Probiotics has been a popular area of research during the past century, owing to the health benefits thought to be associated with their use. However, solid evidence to support the benefits of these “friendly” bacteria and yeasts is still lacking.

One area that research has focused on is the possible beneficial effects probiotics have on the immune system. For example, a 2004 study looked at the effects of giving probiotic enriched milk to students over a six week exam period. Analysis showed that those who took the probiotic enriched milk showed an increased production of lymphocytes and CD56.

Another study carried out in 2007 at University College Cork in Ireland examined the effects of feeding pigs milk that was fermented with Lactobacillus bacteria. Results showed that the milk prevented Salmonella infection among the pigs.

Some other areas probiotic research has focused on are described below:

• Colon cancer - Several studies have analyzed the efficacy of probiotics in the prevention of colon cancer. For example, the SYNCAN study found that a symbiotic preparation can lower the expression of colorectal biomarkers.
• Antibiotic-associated diarrhea (AAD) - Some evidence does support that Lactobacillus rhamnosus GG prevents AAD in children when it is administered at high doses. Antibiotics tend to eliminate many protective bacteria in the gut, which can cause diarrhea. Replenishing the gut with probiotics is thought to prevent growth of the harmful bacteria that produce toxins and cause illness.
• Eradication of Helicobacter pylori - A meta-analysis of 14 trials showed that supplementing antibiotic treatment for H. pylori with probiotics can increase eradication rates. H. pylori can lead to peptic ulcers.
• Allergy - A meta-analysis of 25 trials suggested that taking a probiotic supplement during pregnancy may prevent atopic sensitivity in infants. Probiotics were not shown to improve asthma or wheezing.
• Hepatic encephalopathy - One study showed that among patients with minimal hepatic encephalopathy, treatment with a probiotic preparation reversed the condition in 50% of cases.
• Pouchitis - Evidence suggests that probiotics may be effective at reducing pouchitis and preventing its relapse after disease remission.
• Lactose intolerance - Lactose intolerance is a common condition of the gut caused by an inability to digest lactose, the sugar present in milk and dairy products. People with this condition are deficient in the enzyme lactase, a protein produced in the small intestine to help break down lactose. Some studies suggest that Lactobacillus acidophilus produces lactase, therefore restoring the breakdown and absorption of lactose.
• Necrotizing enterocolitis - Several studies suggest that probiotics may lower the risk of necrotizing enterocolitis and death in infants who are born premature. One meta-analysis suggested that this risk is decreased by as much as 50% when probiotics are used.