Enhancing immune response

Health experts have known that probiotics—healthy bacteria in our digestive tracts—play a role in immune function, but they don’t know exactly how and why. To study these questions, researchers randomly selected 211 healthy adults to receive one of the following daily for six weeks:

• A probiotic supplement containing bacteria called Bifidobacterium animalis subspecies lactis (BB-12)
• A probiotic supplement containing bacteria called Lactobacillus paracasei subspecies paracasei (L. casei 431)
• A placebo supplement containing no probiotic bacteria

Each study participant was vaccinated against the flu two weeks after beginning the supplements and continued the supplements for an additional four weeks after vaccination. Blood and saliva samples were collected at the start of the study (before supplementation) and six weeks later when the study completed.

The researchers analyzed the samples for levels of:

• Immunoglobulin G (IgG): a protein called an antibody, produced by the body when we come in contact with bacteria and viruses, which circulates in the blood and other body tissues. Immunoglobulins latch onto microbes, identifying them as harmful, so other components of the immune system can then destroy them.
• Immunoglobulin A (IgA): IgA is similar to IgG, except that instead of being found in blood, it is an antibody found in saliva and mucus. IgA is a “first responder” to microbes when they enter the body through the mouth or nose.

After six weeks of probiotic supplements, the researchers found that between baseline and six weeks, compared with the placebo group, both supplement groups experienced:

• Larger increases in blood levels of IgG specific to the vaccine flu virus
• Larger increases in saliva levels of IgA specific to the vaccine flu virus
• Larger increases in total antibody concentrations in blood and saliva

Fighting flu

This study found certain probiotic supplements enhanced the body’s immune response to flu vaccination. Better vaccine response means you’re more likely protected against influenza when it comes around. Our tips can help you use this information to develop your best flu fighting plan.

• If you are immune-compromised (have a condition affecting immune function) or have other serious health conditions, ask your doctor if probiotics are safe for you.
• If you decide to try probiotics, for best effect take them daily for a few days to a couple of weeks prior to flu vaccination, and continue for several weeks after vaccination.
• The effects of probiotics are strain-specific; for best effect, try a supplement that contains one or both of the bacteria strains studied.
• Other ways to reduce your odds of coming down with the flu include washing your hands frequently, getting enough sleep, including plenty of vegetables and fruit in your daily diet, and drinking adequate fluids.
• To protect others against flu, cover your mouth and nose when you cough or sneeze.

(Br J Nutr 2012;107:876–84)