constipation or diarrhea.94 Although constipation is a common symptom in the elderly, age-associated alterations in colonic motility have been difficult to show. Some studies indicate that colonic transit slows with aging, particularly in women. Others found no significant difference in transit between young and elderly subjects.95 Age-associated reduction in the nitric oxide–containing neurons in the myenteric plexus involved in receptive relaxation has been reported.96, 97 The remaining myenteric neurons may be functionally impaired. Release of the excitatory neurotransmitter acetylcholine was diminished in the colon of aged rats, an effect that appeared to be due to decreased calcium influx.98 Interestingly, neurotransmitter release from myenteric neurons in the aged colon could be restored to youthful levels by use of calcium ionophores that bypass membrane calcium channels. Impaired calcium signaling may be a fundamental alteration in aging, because it has also been shown in peripheral sensory neurons99 and muscle. It should be pointed out that inclusion of chronic laxative users in investigations of colonic function in aging should be interpreted cautiously, because long-term use of phenolphthalein results in loss of interneurons. Other cathartic laxatives, such as senna, do not cause significant anatomic damage in animal studies when used for up to 5 months.100, 101 Diverticular disease Diverticulosis is an abnormality commonly described in the aging colon and predisposes to the subsequent development of diverticulitis.94 By the age of 50 years, one third of Americans will have diverticulosis coli; by the age of 80 years, approximately two thirds will be affected. Most are asymptomatic, with 10%–20% developing complications such as diverticulitis or hemorrhage.102 Decreased tensile strength of the muscle wall and increased intra-abdominal pressures required for evacuation have been implicated in the development of diverticuli. Human aging is associated with an increase in collagen in the colon wall that is accompanied by a significant decrease in tensile strength,103 which may predispose to herniation of the mucosa. Other factors include slow colonic transit and increased frequency of segmenting contractions, resulting in increased water resorption and hard feces. Decreased fiber intake likely also contributes to the production of hard feces and excessive straining, because both animal and human studies indicate that addition of fiber to the diet decreases intraluminal pressures in the colon.104 According to data from the National Demographic and Health Survey (NDHS), hospital admissions and office visits for diverticulitis increased by 14% from 1997 to 2002, with 261,180 hospital admissions and 1,493,865 office visits in 2002. Emergency department visits for diverticulitis increased by 84% for the same period from 87,512 to 161,364 visits, underscoring the impact of the aging population on emergency department resources. Current management stresses the use of a high-fiber diet to prevent recurrence of diverticulitis. Approximately 20% of patients require surgical treatment, with elective laparoscopic treatment becoming increasingly prevalent in management.105 IBS IBS is a common disorder, with 1.5–2.7 million physician visits yearly106 and with women predominating (2.4–3.3 times the rate in men). Common symptoms include abdominal pain, cramping, bloating, distention, and altered stool consistency (loose or hard). A cross-sectional