Experts have recommended that elderly people should take probiotic supplements to protect against bowel conditions.
Speaking following a research report from Reading University, scientists said that people over 60 have many fewer "friendly" bacteria in their digestive systems and could therefore benefit from the drinks, yogurts or supplements currently on the market.
Maintaining a balance within the body of bacteria that assist in digestion and those that cause disease is important in avoiding conditions such as Irritable Bowel Syndrome, they added.
Speaking at a briefing to announce the results, Dr Sandra McFarlane said that the balance tips as people get older, pinpointed at around 60-years-old, and this means older people have 1,000 times fewer friendly bacteria on average than younger adults.
Professor Glenn Gibson, the study's head researcher, said that this helped to explain why recent victims of an E.coli outbreak in Scotland were elderly.
Probiotics could also be helpful for younger people who are taking antibiotics, the scientists said.