachusetts General Hospital (Massachusetts, USA) between 1964 and 1973 (
1) showed no difference between sexes (
1). However, more recent data have shown that although diverticular disease is still more common among men 50 years or younger, the incidence among women predominates in older age groups (
5,
7,
9). The ratio of men to women with diverticulitis among 61 patients admitted to the Medical Center Hospital in San Antonio who were younger than 40 years of age was 2:1, while women were more frequently admitted in the older age group with a ratio of 1.5:1 (
9). The rates of hospitalization were higher among men younger than 50 years of age, but higher for women older than 50 years of age in a review of hospital discharges from 1989 to 2000 in England (United Kingdom) (
7). This was consisent with the findings of a Canadian study (
5) reporting that men had a hospitalization rate for diverticular disease of 45 per 100,000 in the 40- to 49-year age group compared with 38 per 100,000 in the same age group of women. The incidence was 299 per 100,000 in the 80 years and older age group among men, and 436 per 100,000 in the same age group among women. Women had a higher overall admission rate compared with men between 1998 and 2005 in the review of the NIS database (
2) mentioned above. Men accounted for 39% of admissions compared with 60.7% for women. This pattern was still evident at the end of the study period (female rate of admission 58.9%; male rate of admission 41.1%). Possible hypotheses for these sex differences have included the protective effect of testosterone on preventing weakening of the colonic wall, and the effect of pregnancy and labour and delivery on contributing to weakening of the wall of the colon.
Diverticular disease has long been regarded as a disease of western countries. The highest prevalence of this condition is in the United States, Europe and Australia, where approximately 50% of the population 60 years of age and older have diverticulosis (
5,
6). This common occurrence is in contrast to that in the developing world, where countries in Africa and Asia have prevalence rates of less than 0.5% (
6,
11,
12). The western diet, particularly its deficiency in dietary fibre, has long been implicated as a causative factor for these geographical variations (
6,
13–
16). This hypothesis was supported by a study that compared stool weight and transit time in 1200 individuals in the United Kingdom and rural Uganda (
13). The United Kingdom subjects, who were shown to have lower fibre intake, had a transit time of 80 h and a mean stool weight of 110 g/day. This was significantly lower than in the Ugandan subjects, who had much shorter transit times (34 h) and greater mean stool weights (450 g/day). The prolonged transit time and small stool volumes were believed to predispose to diverticular disease by increasing intraluminal pressure. Moreover, there is growing evidence that the rates of symptomatic diverticular disease are on the rise because areas in the developing world are becoming increasingly westernized (
14,
15). For example, the rates of diverticular disease have increased among urban black populations of South Africa compared with rural black populations in the same country (
14). The role of dietary fibre deficiency as a contributor to diverticular disease was further supported by a large prospective cohort study of more than 47,000 men who were followed over a four-year period (
16). Dietary fibre intake was found to be inversely associated with the risk of developing diverticular disease, with an RR of 0.58 (95% CI 0.41 to 0.83; P=0.01).
In addition to the geographical variability in the prevalence of diverticular disease, there is significant variability in the location of diverticula within the colon in different regions of the world. In western countries, it has been well described that diverticulosis is primarily left sided, particularly involving the sigmoid colon (
2,
6–
8). This is in contrast to findings in Asia, where right-sided diverticulosis dominates (
17–
19). In a review of 615 cases of diverticulosis detected on double-contrast barium enema examinations between 1975 and 1982 in Tokyo, Japan (
17), 70% were right sided. Similar diverticular distribution has been shown in Hong Kong and Singapore (
18,
19). The reason for these differences remains unclear. Early hypotheses suggested that left-sided diverticula were acquired, whereas right-sided diverticula were more likely to be true diverticula and, thus, congenital (
20,
21). However, subsequent studies have shown that, similar to left-sided diverticula, the majority of right-sided diverticula are ‘false’ and are likely acquired (
18,
22). In fact, as Asian populations have begun to adopt a more westernized diet, the rates of diverticular disease have been shown to increase to the same extent noted in the west (
17). This increase in diverticular disease, however, remains predominantly right sided. Factors other than deficiencies in dietary fibre are likely to play a role in the development of right-sided diverticulosis as demonstrated by studies that show that even with a high-fibre diet, the rates of right-sided disease are high. For example, a study from China (
23) reported a diverticulosis rate of 62% in patients with high-fibre intake (greater than 14 g/day). More research is needed in this area to better identify potential causative factors.