New diverticulosis data challenge long-held belief

Not only is there no link between low-fiber diets and diverticulosis, but the incidence of diverticulitis is not nearly as common as was previously believed.

Those are the conclusion of two studies that challenge long-held beliefs about the causes of these conditions.

In the first study, the University of North Carolina at Chapel Hill, and colleagues looked at 539 patients with colonic diverticula and 1,569 controls, all culled from the Vitamin D and Calcium Polyp Prevention Study, a double-blind placebo-controlled trial of vitamin D and/or calcium for the prevention of colonic adenomas.

Patients with a self-reported history of diverticulosis or diverticulitis were excluded, as were cases with a history of colon resection, inflammatory bowel disease, or familial history of colon cancer. Most (88%) had descending or sigmoid colon diverticula, and these patients were significantly older and more likely to be male than were controls.

There was no difference between cases and controls in mean dietary fiber intake and reported supplemental fiber intake. Nor was there any significant link when investigators compared the highest quartile of fiber intake to the lowest. They found no associations between dietary fiber intake by subtype (for instance, beans, grains, fruits, and vegetables) and diverticulosis.

Forty years ago, it was popularized the hypothesis that inadequate dietary fiber intake and constipation were the cause of sigmoid diverticulosis. Although the fiber hypothesis is conceptually attractive and widely accepted, it has not been rigorously examined.

And while the data were based on food frequency questionnaire — which could be subject to measurement bias — that the mean total fiber intake in the highest quartile was 25 g, versus 8 g in the lowest. This wide range makes it unlikely that homogeneity of intake accounts for the null association of fiber with the presence of diverticula.

A study by the University of California Los Angeles/ Veteran’s Affairs Center for Outcomes Research and Education, sought evidence for the belief that up to 25% of patients with diverticulosis will develop diverticulitis. He and colleagues performed a retrospective survival analysis of 2,222 patients from the Veteran’s Affairs Greater Los Angeles Healthcare System with colonic diverticu losis and a median follow-up of 6.5 years.

Patients were excluded if they had any ICD-9 code for diverticulitis or documentation of diverticulitis in the medical record notes at any point before the index date of diverticulosis.

When the researchers looked only at imaging-confirmed cases, 23 patients (1%) developed acute diverticulitis during the study period. This jumped to 95 patients (4.3%) when clinical diagnoses were also used, for an incidence of six cases per 1,000 patient-years.

Looking at predictors for progression, the authors found that only age was related to the development of diverticulitis, with every year of age at diverticulosis detection conferring a 2.4% lower hazard of developing diverticulitis.

The “widely cited figures” that up to a quarter of patients with diverticulosis will develop acute diverticulitis is based on data collected before the time of routine colon screening. Therefore, the true denominator of individuals harboring diverticulosis was not accounted for in these caIculations.

Future series or patient registries may better standardize the definition of diverticulitis in a prospective cohort. Meanwhile, prevalence data such as these “may help to reframe discussions with patients regarding their probability of developing clinically significant diverticulitis.”

Even as these two findings change the way providers counsel patients about the cause and impact of diverticula, a third study, adds another wrinkle: Patients who develop diverticulitis are at increased risk for a diagnosis of irritable bowel syndrome later on.

The VA Greater Los Angeles Healthcare System, and colleagues looked at 1,105 chartconfirmed cases of diverticulitis, identified retrospectively from the same dataset used. All cases were matched with controls seen on the same day, the mean follow-up period was 6.3 years, and patients with pre-existing IBS or functional bowel diagnosis were excluded from the study.

The primary outcome was a new IBS diagnosis after the index diverticulitis attack (for cases) or enrollment date (for controls). They found 24 cases of newly diagnosed IBS during the study period: 20 among diverticulitis cases, and 4 among controls. The translated to a hazard ratio of 4.7 among cases compared with controls, even after adjustment for age, sex, ethnicity, race, inpatient versus  outpatient status, and comorbidity score.

Inflammation may alter gastrointestinal reflexes, amplify visceral sensitivity, render bowel more susceptible  to negative effects of microbiota, and alter motility in IBS. Another putative mechanism of chronic diverticular disease involves shifts in intestinal microbiota leading to chronic inflammation, similar to theoretical models of IBS.

Future research should identify demographic and clinical predictors of post-diverticulitis irritable bowel syndrome and evaluate its incidence in prospective studies to better determine whether the link is casual or merely associative.

A fourth study could help researchers reduce the risk of the painful inflammatory condition: Among diverticulosis patients, higher levels of serum vitamin D were associated significantly with a lower risk of diverticulitis.

In her analysis, colleagues identified 9,116 diverticulosis patients and 922 diverticulitis patients from the Partners Healthcare Research Patient Data Registry. All patients had at least one prediagnostic serum vitamin D level on record between 1993 and 2012.

The Massachusetts General Hospital, Boston, found that patients with uncomplicated diverticulosis had mean levels of 29.1 ng/mL, versus 25.3 ng/mL in the diverticulitis patients.

A sensitivity analysis that compared the mean prediagnostic values between cases and controls that had more than one reported vitamin D level yielded similarly significant results: The mean vitamin D level of uncomplicated diverticulosis was 33.0 ng/mL, compared with 28.1 ng/mL for acute diverticulitis patients (P less than .0001), then 28.8 ng/mL for complicated diverticulitis patients for surgical diverticulitis cases and 25.5 ng/mL for recurrent diverticulitis patients.

“Compared with patients with acute diverticulitis without other sequelae, patients in the subgroups who developed abscess, required surgery, or had recurrent attacks were observed to have lower prediagnostic levels of vitamin D,” the researchers wrote. These differences between diverticulitis subgroups did not reach significance except in the cohort of patients who required surgery, who had the lowest levels of all. Taken together with prior studies showing an inverse association of 25 (OH) D and risk of colonic cancer and inflammatory bowel disease, these results highlight the potential importance of vitamin D in the maintenance of colonic health. Additional studies in cohorts with more detailed information on potential confounders of this association are warranted.